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

Yongfeng Cai, Yuejun Wang, Peter A. Cawood, Weiming Fan, Huichuan Liu, Xiaowan Xing, Yuzhi Zhang

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Abstract

Lenses 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 (14.3-18.4ppm), resembling Nb-enriched basalts. The eNd(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±7Ma, whereas two samples for Group 2 give U-Pb zircon ages of 813±11Ma and 814±12Ma. 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 (~815-800Ma) 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.

Original languageEnglish
Pages (from-to)13-28
Number of pages16
JournalPrecambrian Research
Volume245
DOIs
Publication statusPublished - May 2014
Externally publishedYes

Keywords

  • Ailaoshan zone
  • Amphibolite
  • Neoproterozoic subduction
  • Petrogenesis
  • Zircon U-Pb dating

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