滩间山群的重新厘定——来自柴达木盆地周缘玄武岩年代学和地球化学证据

Redetermination of the Tanjianshan Group: Geochronological and Geochemical Evidence of Basalts from the Margin of the Qaidam Basin

柴达木盆地周缘滩间山群在岩石组合、玄武岩同位素年代学和地球化学特征以及在区域成矿过程中作用具有明显差异。柴北缘和柴南缘（东昆仑地区）滩间山群具有不同的岩石组合和沉积建造：柴北缘滩间山群下部为中基性海相火山岩,上部为碎屑岩-碳酸盐岩;柴南缘下部为中基性-中酸性火山岩夹碎屑岩,中部为碎屑岩夹中基性火山岩,上部为碳酸盐岩夹碎屑岩。柴北缘和柴南缘滩间山群中玄武岩年代学和地球化学对比研究表明,柴北缘玄武岩形成时限约在510~460Ma,代表了寒武纪—奥陶纪岩浆作用;柴南缘形成时限约在450~440Ma,为中奥陶世-早志留世喷发产物。柴北缘滩间山群玄武岩总体上具有岛弧火山岩性质,代表了早古生代区域上洋陆俯冲过程中不同阶段的产物;柴南缘滩间山群玄武岩具有E-MORB特征,为祁漫塔格有限洋（弧后盆地）打开过程中的产物。

The Tanjianshan Group distributed widely on the margin of the Qaidam basin is characterized by distinct differences in rock assemblages,isotopic chronology and geochemical features of basalts,as well as regional mineralization.It has different rock assemblages and sedimentary formation on the northern and southern margins of the Qaidam basin.The Group on the north consists of intermediate-basic marine-facies volcanic rocks on the bottom,and classic rocks and carbonate rocks on the top,whereas the Group on the south consists of intermediate-basic and intermediate-acidic volcanic rocks intercalated with minor clastic rocks,clastic rock interlayed with minor intermediate-basic volcanic rock in the middle,and carbonatic rock intercalated with minor clastic rocks.The isotopic geochronology and geochemical comparison of basalt from the Tanjianshan Group on the southern and northern margins of the Qaidam basin show that the basalt on the north formed ca.510 to 460 Ma,representing the Cambrian-Ordovician magmatism,while the basalt from the south formed at ca.450 to 440 Ma and was the product of Middle Ordovician-Early Silurian magmatic eruption.In general,the basalt of the Tanjianshan Group in the north margin of the Qaidam basin has the features of island-arc volcanic rocks,and should be the product of subduction of regional oceanic continent during the Early Paleozoic,while the basalt on the southern margin has the features of E-MORE lavas and should represent the remnants of fragmented oceanic crust during the opening of the Paleo-Qimantege ocean（post-arc basin）.