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7481075 
Journal Article 
Metamorphic evolution of a subduction complex, South Shetland Islands, Antarctica 
Trouw, RAJ; Simões, LSA; Valladares, CS; , 
2004 
Yes 
Journal of Metamorphic Geology
ISSN: 0263-4929
EISSN: 1525-1314 
16 
4 
475-490 
English 
CCC:000074326800001 
A subduction complex composed of ocean floor material mixed with arc-derived metasediments crops out in the Elephant Island group and at Smith Island, South Shetland Islands, Antarctica, with metamorphic ages of 120-80 Ma and 58-47 Ma? respectively. Seven metamorphic zones (I-VII) mapped on Elephant Island delineate a gradual increase in metamorphic grade from the pumpellyite-actinolite facies, through the crossite-epidote blueschist facies, to the lower amphibolite facies. Geothermometry in garnet-amphibole and garnet-biotite pairs yields temperatures of about 350 degrees C in zone III to about 525 degrees C in zone VII. Pressures were estimated on the basis of Si content in white mica, Al(2)O(3) content in alkali amphibole, Na(M4)/Al(IV) in sodic-calcic and calcic amphibole, Al(VI)/Si in calcic amphibole, and jadeite content in clinopyroxene. Mean values vary from about 6-7.5 kbar in zone II to about 5 kbar in zone VII. Results from the other islands of the Elephant Island group are comparable to those from the main island; Smith Island yielded slightly higher pressures, up to 8 kbar, with temperatures estimated between 300 and 350 degrees C. Zoned minerals and other textural indications locally enable inference of P-T-t trajectories, all with a clockwise evolution. A reconstruction in space and time of these P-T-t paths allows an estimate of the thermal structure in the upper crust during the two ductile deformation phases (D(1) & D(2)) that affected the area. This thermal structure is in good agreement with the one expected for a subduction zone. The arrival and collision of thickened oceanic crust may have caused the accretion and preservation of the subduction complex. In this model, D(1) represents the subduction movements expressed by the first vector of the clockwise P-T-t path, D(2) reflects the collision corresponding to the second vector with increasing temperature and decreasing pressure, and D(3) corresponds to isostatic uplift accompanied by erosion, under circumstances of decreasing temperature and pressure. 
Physical Sciences - Other Topics; accretionary wedge, geothermobarometry, P-T-t paths, Sanbagawa type; metamorphism; western pacific, empirical-model, phase-relations, pressure, amphibole,; garnet, rocks, calibration, temperature, plagioclase