Paper No. 6
Presentation Time: 9:15 AM
LATE ARCHEAN-EARLY PALEOPROTEROZOIC CONTINENTAL ASSEMBLY OF INDIA AND EAST ANTARCTICA
Re-Os dating of molybdenite associated with a major porphyry-style Cu-Mo-Au deposit at Malanjkhand along the southern margin of the Central Indian Tectonic Zone (CITZ) suggests that the joining of peninsular with mainland India (south and north Indian cratons) took place at about 2.5 Ga along a proto-CITZ. This join is marked by an abundance of disparate and juxtaposed terranes and an imprint of shear deformation that penetrates well into the margins of south-bounding terranes, each with unique lithostratigraphic domains and metallogenic histories. Re-Os dating of molybdenite in a reworked quartz reef, proposed to represent the original high silica cap at Malanjkhand, suggests that amalgamation continued until at least ~2.45 Ga (Stein et al., in press, Precambrian Research). The E to W assembly of Late Archean terranes comprising peninsular India (~2.56-2.51 Ga) slightly preceded the oblique meeting of the north and south Indian cratons along the proto-CITZ. The western extension of the CITZ is hidden under the Deccan basalts. This extension may represent younger (Grenvillian, Pan-African) reactivation, whereas the proto-CITZ may swing northward along the Aravalli-Dehli fold belt. At least part of the eastern extension of the CITZ wraps around the Singhbhum craton and turns southward, where it merges with the complex UHT Eastern Ghats belt. Similarities between the Eastern Ghats and the Napier complex in East Antarctica have been long debated. It is proposed here that the Vestfold Hills complex in East Antarctica may be related to the proto-CITZ. The microcontinent hosting the Malanjkhand porphyry Cu-Mo-Au deposit shares striking temporal and magmatic similarities with the Vestfold Hills complex. Both are characterized by Late-Archean-Early Proterozoic calc-alkaline subduction-related magmatism and may be vestiges of terrane(s) associated with closure along the proto-CITZ. Thus, it is suggested that the Napier and Vestfold Hills complexes were part of the Indian subcontinent at ~2.5 Ga and were detached and joined to East Antarctica either during Grenvillian or Pan-African time. This study is one of a growing number of Re-Os studies in which molybdenite geochronology is used to track the magmatic-metamorphic-metallogenic history of a major orogenic cycle.