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7465573 
Journal Article 
Geology and metamorphism of the Ladakh terrane and Shyok suture zone in the Chogo Lungma-Turmik area (northern Pakistan) 
Rolfo, F; Lombardo, B; Compagnoni, R; Le Fort, P; Lemennicier, Y; Pecher, A 
1997 
Yes 
Geodinamica Acta
ISSN: 0985-3111 
10 
5 
251-270 
English 
WOS:000071315300004 
Metamorphism of the Askore Amphibolite, metabasaltic and metasedimentary medium-grade hornblende-bearing schists at the northernmost portion of the Ladakh Terrane and of the Shyok Suture Zone, mainly a low-grade volcano-sedimentary series, has been studied in the area between the Chogo Lungma glacier and the Indus river halfway between Skardu and Rondu. In the Askore Amphibolite the peak assemblage in the amphibolite facies defines the regional metamorphic foliation, and is overprinted by a later static recrystallization at comparable P-T conditions. In spite of similar peak temperatures (630 - 650 degrees C), geobarometry based on amphibole composition reveals a marked difference between garnet - epidote - andesine amphibolites exposed just above the Main Mantle Thrust at the head of Turmik valley, which equilibrated at high pressures (about 10 kbar) in late Miocene (Tortonian), and biotite epidote - oligoclase amphibolites outcropping at the mouth of Turmik valley, which equilibrated at pressures of c. 6 kbar before late Eocene (Priabonian). The Dasu Ultramafite and other smaller lens-shaped bodies of low-to medium-grade metaperidotite separate the Ladakh Terrane from the Shyok Suture Zone. They are antigorite serpentinites, often with talc and magnesite, in which relict cumulitic structures are locally recognisable. The ultramafites may represent remnants of oceanic lithosphere separating the Ladakh-Kohistan island are from the Asian plate, or they may be deep crustal rocks stripped from the basement of the are. The mostly greenschist-facies Shyok Suture Zone shows the lithology of a calc-alkaline volcano-sedimentary series. It is supposed to be a remnant of a back are basin of early Cretaceous age, separating the are from the southern margin of Asia. Chloritoid, kyanite and biotite have been found in individual thrust sheets occurring al different structural levels and totally subordinate in volume to very low-and low-grade rocks. Such sharp differences in mineral paragenesis, together with field evidence of local shear, suggest a complex internal structure for the Shyok Suture Zone. From the head of Chogo Lungma glacier to the Basha valley, close to the contact with the Karakorum Metamorphic Complex, the rocks of the Shyok Suture Zone record a late Miocene metamorphic event al medium pressures and temperatures. Thermobarometric and geochronological evidence suggests that this event can be related to the exhumation and thrusting of the Karakorum metamorphic core over the Shyok Suture Zone. 
collision tectonics; metamorphism; island arcs; Ladakh; Pakistan; Himalayas