Carbonatite-silicate metasomatism of mantle xenoliths from Santa Cruz province, Patagonia, Argentina.

NTAFLOS, TH; BJERG, E A; KURAT, G; HINTON, R; LABUDIA, C; UPTON, B G J

Rio de Janeiro

Congreso; 31st International Geological Congress; 2000

The hills of La Huerta and Valle Fertil, wich belong to the Western Pampean Ranges in the Province of San Juan, NW Argentina, mainly consist of metagabboic to metadioritic rocks that intruded the Proterozoic basement in the Early Middle Ordovician (Famat <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:21.0cm 842.0pt; margin:70.9pt 3.0cm 70.9pt 3.0cm; mso-header-margin:35.45pt; mso-footer-margin:35.45pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Upper mantle xenoliths from Gobernador Gregores, Santa Cruz, Argentina, comprise spinel-lherzolites, harzburgites, orthopyroxenites, clinopyroxenites and wehrlites. Amphibole, calcite and phlogopite-bearing xenoliths are of particularinterest because they contain glassy patches of up to 1 cm in diameter. Matrix chromian diopside has a spongy envelop consisting of intergrowths of pale-green clinopyroxene (cpx) and a brownish glass, indicating a metasomatic event. Disseminated dark mica plates and pargasitic amphiboles are affected by the same metasomatic event which caused the cpx breakdown.