矿床地球化学国家重点实验室知识库

Scattered T-DM2 (3.8 - 3.2 Ga) for 3.28 - 2.99 Ga zircons from the Proterozoic Delhi Supergroup in northwestern India provide evidence for generation of juvenile crust and reworking of older crust. Depleted mantle-like epsilon(Hf(t)) values (+ 7.2 to + 5.6) for 2.86 - 2.71 Ga zircons indicate that generation of juvenile crust occurred during this period and ceased at 2.71 Ga. Extensive magmatism at 2.66 - 2.34, 2.11 - 2.01 and 1.60 - 1.37 Ga was dominated by reworking of pre-existing crust with variable ages, and the last two periods were accompanied by formation of juvenile crust. An Eoarchaean age of 3671 +/- 15 Ma represents the oldest age found in NW India. Zircons formed during supercontinent assembly have positive to negative epsilon(Hf(t)) values, suggesting involvement of juvenile and ancient crust, whereas largely positive epsilon(Hf(t)) values for zircons crystallized subsequent to supercontinent amalgamation suggest involvement of predominantly juvenile crust. Correlation of detrital age patterns and tectonomagmatic events indicates a conjugate position for northern Indian and the Cathaysia Block of South China during the assembly of Nuna. The South China Block remained juxtaposed to India until its separation from Pangaea in the late Palaeozoic.