滇西勐养花岗岩体暗色包体的地球化学特征及成因

发布时间：2018-08-14 19:17

【摘要】：勐养侵入岩体主要由黑云母二长花岗岩(128 Ma)、花岗闪长岩(113 Ma)和辉长质(123 Ma)、闪长质包体(120Ma)组成。暗色包体主要分布在花岗闪长岩中,包体岩性主要为辉长岩包体和闪长岩包体。包体具有岩浆结构,部分包体具有塑性流变特征,有些包体具有淬冷边和反向脉,包体中可见针状磷灰石,表现出岩浆混合的岩相学特征。岩石地球化学特征研究表明,寄主岩石与暗色包体同为准铝质-过铝质、钙碱性-高钾钙碱性系列岩石。寄主岩石与暗色包体的的稀土配分曲线模式和微量元素原始地幔标准化蛛网图形态基本一致,为岩浆混合作用的结果。所有样品均富集大离子亲石元素(如Rb、Th、U和Nd)、亏损高场强元素(如Nb、Ta、Ce和Zr)。勐养早白垩世侵入岩形成于岩浆弧环境。暗色包体具有低的Si O2含量(Si O2为48.02%和59.8%)和高的Mg#值(Mg#=48.1~68.5),表明暗色包体的原生岩浆应是板块俯冲带流体交代地幔橄榄岩的部分熔融的产物,并受后期岩浆混合作用的改造。暗色包体锆石的εHf(t)为3.6~6.2,Nb/Ta值为12.1~15.4,显示岩浆源区具有亏损地幔特征。黑云二长花岗岩的Mg#=33.5,Nb/Ta值为10.9,表明岩浆主要来源于古老的地壳物质的部分熔融。花岗闪长岩锆石的Mg#=44,Nb/Ta值为12.5,岩浆主要来源于地幔和地壳,为黑云二长花岗岩与幔源岩浆混合作用的产物。腾冲地块早白垩世勐养侵入岩体及其暗色包体的的成因,是左贡—保山板块洋壳向南西俯冲在波密—腾冲地块之下,使区域地壳不断加厚并导致区域重力均衡隆升,深部地壳物质在加热后抬升减压过程中发生部分熔融,形成大量的花岗岩浆。由于俯冲洋壳板块在俯冲、碰撞过程中诱导的幔源岩浆与重熔物质发生岩浆混合作用,形成花岗闪长岩和暗色包体。
[Abstract]:The Mengyang intrusive body is mainly composed of biotite monzogranite (128 Ma),) granodiorite (113Ma) and xenolitic (123 Ma), diorite inclusion (120Ma). The dark inclusion is mainly distributed in granodiorite, and the xenoliths are mainly gabbro and diorite xenoliths. The inclusions have magmatic structure, some inclusions have plastic rheological characteristics, some inclusions have quenched edges and reverse veins, and acicular apatite can be found in the inclusions, showing the petrographic characteristics of magmatic mixing. The geochemical characteristics of the host rocks show that the host rocks are similar to the dark inclusions in the pseudo-aluminum-peraluminous, calc-alkaline and high-potassium calc-alkaline series rocks. The REE distribution curve model of host rocks and dark inclusions is basically consistent with the morphology of trace elements in the original mantle-standardized cobweb diagram, which is the result of magmatic mixing. All samples are homogeneously rich in large ion lithophile elements (such as RBC Thyu and Nd), depleted high field strength elements such as NbBU Tahou ce and Zr). Mengyang early Cretaceous intrusive rocks were formed in magmatic arc environment. The dark inclusion has a low Sio 2 content (48.02% Sio 2 and 59.8% Sio 2) and a high Mg# value (Mg#=48.1~68.5), indicating that the primary magma of the dark inclusion is the product of partial melting of the mantle peridotite from the fluid metasomatic mantle in the plate subduction zone and is modified by late magma mixing. The 蔚 Hf (t) of the dark inclusion zircon is 3.6 ~ 6.2nb / Ta = 12.1 ~ 15.4, which indicates that the magmatic source region has the characteristics of depleted mantle. The mg #5 Nb / Ta value of the bifeldite is 10.9, indicating that the magma mainly originated from the partial melting of the ancient crustal material. The zircon mg #n4N / Ta value of granodiorite is 12.5. The magma is mainly derived from the mantle and crust, and is the product of the mixing of the bifeldite and mantle magma. The genesis of the early Cretaceous Mengyang intrusive rock mass and its dark inclusion in the Tengchong block is that the oceanic crust of the Zuogong-Baoshan plate subducts under the southern and western direction of the Bomy-Tengchong block, which makes the regional crust thicker and leads to a balanced uplift of regional gravity. During the process of uplift and decompression, the deep crustal material partially melts and forms a large amount of granite magma. Due to the subduction of the subducted oceanic crust plate, the magmatic mixing of the mantle magma and the remelting material induced during the collision process resulted in the formation of granodiorite and dark inclusion.
【作者单位】：成都地质矿产研究所;华北油田勘探开发研究院;
【基金】：中国地质调查局“云南1∶5万梁河县、江东、帕底幅区域地质调查项目”(1212010784007)资助~~
【分类号】：P588.121

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