Geochronological and Geochemical Constraints on the Petrogenesis of Early Paleoproterozoic(2.40–2.32 Ga) Nb-Enriched Mafic Rocks in Southwestern Yangtze Block and Its Tectonic Implications

更新时间:2023-05-28

【摘要】Recent geological survey has identified the Early Paleoproterozoic meta-mafic intrusions in the southwestern Yangtze Block.We present geochronological,whole-rock geochemical and Nd isotopic data for these meta-mafic rocks to better address the tectonic evolution of the Yangtze Block during the Early Paleoproterozoic Period.Geochronological data show that the meta-mafic rocks have zircon ages of 2 395-2 316 Ma.They have high TiO2 contents of 1.40 wt.%-3.66 wt.% and Nb concentrations of 13.7 ppm-45.5 ppm,thus aregrouped as Nb-enriched mafic rocks.These mafic rocks are characterized by tholeiitic compositions with enrichment of LREEs and LILEs,and can be divided into two groups.Group 1 samples display E-MORB-like geochemical characteristics.Group 2 samples have positive ENd（t） values of 4.0-5.0.Geochemical data indicate that all meta-mafic rocks were likely derived from a depleted asthenospheric mantle.REE modeling indicates lower degree of partial melting for Group 2 samples（3%-10%） relative to Group 1 samples（15%-20%）.Taking into account contemporaneous post-collisional granitoids in southwestern Yangtze Block,we propose that these meta-mafic rocks were formed in a post-collisional extension setting.These meta-mafic rocks can be compared with those in Africa,South America and Europe,and might be linked with the Arrowsmith orogenic belt.

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