别若则错地区早白垩世晚期闪长岩LA-ICP-MS锆石U-Pb测年、地球化学特征及地质意义

LA-ICP-MS Ziron U-Pb Dating,Geochemical Characteristics and Geoglogical Implication of Late Early Cretaceous Diorite in Bieruozecuo Area

别若则错地区早白垩世晚期闪长岩体侵位于去申拉组、多尼组中,内部可见较多的暗色镁铁质包体。通过对闪长岩进行LA-ICP-MS锆石U-Pb测年,获得(108.3±1.4)Ma、(107.7±1.3)Ma两个岩石结晶年龄,形成时代为早白垩世晚期。岩石具高Al_2O_3、Na_2O和低TiO_2、MgO、MnO特征,为准铝质钙碱性系列岩石(ACG)。稀土元素总量为58.99×10^(-6)~84.84×10^(-6),(La/Yb)N为4.53~5.97,δEu=1.03~1.29。在球粒陨石标准化稀土元素分布模式上呈右倾形态,在原始地幔标准化蛛网图上,富集Ba,K,Rb,亏损Nb,Ce,Zr,初步认为该岩石主要源于受俯冲流体交代的地幔楔的部分熔融,岩石中表现出的轻微混染特征可能受俯部块片脱水形成的流体交代地幔楔作用控制。闪长岩形成于一种成熟度较高的俯冲火山弧环境,是班公湖-怒江洋向南俯冲消减的产物。

The late Early Cretaceous diorites in bieruozecuo area intruded into qushenla formation and duoni formation which can find many dark mafic enclaves inside.Thuogh the LA-ICP-MS ziron U-Pb dating of the quartz diorites,obtained two rock crystal age:(114.52±0.91)Ma、(116.6±1.4)Ma,which formed in late Early Crtaceous.The rock belongs to metaluminous high-K calc-alkalic series which is characteristic of high Al2O3,Na2O and low TiO2,MgO.The content of REE is 58.990×106～84.840×10-6,(La/Yb)N is 4.53～5.97,δEu=1.03～1.29.Its chondrite-normalized REE patterns are of rightly-oblique type.In the primitive mantle normalized trace element spidergrams,the rock is enriched in K,Rb and depleted in Ba,Nb,P,Ti,which is preliminary regarded that the rock was derived from partial melting of partial melting of mantle wedge replaced by subdution gluid with no significant crustal contamination.while the slight contamination rock formed may be controlled by mantle wedge replaced by subdution gluid which the prone plate dehydrate took shape.The diorites came into being a kind of high maturity tectonic subduction volcanic arc environment relative to subdution,which may be relative to the Bangong Co-Nujiang oceanic crust subducted southward.