The Oyut Ulaan Volcanic Group: stratigraphy, magmatic evolution and timing of Carboniferous arc development in SE Mongolia
The Oyut Ulaan Volcanic Group: stratigraphy, magmatic evolution and timing of Carboniferous arc development in SE Mongolia
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DOI：
10.1144/0016-76492009-094
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发表时间：
2010-04
影响因子：
2.7
通讯作者：
J. H. Blight;M. Petterson;Q. Crowley;D. Cunningham
中科院分区：
文献类型：
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作者：
J. H. Blight;M. Petterson;Q. Crowley;D. Cunningham
摘要：中亚古生代-中生代的构造演化，包括组成蒙古的巨大地体拼贴，一直是一个相当有争议的话题。奥乌特-乌兰火山群是蒙古东南部的一套火山岩和沉积岩，构成了泥盆纪-二叠纪塞罕杜兰因利耶的南部。野外考察和测绘在奥乌特乌兰火山群中建立了四个不同的建造，记录了中亚造山带部分地区石炭纪期间弧形活动的性质。这四个组的物理火山学和沉积学特征表明有三种明显的喷发样式：(1)活跃侵蚀弧环境中的周期性安山岩火山作用，其中也包括大河流和沼泽；(2)高喷发的高原安山岩火山作用；(3)爆发性流纹岩喷流作用。火山岩的地球化学分析表明，该群代表了与俯冲有关的成熟大陆弧火山作用。地球化学结果证明了一个不断演变的岩浆系统，火山-沉积模型的表面过程可能与之有关。岩浆脉冲和补给是从化学地层学的变化中确定的。新获得的火山岩系锆石年龄确定其侵位(喷发)年龄为323.0±0.70 Ma(石炭世中期或密西西比世晚期)。奥伊特乌兰火山群下部花岗岩卵石的锆石U-Pb值为338.9±0.40 Ma，表明弧状深成岩体在奥伊特乌兰火山活动发生前10 Ma侵位，并在不久后遭受侵蚀。我们的工作为蒙古东南部最终的吸积和大陆组装提供了时间限制，也揭示了演化的吸积造山带内岩浆弧系的岩石学发展。
Abstract: The Palaeozoic–Mesozoic tectonic evolution of Central Asia, including the vast terrane collage that makes up Mongolia, has been a topic of considerable debate. The Oyut Ulaan Volcanic Group is a sequence of volcanic and sedimentary rocks in SE Mongolia that forms the southern part of the Devonian–Permian Saykhandulaan Inlier. Fieldwork traverses and mapping have established four distinct formations in the Oyut Ulaan Volcanic Group that record the nature of arc activity in part of the Central Asian Orogenic Belt during the Carboniferous. Physical volcanological and sedimentological characteristics of the four formations suggest three clear eruptive styles: (1) periodic andesite volcanism in an actively eroding arc setting that also contained large rivers and swamps; (2) highly effusive plateau andesite volcanism; (3) explosive rhyolitic effusion. Geochemical analyses of volcanic lithologies suggest that the group represents subduction-related, mature, continental arc volcanism. Geochemical results document an evolving magma system to which surface processes of the volcano-sedimentary model may be linked. Magma pulses and replenishments are identified from variations in chemostratigraphy. Newly obtained zircon ages from the volcanic succession fix its emplacement (eruption) at 323.0 ± 0.7 Ma (mid-Carboniferous or late Mississippian). A granite cobble from the lower part of the Oyut Ulaan Volcanic Group gives a U–Pb zircon age of 338.9 ± 0.4 Ma indicating that arc plutons were emplaced 10 Ma prior to the Oyut Ulaan volcanism and were eroded soon after. Our work provides timing constraints for final accretion and continental assembly in SE Mongolia, and also sheds light on the petrological development of a magmatic arc system within an evolving accretionary orogen.