Paleoproterozoic granulites from Heling'er: Implications for regional ultrahigh-temperature metamorphism in the North China Craton
Paleoproterozoic granulites from Heling'er: Implications for regional ultrahigh-temperature metamorphism in the North China Craton
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DOI：
10.1016/j.lithos.2012.05.024
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发表时间：
2012-09
期刊：
影响因子：
3.5
通讯作者：
Shoujie Liu;T. Tsunogae;Wenshan Li;Hisako Shimizu;M. Santosh;Y. Wan;Jianghai Li
中科院分区：
文献类型：
--
作者：
Shoujie Liu;T. Tsunogae;Wenshan Li;Hisako Shimizu;M. Santosh;Y. Wan;Jianghai Li
内蒙古缝合带（IMSZ，包括孔兹岩带）是华北克拉通（NCC）内阴山地块和鄂尔多斯地块古元古代碰撞期间形成的增生造山带的一部分。 IMSZ 内的麻粒岩以高温 (HT) 至超高温 (UHT) 变质作用为特征，在土贵乌拉和吴川等地保存了适合 UHT 条件的诊断性矿物组合。我们在这里报告了赫林尔的一个新地点，位于 IMSZ 的南部区域，这里含有尖晶石-石榴石-硅线石的麻粒岩记录了超高温变质条件。这些岩石中斑斑矿物中包裹体存在的顺进组合包括硅线石+石英+尖晶石，而粗粒石榴石+硅线石+石英+尖晶石+堇青石+斜长石+钾长石+磁铁矿+钛铁矿代表峰组合。逆行阶段的标志是石榴石和尖晶石上形成的斜方辉石和堇青石边缘。黑云母标志着高级变质作用的最后水化阶段。尖晶石和石英直接接触，尖晶石的 Zn、Cr 和 Fe3+ 含量较低。应用钛锆石和三元长石地温计可在峰值阶段产生高达 ~940°C 的温度。基于整体化学和矿物组合的矿物相平衡模型表明，石榴石+斜长石+尖晶石+堇青石+硅线石+石英+钛铁矿+磁铁矿的峰值组合在6.5-7.5kbar下稳定在1030°C，因此我们推断这些岩石中变质峰的温度范围为940-1030°C。和林儿新发现的超高温岩石，年代为1.92Ga，与先前报道的土贵乌拉和乌川两个超高温地点一起，表明古元古代超高温变质作用发生在IMSZ内的区域范围内，可能与俯冲-吸积-碰撞构造和华北克拉通并入哥伦比亚超大陆有关。
The Inner Mongolia Suture Zone (IMSZ, incorporating the Khondalite Belt) forms part of an accretionary orogen developed during the Paleoproterozoic collision between the Yinshan Block and Ordos Blocks within the North China Craton (NCC). The granulites within the IMSZ are characterized by high-temperature (HT) to ultrahigh-temperature (UHT) metamorphism with diagnostic mineral assemblages for UHT conditions preserved in some localities such as Tuguiwula and Wuchuan. We report here a new locality in Heling'er, located within the southern domain of the IMSZ where spinel–garnet–sillimanite-bearing granulites record UHT metamorphic conditions. The prograde assemblages occurring as inclusions in porphyroblastic minerals in these rocks include sillimanite+quartz+spinel, whereas coarse grained garnet+sillimanite+quartz+spinel+cordierite+plagioclase+K-feldspar+magnetite+ilmenite represent the peak assemblages. The retrograde stage is marked by orthopyroxene and cordierite rims developed on garnet and spinel. Biotite marks the final hydration stage of the high-grade metamorphism. Spinel and quartz occur in direct contact, with the spinel showing low Zn, Cr, and Fe3+. Application of Ti-in-zircon and ternary feldspar geothermometers yields temperatures up to ~940°C for the peak stage. Mineral phase equilibria modeling based on the bulk chemistry and mineral assemblages shows that the peak assemblage of garnet+plagioclase+spinel+cordierite+sillimanite+quartz+ilmenite+magnetite was stabilized at 1030°C at 6.5–7.5kbar, thus we infer a 940–1030°C temperature range for peak metamorphism in these rocks. The newly discovered UHT rocks in Heling'er, dated as 1.92Ga, together with the two previously reported UHT localities at Tuguiwula and Wuchuan, suggest that the Paleoproterozoic UHT metamorphism occurred on a regional scale within the IMSZ, probably in association with the subduction–accretion–collision tectonics and the incorporation of the NCC within the Columbia supercontinent.