Neoproterozoic subduction along the Ailaoshan zone, South China: Geochronological and geochemical evidence from amphibolite

Abstract

a b s t r a c tLenses of amphibolites occur along the Ailaoshan suture zone at the southwestern margin of the Yangtze Block, South China. Petrological, geochemical and zircon U-Pb geochronological data indicate that they are divisible into two coeval groups. Group 1, represented by the Jinping amphibolite, has mg-number of 71-76 and (La/Yb)cn ratios of 7.2-7.7, and displays a geochemical affinity to island arc volcanic rocks. Group 2 amphibolites occur at Yuanyang and are characterized by high Nb contents (14.3-18.4 ppm), resembling Nb-enriched basalts. The ε Nd (t) values for Group 1 range from −3.45 to −2.04 and for Group 2 from +4.08 to +4.39. A representative sample for Group 1 yields a U-Pb zircon age of 803 ± 7 Ma, whereas two samples for Group 2 give U-Pb zircon ages of 813 ± 11 Ma and 814 ± 12 Ma. Petrogenetic analysis suggests that Group 1 originated from an orthopyroxene-rich source and Group 2 from a mantle wedge modified by slab-derived melt. In combination with other geological observations, these amphibolites are inferred to constitute part of an early Neoproterozoic (∼815-800 Ma) arc-back-arc basin system. The Neoproterozoic amphibolites and related rocks along the Ailaoshan zone may be the southward extension of the Neoproterozoic supra-subduction zone that developed along the western margin of the Yangtze Block.

Where was the Ailaoshan Ocean and when did it open: A perspective based on detrital zircon U–Pb age and Hf isotope evidence

“…Wang et al, 2014). It is worthy to note that although previous studies on intrusions (e.g., Cai et al, 2014) indicate that most Neoproterozoic zircons in western margin of the Yangtze Block have positive εHf(t) values, both positive and negative εHf(t) values are shown for the detrital zircons with Neoproterozoic ages in our study. Previous detrital zircon data have also shown that Neoproterozoic zircons have both positive and negative εHf(t) values (e.g.…”

“…1) (Z. Zhu et al, 2006;Zhao and Zhou, 2007;Zhu et al, 2008;Cai et al, 2014) and intermediate-acid intrusions (Fig. 1) (Li et al, 2002;Zhou et al, 2002a;X.…”

“…1) (Li et al, 2002;Zhou et al, 2002a;Z. Li, 2003;Zhou et al, 2006;Wang et al, 2011;Cai et al, 2014;Qi et al, 2012Qi et al, , 2014. This belt has recently been suggested as a Neoproterozoic arc (i.e., Hannan-Panxi-Yuanjiang arc), comprising Neoproterozoic (Tonian to Cryogenian; 880-720 Ma) arc-related igneous rocks (Zhou et al, 2002b(Zhou et al, , 2006Sun et al, 2008Sun et al, , 2009).…”

“…The Ailaoshan Belt continues to the Jinshajiang Belt to the northwest (Mo et al, 1998;Zhong et al, 1998;Wang et al, 2000), whereas its southeast extension is largely uncertain and various geological terranes in northern Vietnam/Laos have been proposed (Findlay, 1997;Lepvrier et al, 2008). Strike-slip deformation associated with the Cenozoic India-Asia collision has tectonically reactivated the Ailaoshan Belt along a series of faults, e.g., the Red River, Ailaoshan, Jiujia-Anding and Amojiang-Lixiangjiang and Tengtiaohe Cai et al (2014)). Abbreviations: SM, Song Ma; AL, Ailaoshan; JS, Jinshajiang; LC, Langcangjiang; CM, Changling-Menglian; CMa, Chiang Mai; SK, Sra Kaeo; NU, Nan-Uttaradit; BN, Bangong-Nujiang; SB, Shan Boundary.…”

Provenance and tectonic-paleogeographic evolution: Constraints from detrital zircon U–Pb ages of Late Triassic-Early Jurassic deposits in the northern Sichuan basin, central China

“…The age group matches temporally with the breakup of the supercontinent Rodinia (Li et al, 2008), which is responsible for the fact that Neoproterozoic magmatism was widespread in the Yangtze block, especially in the Jiangnan orogen ( Fig. 9d and e), but scarce in the southern NCB (e.g., Cai et al, 2014Cai et al, , 2015Wang et al, 2010;Zhang and Zheng, 2013;Zheng, 2003;Fig. 9a).…”