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2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 7
Presentation Time: 9:30 AM

TRACE ELEMENTS AND ND-ISOTOPIC PROVENANCE OF THE MID-PROTEROZOIC VINDHYAN BASIN, INDIA: A MID-PROTEROZOIC FORELAND BASIN?


CHAKRABARTI, Ramananda, Earth and Environmental Sciences, Univ of Rochester, 227 Hutchison Hall, Rochester, NY 14627, BASU, Asish R., Department of Earth and Environmental Sciences, Univ of Rochester, 227 Hutchison Hall, Rochester, NY 14627 and CHAKRABARTI, Amitabha, Geology and Geophysics, Indian Institute of Technology, Kharagpur, 721302, India, ramananda@siena.earth.rochester.edu

We report trace element and Nd-isotopic geochemistry for the Proterozoic Vindhyan Supergroup of rocks in central India. The Vindhyan Basin with an area of 178,000 km2 is one of the largest Proterozoic basins of the world and comprises a 4200m thick sequence of mostly undeformed and unmetamorphosed sediments, dominantly immature and siliciclastic in the lower part succeeded by more carbonate rich sediments to the top. U-Pb zircon ages of ~1630Ma of a rhyolitic tuff (porcellanite) horizon in the basal part of the basin gives the approximate age of initiation of sedimentation.

We analyzed 40 trace elements and Nd-isotopes in the different lithounits of the Vindhyan Basin. Our preliminary data indicate that the lithounits have more radiogenic Nd-isotopic composition (εNd(1630)=-7 to +4) compared to the basement Bundelkhand gneiss (εNd(1630)=-12). This data clearly contradict the currently held view of a Bundelkhand gneissic provenance for these sediments. The tuff samples collected from different parts of the basin show a wide range in their initial Nd-isotopic composition (ε Nd(1630)=-6 to +4), suggesting their derivation from a depleted Proterozoic sub-oceanic mantle source and mixing with the host sediments.

Chondrite normalized REE data of the lithounits show a generally uniform fractionated pattern. The rhyolite tuff samples show the highest degree of fractionation (LaN/LuN=13-15) compared to the basement gneiss (LaN/LuN=10) and the other sedimentary units (LaN/LuN=5.5-9.5). The observation also supports our contention that the Bundelkhand gneiss is not the major source of the sediments deposited in the basin.

The Vindhyan basin, like several other proterozoic basins of the Indian Peninsular Cratons, is disposed along the margin of these cratons in contact with the Middle Proterozoic Mobile belt. This mobile belt, comprising the Eastern Ghats, the Satpura belt of central India and the Delhi-Aravalli belt of north-west India, is suggested to be the source of the Vindhyan basin sediments.

Session No. 197

Precambrian Geology
Wednesday, 10 November 2004: 8:00 AM-12:00 PM
Geological Society of America Abstracts with Programs. Vol. 36, No. 5, p.459
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