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首页> 外文期刊>Journal of Asian earth sciences >Generation and emplacement of Triassic granitoids within the Songpan Ganze accretionary-orogenic wedge in a context of slab retreat accommodated by tear faulting, Eastern Tibetan plateau, China
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Generation and emplacement of Triassic granitoids within the Songpan Ganze accretionary-orogenic wedge in a context of slab retreat accommodated by tear faulting, Eastern Tibetan plateau, China

机译：青藏高原东缘断裂断层带退缩的松潘甘孜增生造山楔内三叠纪花岗岩的生成与侵位

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摘要

The eastern Songpan Ganze accretionary-orogenic wedge (northern Tibetan plateau) is characterized by extensive magmatism coeval with Middle to Upper Triassic closure of the Paleotethys Ocean along a double subduction system, traced by the Kunlun-Anyemaqen suture to the north and the Jinsha-Litang suture to the south. New field, petrographic and geochemical data on Mesozoic plutons intrusive into Triassic metasediments of the eastern Songpan Ganze wedge are presented and integrated in a review of available data for the region. Three types of granitoids are distinguished: (ⅰ) high-K calc-alkaline granite to grano-diorite (Yanggon, Maoergai, Markam, Sheng Meng, Xue Sheng, Taiyanghe, Menggu, Manai, Dusong Xian, Tagong and Jiulong plutons), (ⅱ) high-K alkaline granite (Nyanbaoyeche and Rilong plutons and the Niuxingou shoshonitic syenite), and (ⅲ) peraluminous S-type granite (Markam and Manai leucogranites). Elemental and isotopic signatures of these granitoids are consistent with the implication of both crustal (Yangtze craton, and Songpan Ganze metasediments) and mantle (asthenospheric mantle and metasoma-tised lithospheric mantle) sources. Based on (ⅰ) the ages of the plutons that are concomitant with the end of the northern and southern subductions of the Paleo-Tethys, (ⅱ) the position of the plutons intrusive in the crustal technically accreted units decoupled from the downgoing plate of this double subduction system, (ⅲ) the diversity of their petrological and geochemical signatures, we propose that magma emplaced in the Songpan Ganze accretionary-orogenic wedge were generated at the end of the Paleotethys closure in a context of slab retreat, accommodated by a tear fault along the passive margin of the South China block. Indeed, we argue that this context is the most favourable to trigger synchronous partial melting of (ⅰ) the suprasubduction enriched mantle wedge owing to lowering of the mantle solidus by metasomatism, (ⅱ) the upwelled undepleted asthenospheric mantle into the tear fault owing to decompression, (ⅲ) the metasomatized lithospheric continental mantle of the Yangtze craton owing to the temperature increase associated to the asthenospheric upwelling and (ⅳ) the rocks of the Songpan Ganze accretionary wedge composed of metasediments and Yangtze continental margin basement owing to the combined effects of increased radioactive heat production and mantle heat flux. We propose that the concentration of plutons along the eastern margin of the Songpan Ganze results from focussed migration and emplacement of the granitic magmas guided by the development of a tear fault along the former passive eastern margin of the Yangtze craton as a consequence of the Paleotethys slab retreat.
机译：松潘甘孜州东部增生造山楔（藏北高原）的特征是广泛的岩浆活动，与古埃及的中三叠世上三叠世封闭，沿双重俯冲系统，北至昆仑—阿涅玛琴缝合线以及金沙—理塘向南缝合。提出了新的田野，岩石学和地球化学数据，这些数据涉及侵入松潘干泽楔东部的三叠纪准沉积物中的中生岩体，并将其整合到该地区的现有数据中。区分了三种类型的类花岗岩：（ⅰ）高K钙碱性花岗岩到花岗闪长岩（Yanggon，Maergai，Markam，圣梦，薛圣，Taiyanghe，Menggu，Manai，Dusong Xian，Tagong和Jiulong岩体），（ ⅱ）高钾碱性花岗岩（Nyanbaoyeche和Rilong岩体和纽兴沟shoshonitic正长花岗岩），和（ⅲ）高铝质S型花岗岩（Markam和Manai leucogranites）。这些花岗岩的元素特征和同位素特征与地壳（长江克拉通和松潘甘泽变质沉积物）和地幔（软流圈地幔以及由水体变质的岩石圈地幔）来源的含意一致。基于（ⅰ）与古特提斯北部和南部俯冲结束相伴的轻子的年龄，（ⅱ）轻子侵入体在地壳技术增生单位中的位置与该板的下沉板分离双重俯冲系统，（ⅲ）岩石和地球化学特征的多样性，我们认为，在松潘甘孜增生造山楔中放置的岩浆是在板岩撤退的背景下，在古生代关闭的末尾产生的，并被一个裂隙断层所容纳。沿华南地块的被动边缘。的确，我们认为这种情况是最有利的，因为交代作用降低了地幔固相线，从而触发了（ⅰ）超俯冲富集的地幔楔的同步部分熔融；（ⅱ）由于减压而上升的未耗尽的软流圈地幔进入了撕裂断层。 ，（ⅲ）由于软流圈上升相关的温度升高，使长江克拉通的岩石圈陆交界变质；（ⅳ）松潘甘孜增生楔的岩石由变质沉积物和扬子大陆边缘基底组成，归因于增加的综合作用放射性产热和地幔热通量。我们认为，松潘甘孜河东缘的岩体集中是由于古罗马系板块沿长江克拉通前被动东缘的裂隙发育，导致了花岗岩岩浆的集中迁移和定位。撤退。

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