A Precambrian Andean -Type Flysch: Petrology and Geochemistry of Yangzhanling Flysch in Southern Anhui, China

Xia Bangdong; Ma Xueming

A suit of late Proterozoic Sandstones and shales up to 2800m thick is wide-spreaded in Southern Anhui province. It has been identified by many researchers as a flysch according to a series of characteristics,such as rhythms,grading textures,contemporoneous deformations, sole marks etc.. It lays with a unconformity on Xikou Group of mainly mudstones and is covered by Dunjia coarser detrital deposits and Puling-Jintan volcanic rocks. All above mentioned strata are slightly metamorphosed. The Yanzhanling flysch arenites are debris gray wackes, which are quartz intermediate, plagioclase-rich and very metamorphic lithic. Result of heavy mineral analysis shows that they were derived from igeneous, metamorphic and sedimentary rocks. It is suggested that this flysch deposits have a source area composited of intermediate-acid volcanic rocks,granites,slightly metamorphosed rocks and sedimentary rocks,and also suggested that intermediate-acid magma was erupted during the time of flysch sedimentation, as a thicker intercalations of intermediate-acid are present in the flysch deposits. Using the QFL diagram of Dickinson et al. (1979),the source area of this flysch arenites belong to the domain between magmatic arc and rocyclic erogenic belt. Using the QFL diagram of Crook(1974),the flysch arenites have the andean-type tectonic framework. From 27 samples of flysch arenites,the content of SiO₂-is 70. 19%,K₂O/Na₂O: 0. 84,FeO+MgO:6. 37%,TiO₂:0. 74%,Al₂O₃/SiO₂:0. 20, Al₂O₃/(CaO + Na₂O) : 2. 74,according to these data, the flysch can be identified as a andean-type (from Grook, 1974)or active continental margin (from Bhatia, 1983;Roser et al.,1986). From 8 samples of flysch arenites, content of ∑ REE is 184. 29, ∑LREE/∑HREE:8. 21,Eu/Eu* : 0. 69,etc. and the flysch can also be i-dentified as andean-type. Besides,post-flysch deposits-the Puling Formation is a tholeiite-spilite assemblage.locates near the northern side of flysch basin,and the contemporaneous Jingtan Formation is a suit of andesits,dacits and pyroclastic rocks of calc-aikali series .locating near the sourthern side of the flysch basin. So, it can be confirmed that this flysch is of a andean-type developing in a tectonic framework of inter-arc basin.

A Precambrian Andean -Type Flysch: Petrology and Geochemistry of Yangzhanling Flysch in Southern Anhui, China

Department of Earth Sciences,Nanjing University

Received Date: 1991-04-15

Publish Date: 1993-06-10

Abstract: A suit of late Proterozoic Sandstones and shales up to 2800m thick is wide-spreaded in Southern Anhui province. It has been identified by many researchers as a flysch according to a series of characteristics,such as rhythms,grading textures,contemporoneous deformations, sole marks etc.. It lays with a unconformity on Xikou Group of mainly mudstones and is covered by Dunjia coarser detrital deposits and Puling-Jintan volcanic rocks. All above mentioned strata are slightly metamorphosed. The Yanzhanling flysch arenites are debris gray wackes, which are quartz intermediate, plagioclase-rich and very metamorphic lithic. Result of heavy mineral analysis shows that they were derived from igeneous, metamorphic and sedimentary rocks. It is suggested that this flysch deposits have a source area composited of intermediate-acid volcanic rocks,granites,slightly metamorphosed rocks and sedimentary rocks,and also suggested that intermediate-acid magma was erupted during the time of flysch sedimentation, as a thicker intercalations of intermediate-acid are present in the flysch deposits. Using the QFL diagram of Dickinson et al. (1979),the source area of this flysch arenites belong to the domain between magmatic arc and rocyclic erogenic belt. Using the QFL diagram of Crook(1974),the flysch arenites have the andean-type tectonic framework. From 27 samples of flysch arenites,the content of SiO₂-is 70. 19%,K₂O/Na₂O: 0. 84,FeO+MgO:6. 37%,TiO₂:0. 74%,Al₂O₃/SiO₂:0. 20, Al₂O₃/(CaO + Na₂O) : 2. 74,according to these data, the flysch can be identified as a andean-type (from Grook, 1974)or active continental margin (from Bhatia, 1983;Roser et al.,1986). From 8 samples of flysch arenites, content of ∑ REE is 184. 29, ∑LREE/∑HREE:8. 21,Eu/Eu* : 0. 69,etc. and the flysch can also be i-dentified as andean-type. Besides,post-flysch deposits-the Puling Formation is a tholeiite-spilite assemblage.locates near the northern side of flysch basin,and the contemporaneous Jingtan Formation is a suit of andesits,dacits and pyroclastic rocks of calc-aikali series .locating near the sourthern side of the flysch basin. So, it can be confirmed that this flysch is of a andean-type developing in a tectonic framework of inter-arc basin.

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A Precambrian Andean -Type Flysch: Petrology and Geochemistry of Yangzhanling Flysch in Southern Anhui, China

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