Petrology and geochemistry of Tehuitzingo serpentinites (Acatlán Complex, SW Mexico)

摘要

Petrographic and geochemical studies of the serpentinites from the Tehuitzingo body, the main ophiolitic outcrop of the Paleozoic Acatlán Complex of southern Mexico, provide new petrogenetic evidence and preliminary data on the nature of the fuids that interacted with an original mantle peridotite. Textures of the studied serpentinites show the principal events of recrystallization and metasomatism, but the diagnostic phases associated with the high pressure events related to subduction were erased. Preliminary H and O isotope studies in serpentinite and chorite suggest the involvement of marine water, probably under oceanic conditions during the frst serpentinization event. Accessory chromite in the serpentinites is characterized by #Cr ~0.6 and serpentinites display low abundances of Ti, Na, Nd, Sm, Lu and Hf, which suggest that Tehuitzingo serpentinites represent relicts of a depleted mantle formed in a suprasubduction zone, probably in a back-arc setting that experienced partial melting in excess of 18%. Normalized REE patterns of the studied serpentinite samples are characteristic of peridotites from both suprasubduction (SSZ) and mid-ocean ridge (MOR) zones. This preliminary, but important, result may be related to the probable presence of lithospheric mantle slivers tectonically juxtaposed on the Acatlán Complex.