Geochemical Characteristics And Geological Significance Of The Volcanic Rocks From Mianlue Suture Zone (Zhongtanggou-guozhen), South Qinling

The Mianlue suture zone located in Lueyang–Mianxian–Gaochuan areas in Shaanxiprovince is another ancient plate suture zone that is important for the evolution of the Qinlingorogenic belt discovered about20years. The author redefines theZhongtanggou–Zhaojiaheba arc volcanic blocks and Guozhensigou arc volcanic blocksduring the process of wild-field geological survey in the Lueyang–Kangxian areas of theMianlue suture zone. Dominated by systematic studies on wild–field geological characteristic,petrology, petrologic geochemistry and isotopic geochronology of the volcanic rocks in thestudy areas, the following cognitions are acquired in the assay after the wild–field geologicalmapping and detailed indoor experiments and analysis to the collected samples of the studyarea.1. The suite of the volcanic rocks exposed in Zhongtanggou–Zhaojiaheba andGuozhensigou areas of the Mianlue suture zone are mainly composed of metamorphicandesite rocks and metamorphic basalt and metamorphic dacite rocks. They mainly belongedto calc–alkaline series.2. The Zhongtanggou–Zhaojiaheba volcanic blocks were mainly greenschist faciesmetamorphic rocks, which comprise mainly metamorphic andesite rocks and subordinatelymetamorphic basalt and metamorphic dacite rocks, belonging mainly to the calc–alkalineseries. The characteristics of trace elements, in combination with features of volcanic rocks,indicated that the volcanic rocks from Zhongtanggou area were formed in a typical tectonicsetting of island arc. The authors hold that the material source of metamorphic andesite andmetamorphic basalt rocks might have been closely related to a locally depleted area in theaddition of continental crustal material. The material source of metamorphic dacite wasprobably related to the partial melting of the crustal granitic magma.3. The Guozhensigou volcanic blocks had affected by alteration and metamorphism,which comprise metamorphic andesite rocks and metamorphic basalt and metamorphic daciterocks, belonging mainly to the calc–alkaline series. Characteristics of trace elements and theassemblage of volcanic blocks and discrimination diagrams of structural environmentindicated that the volcanic rocks from Guozhensigou area occurred in a typical tectonic setting of an island arc. It is proposed that the material source of metamorphic andesite andmetamorphic basalt rocks might be closely related to a locally depleted in the mantle wedge,which possessed the similar character of the ocean island basalts, and the participation ofcontinental crustal material. The material source of metamorphic dacite might be related to apartial melting crust–source granitic magma.4. The redefinition of arc island volcanic rocks in Zhongtanggou–Guozhen areas,provided a more reliable reference of field geological data and geochemical data for thestructural setting of Sanchazi volcanic rocks in Mianlue suture zone, and supplied animportant foundation of the formation and evolution of the Mianlue suture zone. Combinedwith the Neoproterozoic volcanic rocks of the Mianlue suture zone and the previousinformation with Mianlue tectonic evolution of the Triassic. We believe that not only alimited ocean basin developed in late Paleozoic, but also a more ancient ocean basin existedin Neoproterozoic, which indicating that the Mianlue suture zone was a complex melangebelt contained different times, different characteristics, complex composition andevolutionary history. Therefore, this study has great significance both in further studying theMian–Lue tectonic zone structure and tectonic evolution as w ell as addressing continentaldynamic issues such as the breakup of Rodinia supercontinent and other continents in theYangt zeblock north margin.