DSpace at VNU: LA-ICPMS zircons U Pb dating of Permo-Triassic and Cretaceous magmatisms in Northern Vietnam - Geodynamical implications

Journal of Asian Earth Sciences 48 (2012) 72–82 Contents lists available at SciVerse ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes LA-ICPMS zircons U/Pb dating of Permo-Triassic and Cretaceous magmatisms in Northern Vietnam Geodynamical implications Franỗoise Roger a,, Henri Maluski a, Claude Lepvrier b, Tich Vu Van c, Jean-Louis Paquette d a Université Montpellier 2, CNRS UMR 5243, Géosciences Montpellier, 34095 Montpellier Cedex 5, France ISTEP, UMR 7193-CNRS-Université P&M Curie, Place Jussieu, 75252 Paris Cedex 05, France c National University of Vietnam, 334 Nguyen Trai Thanh Xuan, Hanoi, Viet Nam d Laboratoire ‘‘Magmas et Volcan’’ (CNRS UMR 6524), Université B Pascal, F-63 038 Clermont-Ferrand Cedex, France b a r t i c l e i n f o Article history: Received 15 March 2011 Received in revised form December 2011 Accepted 20 December 2011 Available online January 2012 Keywords: Nappes Indosinian orogeny Cretaceous magmatism Paleo-Pacific subduction Paleotethys NE Vietnam a b s t r a c t In northeastern Vietnam, the major tectonic episode responsible for nappes emplacement is Triassic These allochtonous structures are intruded by granitic melts Two post-tectonic massifs showing no sign of deformation have been dated by the LA-ICPMS zircon U–Pb techniques Dating reveals a multiphase history with zircon cores showing evidence of Proterozoic magmatism The emplacement of the Phia Bioc granite intrusive in allochtonous units is 248–245 Ma, an age which assesses a younger limit for the major nappes tectonic This tectonic could be synchronous of the tectonometamorphic strike-slip faulting events (250–245 Ma) defined in the Truong Son Belt as the Indosinian orogen The Phia Bioc intrusion is probably linked with the intra-plate magmatism of the Emeishan Large Igneous Province or with magmatism associated with the Paleotethys closure The age of the Phia Oac granite intrusion in displaced units is much younger, at 87.3 ± 1.2 Ma This granite is probably linked to the magmatic activity produced during the Paleo-Pacific plate subduction under the SE Asia continental plate during the Mesozoic Although the Cenozoic Red River fault system is close to these two plutons, this last thermotectonic episode has not been strong enough to disturb the U/Pb system Zircons rims not show any Tertiary magmatic or metamorphic overprint Ó 2012 Elsevier Ltd All rights reserved Introduction It is commonly accepted that the major geodynamic event responsible for the build up of SE Asia took place in the Triassic period during the Indosinian orogeny (Fromaget, 1941a,b), resulting from continental collisions between several Gondwana-derived blocks subsequent to the closure of the Paleotethys ocean One branch of the Paleotethys is represented by the Permo-Triassic Song Ma ophiolitic suture (Fig 1A and B), which separates the South China and Indochina blocks In Vietnam, North and South of the suture, a thermotectonic overprint has been demonstrated through radiometric investigations (U–Pb and Ar–Ar methods) applied to metamorphic and magmatic minerals As a result, the major periods of thermotectonic activities are ca 420–470 Ma, 240–250 Ma and 20–35 Ma (Nagy et al., 2001; Vu Van Tich, 2004; Maluski et al., 2005, 1995, 2001; Roger et al., 2007; Maluski and Lepvrier, 1998; Lepvrier et al., 1997; Carter et al., 2001; Leloup et al., 1993, 1995, 2001; Searle, 2006, 2007; Searle et al., 2010) ⇑ Corresponding author E-mail address: Francoise.Roger@gm.univ-montp2.fr (F Roger) 1367-9120/$ - see front matter Ó 2012 Elsevier Ltd All rights reserved doi:10.1016/j.jseaes.2011.12.012 Two distinct structural domains coexist on each side of this suture Along and south of the Song Ma suture, in the Truong Son range (Fig 1), the Triassic structures are characterized by high strain ductile deformation and metamorphism along partially mylonitic NW–SE trending strike-slip faults (Lepvrier et al., 1997, 2008) Ar–Ar and U–Pb dating have been conducted in this belt establishing that this major thermotectonic event (the Indosinian orogeny) took place around 245–250 Ma (Maluski et al., 1995; Lepvrier et al., 1997; Maluski and Lepvrier, 1998; Roger et al., 2007) The northeastern part is dominated by originally flat structures corresponding to large nappes, which have been later refolded This geometry was first described through classical field geology (Deprat, 1915) and has been confirmed recently by Lepvrier et al (2011) What is the age of this nappe tectonics? Does it occur synchronously with the thermotectonic event responsible of the development of ductile strike-slip faults in the Truong Son belt? An answer to these questions can be indirectly provided by LA-ICP-MS U–Pb zircon dating of intrusive granitic bodies emplaced through the allochtonous metasedimentary terranes of NE Vietnam Is there any influence of the Cenozoic tectonics as locally observed in Vietnam (Bu Khang massif and Red River Shear Zone Fault) on these U/Pb data (Maluski et al., 1997; Jolivet et al., 1999; Leloup et al., 1993, 1995, 2001)? 73 F Roger et al / Journal of Asian Earth Sciences 48 (2012) 72–82 Geological outline of the Northern Vietnam 2.2 Magmatic bodies 2.1 Tectonics Several granitic and gabbro-syenitic to ultramafic bodies of various sizes intrude the Paleozoic metasedimentary rocks of the nappe and the Song Hien displaced unit (Fig 2) The larger intrusion is represented, West-Northwest of Bac Can, by the Phia Bioc granite which forms a crescent-shaped body, convex to the East and bounded by a thrust fault This magmatic body intruded into the Silurian series, consists in a biotite–muscovite bearing granite with occurrences of amphiboles bearing melts This granite is porphyroid, undeformed and locally contains enclaves of microdiorites It can be considered as a post-tectonic granite surrounded by a thermal metamorphic zone including horns Two samples of the granite have been collected for dating: sample VT19 (N22°240 1800 ; E105°410 1500 ) and sample VT16 (N22°070 4700 ; E105°460 4500 ) (Fig 2) According to Tran Van Tri (1979), the Phia Bioc granite is Pre-Ladinian (235–230 Ma) because it locally crosscuts Lower Triassic sediments but occurs as pebbles in the basal conglomerates of the Ladinian sedimentary formation The same author obtained K–Ar ages scattered of 230–306 Ma for this granite Moreover to the South, the Cho Chu granite, which belongs to nB ien Phu N Ye n Fa ult tur e Son a SOUTH CHINA SEA R S Hai Nan Thanh Hoa gC T O n t Die - t ul A ul Su Bu Khang Massif L Ti e HANOI Fa Ma Fa er Da iv 20°N ng R ng So ed So R 22°N A CHINA ng Ba Fault Cao Song Chay Massif Vinh U O N G Mek 18°N S ong O N Rive Dailoc Massif B E r Da Nang L THAILAND T 16°N Tamky-Phuoc Son Suture Tra Bong Dien Binh Complex KONTUM BLOCK PO 14°N K o CAMBODIA g an W Ch ao 12°N Fa ult Zo ne Fa ult Dalat HO CHI MINH TOWN 10°N Suture Fault 102°E 104°E 106°E QAIDAM 108°E 110°E B NORTH CHINA BH SG QIANGTANG Lon gm Sha en n LHASA Yi INDIA Qinling ckk looc bbl ee tz g n Ya Da10 bie ck lo SOUTH CHINA CHINA sia b SOUTH ay tha Ca Si A INDOCHIN SIBUMASU West Burma Three different main structures define a prominent NW–SE structural orientation south of the Red River Fault: the Tule volcano-detrital basin, limited to the South by the Song Da continental rift system which bounds the Song Ma shear zone (Figs 1A and 2) The latter joins to the NW with the Dien Bien Phu Fault Volcanic rocks in the Tule massif emplaced during two main periods, in the middle-late Jurassic (176–145 Ma) and the late Cretaceous (80–60 Ma) (Anh et al., 2003) The main tectono-metamorphic activity of the Song Ma shear zone has been precisely dated using Ar–Ar dating and relates to the Indosinian orogeny at ca 250 Ma (Lepvrier et al., 1997; Maluski and Lepvrier, 1998; Maluski et al., 1999) Up to now, in NW Vietnam, no Paleozoic magmatism has been found south of the Red River Fault When crossing the Cenozoic massif of the Day Nui Con Voi bounded to the northeast by the Song Chay Fault (Fig 2), the NW–SE structural direction disappears The most prominent structure is represented by the Dulong-Song Chay massif which extends towards the North in South China (Roger et al., 2000; Maluski et al., 2001; Carter et al., 2001; Yan et al., 2006): granitic and orthogneissic series form the crystalline core with a dome-like structure overlain by muscovite bearing marbles in its northern part and cordierite-sillimanite bearing schists in its southernmost edge Orthogneissic rocks were dated by Roger et al (2000) who obtained on zircons a U–Pb emplacement age of 428 ± Ma for the porphyritic monzogranitic protolith An overprinted metamorphism was dated by Ar–Ar at 234–236 Ma, clearly related to the Indosinian tectonometamorphic episode, as elsewhere displayed in the Song Ma structure and southerly by the entire Truong Son Belt (Maluski et al., 2001; Lepvrier et al., 2004, 2008) Finally, a slow-doming episode at 180 Ma is also recorded by Ar–Ar analysis on micas along a N–S cross section (Roger et al., 2000; Maluski et al., 2001) Low temperature apatite fission-track data from along the same transect record a later Cenozoic exhumation that involved some reactivation of bounding faults, with a normal sense of movement (Maluski et al., 2001) To the East of the Song Chay Massif, the geological map displays an arch-shaped structure convex to the SE (Fig 2) Cambrian formations surround the eastern and southern limits of the crystalline core, with micaschists, quartzites and limestones To the East and South East, these lower Paleozoic formations are overlain by lower to middle Devonian limestones and quartzites More to the East, a crescent-shaped middle Ordovician shales and sandstones series is intruded by granitoids Finally, still to the East, lower and upper Paleozoic schists are covered by a large Triassic detrital formation with clayish shales, sandstones and conglomerates All these arched formations are bounded by mylonitic faults p.p Following Deprat (1915), this geometry corresponds to a major nappe structure In spite of errors pointed out by Bourret (1922), as for example for the Pia Oac massif, this interpretation is still partially valid, except for the sense of displacement of the nappes system which is N to NE-directed (Lepvrier et al., 2011) To the East of the major basal contact of the nappe, the Lower Triassic Song Hien Formation develops and forms another displaced unit (Lepvrier et al., 2011) (Fig 2) Upper Triassic to Lower Jurassic formations, are largely exposed in the external zones and also form isolated outcrops resting on the Paleozoic formations of the nappe To the south of Lang SonThai Nguyen city these upper Triassic sedimentary rocks unconformably overlie the Lower–Middle Triassic series of the displaced unit In the external part of the area, to the East of Cao Bang and to the North of Yen Minh the Paleozoic formations represent a distinct autochtonous domain (Lepvrier et al., 2011) Cretaceous granitoids Emeishan Large Igneous Province EAST MALAYA Fig Simplified maps of Vietnam (A) and of SE Asia (B) showing major blocks and structures discussed in the text SG: Songpan-Garzê belt, BH: Bayan Har terrane, Yi: Yidun (or Litang-Batang) block, Si: Simao terrane Main sutures of Paleotethys: r: Jinsha, s: Yushu-Batang, t: Ailaoshan, u: Song Ma, v: Nan-Uttaradit, w: Changning-Menglian, x: Sra Kaeo, y: Bentong-Raub, z: Kunlun-Anyenaqen, {: Qinling-Dabie (After Roger et al., 2003, 2008, 2010 and Metcalfe, 2002.) 74 F Roger et al / Journal of Asian Earth Sciences 48 (2012) 72–82 103° Dulong-Song Chay Massif CHINA 23° 105° 104° 106° Suoi Cun Complex YEN MINH MINH YEN Fan Si Pan Granite Phia Oac HA GIANG GIANG HA Phia Oac Oac Granite Granite Phia v v v v v Phu Phu Sa Sa Phin Phin v v Complex Complex v O NG F Permian-Triassic Neogene Paleozoic Jurassic-Cretaceous Proterozoic J THAI NGUYEN J PHU THO J VIET TRI K HANOI ∼ ∼ ∼ HAI PHONG HOA BINH BINH HOA ∼ ∼ ∼ Kim Boi Massif ∼ ∼ ∼ ∼ ∼ ∼∼ ∼ Magmatic Rocks Quaternary O J D 50 km Sedimentary Rocks LANG SON Nui Chua Complex CH AY K O LTT UUL FFAA NGHIA NGHIA LO LO v RI VE R LLTT UU AA 21° ∼ SON LA v SS ∼ ∼ ∼ ∼ K I ∼∼ RE D v v TUYEN QUANG VO DIEN DIEN BIEN BIEN PHU PHU ∼ N v v Cho Chu Phu Ngu O IC U v VT19 BAC CAN T UL FA N D O TULE v v BAC CAN D O LUC YEN Phia Bioc Bioc Phia * CHO DON DON CHO N IEEN HHI AY ∼ ∼∼ ∼ ∼ ∼ ∼ RE ∼ ∼U∼ ∼ ∼ ∼∼ ∼∼A SU∼T ∼ M∼ LTT ∼ UUL ∼ SONG∼ FFAA ∼ A DDA ∼ ∼ G NNG ∼ ∼∼ ∼ ∼ SSOO ∼ ∼ ∼∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼ ∼∼ ∼ ∼ ∼∼ ∼ ∼ ∼∼ ∼ v v LAOS CHO DON v v Phia Bioc Bioc Granite Granite Phia * D G AN OB CA v LAI CHAU O D K G NG ON SSO K SAPA SAPA v D DIIE D EN NB BIIE EN NP PH HU U FFA AU ULLTT 22° BABE LAKE K CHO RA VT16 VT16 CAO BANG CHO RA * VT 235 BABE LAKE Paleocene Late Permian-Late Triassic Cretaceous Paleozoic Jurassic-Early Cretaceous Proterozoic Mafic rocks ∼ ∼ Thrusts (nappe contact) } Foliation Strike-slip fault Gneiss Song Chay v v Volcano-detritic * Sample Fig Simplified geological map of NE Vietnam (adapted from Geology of Vietnam (North Part) Hanoi, General Department of Geology 1979 and Lepvrier et al (2011) the same magmatic complex is unconformably covered by Upper Triassic sandstones and conglomerates (Fig 2) More to the North–Northeast, the Phia Oac granite, located South of Nguyen Binh and Tinh Tuc villages is also an undeformed post-tectonic granite (Bourret, 1922) It is a two-micas leucocratic granite, with phenocrysts of feldspars (sample VT 235; N22°370 2900 ; E105°520 42) which has been emplaced through the ductilely deformed allochthonous Devonian series This formation is exposed on the western flank of the massif and to the East through the Lower Triassic Song Hien Formation that also forms a displaced unit (Lepvrier et al., 2011) (Fig 2) The pluton is surrounded by a contact metamorphic aureole formed by cordierite–andalusite–biotite schists and horns Izokh et al (1964) obtained K–Ar ages of 85– 95 Ma on biotite and muscovite U–Pb geochronology 3.1 LA-ICPMS: instrumentation and analytical method Separated grains were mounted in epoxy resin disks, polished to reveal equatorial cross sections U–Th–Pb geochronology of zircon was conducted by laser ablation inductively coupled with plasma spectrometry (LA-ICPMS) at the Laboratoire Magmas et Volcans, Clermont-Ferrand (France) The analyses involve the ablation of minerals with a Resonetics Resolution M-50 powered by an ultra short pulse ATL Atlex Excimer laser system operating at a wavelength of 193 nm (detailed description in Müller et al., 2009) Spot diameters of 26 lm associated to repetition rates of Hz with a laser energy of mJ were used The ablated material is carried into helium, and then mixed with nitrogen and argon, before injection into a plasma source of an Agilent 7500 cs ICP-MS equipped with a dual pumping system to enhance the sensitivity The analytical method is basically similar to that developed by and reported in Tiepolo (2003) and Paquette and Tiepolo (2007) The signals of 204(Pb + Hg), 206Pb, 207Pb, 208Pb, 232Th and 238U masses are acquired The occurrence of common Pb in the sample can be monitored by the evolution of the 204(Pb + Hg) signal intensity, but no common Pb correction was applied owing to the large isobaric interference from Hg The 235U signal is calculated from 238 U on the basis of the 238U/235U = 137.88 Single analyses consisted of 30 s of background integration with laser off followed by integration with the laser firing and a 30 s delay to wash out the previous sample (approximately 10 s for six orders of magnitude) and to prepare the next analysis Data are corrected for U– Pb and Th–Pb fractionation occurring during laser sampling and for instrumental mass discrimination (mass bias) by standard bracketing with repeated measurements of GJ-1 zircon standard (Jackson et al., 2004) Data reduction was carried out with the software Ò package GLITTER (developed by the Macquarie Research Ltd.), (Van Achterbergh et al., 2001; Jackson et al., 2004) For each analysis, the time-resolved signal of single isotopes and isotopic ratios was monitored and carefully inspected to verify the presence of perturbations related to inclusions, fractures, mixing of different Table Analytical results of LA-ICPMS U-Pb dating Spot no Zircon Concentration (ppm) Th U Th/U Raw ratios 207 Pb/206Pb Apparent ages (Ma) ±1r 206 Pb/238U ±1r 207 Pb/235U ±1r 208 Pb/232Th ±1r 207 Pb/206Pb ±1r 206 Pb/238U ±1r 207 Pb/235U ±1r 208 Pb/232Th ±1r Z6-C Z6-R Z5-R Z4-R Z4-C Z1-C Z7-R1 Z7-C Z7-R2 Z8-R Z8-C Z9-R Z9-C Z10-R Z10-C Z11-R1 Z11-C Z11-R2 Z14-C Z14-R Z21-R Z20-R1 Z20C Z20-R2 Z18-R1 Z18-C Z18-R2 136 271 482 229 237 579 198 177 224 224 168 606 529 222 213 116 300 176 237 313 163 180 156 203 200 54 301 284 1605 800 412 272 744 478 209 483 833 199 3944 481 389 288 332 882 396 519 393 245 564 135 376 611 128 1915 0.48 0.17 0.60 0.55 0.87 0.78 0.42 0.84 0.46 0.27 0.85 0.15 1.10 0.57 0.74 0.35 0.34 0.44 0.46 0.79 0.67 0.32 1.15 0.54 0.33 0.43 0.16 0.07224 0.05215 0.05191 0.05146 0.05152 0.05249 0.05169 0.05257 0.05294 0.05141 0.05427 0.05124 0.07077 0.05244 0.05397 0.05089 0.17409 0.05190 0.15295 0.05127 0.05049 0.05300 0.09554 0.05129 0.05405 0.07031 0.05113 0.00106 0.00072 0.00075 0.00087 0.00096 0.00076 0.00091 0.00115 0.00086 0.00076 0.00119 0.00066 0.00095 0.00094 0.00105 0.00093 0.00213 0.00090 0.00210 0.00095 0.00104 0.00089 0.00169 0.00095 0.00086 0.00111 0.00069 0.13885 0.03976 0.03797 0.03968 0.0392 0.03928 0.03955 0.03854 0.03909 0.03977 0.03906 0.03917 0.14509 0.03962 0.03889 0.03873 0.36343 0.03922 0.24238 0.03951 0.03919 0.03856 0.14095 0.03886 0.03822 0.14200 0.03899 0.00173 0.00049 0.00047 0.0005 0.00049 0.00049 0.0005 0.0005 0.00049 0.00049 0.0005 0.00048 0.0018 0.0005 0.0005 0.00049 0.00449 0.0005 0.00306 0.0005 0.0005 0.00049 0.00183 0.0005 0.00048 0.0018 0.00049 1.38336 0.28594 0.2718 0.28163 0.27847 0.28432 0.28189 0.27943 0.28537 0.28192 0.29229 0.27673 1.41596 0.28649 0.28948 0.27185 8.72533 0.28070 5.11234 0.27937 0.27287 0.28185 1.85705 0.27483 0.28484 1.37692 0.27492 0.02214 0.00436 0.00432 0.00505 0.00544 0.00453 0.00527 0.00630 0.00499 0.00456 0.00660 0.00400 0.02116 0.00542 0.00591 0.00526 0.12220 0.00519 0.07782 0.00547 0.00584 0.00505 0.03463 0.00537 0.00490 0.02350 0.00417 0.04399 0.01219 0.01183 0.01219 0.01200 0.01234 0.01283 0.01191 0.01214 0.01215 0.01214 0.01227 0.04271 0.01204 0.01263 0.01198 0.09439 0.01253 0.08243 0.01248 0.01249 0.01202 0.06440 0.01192 0.01377 0.04123 0.01300 0.00094 0.00027 0.00025 0.00027 0.00026 0.00026 0.00030 0.00028 0.00028 0.00029 0.00029 0.00028 0.00095 0.00029 0.00031 0.00031 0.00217 0.00031 0.00205 0.00031 0.00033 0.00032 0.00163 0.00032 0.00036 0.00111 0.00034 992.8 291.8 281.4 261.6 264 306.9 271.6 310.4 326.1 259 381.9 251.4 950.7 304.6 369.7 235.9 2597.4 281.1 2379.1 253 217.6 328.8 1538.7 253.8 372.9 937.5 246.8 29.6 31.2 32.9 38.2 42.1 32.8 40.0 48.9 36.6 33.7 48.3 29.2 27.1 40.1 43.5 41.8 20.3 39.3 23.2 42.2 46.9 37.4 32.9 42.0 35.5 32.0 30.8 838.2 251.4 240.2 250.9 247.8 248.3 250 243.8 247.2 251.4 247 247.7 873.4 250.5 246 245 1998.4 248 1399.1 249.8 247.8 243.9 850 245.7 241.8 856 246.6 9.8 3.0 2.9 3.1 3.1 3.0 3.1 3.1 3.0 3.1 3.1 3.0 10.1 3.1 3.1 3.1 21.3 3.1 15.9 3.1 3.1 3.0 10.4 3.1 3.0 10.2 3.0 881.9 255.4 244.1 252 249.4 254.1 252.2 250.2 254.9 252.2 260.4 248.1 895.7 255.8 258.2 244.2 2309.7 251.2 1838.2 250.2 245 252.1 1065.9 246.5 254.5 879.1 246.6 9.4 3.4 3.5 4.0 4.3 3.6 4.2 5.0 4.0 3.6 5.2 3.2 8.9 4.3 4.7 4.2 12.8 4.1 12.9 4.4 4.7 4.0 12.3 4.3 3.9 10.0 3.3 870.1 244.9 237.8 244.9 241.2 247.9 257.7 239.2 244 244.1 243.8 246.4 845.4 241.8 253.7 240.7 1823.1 251.7 1601 250.7 250.9 241.6 1261.4 239.5 276.5 816.7 261.1 18.3 5.5 4.9 5.4 5.3 5.2 6.0 5.6 5.5 5.7 5.9 5.6 18.5 5.8 6.2 6.2 40.2 6.3 38.4 6.3 6.5 6.4 31.0 6.3 7.2 21.5 6.8 VT 19 16 17 18 19 20 21 22 23 24 27 28 29 30 31 32 33 34 35 38 39 40 41 42 43 44 Z9 Z10-R1 Z10-C Z10-R2 Z11-R1 Z11-R2 Z12-C Z1-R Z1-C Z3-R1 Z3-C Z3-R2 Z4-R1 Z4-R2 Z7-C Z8-R1 Z8-C Z8-R2 Z14-R1 Z14-R2 Z15-R Z15-C Z6-R Z6-C Z1-R 600 397 799 638 250 773 995 967 457 1127 829 795 349 182 495 1435 1458 1257 736 837 631 510 1109 979 844 1031 621 888 811 1435 1155 1547 961 775 1645 1408 1379 1360 232 628 1632 1933 1364 1729 1563 728 716 1707 1488 1090 0.58 0.64 0.90 0.79 0.17 0.67 0.64 1.01 0.59 0.68 0.59 0.58 0.26 0.79 0.79 0.88 0.76 0.92 0.43 0.54 0.87 0.71 0.65 0.66 0.77 0.05664 0.05111 0.05169 0.05272 0.05241 0.05609 0.05199 0.05219 0.05139 0.05217 0.05286 0.05333 0.05472 0.05506 0.05280 0.05193 0.05256 0.05110 0.05179 0.05346 0.05269 0.05250 0.05180 0.05362 0.05149 0.00077 0.00078 0.00070 0.00071 0.00068 0.00077 0.00066 0.00068 0.00070 0.00069 0.00069 0.00070 0.00091 0.00199 0.00084 0.00067 0.00068 0.00065 0.00079 0.00142 0.00074 0.00076 0.00072 0.00091 0.00071 0.0366 0.03932 0.03848 0.03814 0.03797 0.03828 0.03841 0.03839 0.03851 0.03812 0.03718 0.03734 0.03784 0.03633 0.03859 0.03884 0.03783 0.03835 0.03768 0.03340 0.03797 0.04056 0.03890 0.03739 0.03945 0.00045 0.00048 0.00047 0.00046 0.00046 0.00047 0.00047 0.00047 0.00047 0.00046 0.00045 0.00046 0.00047 0.00052 0.00048 0.00047 0.00046 0.00047 0.00047 0.00045 0.00047 0.00050 0.00048 0.00047 0.00049 0.28586 0.27715 0.27433 0.2773 0.27444 0.29608 0.27538 0.27632 0.27296 0.27424 0.27104 0.27459 0.28552 0.27584 0.28100 0.27816 0.27421 0.27027 0.26912 0.24625 0.27585 0.29361 0.27787 0.27645 0.28017 0.00428 0.00452 0.00408 0.00412 0.00394 0.00445 0.00392 0.00400 0.00409 0.00401 0.00394 0.00398 0.00506 0.00991 0.00478 0.00398 0.00394 0.00387 0.00445 0.00659 0.00427 0.00466 0.00424 0.00496 0.00424 0.01261 0.01218 0.01176 0.01196 0.01415 0.01330 0.01182 0.01166 0.01184 0.01185 0.01205 0.01224 0.01321 0.01171 0.01222 0.01190 0.01194 0.01194 0.01237 0.01258 0.01152 0.01227 0.01220 0.01175 0.01213 0.00022 0.00021 0.00020 0.00020 0.00026 0.00023 0.00020 0.00020 0.00021 0.00021 0.00021 0.00022 0.00029 0.00032 0.00023 0.00021 0.00022 0.00022 0.00025 0.00031 0.00022 0.00024 0.00024 0.00024 0.00024 476.7 245.9 271.8 316.8 303.2 455.6 284.9 293.8 258.4 293 322.9 342.7 400.1 414.6 320.4 282.1 309.8 245.4 276.2 348.2 315.2 307.1 276.8 355 263 30.2 34.6 30.7 30.4 29.2 29.8 28.9 29.5 31.0 29.8 29.4 29.1 37.3 78.3 35.7 29.0 29.0 29.2 34.7 58.8 31.7 32.8 31.4 37.8 31.2 231.7 248.6 243.4 241.3 240.3 242.1 243 242.8 243.6 241.1 235.3 236.3 239.4 230 244.1 245.7 239.4 242.6 238.4 211.8 240.2 256.3 246 236.6 249.4 2.8 3.0 2.9 2.9 2.9 2.9 2.9 2.9 2.9 2.9 2.8 2.8 2.9 3.3 3.0 2.9 2.9 2.9 2.9 2.8 2.9 3.1 3.0 2.9 3.0 255.3 248.4 246.1 248.5 246.2 263.3 247 247.7 245.1 246.1 243.5 246.4 255 247.3 251.5 249.2 246.1 242.9 242 223.5 247.4 261.4 249 247.8 250.8 3.4 3.6 3.3 3.3 3.1 3.5 3.1 3.2 3.3 3.2 3.1 3.2 4.0 7.9 3.8 3.2 3.1 3.1 3.6 5.4 3.4 3.7 3.4 4.0 3.4 253.4 244.6 236.3 240.2 284 267 237.5 234.4 238 238.1 242.1 245.8 265.2 235.3 245.5 239.1 239.8 239.9 248.5 252.7 231.6 246.6 245.1 236.1 243.8 4.3 4.3 3.9 4.0 5.2 4.6 4.0 4.0 4.2 4.2 4.3 4.3 5.7 6.5 4.6 4.3 4.3 4.3 5.0 6.2 4.4 4.8 4.7 4.9 4.7 75 (continued on next page) F Roger et al / Journal of Asian Earth Sciences 48 (2012) 72–82 VT 16 49 50 51 52 53 54 55 56 57 60 61 62 63 64 65 66 67 68 71 72 73 74 75 76 77 78 79 76 Table (continued) Spot no Zircon Concentration (ppm) Th U Th/U Raw ratios 207 Pb/206Pb Apparent ages (Ma) ±1r 206 Pb/238U ±1r 207 Pb/235U ±1r 208 Pb/232Th ±1r 207 Pb/206Pb ±1r 206 Pb/238U ±1r 207 Pb/235U ±1r 208 Pb/232Th ±1r Z1-C Z2 438 1225 629 1471 0.69 0.83 0.05152 0.05111 0.00097 0.00070 0.03921 0.03878 0.00050 0.00048 0.27856 0.27334 0.00548 0.00412 0.01226 0.01208 0.00026 0.00024 264.1 245.6 42.6 31.0 247.9 245.3 3.1 3.0 249.5 245.4 4.4 3.3 246.3 242.7 5.3 4.8 VT 235 10 11 12 13 42 43 44 46 48 49 50 53 54 57 58 59 60 61 Z15-R1 Z15-C Z14-R Z7-C Z7-R Z6-R Z1-R1 Z1-C Z1-R2 Z2-C Z3-R1 Z3-C Z3-R2 Z9-R1 Z9-C Z19-C Z19-R Z12-R1 Z12-C Z12-R2 178 201 854 208 318 86 304 355 1181 263 1160 483 339 234 1021 136 274 431 3200 247 584 982 414 841 1893 436 5914 1334 2718 2058 9121 1952 8243 4604 827 1847 2386 3081 1644 1736 0.305 0.205 2.062 0.247 0.168 0.198 0.051 0.266 0.435 0.128 0.127 0.248 0.041 0.051 1.235 0.074 0.115 0.140 1.946 0.142 0.05021 0.04835 0.04975 0.06707 0.04834 0.04979 0.0478 0.04707 0.04883 0.04899 0.04862 0.04758 0.04909 0.05305 0.05834 0.04766 0.04791 0.05063 0.05019 0.04793 0.00111 0.00084 0.0012 0.00079 0.00108 0.00126 0.00057 0.00079 0.00067 0.0007 0.00057 0.00081 0.0006 0.00072 0.00119 0.00074 0.0008 0.00076 0.00087 0.00083 0.01334 0.01327 0.01331 0.12819 0.01404 0.01339 0.01357 0.01372 0.01342 0.0137 0.01367 0.01337 0.01347 0.01387 0.01711 0.0136 0.01313 0.01303 0.01454 0.01326 0.00017 0.00016 0.00017 0.00154 0.00018 0.00017 0.00016 0.00017 0.00016 0.00016 0.00016 0.00016 0.00016 0.00017 0.00021 0.00016 0.00016 0.00016 0.00018 0.00016 0.09239 0.08847 0.09128 1.18561 0.09357 0.09191 0.08945 0.08904 0.09035 0.09256 0.09169 0.08774 0.0912 0.1015 0.13762 0.08941 0.08678 0.09097 0.10062 0.08766 0.0021 0.00162 0.00224 0.0158 0.00213 0.00236 0.00118 0.00157 0.00134 0.00141 0.00119 0.00156 0.00123 0.00149 0.00287 0.00147 0.00152 0.00146 0.00183 0.00159 0.0042 0.00428 0.00407 0.0376 0.00451 0.00474 0.00448 0.0045 0.00422 0.00509 0.00479 0.00456 0.00569 0.01307 0.00565 0.00507 0.00412 0.00461 0.00389 0.00447 0.0001 0.0001 0.00007 0.00063 0.00013 0.00016 0.00009 0.00009 0.00007 0.0001 0.00008 0.0001 0.00012 0.00028 0.00012 0.00014 0.00012 0.00012 0.00009 0.00013 204.5 116.5 183.2 839.8 116 185.1 88.5 52.5 139.7 147.6 129.5 77.6 152.3 330.9 541.9 81.4 93.7 224 203.8 94.8 50.7 40.6 55.2 24.3 51.7 57.7 29.0 39.0 32.0 33.0 27.1 40.7 28.2 30.4 44.6 37.2 40.1 34.3 39.7 41.5 85.5 85 85.2 777.5 89.9 85.7 86.9 87.8 85.9 87.7 87.6 85.6 86.3 88.8 109.3 87.1 84.1 83.4 93 84.9 1.1 1.0 1.1 8.8 1.1 1.1 1.0 1.1 1.0 1.0 1.0 1.0 1.0 1.1 1.4 1.1 1.0 1.0 1.1 1.0 89.7 86.1 88.7 793.9 90.8 89.3 87 86.6 87.8 89.9 89.1 85.4 88.6 98.2 130.9 87 84.5 88.4 97.3 85.3 2.0 1.5 2.1 7.3 2.0 2.2 1.1 1.5 1.3 1.3 1.1 1.5 1.1 1.4 2.6 1.4 1.4 1.4 1.7 1.5 84.8 86.3 82.1 746 90.9 95.5 90.3 90.8 85.1 102.5 96.6 91.9 114.7 262.5 113.8 102.2 83.1 93 78.4 90.1 2.1 2.0 1.4 12.3 2.7 3.1 1.7 1.8 1.4 2.1 1.7 2.0 2.4 5.6 2.4 2.9 2.4 2.4 1.8 2.6 R = rim and C = center 75 78 Zr1 A Zr20 74 61 49 Zr8 100 μm 55 47 Zr9 Zr2 B 46 C 60 79 Zr18 45 G 54 50 Zr6 100 μm D 57 Zr7 50 49 56 Zr3 48 100 μm age domains or common Pb Calculated ratios were exported and Concordia ages and diagrams were generated using the Isoplot/ Ex v 2.49 software package by Ludwig (2001) The analytical data are provided in Table where errors are given at ±1r In the text and figures, all uncertainties in ages are given at the 95% confidence level (±2r) The discordant data were considered only if they allowed possible discordia lines to be defined on the Concordia diagrams; otherwise they were not taken into account because of doubtful interpretation In laser-ablation ICPMS analyses several factors that cannot be easily detected from the inspection of the time-resolved signals might contribute to discordance (e.g common Pb, mixing of different age domains, small cracks or inclusions) 3.2 Results 44 43 Zr15 53 3.2.1 Description of zircons The zircons crystals from the three samples (VT 19, VT16 and VT 235) dated by LA-ICPMS were mostly euhedral, transparent, colorless, stubby to elongate in shape, ranging in size between 100 and 300 lm Before isotopic analyses, backscatter electron (BSE) and cathodoluminescence (CL) images were acquired for all grains using a scanning electron microscope (SEM) in order to check spot positions with respect to the internal microstructures BSE and CL images show that most zircons had complex internal structures (sector zoning and inherited core for VT 235) (Fig 3) Well preserved euhedral growth zones, with unperturbed oscillatory zoning typical of magmatic growth (Hanchar and Miller, 1993) were also present No non-magmatic mechanism has been 76 100 μm 77 100 μm E 42 100 μm F 100 μm Fig Cathodoluminescence images of dated zircons crystals from: (A–D) the Phia Bioc granite (VT16) and (E–G) the Phia Oac granite (VT 235) Circles indicate the analytical spots with a diameter of about 26 lm The numbers in italics refer to analytical data in Table F Roger et al / Journal of Asian Earth Sciences 48 (2012) 72–82 45 46 77 F Roger et al / Journal of Asian Earth Sciences 48 (2012) 72–82 demonstrated to produce oscillatory zoning in zircon (Hoskin, 2000) Non-magmatic zircon (i.e metamorphic, recrystallized, or hydrothermal) tends to have poorly-defined internal zoning with sometimes a non-geometric patchy zoning (Pidgeon, 1992; Hanchar and Miller, 1993; Hoskin and Black, 2000) Igneous zircon has typically higher Th/U ratios (>0.1) that usually not overlap with Th/U ratios of non-igneous zircon (Williams and Claesson, 1987; Vavra et al., 1996; Hoskin and Black, 2000; Hartmann and Santos, 2004) events (Neo-Proterozoic) in the region 21 analyses (rims and cores) (Table 1) form a concordant to sub-concordant cluster yielding an age of 248.5 ± Ma (MSWD = 0.91) and a weighted average 207 Pb/206Pb age of 247 ± 1.5 Ma (MSWD = 1.03) (Fig 4A) The Th/U ratio of the concordant Permo-Triassic core (Th/U = 0.741–0.872) is indistinguishable from the range observed in concordant PermoTriassic rims analyses (Th/U = 0.154–0.872) These values are typical of igneous zircons and the U–Th–Pb age of 248.5 ± Ma is interpreted as the emplacement age of the magmatic protolith 3.2.2 Phia Bioc granite-Ba Be lake sample (VT 16) A total of 27 analyses, carried out on 13 crystals are listed in Table and plotted in Fig CL images show that most zircons have complex internal structures (Fig 3A–C) Six zircons show inherited cores with U contents from 128 to 882 ppm and Th/U ratios from 0.340 to 1.155 Among these cores, three spots (no 67, 71, 75) indicating inherited 207Pb/206Pb age components from 2.4 to 2.6 Ga and 1.6 Ga, were not retained in the discussion and the interpretation (cf III-1) (Figs 3A and 4A) They probably correspond to a mixture between an old core and the younger rim around 245–250 Ma (spot no 66, 68, 72; 74, 76) (Table 1) Rims and cores of three other zircons (Zr: 6, and 18) have been investigated and cores have a sub-concordant position and yield 206Pb/238U age of 855 ± 44 Ma (MSWD = 3.1), 207Pb/235U age of 886 ± 11 Ma (MSWD = 0.92) and 207 Pb/206Pb age 961 ± 33 Ma (MSWD = 0.92) Rims (spots no 50, 62, 77, 79) have a concordant to sub-concordant position around 245–250 Ma and are characterized by higher U concentrations ranging from 1605 to 3944 ppm, with lower Th/U from 0.154 to 0.169 All these features indicate the occurrence of old magmatic 3.2.3 Phia Bioc granite-Bac Can sample (VT 19) A total of 33 spots were analyzed on 13 zircons from this sample The U and Th contents of rims and cores are very similar, ranging from 621 to 1707 ppm and from 250 to 1458 ppm, respectively Rims and cores of zircons have Th/U ratios bracketed between 0.174 and (Table 1), typical values of igneous zircon All ellipses form a concordant to sub-concordant cluster yielding an age of 245 ± Ma (MSWD = 1.7) and the weighted average of 206Pb/238U ages is 242 ± Ma (MSWD = 1.7) (Table and Fig 4B), which is interpreted to represent the emplacement age of the magmatic protolith A VT 19 : Phia Bioc granite - Bac Can 260 206 0.039 23 Spots T = 245 ± Ma (MSWD = 1.7) 240 220 0.033 200 0.031 0.21 0.23 0.25 254 250 246 242 238 234 230 226 T = 242 ± Ma 23 spots MSWD = 1.7 207 0.27 Pb/235U 0.29 0.31 VT 235 : Phia Oac granite VT 16 : Phia Bioc granite - BaBe B 2200 206 0.14 71 78,49,63 0.039 75 220 0.23 0.25 256 252 248 244 240 236 232 0.016 0.27 100 300 90 0.014 0.04 80 0.012 (MSWD = 1.03) 100 Pb/235U 10 Fig Zircon U–Pb concordia diagrams from Phia Bioc granite Both undeformed granites are analyzed: VT 19 near Bac Can village (A) and VT 16 near the Ba Be lake (B) (Fig 2) Error ellipses and uncertainties in ages are ±2r 54 12 12 43 46 48 57 4250 13 49 10 44 61 58 16 spots T = 247.1 ± 1.3 Ma 207 120 T = 87.3 ± 1.2 Ma 110 (MSWD = 1.5) 206 200 130 0.020 0.018 21 spots Pb/238U Age (Ma) 0.035 0.08 240 0.031 0.21 500 (MSWD = 0.91) 0.033 0.0 0.022 /235 T = 248.5 ± 1.8 Ma 260 0.037 0.1 600 11 700 78,49,63 207 Pb/238U 0.041 900 20 Spots 840 Pb U 0.13 1.15 1.25 1.35 1.45 1.55 206 0.2 0.12 920 T = 961±33 Ma 880 0.15 1800 1400 1000 960 67 206 0.3 27 spots Pb/238U Pb/238U 0.4 0.16 206 0.035 (206Pb/238U) Age (Ma) 0.037 0.010 0.07 0.09 54 60 53 (206Pb/238U) Age (Ma) Pb/238U 0.041 Pb/238U 0.043 3.2.4 Phia Oac granite (VT 235) CL images show growth zoning typically observed in magmatic zircons (Fig 3E–G) We performed a total of 20 spot analyses on both cores and rims of 10 grains Among these, 16 analyses (Table 1) form a concordant to sub-concordant cluster yielding a mean age of 87.3 ± 1.2 Ma (MSWD = 1.5) with a mean 206Pb/238U age of 85.9 ± 0.7 Ma (MSWD = 1.7) The rims show highly variable U and Th concentrations (U = 414–9121 ppm, Th = 86–3200 ppm), whereas the core areas have more uniform U (982–2058 ppm) and Th (201–483 ppm) concentrations The Th/U ratios is ranging from 0.127 to 2.062 except for three rims (spot 42, 50, 53) which have lower Th/U ratios (0.041–0.051) as well as more homogeneous Th and U concentrations (Th = 234–339 ppm and U = 4504–8243 ppm) In zircon 7, the core (spot no 11) has a sub-concordant position and yields a 206Pb/238U age of 777.5 ± 18 Ma (±2r), and a 207Pb/235U age of 794 ± 15 Ma Rims are much younger at around 90 Ma (Table 1, Fig 5) The three analyses (spot 53, 54, 60) produced discordant ages, which probably correspond to a mixture between an old core and a younger rim around 87 Ma (Fig 3G) We interpret the 87.3 ± 1.2 Ma age as reflecting the magma emplacement age of the Phia Oac granite 94 92 90 88 86 84 82 80 (12) T = 86 ± Ma 0.11 0.13 206 0.00 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Pb/238U 1.4 Fig Zircon U–Pb concordia diagrams from Phia Oac granite (VT 235) Error ellipses and uncertainties in ages are ±2r 78 F Roger et al / Journal of Asian Earth Sciences 48 (2012) 72–82 Discussion Among the zircons analyzed from Phia Bioc granite (VT 16) and Phia Oac granite (VT 235), two inherited magmatic cores are in concordant to sub-concordant position around 800–900 Ma This highlights the occurrence of Neo-proterozoic magmatic episodes in NE Vietnam A major Neo-proterozoic (1–0.75 Ga) event has already been recognized within the South China Block, correlated to the amalgamation and then break-up of the Rodinia Continent (Li, 1999; Li et al., 2002, 2006; Zhou et al., 2002, 2006a,b, 2007; Roger et al., 2010) An outstanding fact is the lack of Paleozoic ages (around 460– 420 Ma) within the cores of the zircons, although a magmatic intrusive event is known in northeastern Vietnam in the Song Chay massif (428 ± Ma) (Roger et al., 2000; Carter et al., 2001), at close distance from these granites (Figs and 2) A similar range of metamorphic and magmatic ages, related to the pre-Devonian Early Paleozoic event are known in South China (Wang et al., 2007b) as for example in the Xuefeng Shan belt where 420– 450 Ma ages are locally recorded In the Yunkai massif a tectonothermal event occurred also during the Silurian: magmatic zircons yield U–Pb ages ranging between 440 and 410 Ma and detrital zircons from paragneisses have been dated at 423 ± Ma (Wang et al., 2007c; Lin et al., 2008) This event is expressed in the South China Block and in the autochtonous domain of North Vietnam (Dong Van and Cao Bang areas) by the Devonian unconformity In Vietnam (in the Indochina block), the Ordovician–Silurian major metamorphic and magmatic event has also been found in the Kontum Block, where Ordovician ages (465–470 Ma) occur in granulites and could represent a minimum age for a HT metamorphic episode (Roger et al., 2007) (Fig 1A) Silurian ages (420–440 Ma) have also been found in the Dien Binh series which outcrop east of the Po Ko fault zone, on the western edge of the Kontum massif (Nagy et al., 2001; Vu Van Tich, 2004; Maluski et al., 2005; Roger et al., 2007) (Fig 1A) Silurian ages are also found in the Dailoc orthogneissic massif in the central part of the Truong Song range (Carter et al., 2001) (Fig 1A) Triassic ages are obtained on the Phia Bioc massif, where the two samples VT19 and VT16, record an emplacement age of 245 ± Ma, and 248.5 ± Ma respectively for this granite intrusion (Fig 4A and B) In the studied area of NE Vietnam, the Ordovician and Devonian shales and sandstones, which are part of the nappe system, are intruded by the Phia Bioc granite This granite is clearly undeformed These observations imply that the major tectonometamorphic event in the northeastern area of Vietnam, represented by nappes thrusting, cannot be younger than 248.5 ± Ma This result is in close agreement with the regional unconformity of the Upper Triassic sediments on the Lower Paleozoic deformed metasedimentary rocks (Deprat, 1914; Fromaget, 1941b; Zhang, 1999; Liang and Li, 2005; Zhang et al., 2011) Furthermore, the Upper Triassic sandstones and conglomerates with coal seams rest upon the undeformed Phia Bioc granite and the Cho Chu granite (Fig 2) To the SE of the South China block (Cathaysia block) (Fig 2), equivalent Triassic ages have been found in Early Mesozoic belts, formed in various geodynamic settings prior the regional Upper Triassic unconformity but involving Lower Triassic strata (e.g., HNGBMR, 1988; Deng et al., 2004; Qiu et al., 2004; Wang et al., 2005, 2007b; Li et al., 2007) Several hypotheses can be invoked to explain this magmatism: Several authors propose a common origin with the Emeishan Large Igneous Province (ELIP) in the South China Block (Wang et al., 2007a; Hoa et al., 2004, 2008; Polyakov et al., 2009; Shelepaev et al., 2010) The Phia Bioc massif intrusion is contemporaneous with the Nui Chua gabbronorite (U–Pb: 251 ± 3.4 Ma), with the rhyolites exposed to the East of Cao Bang in the Suoi Cun Massif (U–Pb: 248 ± 4.5 Ma) and Cho Don granite (Ar–Ar (Bt): 250 ± Ma) (Hoa et al., 2008) (Fig 2) In the Luc Yen area, the Tan Linh gabbrosyenite also yields similar ages of 247 and 243 Ma, according to Rb/Sr and Ar/Ar datings respectively (Hoa et al., 2004) (Fig 2) To the south of the Red River Fault, the Kim Boi cordierite granite has been dated by U–Pb on zircon at 242.4 ± 2.2 Ma (Hoa et al., 2008) For these authors (Hoa et al., 2004, 2008), all these granitoids belong to the same magmatic complex namely the Phia Bioc complex From these data, the duration of this magmatism in NE Vietnam should be bracketed between around 255 and 240 Ma This is a bimodal volcano-plutonic association with mafic–ultramafic rocks (Nui Chua complex) and high alumina granites (Phia Bioc complex) which intrude the nappe structure (Fig 2) This bimodal magmatism is associated with the ELIP in the South China Block and off which the Tule volcanic province is shifted by the left lateral Red River Fault It can be considered as a product of the Permo-Triassic intra-plate magmatism of North Vietnam (Wang et al., 2007a; Hoa et al., 2008; Polyakov et al., 2009; Shelepaev et al., 2010) Nevertheless, the duration of the ELIP in the South China is strongly debated: some authors (Ali et al., 2002; Zheng et al., 2010; Shellnutt et al., in press) consider that this magmatic event is extremely short in time between 260 and 257 Ma while other authors (Fan et al., 2008; Zhong et al., 2007, 2009; Shellnutt and Zhou, 2008) propose a longer duration around 10 Ma Either this magmatism is continuous up to around 250 Ma or the magmatism post-257 Ma would be related to the collision between the Sibumasu and Indochina Blocks (Shellnutt et al., 2011) during the closure of the Paleotethys ocean (Late Permian/Early Triassic) (Lepvrier et al., 2004) The closure of the Paleotethys could be also the process responsible for the emplacement of Phia Bioc granite intrusive in the allochtonous series This ductile nappe tectonics is synchronous with the tectonometamorphic and magmatic events already described and dated along the Paleotethys sutures in western Yunnan (Ailao Shan, and Lancangjiang) and to the Northern Vietnam including the South of the Red River fault zone, in the Song Ma shear zone and in the Truong Son Range, up to the south in the Kontum Massif (Vu Van Tich, 2004; Maluski et al., 2005; Lepvrier et al., 2008; Roger et al., 2007; Peng et al., 2008; Fan et al., 2010; Wang et al., 2010) (Fig 1A) More recently Searle et al (2010) obtained U/Pb ages between 243 and 239 Ma from metamorphic and magmatic rocks along the Red River Fault zone, in Ailao Shan, Diancang Shan and Day Nui Con Voi) (Figs and 2) In the Dulong – Song Chay Massif, the Ar/Ar metamorphism ages have been found around 234– 237 Ma (Maluski et al., 2001; Yan et al., 2006) These younger ages have to be understood as a cooling age linked to the emplacement of the nappe Carter and Clift (2008) consider that in Vietnam the Indosinian tectonics is linked to a continental accretion and tectonic reactivation event along an ancient suture (Song Ma Suture), whereas in South China, Triassic thermotectonic events are linked to the development of an active plate margin through North to North-West directed subduction of the Paleo-Pacific oceanic plate (Li et al., 2006, 2007) This interpretation is still largely debated The reactivation of the Song Ma suture would be driven by the closure of the Paleotethys and the accretion of the Sibumasu block to Indochina (Fig 1) (Carter and Clift, 2008; Lepvrier et al., 2008) The recent discovery of eclogite and high-pressure granulite facies metamorphism (dated at 243 ± Ma) along the Song Ma suture zone in northern Vietnam (Nakano et al., 2008, 2010) suggests that this structure corresponds to the suture zone between Indochina and South China and that the collision occurred during the Early Triassic Furthermore the peak P conditions estimated for the eclogite F Roger et al / Journal of Asian Earth Sciences 48 (2012) 72–82 (>2.1–2.2 GPa) indicate that continental subduction occurred, attesting of a strong continental collision event incompatible with the reactivation model of Carter and Clift (2008) In the same way, Zhou and Li (2000) and Zhang et al (2011) suggest that westward subduction of the Paleo-Pacific plate was probably initiated around mid-Jurassic times According to He et al (2010), in the coastal Southeast China the Triassic tectonics corresponds to N–S compression resulting from the northward collision of the Indochina Block and South China Block The tectonic transition from the Tethys to the Panthalassa (PaleoPacific) orogenic regimes was carried out in the Early Jurassic A detailed geochemical study of the Phia Bioc massif, will lead us to choose between an origin linked to Emeishan plume activity or the magmatism products during the closure of the Paleotethys and continental collision between Indochina and South China Blocks The Cretaceous U–Pb age of 87.3 ± 1.2 Ma obtained on the Phia Oac granite confirms and precises the earlier K–Ar ages of 85– 95 Ma obtained on biotite and muscovite (Izokh et al., 1964) Those ages are coherent with field relations between the granite and the lower Triassic sedimentary rocks of the Song Hien displaced unit Up to now Cretaceous ages (79–105 Ma) on magmatic material in Northern Vietnam were known through old K–Ar on biotite and hornblende measurements in the Phu Sa Phin granite (Phan et al., 1991; Dovjikov, 1965) (Fig 2) In the Tule Basin, Anh et al., 2003 obtained Ar–Ar ages of 80–60 Ma on magmatic rocks Cretaceous granites are not restricted to NE Vietnam but are already known in the Yidun block (eastern Tibet), in the Sibumasu block (Shan Thai Block) and South China Block (Fig 1): Within the Yidun block, the emplacement of the Chola Shan (105 ± Ma) and Haizi (94 ± Ma) granitoids suggests that a magmatic episode occurred during the middle Cretaceous (Reid et al., 2005) (Fig 1) Both intrusions are possibly related to extension associated with the northward subduction of the Tethys underneath Asia (Reid et al., 2007) However, the plutons are close to major faults (the Ganzi and Litang faults) and it is possible that the Cretaceous magmatic activity was related to the fault activity (Roger et al., 2010, 2011) The origin of those two Cretaceous granites remains very uncertain however it is generally accepted that Jurassic – Cretaceous tectonics did not modify the general Triassic architecture of eastern Tibet (e.g Burchfield et al., 1995; Roger et al., 2004, 2010, 2011; Harrowfield and Wilson, 2005; Reid et al., 2005; Wilson et al., 2006) In Thailand, an orogenic episode occurred during the Cretaceous, between 90–70 Ma This tectonic has been dated in southern Thailand (Watkinson et al., 2008) from granitic intrusions To the North, the core complexes of Doi Ithanon and the Chiang Mai-Licang Belt record ages of 85–70 Ma for the metamorphism (Dunning et al., 1995; Macdonald et al., 2010) (Fig 1) Up to now, no clear origin for this orogeny has been expressed For Dunning et al (1995), the collision between Western Burma and the Shan Thai Block could be one of the driving mechanisms (Fig 1) Many more Cretaceous ages have been found on granitic intrusions in the western end of the South China Block (South-Eastern Yunnan and West Guangxi provinces) (Fig 1A) Cheng and Mao (2010) recently presented an exhaustive description of these granites This magmatism occurred between 98 and 77 Ma, with a peak between 80 and 95 Ma For Cheng and Mao (2010), the magmas possibly derived from partial melting of Meso-Proterozoic continental crust driven by lithospheric extension and asthenospheric upwelling of the western Cathaysia block in Late Cretaceous On the same way, Cretaceous granites (around 100 Ma) occur along the S-E coast of the Cathaysia Block (Jiang et al., 2011; Wong et al., 2009; He et al., 2010) These granites are probably linked to the Paleo-Pacific subduction They were intruded during the Late 79 ‘‘Yanshanian’’ episode, and most of them correspond to A-type granites (Zhou et al., 2006a,b) Moreover, high K-calc alkaline granitoids have been observed in Southern Vietnam, in the Dalat area and along the coast (Fig 1) Their U–Pb ages are bracketed between 112 and 88 Ma (Tuy Thi Bich Nguyen et al., 2004) This Andean-type magmatism is interpreted as a result of the NW-directed subduction of the western Paleo-Pacific plate under the SE Asian Continental margin (Taylor and Hayes, 1983) This offset of at least 500 km induced by the left-lateral Red River Fault of the Andeantype magmatism occurred along the S-E coast of the South China block and the Dalat area (S Vietnam) Such an offset confirms the model of Tapponnier et al (1990) and Leloup et al (1993, 1995, 2001, 2007) The value of this offset is debated Recent studies based on tectonic reconstructions also reported limited displacement along the Red River Fault (Wang et al., 1998; Searle, 2006, 2007; Searle et al., 2010) Whereas the granite of the Phia Oac represents the unique Cretaceous granite in NE Vietnam, it should be logical to link this magmatic body with the magmatism associated with the Paleo-Pacific subduction A detailed geochemical study would be necessary to confirm this hypothesis No Tertiary age has been found in the zircons of the Phia Bioc complex and Phia Oac massif in spite of their vicinity from the Red River Fault Zone Metamorphic rocks have been exhumed during the Cenozoic along the Red River Fault but are not restricted to the shear zone In fact, high-grade marble around Sapa to the SW of the fault zone and around Luc Yen to the NE of the fault zone (Garnier et al., 2002), the Fan Si Pan granitic massif (Searle, 2006, 2007) and the Song Chay dome (Roger et al., 2000; Carter et al., 2001) also show Tertiary regional metamorphism outside of the Red River Shear zone (Figs and 2) However, the Tertiary metamorphic and tectonic overprint was not strong enough to cause the (re)crystallization of zircon in these complexes Once more these results confirm that in Vietnam, the Cenozoic thermotectonic event is essentially localized along the Red River Fault and the Bu Khang metamorphic core complex and has no or only a limited influence on the isotopic resetting in the high and middle temperature systems (U/Pb and Ar/Ar) outside these two areas (Figs and 2) The building of Indochina is consequently mainly related to the Triassic Indosinian orogeny Conclusion Our new U/Pb ages demonstrate that in NE Vietnam, as in the entire Truong Son Belt, an overprinting of several tectonometamorphic events is responsible for the current structure Ages of inherited cores in zircons attest for the involvement of an old Neo-Proterozoic lithospheric crust related to the basement of the South China Block Although a magmatic event is known between 460 and 420 Ma, no such ages have been obtained in zircons from these granites U–Pb dating of the undeformed, post nappes Phia Bioc granite at 248–245 Ma implies that the major nappes tectonics in NE Vietnam is older than 248.5 ± Ma This nappe tectonics is older or synchronous of the Indosinian strike-slip tectonics as observed in all the Truong Son range This magmatism could be linked to intra-plate activity of the Emeishan LIP or to the closure of the Paleotethys during the Indosinian orogeny The Cretaceous age (87.3 ± 1.2 Ma) of the Phia Oac granite could likely be related to the Cretaceous magmatism occurring at the same time in South China, probably driven by the lithospheric extension affecting the Cathaysia block as a consequence of the late episode of the Paleo-Pacific plate subduction under the continental margin of the SE Asia Zircons rims not show any Cenozoic magmatic or metamorphic overprint Although the Cenozoic Red River Fault system is 80 F Roger et al / Journal of Asian Earth Sciences 48 (2012) 72–82 close to these two plutons the Cenozoic tectonics has not been strong enough to disturb the U/Pb system These data confirm that the structure of Indochina is mainly related to the Indosinian tectonics References Ali, J.R., Thompson, G.M., Song, X.Y., Wang, Y., 2002 Emeishan basalts (SW China) and the «end-Guadalupian» crisis: magnetobiostratigraphic constraints Journal of the Geological Society of London 159, 21–29 Anh, Tran Tuan, Hoa, Tran Trong, Lan, C.Y., Chung, S.L., Lo, C.H., Wang, P.L., Lee, T.Y., Mertzman, S.A., 2003 Geochemical and Nd-Sr isotopic constraints on the genesis of mesozoic alkaline magmatism in the Tu Le Basin, Northern Vietnam Geophysical Research Abstracts 5, 02096 Bourret, R., 1922 Etudes géologiques sur le Nord-Est du Tonkin Bulletin du Service de la Carte Géologique de l’Indochine Hanoi XI, 1, pp 326 Burchfield, B.C., Chen, Z., Liu, Y., Royden, L.H., 1995 Tectonics of the Longmen Shan and adjacent regions, Central China International Geology Review 37, 661–735 Carter, A., Clift, P.D., 2008 Was the Indosinian orogeny a Triassic mountain building or a thermotectonic reactivation event? Comptes Rendus Geoscience 340, 83– 93 Carter, A., Roques, D., Bristow, C., Kinny, P., 2001 Understanding Mesozoic accretion in Southeast Asia: significance of Triassic thermotectonism (Indosinian orogeny) in Vietnam Journal of Geology 29 (3), 211–214 Cheng, Y., Mao, J., 2010 Age and geochemistry of granites in Gejiu area, Yunnan province, SW China/Constraints on their petrogenesis and tectonic setting Lithos 120, 258–276 Deng, X.G., Chen, Z.G., Li, X.H., 2004 SHRIMP U–Pb zircon dating of the Darongshan– Shiwandashan Geology Review (in Chinese) 50 (4), 426–432 Deprat, J., 1914 Etude des plissements et des zones d’écrasement de la moyenne et de la basse Rivière Noire Mémoire du Service Géologique de l’Indochine (4), 59 Deprat, J., 1915 Etude géologique de la région septentrionale du haut Tonkin (feuille de Pa Kha, Ha Giang, Ma Li Po, Yen Minh) Mémoire du Service Géologique de l’Indochine IV, IV Dovjikov, A.E., 1965 Geology of North Vietnam, scale 1:500,000, with Memoir 650 p Science and Technics Publishing House, Hanoi (in Vietnamese) Dunning, G.R., Macdonald, A.S., Barr, S.M., 1995 Zircon and monazite U–Pb dating of the Doi Inthanon core complex, northern Thailand: implications for extension within the Indosinian Orogen Tectonophysics 251, 1-4197-213 Fan, W., Zhang, C., Wang, Y., Guo, F., Peng, T., 2008 Geochronology and geochemistry of Permian basalts in western Guangxi Province, southwest China: evidence for plume lithosphere interaction Lithos 102, 218–236 Fan, W., Wang, Y., Zhang, A., Zhang, F., Zhang, Y., 2010 Permian arc-back-arc basin development along the Ailaoshan tectonic zone: geochemical, isotopic and geochronological evidence from the Mojiangvolcanic rocks, Southwest China Lithos 119, 553–568 Fromaget, J., 1941a Etudes géologiques sur le Nord de l’Indochine centrale Bulletin du Service Géologique d’Indochine 16, 1–368 Fromaget, J., 1941b LIndochine Franỗaise Sa structure gộologique, ses roches, ses mines et leur relation possible avec la tectonique Bulletin du Service Géologique de l’Indochine XXVI, Garnier, V., Giuliani, G., Maluski, H., Ohnenstetter, D., Trinh, Phan Trong, Quang, Vinh Hoang, Van, Long Pham, Van, Tich Vu, Schwarz, D., 2002 Ar–Ar ages in phlogopites from marble-hosted ruby deposits in northern Vietnam: evidence for Cenozoic ruby formation Chemical Geology 188, 33–49 Hanchar, J.M., Miller, C.F., 1993 Zircon zonation patterns as revealed by cathodoluminescence and backscattered electron images: implications for interpretation of complex crustal histories Chemical Geology 110, 1–13 Harrowfield, M.J., Wilson, C.J.L., 2005 Indosinian deformation of the Songpan-Garzê fold belt, northeast Tibetan plateau Journal of Structural Geology 27, 101–117 Hartmann, L.A., Santos, J.O.S., 2004 Predominance of high Th/U, magmatic zircon in Brazilian shield sandstones Geology 32, 73–76 He, Z.Y., Xu, X.S., Niu, Y., 2010 Petrogenesis and tectonic significance of a Mesozoic granite-syenite-gabbro association from inland South China Lithos 119, 621– 641 HNGBMR (Bureau of Geology and Mineral Resources of Hunan Province), 1988 Regional Geology of the Hunan Province Geological Publishing House, Beijing, pp 286–507 (in Chinese with English summary) Hoa, Tran Trong, Anh, Tran Tuan, Phuong, Ngo Thi, Izokh, A.E., Polyakov, G.V., Balykin, P.A., Lan, Ching-Ying, Thanh, Hoang Huu, Nien, Bui An, Dung, Pham Thi, 2004 Gabbro-syenite associations of East Bac Bo structures: evidences of intraplate magmatism? Journal of Geology Series B 23, 12–25 Hoa, Tran Trong, Izokh, A.E., Polyakov, G.V., Borisenko, A.S., Anh, Tran Tuan, Balykin, P.A., Phuong, Ngo Thi, Rudnev, S.N., Van Van, Vu, Nien, Bui An, 2008 PermoTriassic magmatism and metallogeny of Northern Vietnam in relation to the Emeishan plume Russian Geology and Geophysics 49, 480–491 Hoskin, P.W.O., 2000 Patterns of chaos: fractal statistics and the oscillatory chemistry of zircon Geochimica Cosmochimica Acta 64, 1905–1923 Hoskin, P.W.O., Black, L.P., 2000 Metamorphic zircon formation by solid-state recrystallization of protolith igneous zircon Journal of Metamorphic Geology 18, 423–439 Izokh, E.P., Van Chien, Nguyen, Dinh Huu, Le, 1964 Some main outlines of endogene metallogenesis in Northern Vietnam Geology 29, 30 Jackson, S.E., Pearson, N.J., Griffin, W.L., Belousova, E.A., 2004 The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U–Pb zircon geochronology Chemical Geology 211, 47–69 Jiang, Y.H., Zhao, P., Zhou, Q., Liao, S.Y., Jin, G.D., 2011 Petrogenesis and tectonic implications of Early Cretaceous S- and a-type granites in the northwest of the Gan-Hang rift, SE China Lithos 121, 55–73 Jolivet, L., Maluski, H., Beyssac, O., Goffé, B., Lepvrier, C., Truong Thi, Phan, Van Vuong, Nguyen, 1999 Oligocene-Miocene Bu Khang extentional gneiss dome in Vietnam: geodynamic implications Geology 27 (1), 67–70 Leloup, P., Harrison, T.M., Ryerson, F.J., Wenji, Chen, Qi, Li, Tapponnier, P., Lacassin, R., 1993 Structural, Petrological and Thermal Evolution of a Tertiary Ductile Strike-Slip Shear Zone, Diancang Shan, Yunnan Journal of Geophysical Research 98 (b4), 6715–6743 Leloup, P., Lacassin, R., Tapponnier, P., Schärer, U., Dalai, Zhong, Xiaohan, Liu, Liangshang, Zhang, Shaocheng, Ji, Trinh, Phan Trong, 1995 Ailao Shan-Red River shear zone (Yunnan, China), Tertiary transform boundary of Indochina Tectonophysics 251 (1–4), 3–10 Leloup, P., Arnaud, N., Lacassin, R., Kienast, J.R., Harrison, T.M., Trinh, Phan Trong, Replumaz, A., Tapponnier, P., 2001 New constraints on the structure, thermochronology and timing of the Ailao Shan-Red River shear zone, SE Asia Journal of Geophysical Research 106 (B4), 6683–6772 Leloup, P., Lacassin, R., Tapponnier, P., 2007 Discussion on the role of the Red River shear zone, Yunnan and Vietnam, Journal of the Geological Society London 164, 1253–1260 Lepvrier, C., Maluski, H., Vuong, Nguyen.Van., Roques, D., Axente, V., Rangin, C., 1997 Indosinian NW-trending shear zones within the Truong Son belt (Vietnam) 40Ar–39Ar Triassic ages and Cretaceous to Cenozoic overprints Tectonophysics 283, 105–127 Lepvrier, C., Maluski, H., Tich, Vu.Van., Leyreloup, A., Van Thi, Phan, Van Vuong, Nguyen, 2004 The Early Triassic Indosinian orogeny in Vietnam (Truong Son Belt and Kon Tum Massif); implications for the geodynamic evolution of Indochina Tectonophysics 393, 87–118 Lepvrier, C., Van Vuong, Nguyen, Maluski, H., Truong Thi, Phan, Van Tich, Vu, 2008 Indosinian Tectonics in Vietnam C.R Geosciences 340, 94–111 Lepvrier, C., Faure, M., Van Vuong, Nguyen, Van Vu, Tich, Lin, Wei, Ta Truong, Thang, 2011 North-directed Triassic nappes in Northeastern Vietnam (East Bac Bo) Journal of Asian Earth Sciences 41, 56–68 Li, X.H., 1999 U–Pb zircon ages of granites from the southern margin of the Yangtze block: timing of Neoproterozoic Jinning orogeny in SE China and implications for Rodinia assembly Precambrian Research 97, 43–57 Li, X.H., Li, Z.X., Zhou, H., Liu, Y., Kinny, P.D., 2002 U/Pb zircon geochronology, geochemistry and Nd isotopic study Neoproterozoic bimodal volcanic rocks in the Kangding rift of South China: implications for the initial rifting of Rodinia Precambrian Research 113, 135–155 Li, X.H., Li, Z.X., Li, W.X., Wang, Y., 2006 Initiation of the Indosinian orogeny in South China: evidence for a Permian Magmatic Arc on Hainan Island Journal of Geology 114, 341–353 Li, Z.X., Li, X.H., 2007 Formation of the 1300 km wide intracontinental orogen and postorogenic magmatic province in Mesozoic South China: a flat-slab subduction model Geology 35 (2), 179–182 doi:10.1130/G23193A.1 Liang, X.Q., Li, X.H., 2005 Late Permian to Middle Triassic sedimentary records in Shiwandashan Basin: implication for the Indosinian Yunkai orogenic belt, South China Sedimentary Geology 177, 297–320 Lin, W., Wan, Q., Chen, K., 2008 Phanerozoic tectonics of south China block: New insights from the polyphase deformation in the Yunkai massif Tectonics 27, TC6004 doi:10.1029/2007TC002207 Ludwig, K.R., 2001 User manual for isoplot/Ex rev 2.49 A geochronological toolkit for Microsoft Excel Berkeley Geochronology Center Special Publication 1a, 1–56 Macdonald, A.S., Barr, S.M., Miller, B.V., Reynolds, P.H., Rhodes, B.P., Yokart, B., 2010 P-T-t constraints on the development of the Doi Inthanon metamorphic core complex domain and implications for the evolution of the western gneiss belt, Northern Thailand Journal of Asian Earth Sciences 37, 82–104 Maluski, H., Lepvrier, C., 1998 Overprinting Metamorphism in Vietnam, AGU Fall Meeting EOS 79, 795 Maluski, H., Lepvrier, C., Roques, D., Van Vuong, Nguyen, Van Qhynh, Phan, Rangin, C., 1995 40Ar–39Ar ages in the Da Nang-Dai Lôc plutono-metamorphic complex (Central Vietnam) Overprinting process of Cenozoic over Indosinian thermotectonic episodes Workshop Cenozoic evolution of the Indochina peninsula, Hanoi-Do Son, Vietnam, 65pp Maluski, H., Lepvrier, C., Van Vuong, Nguyen, Wemmer, K., 1997 Overprinting of Indosinian Terranes in the Truong Son Belt (Central to Northern Viet Nam) Strasbourg, European Union of Geosciences 9, 491 Maluski, H., Lepvrier, C., Truong Thi, Phan, Van Vuong, Nguyen, 1999 Early Mesozoic to Cenozoic evolution of Orogens in Vietnam: 40Ar–39Ar datingSynthesis In: Proceedings and abstracts of the International Workshop GPA 99 Journal of Geology, Vietnam pp 81–86 Maluski, H., Lepvrier, C., Jolivet, L., Carter, A., Roques, D., Beyssac, O., Ta Trong, Thang, Nguyen, Duc Thang, 2001 Ar–Ar and fission-track ages in the Song Chay Massif: Early Triassic and Cenozoic tectonics in northern Vietnam Journal of Asian Earth Sciences 19, 233–248 Maluski, H., Lepvrier, C., Leyreloup, A., Van Tich, Vu, Truong Thi, Phan, 2005 40 Ar–39Ar geochronology of the charnockites and the granulites of the Kan Nack complex, Kon Tum Massif, Vietnam Journal of Asian Earth Sciences 25, 653– 677 F Roger et al / Journal of Asian Earth Sciences 48 (2012) 72–82 Metcalfe, I., 2002 Permian tectonic framework and palaeogeography of the SE Asia Journal of Asian Earth Sciences 20, 551–566 Müller, W., Shelley, M., Miller, P., Broude, S., 2009 Initial performance metrics of a new custom-designed ArF excimer LA-ICPMS system coupled to a two-volume laser-ablation cell Journal of Analytical Atomic Spectrometry 24, 209–214 Nagy, E.A., Maluski, H., Lepvrier, C., Schärer, U., Truong Thi, Phan, Leyreloup, A., Van Tich, Vu, 2001 Geodynamic significance of the Kon Tum massif in Central Vietnam: composite 40Ar/39Ar and U/Pb ages from Paleozoic to Triassic Journal of Geology 109, 755–770 Nakamo, N., Osanai, Y., Sajeev, K., Hayasaka, Y., Miyamoto, T., Minh, N.T., Owada, M., Windley, B., 2010 Triassic eclogite from northern Vietnam: inferences and geological significance Journal of Metamorphic Geology 28, 59–76 Nakano, N., Osanai, Y., Minh, N.T., Miyamoto, T., Hayasaka, Y., Owada, M., 2008 Discovery of high-pressure granulite-facies metamorphism in northern Vietnam: constraints on the Permo-Triassic Indochinese continental collision tectonics Comptes Rendus Geoscience 340 (2-3), 127–139 Nguyen, Thuy Thi Bich, Satir, M., Siebel, W., Chen, F., 2004 Granitoids in the Dalat zone, Southern Vietnam: age constraints on magmatism and regional geological implications International Journal of Earth Science 93, 329–340 Paquette, J.L., Tiepolo, M., 2007 High resolution (5 lm) U-Th-Pb isotopes dating of monazite with excimer laser ablation (ELA)-ICPMS Chemical Geology 240, 222– 237 Peng, T., Wang, Y., Zhao, G., Fan, W., Peng, B., 2008 Arc-like volcanic rocks the southern Lancangjiang zone, SW China: geochronological and geochemical constraints on their petrogenesis and tectonic implications Lithos 102, 358– 373 Phan, C.T., et al., 1991 Geology of Cambodia, Laos and Vietnam: Explanatory note to the geological map of Cambodia, Laos and Vietnam at 1:1000,000 Geological Survey of Vietnam, 156p Pidgeon, R.T., 1992 Recrystallization of oscillatory zoned zircon: some geochronological and petrological implications Contribution to Mineralogy and Petrology 110, 463–472 Polyakov, G.V., Shelepaev, R.A., Hoa, T.T., Izokh, A.E., Balykin, P.A., Phuong, N.T., Hung, T.Q., Nien, B.A., 2009 The Nui Chua layered peridotite-gabbro complex as manifestation of Permo-triassic mantle plume in northern Vietnam Russian Geology and Geophysics 50, 501–516 Qiu, J.S., McInnes, B.I.A., Xu, X.S., Allen, C.M., 2004 Zircon ELA-ICPMS dating for Wuliting pluton at Dajishan, southern Jiangxi and new recognition about its relationship to Tungsten mineralization Geology Reviews 50 (2), 125–133 Reid, A.J., Wilson, C.J.L., Liu, S., 2005 Structural evidence for the Permo-Triassic tectonic evolution of the Yidun arc, Eastern Tibetan plateau Journal of Structural Geology 27, 119–137 Reid, A., Wilson, C.J.L., Shun, L., Pearson, N., Belousova, E., 2007 Mesozoic plutons of the Yidun arc, SW China U/Pb geochronology and Hf isotopic signature Ore Geology Reviews 31, 88–106 Roger, F., Leloup, P., Jolivet, M., Lacassin, R., Trinh, Phan Trong, Brunel, M., Seward, D., 2000 Long and complex thermal history of the Song Chay metamorphic dome (Northern Vietnam) by multi-system geochronology Tectonophysics 321, 449–466 Roger, F., Arnaud, N., Gilder, S., Tapponnier, P., Jolivet, M., Brunel, M., Malavieille, J., Xu, Z., 2003 Geochronological and geochemical constraints on Mesozoic suturing in East Central Tibet Tectonics 22 (4), 1037 doi:10.1029/ 2002TC001466 Roger, F., Malavieille, J., Leloup, P., Calassou, S., Xu, Z., 2004 Timing of granite emplacement and cooling in the Songpan-Garzê fold belt (eastern Tibetan plateau) with tectonic implications Journal of Asian Earth Sciences 22, 465– 481 Roger, F., Maluski, H., Leyreloup, A., Lepvrier, C., Truong Thi, Phan, 2007 U–Pb dating of high temperature episodes in the Kon Tum Massif (Vietnam) Journal of Asian Earth Sciences 30, 565–572 Roger, F., Jolivet, M., Malavieille, J., 2008 Tectonic evolution of the Triassic fold belts of Tibet Comptes Rendus Geoscience, Académie des sciences, Paris 340 (2–3), 180–189 Roger, F., Jolivet, M., Malavieille, J., 2010 The tectonic evolution of the SongpanGarzê (North Tibet) and adjacent areas from Proterozoic to Present: a synthesis Journal of Asian Earth Sciences 39, 254–269 Roger, F., Jolivet, M., Cattin, R., Malavieille, J., 2011 Mesozoic-Cenozoic Tectonothermal evolution of the eastern part of the Tibetan plateau (Songpan-Garzê, Longmen Shan area): insights from thermochronological data and simple thermal modelling In: Gloaguen, R., Ratschbacher, L (Eds.), The Geological Society, Special Publications Series ‘‘Growth and Collapse of the Tibetan Plateau, vol 353(1), pp 9–25 doi: 10.1144/SP353.2 Searle, M.P., 2006 Role of the Red River Shear zone, Yunnan and Vietnam, in the continental extrusion of SE Asia Journal of the Geological Society, London 163, 1025–1036 doi:10.1144/0016-76492005-144 Searle, M.P., 2007 Discussion on the role of the Red River Shear zone, Yunnan and Vietnam, in the continental extrusion of SE Asia Journal of the Geological Society 164, 1253–1260 Searle, M.P., Yeh, M.W., Lin, T.H., Chung, S.L., 2010 Structural constraints on the timing of left-lateral shear zone in the Ailao Shan and Diancang Shan Ranges, Yunnan, SW China Geosphere (4), 316–338 doi:10.1130/GES00580.1 Shelepaev, R., Polyakov, G., Hoa, Tran Trong, Phuong, Ngo Thi, Izokh, A., Hung, T.Q., Nien, B.A., Egorova, V., 2010 Nuichua complex (Northern Vietnam) as indicator of Permian-Triassic large igneous province Geophysical Research Abstracts 12, EGU2010-11075-1 81 Shellnutt, J.G., Zhou, M.-F., 2008 Permian, rifting related fayalite syenite in the Panxi region, SW China Lithos 101, 54–73 Shellnutt, J.G., Jahn, B.-M., Zhou, M.-F., 2011 Crustal-derived granites in the Panzhihua region, SW China: implications for felsic magmatism in the Emeishan Large Igneous province Lithos 123, 145–157 Shellnutt, J.G., Denyszyn, S.W., Mundil, R., in press Precise age determination of mafic and felsic intrusive rocks from the Permian Emeishan large igneous province (SW China) Gondwana Research doi: 10.1016/j.gr.2011.10.009 Tapponnier, P., Lacassin, R., Leloup, P., Schärer, U., Dalai, Zhong, Haiwei, Wu, Xiaohan, Liu, Shaocheng, Ji, Lianshang, Zhang, Jiayou, Zhong, 1990 The Ailao Shan/Red River metamorphic belt: Tertiary left-lateral shear between Indochina and South China Nature 343, 431–437 Taylor, B., Hayes, D.E., 1983 Origin and history of the South China Sea Basin In: Hayes D.E (Ed.), The tectonic and geologic evolution of the Southeast Asian Seas and Islands, vol 27 Am Geophys Union Monogr, pp 23-56 Tiepolo, M., 2003 In situ Pb geochronology of zircon with laser ablation-inductively coupled plasma-sector field mass spectrometry Chemical Geology 141, 1–19 Van Achterbergh, E., Ryan, C.G., Jackson, S.E., Griffin, W., 2001 Data reduction software for LA-ICP-MS In: Sylvester, P (Ed.), Laser Ablation-ICPMS in the Earth Science, vol 29 Mineralogical Association of Canada, pp 239–243 Vu Van Tich, 2004 La Chne Indosinienne au Vietnam: Pétrologie et Géochronologie du Bloc Métamorphique de Kon Tum Thèse de DoctoratUniversité Montpellier 2, 202 Tran Van Tri, 1979 Geology of Vietnam: The Northern Part Science Publisher, Hanoi, p 80 Vavra, G., Gebauer, D., Schmid, R., Compston, W., 1996 Multiple zircon growth and recrystallization during polyphase Late Carboniferous to Triassic metamorphism in granulites of the Ivrea Zone (Southern Alps): an ion microprobe (SHRIMP) study Contribution to Mineralogy and Petrology 122, 337–358 Wang, E., Burchfiel, B.C., Royden, L.H., Liangzong, C., Jishen, C., Wenxin L., Zhiliang, C., 1998 Late Cenozoic Xianshuihe-Xiaojiang, Red River and Dali fault systems of southwestern Sichuan and Central Yunnan, China Geological Society of America, Special Papers 327, 108p Wang, Y.J., Zhang, Y.H., Fan, W.M., Peng, T.P., 2005 Structural signatures and 40Ar/ 39Ar geochronology of the Indosinian Xuefengshan transpressive belt, South China Interior Journal of Structural Geology 27, 985–998 Wang, C.Y., Zhou, M.F., Qi, L., 2007a Permian flood basalts and mafic intrusions in the Jinping (SW China)-Song Da (northern Vietnam) district: Mantle sources, crustal contamination and sulfide segregation Chemical Geology 243, 317–343 Wang, Y.J., Fan, W.M., Sun, M., Liang, X.Q., Zhang, Y.H., Peng, T.P., 2007b Geochronological, geochemical and geothermal constraints on petrogenesis of the Indosinian peraluminous granites in the South China Block: a case study in the Hunan Province Lithos 96 (3–4), 475–502 Wang, Y.J., Fan, W.M., Zhao, G.C., Ji, S.C., Peng, T.P., 2007c Zircon U–Pb geochronology of gneiss rocks in the Yunkai massif and its implication on the Caledonian event in the South China Block Gondwana Research 12, 404–416 Wang, Y., Zhang, A., Fan, W., Peng, T., Zhang, F., Zhang, Y., Bi, X., 2010 Petrogenesis of Late Triassic post-collisional basaltic rocks of the Lancangjiang tectonic zone, southwest China, and tectonic implications for the evolution of the eastern Paleotethys: geochronological and geochemical constraints Lithos 120, 529– 546 Watkinson, I., Elders, C., Hall, R., 2008 The kinematic history of the Khlong Marui and Ranong Faults, Southern Thailand Journal of Structural Geology 30, 1554– 1571 Williams, I.S., Claesson, S., 1987 Isotopic evidence for the Precambrian provenance and Caledonian metamorphism of high grade paragneisses from the Seve Nappes, Scandinavian Caledonides Contribution to Mineralogy and Petrology 97, 205–217 Wilson, C.J.L., Harrowfield, M.J., Reid, A.J., 2006 Brittle modification of Triassic architecture in eastern Tibet: implications for the construction of the Cenozoic plateau Journal of Southeast Asian Earth Sciences 27, 341–357 Wong, J., Sun, M., Xing, G., Li, X.H., Zhao, G., Wong, K., Yan, C., Xia, X., Li, L., Wu, F., 2009 Geochemical and zircon U–Pb and Hf isotopic study of the Baijuhuajian metaluminous A-type granite: Extension at 125–100 Ma and its tectonic significance for South China Lithos 112, 289–305 Yan, D.P., Zhou, M.F., Wang, C.Y., Xia, B., 2006 Structural and geochronological constraints on the tectonic evolution of the Dulong-Song Chay tectonic dome in Ynnan province, SW China Journal of Asian Earth Sciences 208, 332–353 Zhang, Y.Q., 1999 Foreland thrust and nappe tectonics of Shiwandashan, Guangxi Geoscience 2, 150–155 Zhang, F., Wang, Y., Chen, X., Fan, W., Zhang, Y., Zhang, G., Zhang, A., 2011 Triassic high-strain zone in Hainan island (South China) and their implications on the amalgamation of the Indochina and South China Blocks: Kinematic and 40 Ar/39Ar geochronolgical constraints Gondwana Research 19, 910–925 Zheng, L., Yang, Z., Tong, Y., Yuan, W., 2010 Magnetostratigraphic constraints on two stage eruptions of the Emeishan continental flood basalts Geochemisty, Geophysics, Geosystems doi: 10.1029/2010GC003267 Zhong, H., Zhu, W.-G., Song, X.-Y., He, D.-F., 2007 SHRIMP U–Pb zircon geochronology, geochemistry, and Nd–Sr isotopic study of contrasting granites in the Emeishan large igneous province, SW China Chemical Geology 236, 112–133 Zhong, H., Zhu, W.-G., Hu, R.-Z., Xie, L.-W., He, D.-F., Liu, F., Chu, Z.-Y., 2009 Zircon U–Pb age and Sr–Nd–Hf isotope geochemistry of the Panzhihua A-type syenitic intrusion in the Emeishan large igneous province, southwest China and implications for growth of juvenile crust Lithos 110, 109–128 82 F Roger et al / Journal of Asian Earth Sciences 48 (2012) 72–82 Zhou, X.M., Li, W.X., 2000 Origin of Late Mesozoic igneous rocks in southeastern China: Implications for lithosphere subduction and underplating of mafic magmas Tectonophysics 326, 269–287 Zhou, M.F., Yan, D.P., Kennedy, A.K., Li, Y., Ding, J., 2002 SHRIMP U–Pb zircon geochronological and geochemical evidence for Neoproterozoic arc-magmatism along the western margin of the Yangtze block, South China Earth and Planetary Science Letters 196, 51–67 Zhou, M.F., Yan, D.P., Wang, C.L., Qi, L., Kennedy, A., 2006a Subduction-related origin of the 750 Ma Xuelongbao adakitic complex (Sichuan province, China): implications for the tectonic setting of the giant Neoproterozoic magmatic event in South China Earth and Planetary Science Letters 248, 286–300 Zhou, M.F., Ma, Y., Yan, D.P., Xia, X., Zhao, J.H., Sun, M., 2006b The Yanbian terrane (Southern Sichuan province, SW China): A Neoproterozoic arc assemblage in the western margin of the Yangtze block Precambrian Research 144, 19–38 Zhou, M.F., Zhao, J.H., Xia, X.P., Sun, W.H., Yan, D.P., et al., 2007 Comment on ‘‘Revisiting the ‘‘Yanbian terrane’’: implications for Neoproterozoic tectonic evolution of the western Yangtze block, South China’’ (Li et al., 2006) Precambrian Research 155, 153–157  ... 206 Pb/ 23 8U ±1r 207 Pb/ 23 5U ±1r 208 Pb/ 232Th ±1r 207 Pb/ 20 6Pb ±1r 206 Pb/ 23 8U ±1r 207 Pb/ 23 5U ±1r 208 Pb/ 232Th ±1r Z6-C Z6-R Z5-R Z4-R Z4-C Z1-C Z7-R1 Z7-C Z7-R2 Z8-R Z8-C Z9-R Z9-C Z10-R Z10-C... presence of perturbations related to inclusions, fractures, mixing of different Table Analytical results of LA-ICPMS U- Pb dating Spot no Zircon Concentration (ppm) Th U Th /U Raw ratios 207 Pb/ 20 6Pb. .. 38 39 40 41 42 43 44 Z9 Z10-R1 Z10-C Z10-R2 Z11-R1 Z11-R2 Z12-C Z1-R Z1-C Z3-R1 Z3-C Z3-R2 Z4-R1 Z4-R2 Z7-C Z8-R1 Z8-C Z8-R2 Z14-R1 Z14-R2 Z15-R Z15-C Z6-R Z6-C Z1-R 600 397 799 638 250 773 995