Changes in Relative Plate Motion during the Isan Orogeny(1670-1500Ma) and Implications for Pre-Rodinia Reconstructions

作     者：A.S.A.A.ABU SHARIB 

作者机构：School of Earth and Environmental ScienceJames Cook University Geology DepartmentBeni-Suef University 

出 版 物：《Acta Geologica Sinica(English Edition)》 (地质学报（英文版）)

年 卷 期：2016年第90卷第1期

页      面：88-105页

核心收录：

学科分类：070904[理学-构造地质学] 0709[理学-地质学] 07[理学] 

基　　金：part of the author's PhD project funded by the Australian government and the ministry of higher education of Egypt 

主　　题：Foliation Intersection/Inflexion Axes (FIA) tectono-metamorphic porphyroblasts bulk horizontal shortening Isan Orogeny. 

摘      要：Foliation inflexion/intersection axes （FIAs） preserved within porphyroblasts that grew throughout Isan orogenesis reveal significant anticlockwise changes in the direction of bulk horizontal shortening between 1670 and 1500 Ma from NE-SW, N-S, E-W to NW-SE. This implies an anticlockwise shift in relative plate motion with time during the Isan orogeny. Dating monazite grains amongst the axial planar foliations defining three of the four FIAs enabled an age for the periods of relative plate motion that produced these structures to be determined. Averaging the ages from monazite grains defining each FIA set revealed 1649^-12 Ma for NE-SW shortening, 1645±7 Ma for N-S shortening, and 1591±10 Ma for that directed E-W. Inclusion trail asymmetries indicate shear senses of top to the SW for NW-SE FIAs and dominantly top to the N for E-W FIAs, reflecting thrusting towards the SW and N. No evidence for tectonism related to early NE-SW bulk horizontal shortening has previously been detected in the Mount Isa Inlier. Amalgamation of the Broken Hill and possibly the Gawler provinces with the Mount Isa province may have taken place during these periods of NE-SW and N-S-directed thrusting as the ages of tectonism are similar. Overlapping dates, tectonic, metamorphic, and metallogenic similarities between eastern Australia （Mount Isa and Broken Hill terranes） and the southwest part of Laurentia imply a most probable connection between both continental masses. Putting Australia in such position with respect to North America during the Late-Paleo-to-Mesoproterozoic time is consistent with the AUSWUS model of the Rodinia supercontinent.