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首页> 外文期刊>Journal of Metamorphic Geology >Early Cambrian eclogites in SW Mongolia: Evidence that the Palaeo-Asian Ocean suture extends further east than expected
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Early Cambrian eclogites in SW Mongolia: Evidence that the Palaeo-Asian Ocean suture extends further east than expected

机译：蒙古西南部的寒武纪早期榴莲岩：证据表明古亚洲洋缝合线向东延伸得比预期的还要远

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摘要

Newly discovered eclogites, Early Cambrian carbonates and chloritoid-bearing metapelites form the Tsakhir Uul accretionary wedge, which was thrust during the Early Cambrian over the Mesoproterozoic Dzabkhan-Baydrag continent. The rock association of the wedge forms a tectonic window emerging through the hangingwall Khantaishir ophiolite unit, which preserves a typical Tethyan-type ophiolitic sequence. The eclogites correspond geochemically to T-MORB modified by fluid circulation. They are composed of garnet, omphacite, amphibole, rutile ±muscovite ±quartz ±epidote and exhibit well-equilibrated matrix textures. Jadeite content of the omphacite reaches up to 45 mol.%, the Si content of muscovite is between 3.40 and 3.45 p.f.u., amphibole is winchite to barroisite, but reaches tschermakitic composition at some rims, and garnet composition is grs_(0.24-0.36), alm_(0.43-0.56), py_(0.05-0.18), sps_(0.00-0.18), The peak assemblage, together with the composition of garnet rims, omphacite, amphibole and muscovite, correspond in a pseudosection to 20-22.5 kbar and 590-610 °C. The tschermakitic rim of amphibole is interpreted as partial reequilibration on decompression below 16 kbar and 600-630 °C. Two muscovite separates from the eclogite yielded an Ar-Ar plateau age of 543.1 ± 3.9 Ma (1σ) and a mean age of 547.9 ± 2.6 Ma (1σ), whereas muscovite from an interbedded garnet-chloritoid micaschist yielded an Ar-Ar plateau age of 536.9 ± 2.7 Ma (1σ); these ages are interpreted as cooling ages. The P-T data, geochemistry of eclogites and cooling ages suggest an affinity between the Tsakhir Uul wedge and the Gorny Altai and the north Mongolian blueschist belt, which are believed typical for subduction of warm oceanic lithosphere and closure of small oceanic basins. Thus, the discovery of the Tsakhir Uul eclogites represents an important finding suggesting extension of the Early Cambrian subduction system of the Central Asian Orogenic Belt far to the east in a region where it was not expected.
机译：Tsakhir Uul增生楔形成了新发现的榴辉岩，早寒武纪碳酸盐和含类氯酸盐的变质岩，它是在早寒武纪中生代古生的Dzabkhan-Baydrag大陆上被推入的。楔形的岩石结合形成了一个构造窗，该窗通过悬空的Khantaishir蛇绿岩单元形成，保留了典型的Tethyan型蛇纹石序列。榴辉岩在地球化学上对应于通过流体循环改性的T-MORB。它们由石榴石，绿宝石，角闪石，金红石±白云母±石英±埃皮科特组成，并具有良好平衡的基质纹理。绿沸石中的翡翠含量最高为45 mol。％，白云母中的Si含量在3.40至3.45 pfu之间，闪石到白铁矿成为闪石，但在某些边缘达到了辉绿岩组成，石榴石的组成为grs_（0.24-0.36）， alm_（0.43-0.56），py_（0.05-0.18），sps_（0.00-0.18），峰组合以及石榴石轮辋，绿辉石，闪石和白云母的组成在假剖面上分别对应于20-22.5 kbar和590 -610°C。闪石的闪石边缘被解释为在低于16 kbar和600-630°C的减压条件下部分重新平衡。从榴辉岩中分离出的两个白云母产生的Ar-Ar高原年龄为543.1±3.9 Ma（1σ），平均年龄为547.9±2.6 Ma（1σ），而互层的石榴石-类氯云母的白云母产生了Ar-Ar高原年龄。 536.9±2.7 Ma（1σ）;这些年龄被解释为冷却年龄。 P-T数据，榴辉岩的地球化学和冷却年龄表明，Tsakhir Uul楔块与Gorny Altai和蒙古北部的蓝片岩带之间具有亲和力，据认为这是俯冲温暖的海洋岩石圈和封闭小洋盆的典型特征。因此，Tsakhir Uul榴辉岩的发现代表了一个重要发现，表明中亚造山带的早寒武纪俯冲系统扩展到了一个未曾预料到的东部地区。

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