Meso-neoproterozoic To Early Paleozoic Tectonics And Mineralization Of Black Shales In Southwest Henan, China

Southwestern Henan, located in the transition zones of the southern sector of the North China Craton(NCC), North Qinling Tectonic Belt and northern sector of the Yangtze Craton(South Qinling Tectonic Belt), have complex tectonic evolution during Meso-Neoproterozoic. Extensive Meso- to Neoproterozoic weakly metamorphosed or unmetamorphosed sedimentary sequences developed in the region. Carbonaceous sediments(e.g. Baishugou Formation, Meiyaogou Formation and Shuigoukou Formation) deposited in the region during Meso-Neoproterozoic and Early Cambrian. By study of sedimentary sequence, Baishugou Formation is carbonaceous mudrocks and carbonates hosted Black Shales, in subtidal-intertidal zone. Meiyaogou Formation is carbonaceous mudrocks hosted, deposited in tidal-flat and neritic facies. Shuigoukou Formation is cherts hosted Black Shales, in margin continental shelf.Mineralogial composition and features were investigated by XRD and EPMA. Illite, barite, hematite and organic related pyrite are more enriched in Meiyaogou Formation than Baishugou Formation. Illite, hematite, barite, celsianite and pyrite are widely developed in Baishugou Formation. Geochemical study revealed the black shales enriched U, P, Ni, Co, Ba and Ag. Among them, Vanadium is the richest transition element, as a result of multi-form of oxidation states. The variable depths of water affect the enrichment degrees of vanadium in Baishugou, Meiyaogou and Shuigoukou Formation.The detrital zircons of carbonaceous schist in the lower part of Baishugou Formation mainly focus on ~2.5 Ga, and minor peaks of ~1.8 Ga, ~2.0-2.3 Ga, and ~1.6 Ga, with εHf(t) values from-10.8 to +9.1. From the middle-top part of the Formation, ~1.8 Ga, ~1.5 Ga, ~1.3Ga and ~1.1 Ga peak ages developed, with significantly high positive εHf(t) values from-4.4 to +14.9. By comparison with U-Pb ages and Hf isotopes of detrial zircons in Mesoproterozoic and Neoproterozoic sedimentary rocks in NCC and North Qinling(NQL), the early sediments may origin from the NCC and the late from the NQL. Coupled with the magmatic events in south margin of NCC and NQL in Meso-Neoproterozoic, the sedimentary provenances changed from NCC to NQL may indicate the accretion of NQL to NCC in ~1.0 Ga. The detrial zircons in this study are similar age spectra and Hf isotopic composition to those from the northern and eastern NCC, which indicate coeval tectonic event related with the evolution of Rodinia Supercontinent.