Middle Neoproterozoic (ca. 715 Ma) slab window along the Yangtze northern margin: Constrained from meta-mafic igneous records

Abstract

We constrain the Neoproterozoic tectonic pattern and subduction termination records of the Yangtze Block through new geochronological, geochemical and Sr-Nd-Pb-Hf isotopic data for the metabasites of the Wudang Group in the South Qinling Belt. Our data show that these meta-igneous rocks formed at ca. 715 Ma and can be compositionally classified into five groups: arc- and MORB-like, high-Nb and Nb-enriched metabasite, and high-Mg andesite. Their εNd(t) values range from + 5.4 to −0.4, (206Pb/204Pb)i from 16.53 to 17.47, (207Pb/204Pb)i from 15.34 to 15.49, (208Pb/204Pb)i from 36.54 to 37.46 with Δ8/4 = +65 ∼ +173 and Δ 7/4 = +4.5 ∼ +10.5, respectively. Their source was the convergent plate margin mantle wedge, modified by subduction-related component or interacting with the OIB-type asthenospheric mantle. Together with available data, the Wudang Group in the South Qinling Belt is characterized by the Neoproterozoic volcano-sedimentary rocks, with the volcanic rocks are dominated by the ca. 850–780 Ma mafic, ca. 780–730 Ma felsic and ca. 720–710 Ma mafic rocks. The Wudang Group is overlain by the ca. 700–630 Ma rift-related Yaolinghe Group with the intervening angular unconformity constrained to an age of ca. 710–700 Ma. Based on regional data from the northern margin of the Yangtze Block, we propose a long-lived Neoproterozoic (∼890–710 Ma) a north facing arc-trench system with south-directed subduction ongoing until ca. 710 Ma. This subduction termination could reflect the development of a tear-induced slab window model in the South Qinling Belt.