metamorphism

Grenville Orogeny Weil et a (1998) Outcrop Photo – paragneiss & marble Outcrop Data Geothermobarometry CaAl2Si2O8 = Ca3Al2Si3O12 + Al2SiO5 + SiO2 GASP - garnet - aluminumsilicate - silica - plagioclase Metamorphic Facies +/- 100 MPa +/- 50oC Porphyroclast Porphyroblast  dP      P  dt  dD  dP      dt  dt   dP      P  dt   dP  dt P  ln P  t  C  ln P  t  C ln P  ln Po  t Po  Pe t Po  Pe t  t  t D*  Po  P  Pe  P  P e   t  D  Do  D*  Do  P e   t  D  Do  P e  y  mx  b   D Do P t   e 1 S S S D S   D Do P t   e 1 S S S P S 206 Pb  204 Pb 206 207 207 Pb  204 Pb Pbo  204 Pb Pbo  204 Pb 238   235   U 238t e 1 204 Pb U 235t e 1 204 Pb Syn-kinematic Closure = 725o C 1011  Ma 1010  Ma 1008  Ma 1000 Ma 984 Ma 976 Ma Cooling rate = T/ t (Tpeak – T c, horblende)/(agemonazite – agehornblende) = 120 oC/10 m.y = 12 oC/m.y 100 200 T (Co) 300 400 500 600 700 800 100 200 300 10 976 Ma 984 Ma 15 400 d (km) 1000 Ma 500 600 700 1006 Ma 20 Prograde Path 25 1010 Ma 30 800 Peak T P (MPa)