Geochronology, petrogenesis, and tectonic setting of Neoproterozoic and Late Paleozoic granitoids of the Manzhouli-Ergun area of Inner Mongolia, China
Abstract
U-Pb dating and Hf isotopic analysis of zircons from various granitoids, combined with major and trace element analysis, was undertaken to determine the petrogenesis and geodynamics of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli-Ergun area of Inner Mongolia, China. Neoproterozoic granitoids are mainly composed of biotite monzogranite with zircon U-Pb ages of 880 ± 10 and 894 ± 13 Ma, and are characterized by enrichment in LILE and LREE relative to HFSE and HREE with negative Nb, Ta, P and Ti anomalies. Late Devonian granitoids are dominantly composed of syenitegranite and mylonitized syenitegranite with zircon U-Pb age of 360 ± 4 Ma, and show a bimodal magmatic association and A-type granitiod geochemical characteristics including high total alkalis, Zr, Nb, Ce and Y contents and high FeOt/MgO, Ga/Al and Rb/Sr ratios. Carboniferous granitoids consist principally of tonalite, granodiorite and monzogranite with U-Pb ages varying from 320 to 306 Ma, and show the strongest adakitic characteristics such as high La/Yb and Sr/Y ratios but low Y and Yb contents. Late Permian granitoids are dominated by granodiorite and monzogranite with zircon U-Pb ages ranging between 257 and 251 Ma and show low Sr and Yb content characteristic of Himalaya-type granitoid. Isotopically, the ɛHf(t) values of Neoproterozoic granitoids range from +2.30 to +4.14 and two-stage model ages (TDM2) vary from 1.5 to 1.6 Ga, Late Devonian granitoids display values less radiogenic [ɛHf(t) from +11.95 to +12.77 and TDM2 from 546 to 599 Ma] in comparison to Carboniferous granitoids [ɛHf(t) from +7.82 to +8.47 and TDM2 from 791 to 832 Ma] and Late Permian granitoids [ɛHf(t) from +6.70 to +7.35 and TDM2 in the range of 813-855 Ma]. These data indicate that Neoproterozoic granitoids may have generated in equilibrium with an amphibolitic (plagioclase + amphibole) residue at depths of 30-40 km and are most likely associated with the accretion of Ergun microcontinent block to the southern margin of Siberian craton, Late Devonian granitoids may have been formed by partial melting of a new mantle-derived juvenile crust in a post-orogenic extensional setting, Carboniferous granitoids appear to have been produced by high-pressure melting of a garnet-rich eclogitic source during collision of Xing'an and Songnen blocks, and Late Permian granitoids may have generated in equilibrium with a granulitic (garnet + plagioclase) residue at depths of 40-50 km and were possibly related to the collision between the North China and Siberia cratons.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMED11C0737G
- Keywords:
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- 3619 MINERALOGY AND PETROLOGY / Magma genesis and partial melting;
- 3640 MINERALOGY AND PETROLOGY / Igneous petrology