Yangtze Plate Volcanic Rocks In The Northern Margin Of Bikou Geochemical Studies

Exposed a large scale in adjacent districts of Shaanxi, Gansu, Sichuan provinces, the BiKou volcanic group in northern margin of the Yangtze block is consisted mainly of BiKou block assigning to West Qinling-Songpan tectonic joint node, which is a key joint field of West and East Qinling, Longmen, Songpan so as to be good insight for the study on the relative joint connection in several units such as, the extend to west of MianLue belt, Longmen. BiKou, Mingshan. Thanks to the specific locality, in a long term, the tectonic nature, characteristic, attribute property of BiKou volcanic group appeal a great of attention and yet still remained controversial, since the volcanic group of BiKou had been found by several geologists in 1944. With regard to the implication of the whole BiKou region and adjacent blocks, the attempt of present study is to further discuss their possible tectonic setting and source regime as well as place a geochemical constraint on the volcanic original geodynamic environment in the BiKou group on the basis of the previous study, Eventually to offer a helper to pursuit the tectonic pattern and evolution of North margin in the Yangzte block during the Neoproterozoic era.With the geochemical help of the silica rocks, meanwhile, coupled with the geochemical, isotope geochemical and isotopic geochronological characteristics of the volcanic rocks obtained from the BiKou group, the conclusions reached are as follow:The MORB: the abundance of SiO₂, MgO, TiO₂ is in a good accordance with those of the typical MORB. The rock N-MORB spider diagram and the Chondrite-normalized all display fairly similarity with MORB curve, suggesting the magmas source and genesis have a closer affinity with the latter. The isotopic geochemical characteristics, such as (⁸⁷Sr/⁸⁶Sr)i=0.7043⁰.7066, ε Nd(t)=+2.069 +6.3548 ; ²⁰⁶Pb/²⁰⁴Pb=16.571¹8.017 (17.215), ²⁰⁷Pb/²⁰⁴Pb=14.328¹5.832(15.350), ²⁰⁸Pb/²⁰⁴Pb=35.896³9.156(37.099), are in a good agreement with the South Atlantic Ocean and Indian Ocean, so are the average value as well.The Thi-OIB and Alk-OIB: Besides the major content have some relative to the OIB, the rock N-MORB spider diagram and the Chondrite-normalized both demonstrates very some resemblance with OIB; what's more, the remarkable affinity expressed in the Pb-Pb isotopic system is ²⁰⁶Pb/²⁰⁴Pb=17.185¹8.763(18.158), ²⁰⁷Pb/²⁰⁴Pb=15.380 15.928 (15.557), ²⁰⁸Pb/²⁰⁴Pb=36.788⁴0.069(38.207), which coincide with the value from the Kerguelen,TristadCunha and Gough island.The IAB: The high total Σ REE is in a variation from 112.67¹37.73 × 10^-6 .with a somewhat negative Eu ( δ Eu =0.86⁰.92); the rocks in the Chondrite-normalized diagram shows a right slopping patterns, 20⁸0 times more than the chondrite; Similarly, the rocks in the N-MORB spider diagram also is such pattern , whereas the...