Carboniferous eclogite and garnet–omphacite granulite from northeastern Hainan Island, South China: Implications for the evolution of the eastern Palaeo‐Tethys

Abstract

High‐P (HP) eclogite and associated garnet–omphacite granulite have recently been discovered in the Mulantou area, northeastern Hainan Island, South China. These rocks consist mainly of garnet, omphacite, hornblende, quartz and rutile/ilmenite, with or without zoisite and plagioclase. Textural relationships, mineral compositions and thermobarometric calculations demonstrate that the eclogite and garnet–omphacite granulite share the same three‐stage metamorphic evolution, with prograde, peak and retrograde P−T conditions of 620–680°C and 8.7–11.1 kbar, 820–860°C and 17.0–18.2 kbar, and 700–730°C and 7.1–8.5 kbar respectively. Sensitive high‐resolution ion microprobe U–Pb zircon dating, coupled with the identification of mineral inclusions in zircon, reveals the formation of mafic protoliths before 355 Ma, prograde metamorphism at c. 340–330 Ma, peak to retrograde metamorphism at c. 310–300 Ma, and subsequent pegmatite intrusion at 295 Ma. Trace element geochemistry shows that most of the rocks have a MORB affinity, with initial εNd values of +2.4 to +6.7. As with similar transitional eclogite–HP granulite facies rocks in the thickened root in the European Variscan orogen, the occurrence of relatively high P−T metamorphic rocks of oceanic origin in northeastern Hainan Island suggests Carboniferous oceanic subduction leading to collision of the Hainan continental block, or at least part of it, with the South China Block in the eastern Palaeo‐Tethyan tectonic domain.

Closing of the east Palaeo‐Tethys Ocean: Source–sink records from Middle Triassic sediments, Hainan Island, China

“…The faults from south to north are the Jiusuo-Lingshui Fault (JLF), Jianfeng-Diaoluo Fault (JDF), Changjiang-Qionghai Fault (CQF) and Wangwu-Wenjiao Fault (WWF). The NE-SE trending faults on Hainan Island, such as the Gezhen and Baisha faults (BSF), developed from west to east (Liu, Hu, et al, 2022;Zhang et al, 2011Zhang et al, , 2019.…”

“…For example, the 248 ± 1 Ma diorite porphyrite vein in the Shilu area (Li et al, 2013) and the 247.4-252 Ma shoshonitic intrusive rocks in Bawangling (Liu, 2016) were formed in the post-orogenic extensional setting. The detrital zircons from this period have F I G U R E 1 1 Distribution map of igneous rocks in Hainan Island (The blue frame shows the igneous rocks in the post-collision extensional tectonic setting, data from Chen, 2020; Chen et al, 2011;Chen, Lin, et al, 2013;Dilek & Tang, 2020;Ding et al, 2005;Du, 2022;Gao, Chen, et al, 2022;Gao, Shi, et al, 2022;Gou et al, 2019;He et al, 2016;He, Wang, Xin, & Zhang, 2018;Hu et al, 2022;Li et al, 2013;Liu, 2016;Liu, Hu, et al, 2022;Long et al, 2022;Tang, 2010;Wen et al, 2013;Xie et al, 2005;Yuan et al, 2019;.…”

Paleoproterozoic collision to Mesozoic crustal reworking in central South China: evidence from drilling data and seismic crustal structure

“…The Nanhua basin records four rifting phases at ~820 Ma, ~800 Ma, 780-750 Ma and 750-690 Ma, followed by the sag phase to 545 Ma (Wang & Li, 2003). The uppermost Proterozoic Sinian strata are predominantly shallow-water dolomitic carbonates and conglomerates during marine transgression (S. G. Liu et al, 2021).…”

“…The 464-442 Ma I-type Xiaying granodiorite-monzogranite complex in the southern margin of the South China Block (Figure 3) and the 450-400 Ma S-and I-type granites in the interior of the South China Block indicate northwestward subduction of the proto-South China Ocean and subsequent collision between the South China Block and an unknown continent . Carboniferous eclogite and high-pressure granulite were reported from northeastern Hainan Island (Figure 3), which is interpreted to indicate subduction of the Paleo-Tethyan Ocean and ensuing collision of the Hainan continental block with Manuscript submitted to JGR: Solid Earth 13 the South China Block (X. C. Liu et al, 2021). In the late Permian to Triassic, the South China Block collided with the North China Craton along the Dabie-Sulu orogenic belt in the north (Yin & Nie, 1993;Zheng, 2008;Liu & Liou, 2011), and with the Indochina Block along the Song Ma suture zone in the south (Zhang et al, 2011;Faure et al, 2014;R.…”

“…The upper crust of the eastern Sichuan Basin displays folded parallel reflectors above the flat-lying sole décollement (i.e., the Main Yangtze décollement) (Yan et al, 2003;He et al, 2011;Li et al, 2018). Based on geological maps and borehole data of chevron-type anticline zone (S. G. Liu et al, 2021), the shallow reflectors at depths of 0-6 km represent Jurassic-Silurian strata of interlayered dolomites, limestones and mudstones (Figure 10b). The underlying Ordovician shales and limestones and Cambrian sandstones and dolomites appear as broadly folded reflectors at depths of 6-8 km.…”