The petrogenesis and evolutionary process of Neoarchean Diaoyutai granite in western Liaoning Province: Evidences from petrofabric
There is a set of granitic complex exposed in the Diaoyutai area,western Liaoning Province,and it is an important part of "Suizhong granite".This set of granitic complex is composed mainly of porphyraceous granodiorite and quartz-bearing diorite,with a small amount of fine-grained biotite diorite (enclaves) and veinlike granite.The contacts of each kind of rock are clear,and we define it as "Diaoyutai granite" in the study.Zircon U-Pb ages show that the porphyraceous granodiorite,quartz-bearing diorite and veinlike granite are formed at 2538 ± 20Ma,2476 ± 56Ma and 2470 ± 18Ma respectively,which are all the products of the Late Neoarchean thermal event.Based on the macro-micro fabric analysis of the granitic complex,we confirm that the porphyraceous granodiorite has the massive structure and the typical accumulative texture that formed in the late stage of anataxis.The fine-grained biotite diorite is finegrained texture and it occurs in the porphyraceous granodiorite in the form of micro mafic enclaves.There developed plastic deformation,xenocrysts,quenching boundary and reverse veins in the enclaves showing the injection of mafic magma during the period of granodiorite melting,and subsequent to the period,the magma cooled rapidly.Dark quartz-bearing diorites intrude under the porphyraceous granodiorite,and the K-feldspar metacrysts increase obviously in the vicinity of the contact zone,showing the heating characteristic of " underplating" emplacement.Meanwhile,the veinlike granite cross cut both the porphyraceous granodiorite and quartz-bearing diorite,and have the characteristic of being highly enriched in melt.Deformation fabric is not well developed in all rocks.In short,the "Diaoyutai granite" recorded the Late Neoarchean crust anatexis and the interaction between crust and mantle.The petrofabric research shows that the Neoarchean crust reconstruction is a process of static,multiple and slow crust anatexis with the cotemporaneous injection of mantle-derived magma,resulting in magma mingling and mixing and subsequent large-scale magma underplating.According to the present study,we therefore conclude that the tectonic setting is a vertical underplating environment of mantle-derived magma,and is probably the magma arc environment far from subduction zones.
Diaoyutai graniteAnataxisAccumulative textureMagma mingling and mixingUnderplating
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万方数据
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