Early Tertiary deformation of the Zhongba–Gyangze Thrust in central southern Tibet

The Yarlung suture mélange, Lopu Range, southern Tibet: Provenance of sandstone blocks and transition from oceanic subduction to continental collision

“…The Yarlung Zangbo Mantle Thrust (YZMT) places ophiolite belt units southward on siliciclastic matrix mélange or Tethyan Himalaya strata, with local red radiolarian chert and/or strata of the synkinemetic Liuqu conglomerate (Paleogene Davis et al, 2002;Eocene Wang et al, 2010;Oligo-Miocene Wei et al, 2011;Oligo-Miocene Li et al, 2015a;19-20 Ma Leary et al, 2016b) in the hanging wall or footwall (Tapponnier et al, 1981;Burg and Chen, 1984;Girardeau et al, 1984;Burg et al, 1987;Ratschbacher et al, 1994;Ding et al, 2005). The siliciclastic matrix mélange was originally described as "wildflysch with exotic blocks" (Tapponnier et al, 1981;Burg and Chen, 1984;Burg et al, 1985;Burg et al, 1987) and is also known as the Yamdrok mélange (Searle et al, 1987), mud-matrix mélange (Wang et al, 2011), Pomunong mélange (Cai et al, 2012), Renbu mélange (Li et al, 2015b), Xiukang mélange (XBGMR, 1979;Yin and Sun, 1988;An et al, 2017), or sedimentary-matrix mélange (Ding et al, 2005;Wang et al, 2017). There has been some confusion in the literature about the boundaries of the siliciclastic matrix mélange unit, and many definitions of the unit have also included imbricated radiolarian chert and/or deformed Tethyan Himalaya strata.…”

“…Cai et al (2012) identified the imbricated radiolarites (the Bainang terrane) as the Tangga mélange and the siliclastic matrix mélange (the Yamdrok mélange) as the Pomunong mélange. The Renbu mélange (Li et al, 2015b), Xiukang mélange (XBGMR, 1979;Yin and Sun, 1988;An et al, 2017), and sedimentary-matrix mélange (Ding et al, 2005;Wang et al, 2017) all refer to the same unit as the Yamdrok mélange from Searle et al (1987). This disambiguation is important when assessing published descriptions of the siliciclastic matrix mélange.…”

“…This disambiguation is important when assessing published descriptions of the siliciclastic matrix mélange. We define the siliciclastic matrix marine limestone, sandstone, and shale in a sandstone and shale matrix (Shackleton, 1981;215 Tapponnier et al, 1981;Searle et al, 1987;Dupuis et al, 2005b;Dupuis et al, 2006;Cai et al, 216 2012;Li et al, 2015b;An et al, 2017;Wang et al, 2017). Kilometer-scale blocks of marine 217 limestone in the mélange and Tethyan Himalaya strata contain Permian to earliest Triassic fossils 218 (Tapponnier et al, 1981;Jin et al, 2015) and are interpreted to be olistostromal blocks derived from the passive margin of India (Liu and Einsele, 1996;Jin et al, 2015), but fossils as young as latest Cretaceous to late Paleocene are found in the mélange blocks and matrix (Tapponnier et al, 1981;Burg and Chen, 1984;Burg et al, 1985;Liu and Aitchison, 2002).…”

“…Basalt blocks from the mélange exhibit geochemical characteristics similar to seamounts such as the Réunion hotspot track (Dupuis et al, 2005b). While blueschist is well-documented in the Indus Suture Zone in the northwestern Himalaya, only local outcrops of blueschist have been documented in the siliciclastic matrix mélange (Ding et al, 2005;Li et al, 2007;Wang et al, 2017). Shackleton (1981) described the southernmost part of the mélange as sedimentary in origin, although this may be in reference to the deformed Tethyan strata to the south that is included in the "sedimentary mélange", while Searle et al (1987) argued for a clearly tectonic origin ~100 km west of Xigaze, consistent with documentation of foliation, lineation, and S-C fabrics in the siliclastic matrix (Burg and Chen, 1984;Cai et al, 2012).…”

“…Generally, thicker trench fill creates an accretionary subduction complex composed mostly of 43 ocean plate stratigraphy while thinner trench fill leads to an erosive subduction complex marked by frontal erosion and/or basal erosion of the margin, forearc subsidence, and inboard migration of the forearc and arc (von Huene and Scholl, 1991;Clift and Vannucchi, 2004;Stern, 2011). of local amphibolite in the ophiolite belt, a few local outcrops of blueschist in the siliciclastic matrix mélange (Ding et al, 2005;Li et al, 2007;Wang et al, 2017), and rocks exhumed by doming and/or normal faulting, the suture zone is regionally metamorphosed to lower greenschist facies (ophiolite belt Burg and Chen, 1984; Tethyan Himalaya strata Burg and Chen, 1984;Burg et al, 1987; Xigaze forearc basin Dürr, 1996;ophiolite belt Huot et al, 2002;Dupuis et al, 2005a;Dupuis et al, 2005b;Cai et al, 2012). The siliciclastic matrix mélange within the subduction complex has long been interpreted to have formed by accretion of ocean plate stratigraphy beneath the ophiolite belt and as the southernmost Asian unit (Shackleton, 1981;Tapponnier et al, 1981;Searle et al, 1987;Cai et al, 2012).…”