The assembly of Rodinia: The correlation of early Neoproterozoic (ca. 900 Ma) high-grade metamorphism and continental arc formation in the southern Beishan Orogen, southern Central Asian Orogenic Belt (CAOB)
The assembly of Rodinia: The correlation of early Neoproterozoic (ca. 900 Ma) high-grade metamorphism and continental arc formation in the southern Beishan Orogen, southern Central Asian Orogenic Belt (CAOB)
复制标题
DOI：
10.1016/j.precamres.2016.12.010
复制
发表时间：
2017-03
影响因子：
3.8
通讯作者：
K. Zong;R. Klemd;Yu Yuan;Zhenyu He;Jing‐Liang Guo;Xiaoli Shi;Yongsheng Liu;Zhaochu Hu;Zeming Zh
中科院分区：
文献类型：
--
作者：
K. Zong;R. Klemd;Yu Yuan;Zhenyu He;Jing‐Liang Guo;Xiaoli Shi;Yongsheng Liu;Zhaochu Hu;Zeming Zh
据报道，中亚造山带（CAOB）南部的北山南造山带（SBOB）和中天山（CTA）地区存在覆盖数百公里的早期广泛的新元古代（约900 Ma）大陆岩浆弧系统。然而，关于同时代的高级变质作用以及因此在罗迪尼亚框架内形成增生造山带的证据是模糊的或不存在的。这项研究为 SBOB 含石榴石片岩（石英 + 石榴石 + 黑云母 + 斜长石 ± 白云母）提供了新的岩石学、地球化学和年代学数据，以限制其新元古代变质历史。变质锆石边缘在 CL 图像中要么是无分区的，要么是显示扇形分区的，并揭示了具有平坦 HREE 模式和负 Eu 异常的 REE 模式，这被解释为与石榴石和斜长石处于化学平衡。锆石 U-Pb 测年得出变质锆石边缘的一致 U-Pb 年龄为 900 ± 3 Ma、897 ± 2 Ma 和 898 ± 4 Ma。一个样本的继承碎屑锆石岩心显示出一致的 U-Pb 年龄为 1397 ± 5 Ma，这与 SBOB 和 CTA 中广泛的中元古代大陆弧的形成时间一致。根据相平衡地温气压测量和平均 P-T 温压计算，在压力 >0.6 GPa 下，角闪岩相的最低 P-T 条件估计为 >600 °C，这被认为是被随后的古生代变质作用所覆盖的。然而，钛锆石温度计仍然使用变质锆石边缘的成分显示出高达 840 °C 的温度，这表明以前的温度大约为 840 °C。 900 Ma 麻粒岩相峰值变质温度。综合岩石学和年代学证据以及区域变质岩的大陆亲和力表明，SBOB 和东部 CTA 在罗迪尼亚的最后组装阶段经历了新元古代早期的增生造山作用。
An early extensive Neoproterozoic (ca. 900 Ma) continental magmatic arc system covering hundreds of kilometers has been reported to occur in the South Beishan Orogenic Belt (SBOB) and the Central Tianshan (CTA) in the southern Central Asian Orogenic Belt (CAOB). However, evidence for coeval high-grade metamorphism and thus the formation of an accretionary orogen in the framework of Rodinia is ambiguous or absent. This study provides new petrological, geochemical and geochronological data for garnet-bearing schists (quartz + garnet + biotite + plagioclase ± muscovite) from the SBOB in order to constrain its Neoproterozoic metamorphic history. The metamorphic zircon rims are either unzoned or display sector zoning in CL-images and reveal REE patterns with flat HREE patterns and negative Eu anomalies, which are interpreted to be in chemical equilibrium with garnet and plagioclase. The zircon U-Pb dating yields concordant U-Pb ages of 900 ± 3 Ma, 897 ± 2 Ma and 898 ± 4 Ma for the metamorphic zircon rims. The inherited detrital zircon cores of one sample display a concordant U-Pb age of 1397 ± 5 Ma that is consistent with the timing of formation for the extensive Mesoproterozoic continental arc in the SBOB and CTA. Based on phase equilibrium geothermobarometry and average P-T thermobarometric calculations, minimum amphibolite-facies P-T conditions are estimated to be >600 °C at pressure >0.6 GPa, which is thought to have been overprinted by subsequent Paleozoic metamorphism. However, the Ti-in-zircon thermometer still reveals temperatures of up to 840 °C using the composition of metamorphic zircon rims, suggesting former ca. 900 Ma granulite-facies peak metamorphic temperatures. The combined petrological and geochronological evidence in conjunction with the continental affinity of the regional metamorphic rocks suggests that the SBOB and the eastern CTA experienced an early Neoproterozoic accretionary orogenesis during the final assembly stage of Rodinia.