Lithos ( IF 3.5 ) Pub Date : 2021-01-07 , DOI: 10.1016/j.lithos.2021.105969 Jialiang Li , Jingao Liu , Yujian Wang , Di-Cheng Zhu , Chen Wu
The Central Asian Orogenic Belt (CAOB) was established in response to multiple subduction-accretion-collision processes. However, the origin and evolution of the accreted arc terranes remain unclear, as exemplified by the question how ancient and juvenile materials were accreted and constructed in the accretionary belts. This question is addressed here by presenting in-situ zircon UPb and Hf isotopic, whole-rock elemental and SrNd isotopic analyses of the four Late Paleozoic igneous rock units from Xilinhot in the southeastern CAOB. The new geochronological and geochemical data support the existence of two Late Carboniferous to Permian magmatic arc systems — Ulistai active continental margin and Baolidao arc belt. These arc systems are characterized by magmatic activity extending from 330 to 250 Ma, with two magmatic “flare-ups” (325–295 Ma vs. 295–270 Ma). The first magmatic “flare-up” (325–295 Ma) includes high-K calc-alkaline rhyolites, dacites and alkali-feldspar granites, which can be interpreted to have originated from re-melting of the juvenile lower crust beneath a continental arc induced by the Paleo-Asian oceanic ridge subduction. The second magmatic “flare-up” (295–270 Ma) reveals a seaward migration of magmatism due to slab rollback subsequent to ridge subduction. The Middle to Late Permian shoshonitic andesites witnessed the closure of the Hegenshan ocean during this period. In combination with previously reported Sr-Nd-Hf isotopic data, we suggest that the Baolidao arc belt and some other arc terranes (e.g., Bainaimiao arc) in the southeastern CAOB were built upon Precambrian microcontinents that have been largely fragmented and significantly reworked. In summary, ridge subduction accompanied by slab rollback played an important role in the rejuvenation of microcontinents and accretion of arc terranes in the southeastern CAOB.
中文翻译:
在中亚东南部造山带中发现晚石炭纪至早二叠纪山脊俯冲:对增生造山带大陆壳的构造和生长的影响
建立中亚造山带(CAOB)是为了应对多种俯冲-增生-碰撞过程。但是,增生的弧形地层的起源和演化仍不清楚,这一问题可以通过增生带中如何增生和构造古代和未成年人的物质来证明。通过提出原位锆石U Pb和Hf同位素,全岩元素和Sr来解决此问题东北东南部锡林浩特地区四个晚古生代火成岩单元的钕同位素分析。新的地质年代和地球化学数据支持存在两个晚石炭纪至二叠纪岩浆弧系统-乌里斯台活动大陆边缘和宝利道弧带。这些电弧系统的特征是岩浆活动从330 Ma扩展到250 Ma,并有两个岩浆“爆发”(325-295 Ma对295-270 Ma)。第一个岩浆“爆发”(325-295 Ma)包括高K钙碱性流纹岩,dacites和碱石长石花岗岩,这可以解释为源自大陆弧下方的少年下地壳重熔由古亚洲洋脊俯冲引起。第二个岩浆“爆发”(295-270 Ma)揭示了岩浆向海的迁移,这是由于板块俯冲后板坯回滚所致。在此期间,中二叠纪至晚二叠纪的安山岩见证了河根山大洋的封闭。结合先前报道的Sr-Nd-Hf同位素数据,我们建议东南部CAOB的宝利道弧带和其他一些弧线地层(例如,白乃庙弧)是建立在前寒武纪微大陆上的,这些大陆已经被零散地碎片化并进行了明显的改造。综上所述,东南俯冲带的俯冲隆起与板块的回滚起着重要的作用,它在微大陆的复兴和弧形地体的增生中起着重要的作用。结合先前报道的Sr-Nd-Hf同位素数据,我们建议东南部CAOB的宝利道弧带和其他一些弧线地层(例如,白乃庙弧)是建立在前寒武纪微大陆上的,这些大陆已经被零散地碎片化并进行了明显的改造。综上所述,东南俯冲带的俯冲隆起与板块的回滚起着重要的作用,它在微大陆的复兴和弧形地体的增生中起着重要的作用。结合先前报道的Sr-Nd-Hf同位素数据,我们建议东南部CAOB的宝利道弧带和其他一些弧线地层(例如,白乃庙弧)是建立在前寒武纪微大陆上的,这些大陆已经被零散地碎片化并进行了明显的改造。综上所述,东南俯冲带的俯冲隆起与板块的回滚起着重要的作用,它在微大陆的复兴和弧形地体的增生中起着重要的作用。