Abstract
Voluminous Late Mesozoic granitoids and the world’s largest Mo deposits occur in the East Qinling. This paper presents the results of Nd–Hf isotopic mapping for the Late Mesozoic granitoids (155–105Ma) and demonstrates their constraint on the basements and distribution of the Mo deposits in the East Qinling. This isotopic map, made by 98 (21 new and 77 published) whole-rock Nd isotopic and 29 (7 new and 22 published) average zircon Hf isotopic data, shows large variations of whole-rock εNd(t) values from −22.1 to −1.5, and the correspondingly Nd model ages (TDM(Nd)) from 2.83 to 0.79Ga, and zircon εHf(t) values from −26.3 to +0.1 and two-stage Hf model ages (TDM2(Hf)) from 2.86 to 0.96Ga. Three regions of variations have been identified from north to south: (a) εNd(t) values range from −22.1 to −10.9 with TDM(Nd) of 2.82–1.47Ga, and εHf(t) values 26.3 to −13.5 with TDM2(Hf) 2.86–2.04Ga; (b) εNd(t) values −13.9 to −1.5 with TDM(Nd) 2.02–0.79Ga, and εHf(t) values −16.2 to +0.1 with TDM2(Hf) 1.96–0.96Ga; and (c) εNd(t) values −6.3 to −4.5 with TDM(Nd) 1.28–1.12Ga, and εHf(t) values −1.0 to −0.3 with TDM2(Hf) 1.25–1.22Ga, respectively. The three regions approximately correspond to the three different terranes, the southern margin of the North China Block (NCB), the North Qinling Belt (NQB) and the South Qinling Belt (SQB), respectively. These demonstrate that the granitoids in the different terranes have distinct sources and their sources change from old to more juvenile from the north (southern margin of the NCB) to the south (SQB). These also reveal the distinct basements for the terranes in Late Mesozoic. The southern margin of the NCB contains widespread Neoarchaean to Paleoproterozoic basement, the NQB comprises Archaean to Neoproterozic basement and the SQB Mesoproterozic to Neoproterozic basement. All these suggest that the three terranes underwent different tectonic evolution and the continental crust of the East Qinling were mainly formed during Archaean to Neoproterozic, different from a typical accretion orogen. The old sources of the granitoids and basements of the terranes constrain the distribution, scale and number of the Mo mineralization and deposits. Mo mineralization is closely related to the small granitic bodies with old continental component sources and Mo deposits are mainly hosted by the terranes with oldest basement. The scale and number of the Mo mineralization and deposits decreased from the southern margin of the NCB to SQB.
Highlights
It is generally considered that there are different continental compositions between a subductional– collisional and an accretionary orogen, what are the differences and how to identify them has not been well understood
This study attempts to discuss this problem by comparing Nd isotopic compositions of granitoids in the Qinling-Dabie orogen, a typical subductional-collisional orogen, with those in southwestern segment of the Central Asian Orogenic Belt (CAOB), the world's largest phanerozoic accretionary orogenic belt
Voluminous Paleozoic and Mesozoic granitoids in the Qinling Orogen have εNd(t) values from −21.9 to −10.9 in the southern margin of the North compositions between the Qinling-Dabie orogen (China) craton (NCC), from −14 to +5.4 in the North Qinling belt (NQB), from −10 to −1.8 in the South Qinling belt (SQB) and from −6.5 to –3.2 in the northern margin of the South China craton (SCC)
Summary
It is generally considered that there are different continental compositions between a subductional– collisional and an accretionary orogen, what are the differences and how to identify them has not been well understood. For citation: Wang X.X., Wang T., Ke C.H., Huang H., Tong Y., Yang Y., Hong D.W., 2017.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.