THE INDIA AND SOUTH CHINA CRATONS AT THE MARGIN OF RODINIA – SYNCHRONOUS NEOPROTEROZOIC MAGMATISM REVEALED BY LA-ICP-MS ZIRCON ANALYSES

The composition of the supercontinent Rodinia is generally clear. Nevertheless there are still discussions and controversies concerning the exact positions of South China and India, for example. Resolution of this controversy constrains not only the reconstruction of Rodinia during its breakup but contributes also to our understanding of Snowball Earth, what is synchronous with the dispersal of the supercontinent.

This talk compares the Neoproterozoic histories of the Lesser Himalaya in northern India and the Yangtze block in southern China. We present U-Pb LA‑ICP‑MS ages of detrital zircon grains from six Indian and three Chinese siliciclastic sedimentary rocks, such as sandstones or diamictites/tillites. In total, 1148 grains were analysed from which 833 measurements gave ages with a degree of concordance between 90 and 110 %. The correlation of the Indian and the Chinese sections is possible using the tillites of both areas purportedly deposited during the Snowball Earth time interval: the Blaini tillite from India and the Nantuo tillite from China.

In addition to the tillites, representative detrital zircon ages from over- and underlying clastic rocks were determined. The Chinese samples are dominated by zircons with Neoproterozoic ages with a main peak between ca. 750 Ma and ca. 950 Ma and are characterized by the absence of Archaean ages. The Indian samples contain abundant Neoproterozoic zircon grains, but also Mesoproterozoic to Archaean ones. For all samples, a local source area that provided the Neoproterozoic zircons is likely. A synchronous Neoproterozoic magmatic event in both cratons probably reflects the breakup of the supercontinent Rodinia and therefore the same tectono-magmatic event. Our results indicate a similar history for India and South China which both underwent at least one synchronous episode of crustal growth during the Neoproterozoic. In addition, our data set shows that both passive margin clastic sequences had the same source area for all zircons older than Neoproterozoic. Therefore we infer that India and South China were close to each other and along the same passive margin during the breakup of Rodinia in the Late Neoproterozoic.