Nature and timing of the Solonker suture of the Central Asian Orogenic Belt: insights from geochronology and geochemistry of basic intrusions in the Xilin Gol Complex, Inner Mongolia, China
Nature and timing of the Solonker suture of the Central Asian Orogenic Belt: insights from geochronology and geochemistry of basic intrusions in the Xilin Gol Complex, Inner Mongolia, China
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DOI：
10.1007/s00531-013-0931-3
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发表时间：
2013
影响因子：
2.3
通讯作者：
Yilong Li;Hanwen Zhou;F. Brouwer;W. Xiao;J. Wijbrans;J. Zhao;Z. Zhong;Huifang Liu
中科院分区：
文献类型：
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作者：
Yilong Li;Hanwen Zhou;F. Brouwer;W. Xiao;J. Wijbrans;J. Zhao;Z. Zhong;Huifang Liu
中亚造山带（CAOB）的索伦克缝合带记录了古亚洲洋的最终闭合。索伦克缝合线最终碰撞的性质和时间长期以来一直存在争议，部分原因是同位素年龄记录不完整以及对关键构造单元地质环境的不同解释。锡林郭勒杂岩由强烈变形的片麻岩、片岩和角闪岩组成，是中亚造山带内的一个关键构造单元。透镜状或类层状角闪岩分散在整个杂岩中，夹有黑云母斜长片麻岩。两种岩石类型都经历了角闪岩相变质作用。根据 LA-ICPMS 锆石 U-Pb 测年，角闪岩的原岩是在 319 ± 4 Ma 侵入黑云斜长片麻岩的基性岩石。基本侵入体源自经过晶体分异并与板片衍生流体混合的改性岩浆。板片衍生的流体是在早古生代海洋俯冲过程中沿着北倾的苏尼左旗-锡林浩特俯冲带形成的，与岩浆源混合，产生了叠加在火山弧化学上的俯冲相关地球化学特征。经过早古生代大洋俯冲和弧陆碰撞之后，苏尼左旗-锡林浩特地区在313~280 Ma之间发生了短暂的伸展阶段。从压缩到伸展的转变过程中的变形和再结晶以及后来岩浆侵入的再加热重置了锡林郭勒杂岩中矿物的同位素系统，由来自黑云斜长片麻岩的 312.2 ± 1.5 Ma 黑云母 40Ar/39Ar 年龄、309 ± 12 Ma 锆石截距年龄和杂岩中角闪岩的 307.5 ± 3.5 Ma 角闪石 40Ar/39Ar 年龄。二叠纪时期，锡林郭勒杂岩体南缘存在一个与弧/弧前相关的海相盆地。大洋盆地的闭合导致晚古生代—中三叠世向北倾俯冲到锡林郭勒杂岩之下，并诱发了杂岩的角闪岩相变质作用。索伦克带的最终缝合发生在 269 Ma 到 231 Ma 之间。这种最新的角闪岩相变质作用，压力为 0.31–0.39 GPa，温度为 620–660 °C，记录于锡林郭勒杂岩的 263.4 ± 1.4 Ma，如角闪岩的角闪石 40Ar/39Ar 年龄以及几个锆石年龄所示。 260 ± 3–231 ± 3 Ma。锡林郭勒杂岩记录了南蒙古微大陆南缘从早古生代（~452 Ma）到中三叠世（~231 Ma）的单一、长寿的俯冲系统的逐渐增生。 CAOB 显示最终缝合前发生了长时间的碰撞。
The Solonker suture zone of the Central Asian Orogenic Belt (CAOB) records the final closure of the Paleo-Asian Ocean. The nature and timing of final collision along the Solonker suture has long been controversial, partly because of an incomplete record of isotopic ages and differing interpretations of the geological environments of key tectonic units. The Xilin Gol Complex, consisting of strongly deformed gneisses, schists and amphibolites, is such a key tectonic unit within the CAOB. Lenticular or quasi-lamellar amphibolites are dispersed throughout the complex, intercalated with biotite–plagioclase gneiss. Both rock types experienced amphibolite-facies metamorphism. The protolith of the amphibolite is a basic rock that intruded into the biotite–plagioclase gneiss at 319 ± 4 Ma based on LA-ICPMS zircon U–Pb dating. The basic intrusion was sourced from a modified magma that experienced crystal fractionation and was admixed with slab-derived fluids. The slab-derived fluids, which formed during Early Paleozoic oceanic subduction along the north-dipping Sonidzuoqi–Xilinhot subduction zone, mixed with the magma source and produced subduction-related geochemical signatures superimposed on volcanic arc chemistry. After Early Paleozoic oceanic subduction and arc-continent collision, a transient stage of extension occurred between 313 and 280 Ma in the Sonidzuoqi–Xilinhot area. Deformation and recrystallization during the switch from compression to extension and reheating by the later magmatic intrusions reset the isotope systems of minerals in the Xilin Gol Complex, recorded by a 312.2 ± 1.5 Ma biotite40Ar/39Ar age from biotite–plagioclase gneiss, a 309 ± 12 Ma zircon intercept age and a 307.5 ± 3.5 Ma hornblende40Ar/39Ar age from amphibolites in the complex. There was an arc/forearc-related marine basin at the southern margin of the Xilin Gol Complex during the Permian. The closure of the oceanic basin led to Late Paleozoic–Middle Triassic north-dipping subduction beneath the Xilin Gol Complex and induced the amphibolite-facies metamorphism of the complex. The final suturing of the Solonker zone occurred from 269 to 231 Ma. This latest amphibolite-facies metamorphism with pressures of 0.31–0.39 GPa and temperatures of 620–660 °C was recorded at 263.4 ± 1.4 Ma to the Xilin Gol Complex, as indicated by the hornblende40Ar/39Ar age from the amphibolites, as well as several zircon ages of 260 ± 3–231 ± 3 Ma. The Xilin Gol Complex documented the progressive accretion of a single, long-lived subduction system at the southern margin of the south Mongolian microcontinent from the Early Paleozoic (~452 Ma) to Middle Triassic (~231 Ma). The CAOB shows protracted collision prior to final suturing.