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

Resumen

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 fluids 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 first 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.