西藏南部冈底斯大陆弧早白垩纪弧前伸展作用
发布时间：2018-07-31 16:22
【摘要】：在现今活动的俯冲带系统中,俯冲板片的后撤或回卷都可能导致弧前伸展作用,但弧前伸展作用是否局限于浅部构造层次,还是涉及整个岩石圈,是理解岛弧构造演化和地球化学效应的重要课题。在西藏冈底斯岩基南缘,保留着世界上典型的弧前盆地——日喀则弧前盆地。在该盆地的北缘,除了发育中新世闪长玢岩脉外,还发育一系列近东西向展布的辉绿岩脉,形成时代为106.6±0.8Ma(锆石U-Pb年龄)。基性岩脉在岩石学、矿物学和地球化学特征上较均一,具体表现为:(1)富集LREE,亏损HREE,但HREE平直;(2)强烈亏损Rb、Ba、Nb和Ta,微弱亏损Ti,但Zr和Hf不具亏损现象;(3)锆石Hf同位素组成(εHf(t)=+11.7~+15.4)较高;和(4)包含捕获的早侏罗世岩浆锆石。上述数据表明:在日喀则弧前盆地形成过程中,伴随着强烈的早白垩纪弧前伸展作用,诱发较亏损地幔发生部分熔融,形成不同于典型岛弧岩浆岩的基性岩,可能是在新特提斯洋北向俯冲过程中,海沟后撤,在弧前形成强烈的地幔角流的结果。同时,日喀则弧前盆地可能构建于早侏罗纪结晶岩系之上。
[Abstract]:In the present active subduction zone system, the retreating or rewinding of the subduction plate may lead to the prearc extension, but whether the prearc extension is confined to the shallow tectonic level or involves the whole lithosphere, It is an important subject to understand the tectonic evolution and geochemical effects of island arc. In the southern margin of the Gangdis rock base in Tibet, the world's typical forearc basin-Xigaze forearc basin is preserved. In the northern margin of the basin, in addition to the developing diorite porphyrite veins, a series of near east-west diabase veins have been developed. The age of formation is 106.6 卤0.8Ma (U-Pb age of zircon). The basic veins are more homogeneous in petrology, mineralogy and geochemistry, The main results are as follows: (1) rich in LREE, depleted in hree, but flat in HREE; (2) strongly depleted in RbbBaNb and Ta, with weak depletion of Ti, but not depleted in Zr and HF; (3) higher in zircon HF isotopic composition (蔚 Hf (t) = 11.7 ~ 15.4); and (4) containing trapped early Jurassic magmatic zircon. The above data indicate that during the formation of Xigaze forearc basin, along with the strong early Cretaceous prearc extension, partial melting of the depleted mantle was induced, resulting in the formation of basic rocks different from typical island arc magmatic rocks. It is possible that the trench retreated during the northward subduction of the Neo-Tethys ocean and a strong mantle corner current was formed in front of the arc. At the same time, Xigaze forearc basin may be built on the early Jurassic crystalline rock series.
【作者单位】： 中国地质科学院地质研究所;中国地质科学院矿产资源研究所;
【基金】：公益性行业科研专项(201511022) 国家重点研发计划(2016YFC0600304) 国家自然科学基金项目(41425010)联合资助
【分类号】：P534.53;P542
[Abstract]:In the present active subduction zone system, the retreating or rewinding of the subduction plate may lead to the prearc extension, but whether the prearc extension is confined to the shallow tectonic level or involves the whole lithosphere, It is an important subject to understand the tectonic evolution and geochemical effects of island arc. In the southern margin of the Gangdis rock base in Tibet, the world's typical forearc basin-Xigaze forearc basin is preserved. In the northern margin of the basin, in addition to the developing diorite porphyrite veins, a series of near east-west diabase veins have been developed. The age of formation is 106.6 卤0.8Ma (U-Pb age of zircon). The basic veins are more homogeneous in petrology, mineralogy and geochemistry, The main results are as follows: (1) rich in LREE, depleted in hree, but flat in HREE; (2) strongly depleted in RbbBaNb and Ta, with weak depletion of Ti, but not depleted in Zr and HF; (3) higher in zircon HF isotopic composition (蔚 Hf (t) = 11.7 ~ 15.4); and (4) containing trapped early Jurassic magmatic zircon. The above data indicate that during the formation of Xigaze forearc basin, along with the strong early Cretaceous prearc extension, partial melting of the depleted mantle was induced, resulting in the formation of basic rocks different from typical island arc magmatic rocks. It is possible that the trench retreated during the northward subduction of the Neo-Tethys ocean and a strong mantle corner current was formed in front of the arc. At the same time, Xigaze forearc basin may be built on the early Jurassic crystalline rock series.
【作者单位】： 中国地质科学院地质研究所;中国地质科学院矿产资源研究所;
【基金】：公益性行业科研专项(201511022) 国家重点研发计划(2016YFC0600304) 国家自然科学基金项目(41425010)联合资助
【分类号】：P534.53;P542
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