滇西勐養(yǎng)花崗巖體暗色包體的地球化學(xué)特征及成因
發(fā)布時間：2018-08-14 19:17
【摘要】：勐養(yǎng)侵入巖體主要由黑云母二長花崗巖(128 Ma)、花崗閃長巖(113 Ma)和輝長質(zhì)(123 Ma)、閃長質(zhì)包體(120Ma)組成。暗色包體主要分布在花崗閃長巖中,包體巖性主要為輝長巖包體和閃長巖包體。包體具有巖漿結(jié)構(gòu),部分包體具有塑性流變特征,有些包體具有淬冷邊和反向脈,包體中可見針狀磷灰石,表現(xiàn)出巖漿混合的巖相學(xué)特征。巖石地球化學(xué)特征研究表明,寄主巖石與暗色包體同為準(zhǔn)鋁質(zhì)-過鋁質(zhì)、鈣堿性-高鉀鈣堿性系列巖石。寄主巖石與暗色包體的的稀土配分曲線模式和微量元素原始地幔標(biāo)準(zhǔn)化蛛網(wǎng)圖形態(tài)基本一致,為巖漿混合作用的結(jié)果。所有樣品均富集大離子親石元素(如Rb、Th、U和Nd)、虧損高場強(qiáng)元素(如Nb、Ta、Ce和Zr)。勐養(yǎng)早白堊世侵入巖形成于巖漿弧環(huán)境。暗色包體具有低的Si O2含量(Si O2為48.02%和59.8%)和高的Mg#值(Mg#=48.1~68.5),表明暗色包體的原生巖漿應(yīng)是板塊俯沖帶流體交代地幔橄欖巖的部分熔融的產(chǎn)物,并受后期巖漿混合作用的改造。暗色包體鋯石的εHf(t)為3.6~6.2,Nb/Ta值為12.1~15.4,顯示巖漿源區(qū)具有虧損地幔特征。黑云二長花崗巖的Mg#=33.5,Nb/Ta值為10.9,表明巖漿主要來源于古老的地殼物質(zhì)的部分熔融。花崗閃長巖鋯石的Mg#=44,Nb/Ta值為12.5,巖漿主要來源于地幔和地殼,為黑云二長花崗巖與幔源巖漿混合作用的產(chǎn)物。騰沖地塊早白堊世勐養(yǎng)侵入巖體及其暗色包體的的成因,是左貢—保山板塊洋殼向南西俯沖在波密—騰沖地塊之下,使區(qū)域地殼不斷加厚并導(dǎo)致區(qū)域重力均衡隆升,深部地殼物質(zhì)在加熱后抬升減壓過程中發(fā)生部分熔融,形成大量的花崗巖漿。由于俯沖洋殼板塊在俯沖、碰撞過程中誘導(dǎo)的幔源巖漿與重熔物質(zhì)發(fā)生巖漿混合作用,形成花崗閃長巖和暗色包體。
[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.
【作者單位】： 成都地質(zhì)礦產(chǎn)研究所;華北油田勘探開發(fā)研究院;
【基金】：中國地質(zhì)調(diào)查局“云南1∶5萬梁河縣、江東、帕底幅區(qū)域地質(zhì)調(diào)查項目”(1212010784007)資助~~
【分類號】：P588.121
[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.
【作者單位】： 成都地質(zhì)礦產(chǎn)研究所;華北油田勘探開發(fā)研究院;
【基金】：中國地質(zhì)調(diào)查局“云南1∶5萬梁河縣、江東、帕底幅區(qū)域地質(zhì)調(diào)查項目”(1212010784007)資助~~
【分類號】：P588.121
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