西藏南部岡底斯大陸弧早白堊紀弧前伸展作用
發(fā)布時間：2018-07-31 16:22
【摘要】：在現今活動的俯沖帶系統(tǒng)中,俯沖板片的后撤或回卷都可能導致弧前伸展作用,但弧前伸展作用是否局限于淺部構造層次,還是涉及整個巖石圈,是理解島弧構造演化和地球化學效應的重要課題。在西藏岡底斯巖基南緣,保留著世界上典型的弧前盆地——日喀則弧前盆地。在該盆地的北緣,除了發(fā)育中新世閃長玢巖脈外,還發(fā)育一系列近東西向展布的輝綠巖脈,形成時代為106.6±0.8Ma(鋯石U-Pb年齡)。基性巖脈在巖石學、礦物學和地球化學特征上較均一,具體表現為:(1)富集LREE,虧損HREE,但HREE平直;(2)強烈虧損Rb、Ba、Nb和Ta,微弱虧損Ti,但Zr和Hf不具虧損現象;(3)鋯石Hf同位素組成(εHf(t)=+11.7~+15.4)較高;和(4)包含捕獲的早侏羅世巖漿鋯石。上述數據表明:在日喀則弧前盆地形成過程中,伴隨著強烈的早白堊紀弧前伸展作用,誘發(fā)較虧損地幔發(fā)生部分熔融,形成不同于典型島弧巖漿巖的基性巖,可能是在新特提斯洋北向俯沖過程中,海溝后撤,在弧前形成強烈的地幔角流的結果。同時,日喀則弧前盆地可能構建于早侏羅紀結晶巖系之上。
[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 鹵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.
【作者單位】： 中國地質科學院地質研究所;中國地質科學院礦產資源研究所;
【基金】：公益性行業(yè)科研專項(201511022) 國家重點研發(fā)計劃(2016YFC0600304) 國家自然科學基金項目(41425010)聯合資助
【分類號】：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 鹵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.
【作者單位】： 中國地質科學院地質研究所;中國地質科學院礦產資源研究所;
【基金】：公益性行業(yè)科研專項(201511022) 國家重點研發(fā)計劃(2016YFC0600304) 國家自然科學基金項目(41425010)聯合資助
【分類號】：P534.53;P542
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本文編號：2156136
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