Đặc điểm khoáng vật các đá peridotit khối núi nưa thanh hóa

OAC DIEM KHOANG VAT CAC D A PERIDOTIT KHOI NUI NJA-THANH HOA D THI VAN THANH, NGUYEN THUY DUONG, TRAN THI THANH NHAN Khoa Dia chat, Dai hoc Khoa hoc Tic nhien Tom tat Thanh phan khoang vat ciia cac da magma sieu mafic kbdi Niii Nua rat dae trung cho mot qua trinh ket tinh dung the dudi sau, nhung bi bie'n ddi ea ban qua trinh tu bien chat dudi tac dung eiia chat luu eon sot lai Su bien ddi hau nhu triet de phan da nguyen thuy ed lien quan vdi mot qua trinh chuyen ddng kien tao ciia ddi sdng Ma, dan tdi toan khd'i sieu mafic bi "nang trdi" lam cho nhiet ap suat ciia khd'i bi giam xud'ng Vdi phan khoang vat olivin (Ol = 51,3 - 59,0%), onhopyroxen (Opx = 9,51 - 16,19%), elinopyroxen (Cpx = 1,12 - 11,08%) ed the suy nghi chiing thude loai peridotit (barburgit va Lersolit) Trong harburgit, olivin chiia 87,28% phan tu forsterit; 10,72% phan tir fayalit va vdi phan tren chiing ed the duge ket tinh d T = 1800"C To hgp khoang vat olivin - enstatit - diopsid - cromspinel vdi phan boa hge duge xac dinh bang phuang phap Microzond, dae trung cho mot phan u'ng ehuyen pha nhiet do, ap suat giam (1800"C - 750"C va 20000atm - lOOOOatm) vi dudi nhiet T = 1500"C va ap suat P < lOOOOatm to hgp pyrop - olivin khdng ben virng va bi phan theo phan ling: Pyrop + Olivin Enstatit -i- Diopsid -i- Cr-spinel Mat khae, su ed mat ciia cac khoang vat nhu antophillit, clorit, serpentin (antigorit, crysotil) va cac tam baxtit gia hinh theo 843 orthopyroxen chung minb cho qua trinh bien chat aien uuui ay suat ed hoi nude va nhiet T = 700 - 750"C, nhiet giam tdi 400 500"C se xuat hien serpentin theo phan ling: 3Mg2[Si04] + H2O + Si02 ^ Mg,[Si40,o](OH)x Trong phan ciia mot sd khoang vat, ham lugng Cr va Ni tuong ddi cao: CrjO, ed 0,04% olivin, 0,59% serpentin va len tdi 1,71 - 1,456% pyroxen; NiO ed 0,41% olivin, 0,3% serpentin va 0,05 - 0,1% pyroxen Dilu ly giai sir xuat bien phong phii ciia cac khoang vat phu (cromspinel) va khoang vat quang di kem Trong bai bao tap the tac gia chi neu len mot so dSn lieu ve dae diem thach hge, khoang vat ciia khd'i Nui Nua vdi mong mudn gdp phan lam sang to bd'i canh dia chat - kien tao ciia ddi sdng Ma Md dau Cac tao mafic - sieu mafic ludn la ddi tugng duge nhieu nha dja chat quan tam Nhtrng ket qua nghien ciru ve kbdi sieu mafic Niii Nua, cac tao sieu mafic ddi sdng Hong, nhung he quang ndi sinh tao rift Sdng Da da cho tha'y vai trd to Idn ciia ehiing viee nghien cuu cac boat ddng kien tao va phan ciia Idp manti tren Khd'i Nui Nua duge nghien eiiu chi tie't tir nbirng nam 70 ve thach hge, khoang vat Nhieu tac gia cho rang khd'i Nui Nua duge tao nen bdi cac da harbugit, dunit va mot lugng nhd Lersolit, veelit Tuy nhien eiing ed tac gia cho rang serpentinit cung la mot hgp phan ciia phiic be Niii Nua, mac du dilu kien tao, ngudn gd'c eua chiing ed nbirng diem dae biet khae Trong bai bao nay, tap the tac gia se trinh bay mdt sd ket qua'nghien ciru gan '^"'' ^ • ^ ^ ^ ' ; ^ " ; ^ r " r : f -nXo '^or^^ - f ^ day (2003-2005) ve dae diem khoang vat 844 sieu mofic klioi Nui Nuo ^£,^7-;,, y^„ Thanh, 2004) ciia ode d^ peridotit b hai vi tri la khu md cromit Co Dinh va md serpentin d phin Nam ciia khd'i Niii Nua Sir phan bd cac tao mafic - sieu mafic Cac da magma mafic - sieu mafic d khd'i Niii Nua phan bd cd quy luat theo khdng gian Dae biet d moong khai thae serpentin tha'y rd harbugit, dunit, dunit pyroxen phan bd ehii yeu d phan giira khd'i, xa ban la Lersolit va d hai ben canh la gabro, gabro - diaba Ngoai ria khd'i ve phia Nam la gabro - diorit Trong khd'i sieu mafic cd mach diaba xuyen len thang diing [anh 1] Dae diem chung eua da la sSm mau, ran cbac, bi vd niit, ea ep manh Hau bet cac da bi serpentin hda Trong cac da tha'y rd cac mang mach crysotil, antigorit a Dqc diem hda hoe eua cac da Thanh phan hda hge ciia cac da sieu mafic khdng khae nhieu Ham lugng MgO kha cao, dat tdi 40,51%, ngheo Si02, ra't it AI2O3 va lugng kilm NajO -1- K2O < 1% Tir dunit den Lersolit ham lugng Si02, MjO^, Fe203, FeO va MgO thay ddi khdng dang ke' Nhung ne'u so sanh phan ciia cac da magma mafic vdi cac da magma sieu mafic se thay rd sir tang dot bien ham lugng Si02, AI2O3, Fe203, FeO, CaO va nguge lai ham lugng MgO giam dang ke • sieu malic D malic eu 60 I I nsg cac nguyen to SiOj AijOj FczOj i_=i MgO CaO Hinh 1: Hdm lugng cdc nguyen to da magma mafic - sieu mafic Nui Nua 845 Bang 1: Thanh phan hda hoc ciia cac da magma thugc khdi Niii Nua (%) Thanh phjn 1* 2* T** 4** ^*** 6* 7** 8* 9* SiO, 39,5 39,46 38,83 42,05 36,83 42,9 39,68 43,36 55,56 T1O2 0,01 0,04 0,03 0,08 0,07 0,04 0,03 0.72 0,80 Al.O, 0,87 1,09 0,50 0,87 1.54 1,71 0,70 14,57 14,73 Fefi^ 6.23 5,93 3,50 6,50 5,40 1,88 2,65 3,92 1,60 FeO 0,95 1,99 4,03 1,70 2.50 4,42 4,78 8,11 9,77 \ MgO 40,5 37,20 41.20 36,82 36,78 36,2 40.90 11.96 6,23 CaO 0,29 2,87, 0,35 0.18 0,61 2,01 1,07 9.18 7,89 Na^O 0,74 0,74 0,11 0,28 0,55 0,81 0.08 1,08 1,15 K,0 0,05 0,05 - - 0,13 0.05 - 0,63 1.18 - Dunit; - Harbugit; - Lersolit; - VecUt; - Gabro - diaba; - Gabro - diorit; - va - thugc khdi Niii Nua; - thugc khdi PacNgm * DdTIti Van Thanh, 2004; ** Nguye'n Van Chien 1964; *** Nguyin DUc Thang 1999 Thanh phan hda hge eua cac da sieu mafic khd'i Pde Nam [8] ham lugng SiOj, MgO thap ban eon AljO, lai cao ban Trong phan cac da mafic - sieu mafic ham lugng cac nguyen to tao quang Cr, Ni, Co rat khae nhau, chiing tap trung chii ye'u da sieu mafic, dae biet ham lugng Ni tap trung ehii yeu dunit tdi 2153 ppm, day la nguyen to thay the' ddng hinh cho Fe^* olivin Nguge lai Cr lai tap trung kha cao Lersolit tdi 1349 ppm b Dqc diem khodng vat Mae dii eae da bi serpentin hoa kha manh nhung lat mong thach hge van quan sat thay olivin, loai orthopyroxen va elinopyroxen Dd la ba khoang vat nguyen sinh ehii yeu eua da sieu mafic Vdi phan khoang vat olivin (ol: 51,3 - 59,0%), orthopyroxen (opx: 9,51 846 16,19%), elinopyroxen (cpx: 1,12 -11,08%), dae trung cho peridotit (Harbugit v^ Lersolit) Trong dd harbugit tha'y ra't ro cdc ta'm ban tinh orthopyroxen vdi kich thudc tdi 0.5cm Chiing thudng bi serpentin hod tao nfin cac ta'm baxtit (serpentin gia hinh theo orthopyroxen) Trong Lersolit thi elinopyroxen chiS'm lugng chii ye'u, nhieu han hin orthopyroxen Ngoai cac khoang vat neu tren, harbugit va Lersolit cd spinel, granat (it), duge xac dinh qua ket qua phan tich ranghen (Bang 2) Bang 2: Gia trj da(A) dae trung eua cac khoang vat peridotit Khoang vat da(A) Olivin 4,85(4) - 2,83(10) - 2,49(10) - 2,40(8) Enstatit-Hyperthen 3,21(10)-2,83(8)-2,48(5) Aropsit-Hedenbergit 3,0(10) - 2,52(10) - 2,13(6) - 2,01(6) Cromit 2,83(9)-3,68(10)-2,52(8) Crompieotit 2,5(10)-2,07(7)- 1,69(4) Spinel 2,94(5) - 2,52(10) - 2,17(6) - 2,09(7) Granat 2,98(9)-3,68(10)-2,52(8) Serpentin 7,28(9)-3,68(10)-2.52(8) Ghi dm: Ket qua phan tich tgi TTTNDC, Cue DC&KSVN, 2004 Nhirng khoang vat neu tren duge xac dinh ddng bd lat mong thach hge, xac dinh bang phan tich ranghen va phan xac dinh bang phan tich microsond 847 Anh Olivin bi serpentin hoa dunit N*x90 Anh Pyroxen thoi harbugit N*x90 Anh Cromit dunit (lat mong) Nx90 848 Anh Olivin bi serpentin hoa dunit N*x90 Anh Pyroxen mot nghieng Lersolit N*x90 Anh Cromit dunit (mai lang) x90 Thanh phdn hoa hge ciia cac khoang vat duge xac dinh bang phuang phap microsond (bang 3) Bang 3: Hgp phan khoang vat tai cac diem phan tich microsond (Gia tri trung hinh %) Tang Trdn Dudi Diem o Forsterit Fayalit Cr-spinel ivin 84,7 7,83 3,07 Forsterit 87,2 Fayalit Am Cr-spinel 10,7 it Diem elinopyroxen Diopsid 84,31 Hedenbergit 3,18 Olivin 2,5 Cr-spinel 4,23 Diopsid 69,93 Hedenbergit 5,01 Olivin 13,59 Cr-spinel 6,1 Diem Cr-spinel Cromit 46,03 Cr-spinel 49,55 Forsterit 2,99 Cromit Cr-spinel Forsterit 45,84 46,06 5.06 De ed cac hgp phan khoang vat khae mdt diem khoang vat duge xac dinh lat mong thach hge, da xir ly sd lieu theo phuang phap tinh toan thach boa [3] Mat khae, ed nhiing khoang vat duge hinh cac phan u^ng chuyen pha dilu kien hoa ly thay ddi Nhu phan u'ng Pyrop -I- Olivin Enstatit 4- Diopsid -t- Cromspinel Do dd, diem ban microsond len olivin, hoac elinopyroxen, spinel, ngoai hgp phan chinh la khoang vat neu tren thi van cd mdt lugng nhd khoang vat khae ma nhirng khoang vat dd tham gia phan ling [bang 3] Trong olivin ngoai hai hgp ph^n ehinh la forsterit va fayalit van ed hgp phan Cr-spinel- ehiem mdt lugng nhd va ed the tdi 3,07% Nguge lai, tai diem phan tich cromspinel, eon cd mdt lugng hgp phan forsterit 0,96-5.02% (d tang tren) va 2,07-8,05% (d tSng dudi) Tuang tu, elinopyroxen, ngoai hgp phan chinh la diopsid va herdenbergit ed cac hgp phan khae nhu olivin, Crspinel Olivin 2,53% (t^ng tren) tdi 13,59% (t^ng dudi), spinel 4,23% (ting tren) va 6,1% (tang dudi) Nhirng dan lieu ndu tren ehiing to da cd phan ling phan to hgp cdng sinh pyrop -i- olivin diln dieu kien ton tai ciia chiing thay doi 849 M C 'O # »n >0 CNI r-_^ oo r~_^ —' ON ( ^ ON oo ON H q z — , o o o en MnO S ã5 :ô O o: S d u d ^ N ^ < ' _ Tt ON • * ON ON ON in ON ' *O o tN •St ON' ON rr 00 o