Geochemical characteristics of the Granitoids of Mikir Hills Massif of Shillong Plateau, Northeast India: Implication for Pan-African Magmatic Activity

M. Faruque Hussain, and Talat Ahmad

Mikir Hills massif (MHM) of the Shillong plateau, in northeastern India extends over an area of about 7000 km2. MHM vis-à-vis Shillong plateau record granite magmatism from 881 to 479 Ma related to Pan-African magmatic event.

The analysed MHM granitoids have SiO2 ranging from 64.5 wt.% to 75.8 wt.%; Al2O3 content ranges from 13 to 14 wt.%; CaO content ranges from 1.3 to 3.3 wt.% and the total alkalies range from 7.2 wt.% to 8 wt.%. The granitoids show steeply fractionated chondrite normalized rare earth element (REE) patterns with (La/Yb)N varying between 18 and 28, strong negative Eu anomaly, and flat heavy REE patterns. They have enriched large ion lithophile element (LILE) abundances relative to high field strength elements (HFSE) with negative Nb, Sr, P and Ti anomalies in the Primitive Mantle normalized multi-elemental patterns. In the tectonic discrimination diagrams, the granitoids plot within volcanic arc granite filed. These geochemical signatures point towards a subduction related magmatism in the Shillong plateau.

The Neoproterozoic granitoids of Shillong plateau with arc geochemical signature and with the plateau at the leading margin of Neoproterozoic Indian plate, place constraints on the evolution of these rocks and their significance in dispersal of Rodinia and subsequent assembly of the Gondwana supercontinent.