A paired metamorphic belt in a subduction‐to‐collision orogen: An example from the South Qilian–North Qaidam orogenic belt,NWChina

Abstract

The early Palaeozoic South Qilian–North Qaidam orogenic belt in northwestern China records a nearly complete history of early‐stage long‐lived oceanic subduction–accretion followed by late‐stage continental collision. Most previous studies have focused on low dT/dP metamorphism (HP–UHP) in this belt whereas the paired high dT/dP belt in the hinterland has received little attention. In this contribution, phase equilibrium modelling is combined with zircon petrochronology to determine the P–T–t evolution of granulites in the North Wulan gneiss complex in the high dT/dP hinterland of the South Qilian–North Qaidam orogen. Granulites record a clockwise P–T path with near‐peak temperatures of ~800–900°C at 5.5–7 kbar. Peak metamorphism was followed by high‐T decompression. Zircon petrochronology reveals protracted zircon growth from c. 474 to 446 Ma during the high‐T portion of the P–T path. High dT/dP metamorphism in the North Wulan gneiss complex was likely the result of heat transfer from the underlying hot asthenosphere and minor coeval magmatism in an arc–back‐arc system during slab retreat and roll‐back of the South Qilian oceanic plate. Broadly contemporaneous but slightly younger HP–UHP metamorphism in the foreland of the South Qilian–North Qaidam orogenic belt indicates that the region records an early Palaeozoic paired metamorphic belt. This early Palaeozoic paired metamorphic belt provides a detailed example of dual thermal regimes in a modern‐style orogenic system that can be applied to understanding the time‐scales and P–T conditions of high dT/dP metamorphism that accompany subduction in Phanerozoic and Precambrian orogenic belts.

Subduction Within the Proto‐Tethys Ocean Revealed by Recognition of the Earliest Phanerozoic Intra‐Oceanic Arc, Northern Tibetan Plateau

“…Metamorphic rocks associated with continental‐margin subduction are represented by ca. 470–450 Ma high temperature‐low pressure metamorphic rocks in the Oulongbuluke block and Late Ordovician eclogites along the North Qaidam belt (Li et al., 2019; Song et al., 2019; Zhang et al., 2016). The Tuoxingou accretionary complex contains psammitic schist with Paleoarchean‐Neoproterozoic detrital zircons, also indicating derivation from the adjacent Precambrian microcontent and accumulation along an active continental margin (Figures 4 and 5).…”

“…It occurs at active continental margins and results in the generation of an Andean-type arc-trench system (Ducea et al, 2015;Xiao et al, 2010Xiao et al, , 2020. Subduction of the Proto-Tethys Ocean along a continental margin is recorded by early Paleozoic continental arc magmatic rocks and metamorphic rocks in the Oulongbuluke block and North Qaidam belt (Li et al, 2018b(Li et al, , 2019Wu et al, 2009;Zhu et al, 2010). Continental arc magmatic rocks in the Oulongbuluke block crystallized at ca.…”

“…This block is further intruded by Ordovician and Triassic felsic to mafic intrusions and covered by early Paleozoic and Cenozoic sediments (Sun et al, 2020). Paleozoic metamorphic rocks (gneiss and granulite) are also reported in the Oulongbuluke block (Li et al, 2018b(Li et al, , 2019. The Qaidam block is another Precambrian microcontinent with Meso-Neoproterozoic metamorphic basement and is mostly covered by Mesozoic to Cenozoic sedimentary basins (Lu et al, 2008).…”

HT–MP metamorphism in Central Qilian Block, NE Tibet Plateau: Implications on the tectonic evolution of the Qilian Orogen

“…Studies on the Palaeozoic orogenic collages in East Asia, such as the Qinling, Qilian and Kunlun orogenic belts indicated that several Precambrian blocks were located on the periphery of the northern margin of eastern Gondwana, which were involved in the evolution of the Proto‐Tethys Ocean during the Early Palaeozoic (e.g., Cawood & Korsch, 2008; Fu et al, 2018, 2019; Li, Niu, et al, 2019; Sun, Dong, et al, 2020; Sun et al, 2022; Xiao et al, 2009; Yan et al, 2015; Yan, Fu, Aitchison, Buckman, et al, 2019, Yan, Fu, Aitchison, Niu, et al, 2019, Yan et al, 2022; Yu et al, 2017, 2019, 2021; Zhang, Zou, et al, 2013; Zhang, Gong, et al, 2013; Zhao et al, 2012; Zhao & Xiao, 2018). The spatial–temporal relationship of these blocks is vital to reasonably understand the evolution of these orogenic belts and the Proto‐Tethys Ocean in the northeastern (NE) Tibet Plateau.…”

Regional high-grade metamorphic peak imprint in zircons from the mafic-ultramafic Jacurici Complex, São Francisco Craton, Brazil

“…U-Pb ages in zircons can be modified by solid-state dissolution-precipitation and by fluid-driven processes related to metamorphic, hydrothermal or magmatic fluids (Hoskin and Black 2000, Corfu et al 2003, Hoskin 2005, Grant et al 2009, Rubatto 2017). Under regional metamorphism at different P-T conditions, zircon will partially to completely recrystallize or form overgrowth rims, possibly preserving multiple geological episodes in its growth patterns (Bauer et al 2007, Fu et al 2009, Rasmussen et al 2011, Phillips et al 2015, Li et al 2019. Coupled cathodoluminescence imaging and in-situ U-Pb dating allows the identification of metamorphic events within the zircon complex internal textures and growth rims.…”