Metamorphic evolution and geochronology of the tectonic mélange of the Dongbatu and Mogutai blocks, middle Dunhuang orogenic belt, northwestern China

Abstract

Mafic granulite and amphibolite in the Dongbatu and Mogutai blocks, middle Dunhuang orogenic belt, northwest China, southernmost Central Asian orogenic belt, occur as lenses within the matrix of metapelite and marble, exhibiting typical block-in-matrix fabrics of tectonic mélange. Three stages of metamorphic mineral assemblages were identified in these lenses. Clockwise metamorphic pressure-temperature (P-T) paths were obtained through geothermobarometry and thermodynamic pseudosection modeling, passing from 656 °C and 10.9 kbar through 830 °C and 16.5 kbar to 657 °C and 4.9 kbar for the mafic granulite, and from 564-645 °C and 3.2-9.6 kbar through 634-727 °C and 6.1-14.2 kbar to 615-664 °C and 3.2-4.2 kbar for the amphibolites, respectively. Metamorphic peak P-T conditions in the metapelitic country rocks were estimated to be 635-675 °C and 6.0-6.9 kbar. The metamorphic peak of the mafic granulite approaches the high P-T facies series, indicative of a subduction zone. Secondary-ion mass spectrometry and laser ablationinductively coupled plasma-mass spectrometry U-Pb dating of metamorphic zircons suggests that the metamorphic event occurred between ca. 420 and 372 Ma. These data further certify that the subduction of the continental margin and subsequent uplift of the Dunhuang orogenic belt represent a longlived tectono-metamorphic event in the Paleozoic.

A Regionally Evolving Transpressional Duplex Along the Northern Margin of the Altyn Tagh Fault: New Kinematic and Timing Constraints From the Sanweishan and Nanjieshan, China

“…The Sanweishan and Nanjieshan are located between the Tarim-Dunhuang Craton to the west and north, the ATF and Tibetan Plateau to the southeast, and Beishan block to the north and east and belong to the northern part of the Paleozoic Dunhuang Orogenic Belt (Figure 1b; Wang et al, 2018;Zhao et al, 2015Zhao et al, , 2016. Exposed Precambrian basement consists of medium-to high-grade metamorphic rocks, including felsic gneiss and tonalite-trondhjemite-granodiorite gneiss, quartzite, marble, amphibolite, and mafic granulite (Wang et al, 2018). Paleozoic magmatic and metamorphic complexes indicate multiple episodes of Paleozoic tectonothermal events (Wang et al, 2018;Zhao et al, 2015Zhao et al, , 2016.…”

“…Exposed Precambrian basement consists of medium‐ to high‐grade metamorphic rocks, including felsic gneiss and tonalite‐trondhjemite‐granodiorite gneiss, quartzite, marble, amphibolite, and mafic granulite (Wang et al, ). Paleozoic magmatic and metamorphic complexes indicate multiple episodes of Paleozoic tectonothermal events (Wang et al, ; Zhao et al, , ). Basement structural grain throughout the Nanjieshan and Sanweishan is typically ENE striking and parallel to many of the previously identified Late Cenozoic faults, suggesting a strong basement control on crustal reactivation (Cunningham et al, ).…”

Discovery of granulite‐facies metamorphic rocks in the Yilan area, Heilongjiang Province, China: Geochronology, geochemistry, metamorphic characteristics, and geological implications

“…We note that the peak temperatures and pressures of the present study are generally the same as those reported on granulite‐facies rocks of the Mashan Complex by the previous scholars (Jiang, 1992; Lennon, 1997; Lu et al, 1996). Metamorphic P–T paths can reveal the tectonic setting of metamorphism (e.g., Hermann, Müntener, & Scambelluri, 2000; Meng et al, 2017; Parsons et al, 2016; Wang, Zhang, Chen, et al, 2018; Wang, Zhang, Lu, et al, 2018; Wang & Guo, 2017; Wei, 2016; Wei & Zhu, 2016; Yin et al, 2014; Yin, Zhao, & Sun, 2015; Yu, Li, Zhang, Peng, et al, 2019; Yu, Zhang, Li, Santosh, et al, 2019; Yu, Li, Zhang, Liu, et al, 2019; Zhao, Wilde, Cawood, & Lu, 2000; Zhao, Cawood, et al, 2001; Zhao, Wilde, et al, 2001). The available data suggest that the Mashan Complex in the Jiamusi Massif underwent regional metamorphism characterized by a clockwise P–T path (Guo et al, 2014; Jiang, 1992; Lennon, 1997; Lu et al, 1996; Yang, Liang, et al, 2021; Yang, Liang, Zheng, Xu, et al, 2020; Yang, Liang, Zheng, Zhang, et al, 2020; Yang, Zheng, et al, 2021).…”

Diverse P‐T‐t Paths Reveal High‐Grade Metamorphosed Forearc Complexes in NW China

“…The presence of Devonian eclogite (H. Y. C. Wang, Chen, et al., 2017) and Silurian‐Devonian HP mafic granulites (H. Y. C. Wang, Chen, et al., 2016, H. Y. C. Wang, Wang, et al., 2017; Zong et al., 2012) demonstrates that the Dunhuang Complex is a tectonic mélange that contains diverse blocks that were subducted to variable depths and P‐T conditions (H. Y. C. Wang, Chen, et al., 2016, 2017; H. Y. C. Wang et al., 2018), as documented by many studies of the HP metamorphism (He et al., 2014; H. Y. C. Wang et al., 2018; Q. W. L. Zhang et al., 2020; Zong et al., 2012). Metabasic rocks of different metamorphic grades form lenses, centimeters to meters in size, entrained in a metasedimentary matrix (Shi et al., 2020; H. Y. C. Wang, Chen, et al., 2016, 2017, H. Y. C. Wang, Wang, et al., 2017) (Figures 2 and 3; Figure S1 in Supporting Information S1); the overall structure is a typical “block‐in‐matrix” mélange (Silver & Beutner, 1980; M. Wood, 2012).…”