Geochronological and geochemical constraints on the coexistent N-MORB- and SSZ-type ophiolites in Babu area (SW China) and tectonic implications

Abstract

Supplemental file 1 Geology of the Babu ultramafic-mafic complex and sample DescriptionsThe Babu ultramafic-mafic complex in the Malipo county, southeastern Yunnan, outcrops in a tectonic nappe between the NW-striking Wenshan-Malipo and Funing strike-slip faults (Fig. 2a; YunnanBGMR 1990). The autochthonous strata are Devonian and Triassic argillaceous and sandy turbidites. The exotic Permian-Carboniferous limestones overlying structurally onto the turbidites may have been deposited originally in seamounts or oceanic islands (Xu et al. 2008a; Zhang et al. 2013a). The Babu ultramafic-mafic complex is distributed in a belt of about 20 km-long and 4 -8 km-wide, and in fault contact with the Triassic Lanmu Formation (T3l; Fig. 2; Xu et al. 2008a; Zhang et al. 2013). The Babu ultramafic-mafic complex is composed of three major units from the base upward: meta-peridotite, diabase-gabbro and mafic lava. No layered gabbro or sheeted dikes have been recognized (Wu et al. 1999; Xu et al. 2008a; Zhang et al. 2013). The meta-peridotite is overlain tectonically by a diabase-gabbro assemblage. The basalt is in fault contact with the meta-peridotite, and the relationship between the basalt and the diabase-gabbro assemblage is not clear.Although strongly serpentinized, the meta-ultramafic rocks are identified as mostly harzburgites with minor pyroxenites and lherzolites (Supplemental file 2).Serpentinized harzburgites show a gray to black to dark green color and strong mylonitic foliations. Major original minerals include pyroxene (50%-55%), olivine (30%-35%), plagioclase (3%-5%), and magnetite (1%-2%). Altered minerals are mainly talc and serpentine (Supplemental file 2b). Fresh olivine is scarce. Most olivine grains have been altered to serpentine, chlorite and talc, whereas pyroxene is altered to bastite. Plagioclase blebs, altered to clay, were noted in some samples.Pyroxenite is composed of subhedral to euhedral clinopyroxene with varying amounts of olivine and extremely rare orthopyroxene.Metagabbro and metadiabase crop out as massive isotropic gabbro and dikes (Fig. 2). They show dark green color and massive structure (Supplemental file 3). Major minerals include augite, plagioclase, hornblende, and magnetite, and olivine in some samples. Most of the augite grains have been altered into amphibole, epidote or chlorite. Plagioclase is more euhedral and has been altered to clay. Amphibole show mainly hypidiomorphic and granular structure and is mainly from the alteration of pyroxene. The amphibole surrounds the euhedral-subeuhedral plagioclase. The metadiabases have ophitic textures, and consist of plagioclase, pyroxene, hornblende and ilmenite (Supplemental file 3). Sparse plagioclase phenocrysts are altered to clay and calcite. Pyroxene is altered to amphibole or chlorite.The mafic lavas consist of massive basalt, amygdaloidal basalt and porphyritic basalt (Supplemental file 3). Pillow basalt also crops out in the Tongchang village being inter-bedded with cherts and limestones (Fig. 2). They show mainly greenschist facie...

Neoproterozoic to Early Triassic tectono-stratigraphic evolution of Indochina and adjacent areas: A review with new data

“…Some authors have suggested the existence of an oceanic crust between north Vietnam and South China, of which remnants are preserved along the so-called Dian Qiong suture. Along this zone, Early Carboniferous-Permian gabbro, pillow basalts, and mafic dykes have been found in in NE Vietnam, Yunnan, and Guangxi Provinces, and were interpreted as the "Babu ophiolites" (Cai and Zhang, 2009;Halpin et al, 2016;Liu et al, 2018;Tran et al, 2007).…”

Triassic detrital records in the western Dian‐Qiong suture, South China: Implications for the eastern Paleo‐Tethys evolution

“…Given the detrital zircon age spectra of five sandstone samples (Figure 4a-e), the G1 is similar to the ages of island volcanic arc (c. 256-240 Ma) in Napo, Jingxi and Pingxiang areas (Gan et al, 2021;Hu et al, 2012;Liu, Li, et al, 2018;Qin et al, 2011Qin et al, , 2012Xiang et al, 2021) and scattered granitic plutons in the NVT (Chen et al, 2014;Roger et al, 2012). The G2 are consistent with the tim- et al, 1993) and diagenetic K-metasomatism (Fedo et al, 1995), respectively; (b) Ternary Al 2 O 3 -Zr-TiO 2 plot (after Garcia et al, 1994) the Early Carboniferous-Middle Permian (Liu, Peng, & Guo, 2018;Tran et al, 2007;Zhang et al, 2013), younger than the age of Jinshajiang-Ailaoshan-Song Ma-Song Chay ocean (439-280 Ma, Jian et al, 2009a, 2009bVuong et al, 2013). After the intense and short tectonothermal activity induced by the Emeishan plume (c. 260 Ma, Fan et al, 2008;Zhou et al, 2006), this ocean started and continued to subduct Roger et al, 2012), which led to the widespread syncollision felsic magmatism and strong tectonic deformation (Faure et al, 2014(Faure et al, , 2016Lepvrier et al, 2011).…”

“…The western DQS extends NW‐SE to the south of the Nanpanjiang foreland basin, South China and was interpreted as the potential suture zone between the SCB and NVT (Figure 1a, Cai & Zhang, 2009). Given the existing geological evidence, the scattered ophiolites within this suture probably represent the dismembered crust of the Paleo‐Tethys branch ocean that opened and spread during the Early Carboniferous–Middle Permian (Liu, Peng, & Guo, 2018; Tran et al, 2007; Zhang et al, 2013), instead of a rift basin originated from the Emeishan mantle plume (Faure et al, 2014, 2016; Hoa et al, 2008, 2016). The Late Permian–Middle Triassic basalts, andesites and rhyolites in Napo, Jingxi and Pingxiang areas, to the north/northeast of the western DQS, are interpreted as island volcanic arc responding to the subduction of this ocean (Hu et al, 2012; Qin et al, 2011, 2012; Xiang et al, 2021).…”

“…We investigate the provenance and tectonic setting of , 1976;BGMRY, 1976aBGMRY, , 1976bBGMRY, , 1978Zhang et al, 2019). Abbreviations: 1-Middle Triassic Lanmu formation; 2-Lower Triassic Ximatang and Yongningzhen formations, and middle Triassic Gejiu formation; 3-Permian; 4-Carboniferous-Devonian; 5-Cambrian; 6-Mesozoic granite; 7-Early Palaeozoic granite (northern Song Chay massif); 8-Metabasalt; 9-Metadiabase and metagabbro; 10-Meta-ultramafic rock; 11-Unconformity; 12-Faults; 13-Strike-slip faults; 14-Thrust faults; 15-Section location; 16-Detrital zircon U-Pb isotope analysed samples with youngest age peaks (red star) and existing geochronological data for the Babu ophiolite (Liu, Peng, & Guo, 2018;Wu et al, 1999;Zhang et al, 2013), volcaniclastic sandstone (Yang et al, 2017) and early Permian radiolarian chert (Feng & Liu, 2002 [18][19][20][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]…”

“…Given the discovery of the MORB‐like ophiolites, OIB‐like basalts, mafic‐felsic island arc volcanic rocks and deep‐marine sediments in the China–Vietnam border region (Feng & Liu, 2002; Guo et al, 2004; Wu et al, 2000; Zhong et al, 1999), Cai and Zhang (2009) proposed the Dian‐Qiong suture (DQS) to define another Paleo‐Tethys branch ocean developed between the SCB and Northern Vietnam terrane (NVT; Figure 1a). New geochronological and geochemical evidence of these ophiolites and island arc volcanic rocks reveals that this ocean formed during the Early Carboniferous–Middle Permian (334–265 Ma, Liu, Peng, & Guo, 2018; Thanh et al, 2014; Tran et al, 2007; Zhang et al, 2013) and subducted during the Late Permian to Middle Triassic (256–240 Ma, Gan et al, 2021; Hu et al, 2012; Liu, Li, et al, 2018; Qin et al, 2011, 2012; Xiang et al, 2021). However, the subduction polarity and closure process of the Dian‐Qiong ocean remain controversial.…”