The Early Palaeozoic mega‐thrusting of the Gondwana‐derived Altay–Lake zone in western Mongolia: Implications for the development of the Central Asian Orogenic Belt and Paleo‐Asian Ocean evolution

Abstract

The position of structures of Mongolia during Rodinia break‐up and Paleo‐Asian Ocean opening is debatable, and reconstructions between them are poorly known. In this paper, we apply an integrated approach to the not widely known yet distinctive structure (ribbon‐like) of the Lake and Mongolian Altay zones in western Mongolia, relating these with the surrounding Tuva–Mongolian and central Mongolian microcontinents (CMMs) development within the Central Asian Orogenic Belt (CAOB) and Paleo‐Asian Ocean evolution. We present a summary of the Neoproterozoic–early Palaeozoic tectonic development of western Mongolia and the CAOB and suggest a new comprehensive model for its evolution. The Lake zone of Mongolia is a major zone of ophiolite and arc complexes within the CAOB. The main sections of ophiolites are located along the west margin, bordering with Precambrian crystalline basement of the CMM. The ophiolites are distributed from north to south and have been dated to have similar ages. A classic oceanic plate stratigraphy section is preserved in the Lake zone. Serpentinite mélange and other volcanogenic‐terrigenous assemblages from the Lake zone are characterized by a system of nappe sheets thrust over the Dzavkhan block of the CMM. The ribbon‐like structure that the southern part of the Altay–Lake zone preserves at present provides an explanation for the development between the Gondwana‐derived microcontinent and Paleo‐Asian Ocean. During the pre‐Neoproterozoic, convergence accretion between Siberia and the CMM formed the Tuva–Mongolian belt, which later converted to the Altay–Lake collision zone associated with the thrusting of its eastern margin. All well‐known ophiolites of western Mongolia (Agardag, Khantayshir, and Dariv) as well as ophiolites of the Erdene Uul area mostly correspond to an “open‐ocean” phase with drifting microcontinents between 655 and 540 Ma or Neoproterozoic. In the early Neoproterozoic, the Altay peninsula‐like ribbon microcontinent after rifting of East Gondwana gradually drifted to Siberia. In this time, the east margin of the Paleo‐Asian Ocean was developed as a passive margin with the Dzavkhan Block. The Paleo‐Asian ocean plate simultaneously drifted to the CMM, whereas the Altay microcontinent moved into Siberia‐CMM. In middle‐upper Neoproterozoic times, the eastern part of the Paleo‐Asian ocean plate was thrusted over the CMM, obducting ophiolites (e.g., Tas Khairkhan), in the early Cambrian time, an oceanic spreading centre (?) of the Paleo‐Asian Ocean reached the CMM and stopped obduction. In the Neoproterozoic, the west margin of the Paleo‐Asian Ocean was developed as an active continental margin, with subduction under the Gondwana‐derived microcontinent. In the early Cambrian, there was significant subduction rollback and accretion of seamounts (Turgen). Later, in middle Cambrian–early Ordovician times, a large turbidite sequence was deposited in Altay. During the Devonian to Carboniferous, the Paleo‐Asian Ocean was preserved as a remnant ocean or big sea (Lake zone), accumulating ...

Geochronology and trace elements of zircon in the Southern Chinese Altay: Implications for tectonic setting

“…Overall, the rocks in Southern Altay show continental-arc affinities (Figure 8f). Therefore, we support the proposal that the continental arc along Southern Altay was triggered by the active continental margin of the Altay-Mongolian block during the Devonian (Khukhuudei et al, 2020;Yang et al, 2011).…”

Paleozoic Geodynamics and Architecture of the Southern Part of the Mongolian Altai Zone

“…Several units of the Mongolian Altai Zone contain serpentinite mélanges (Ulgii zone), ultramafic and gabbroic mélanges (Hovd zone), or associations of serpentinites, gabbros, and metabasalts (Tsagaanshuvuut zone), interpreted as remnants of dismembered ophiolites possibly of late Proterozoic–lower Cambrian age (Dergunov et al., 2001; Khukhuudei et al., 2020). However, the age of these rocks has not been defined isotopically, and in some places even represent underlying Lake Zone Neoproterozoic to Cambrian ophiolite rocks imbricated with the Mongolian Altai Zone sequences, as is the case of the Hovd domain (Soejono et al., 2017).…”

“…The early accretionary evolution of the Mongolian Collage System is characterized by early Cambrian thrusting of the Lake Zone over the Precambrian continental blocks (e.g., Dijkstra et al, 2006;Khomentovsky & Gibsher, 1996;Khukhuudei et al, 2020Khukhuudei et al, , 2022Štípská et al, 2010;Tomurtogoo, 1980). This was followed by a Togtokh et al, 1993).…”

“…The Mongolian Altai Zone consists mainly of thick late Cambrian and Ordovician sedimentary packages covered by Silurian and Devonian volcano‐clastic sequences (Badarch et al., 2002; Byamba, 2009; Jiang et al., 2017; Tomurtogoo, 2012). It has been proposed that this volcanic‐sedimentary wedge formed due to the continuous subduction of an oceanic plate beneath a string of Mongolian continents and a late Proterozoic to early Cambrian oceanic unit called the Lake Zone (Khukhuudei et al., 2020; Kovalenko et al., 1996; Ruzhentsev & Burashnikov, 1996; Zonenshain et al., 1990) which was intruded by the 1,800 km‐long magmatic arc (Janoušek et al., 2018; Rudnev, Babin, et al., 2013; Rudnev et al., 2009; Rudnev, Kovach, & Ponomarchuk, 2013). Erosion of the arc and basement continental crust then produced detrital material that was filling the wedge throughout the entire early Paleozoic (Jiang et al., 2017; Kozakov et al., 2009; Long et al., 2020; Soejono et al., 2018).…”

Accretionary tectonics, deep structures and metallogeny of southern Altaids

“…In order to better reconstruct the structures and tectonic evolution during Rodinia break‐up and PAO opening, Khukhuudei, Kusky, Otgonbayar and Wang (, this issue) applied an integrated approach to the not widely known yet distinctive structure (ribbon‐like) of the Lake and Mongolian Altay zones in western Mongolia, relating these with the surrounding Tuva–Mongolian and central Mongolian microcontinents development within the CAOB and PAO evolution. The authors present a summary of the Neoproterozoic–early Palaeozoic tectonic development of western Mongolia and the CAOB and suggest a new comprehensive model for its evolution.…”