Search

[Display omitted] • Ediacaran magmatism and sedimentation occurred in the Bayankhongor Zone and the northeastern edge of the Baidrag Block. • Magmatic and sedimentary units formed in a back-arc basin (not belonging to ophiolite) • Multiple crustal blocks and oceans closing by subduction in peri -Siberian realm. Geochronological and geochemical investigation of the magmatic and sedimentary rocks from the south-eastern tip of the Bayankhongor Zone (central Mongolia) constrains the Neoproterozoic evolution of the northern margin of the Baidrag Block. There, ultramafic to felsic igneous rocks of the Khan-Uul Massif intruded the volcano-sedimentary sequence of the Ulziit Gol Unit. U–Pb zircon ages show that both the plutonic and volcanic rocks were coeval products of the same Ediacaran (598–564 Ma) magmatism. Most of the samples have low contents of high field strength elements typical of arc-related magmas; however, some mafic rock samples display N-MORB-like chemistry. Magmatic rocks in the Khan-Uul Massif and Ulziit Gol Unit yielded exclusively positive initial ε Hf in zircon values (+4.9 to +13.8), implying derivation from depleted-mantle sources. Furthermore, heterogeneity of the whole-rock initial ε Nd values (–4.0 to +2.1) documents that fractional crystallization was accompanied by variable crustal contamination. The detrital zircon age patterns of the sandstone and tuffites in the Ulziit Gol Unit indicate that the sequence was filled dominantly by Ediacaran magmatic detritus derived from the Khan-Uul Massif and its volcanic equivalents, while the older cratonic material from the Baidrag basement represented only a subordinate component. Combined magmatic and sedimentary records imply that both the Khan-Uul Massif and the Ulziit Gol Unit may have formed in the same back-arc basin environment. This challenges the previous view that the entire Bayankhongor Zone was ophiolitic in nature. Distribution of coeval Ediacaran supra-subduction systems on the scale of the Mongolian Collage indicates the closure of multiple oceanic basins rimming the Siberian Continent. Following Rodinia break-up, this peri -Siberian realm was presumably formed by sub-parallel continental ribbons and oceanic basins. It is proposed that the amalgamation of these blocks and closure of intervening oceans reflected the Ediacaran advancing mode of the Palaeo-Pacific subduction. [ABSTRACT FROM AUTHOR]

The Erqis tectonic belt, situated at the junction of the Chinese Altai‐East Junggar, originated through the subduction of the Ob‐Zaisan Ocean, playing a pivotal role in unraveling the tectonic evolution of the southern Altaids. Tectonic and provenance analyses discern three distinct arcs: the Chinese Altai in the north exhibits a protracted history from the late Cambrian to early Permian with a slender accretionary complex (AC) termed the Supute AC; the Kuerti intra‐oceanic arc in the middle emerged during the Silurian to Devonian coevally with a minor AC known as the Tesibahan AC; and the Dulate arc in the south predominantly evolved from the Middle Devonian to Permian, giving rise to the Fuyun AC that independently developed on its northern margin at least until ∼273 Ma. Our findings indicate the existence of multiple arcs within the Ob‐Zaisan Ocean, forming an archipelago paleogeography in the Paleo‐Asian Ocean. Provenance studies lead us to propose that cryptic sutures demarcating the Chinese Altai, Kuerti, and Dulate lie approximately along the Kuerti and Tesibahan faults, respectively, and that the oceanic branches between these arcs subducted northward beneath the Chinese Altai and Kuerti arcs and southward beneath the Dulate arc. Additionally, our work demonstrates the closure of the Ob‐Zaisan Ocean most probably postdates ∼273 Ma. Combining our data with previous research, we present a novel tectonic evolution model, elucidating several arc amalgamations with multiple subduction polarities between Chinese Altai and East Junggar throughout the late Cambrian to Permian. Key Points: The Erqis tectonic belt predominantly comprises accretionary complex and slices of arcsThe cryptic suture between Chinese Altai and East Junggar extends along the Tesibahan‐Mayine'bo faults rather than the Erqis faultThe Ob‐Zaisan Ocean had subducted southward beneath the East Junggar and closed later than the Permian [ABSTRACT FROM AUTHOR]

The Devonian tectonic setting is still controversial in the Proto‒Tethyan North Qilian belt. The Hexi Corridor of the North Qilian belt occupies a key position in constraining the tectonic evolution of the Proto‒Tethyan Ocean and the growth of the Asian continent. Turbidites, as an important component of the Jiayuguan mélange in the Hexi Corridor, consist of conglomerate, pebbly sandstone, sandstone, siltstone, calcareous mudstone, and chert that feature typical Bouma sequences of Ba, Bc, Bcd, Babc and/or Bab. They are strongly deformed into NW‒trending folds with NE‒ and SW‒inclined thrust faults. Detrital zircon U‒Pb dating results demonstrate that these sediments successively young to the southwest with maximum depositional ages (MDA) ranging from 560 Ma to 411 Ma, indicating that the youngest block was deposited after 411 Ma. Petrological, geochemical and detrital zircon U‒Pb age data indicate the sedimentary rocks provenanced from weak weathering, recycling, and multiple mixing sources, and that the dominant source was the Andean‒type Alxa arc. Together with the published data, we suggest that double‒sided subduction of the North Qilian Ocean (Proto‒Tethyan Ocean) occurred between the North Qilian arc and the Andean‒type Alxa arc during the early Devonian. Key Points: Jiayuguan turbidite consist of conglomerate, sandstone, calcareous mudstone and chert with Bouma sequences of Ba, Bc, Bcd, Babc and/or BabThese turbidite fragments successive youngs to southwest and sourced from the Alxa Andean‐type arcAn archipelagic ocean paleogeography existed between the Paleo‐Asian Ocean and the Proto‒Tethys Ocean during early Devonian [ABSTRACT FROM AUTHOR]

The evolution and closure timing of the Paleo-Asian Ocean are controversial in the Eastern Tianshan orogen, southern Altaids. The Dananhu arc of the Eastern Tianshan was involved in the long-lived evolution and terminal tectonic events during the formation of the Altaids, and its magmatic rocks are the faithful recorder. To constrain the subduction history of the Paleo-Asian Ocean, we review the tectonic of the Dananhu arc, by summarizing the geochemical and geochronological data of granites and volcanic rocks and mineral deposits, which will shed light on the accretionary history, closure of the Paleo-Asian Ocean, and the continental growth in Altaids. Zircon U-Pb ages of the granitic rocks across the middle of the Dannanhu arc range from 453 Ma to 227 Ma and demonstrate overall southward younging through four main areas: the Kalatage belt (ca. 453–299 Ma), the Keizer belt (ca. 401–268 Ma), the Tuwu belt (360–302 Ma), and the Kanguer subduction complex (ca. 288–227 Ma). These granitic rocks are calc-alkaline arc-related and adakitic granites that are enriched in Si and K. They increase in Th/Yb and decrease in Cr and Ce/Pb southwards over time. The consistent geochemical variations indicate progressive maturity of the arc crust. Their whole-rock εNd(t) and zircon εHf(t) values coordinated with the progressive change in the crustal thickness estimated by the granites indicate a multi-phase switching of subduction. The Ordovician to Permian granitic rocks in the arc have stable high whole-rock εNd(t) values (ca. +5 – +10), and zircon εHf(t) values (ca. +7-+16), which significantly shifted to +2 – +4 and +4 – +12 during ca. 243–227 Ma. These changing relations accompanied a sudden crustal thickening, suggesting that continental crustal material was involved in the petrogenesis of these rocks during the convergence among the Dananhu arc, the Harlik and the Yamansu-central Tianshan continental arc. [ABSTRACT FROM AUTHOR]