Unravelling a Devonian–Triassic seamount chain in the South Tianshan high‐pressure/ultrahigh‐pressure accretionary complex in the Atbashi area (Kyrgyzstan)

Abstract

Seamounts are common occurrences on the extant oceanic floors of the earth, and accreted single seamounts are also widely distributed on the modern active margins, but recognition of single seamounts is an uneasy job in the ancient orogens, and the detection of a chain of accreted seamounts is even harder, therefore understanding the multiple accretion of ancient seamounts is nearly negligible. A combined analysis of geochronology and geochemistry was conducted on the basic eclogitic rocks from the Atbashi Accretionary Complex in the Kyrgyz South Tianshan, in a bid to unravel the accretion process of a chain of seamounts in the Paleo‐Asian Ocean in the southern Altaids. A set of reliable U–Pb zircon ages of 397.6 ± 8 Ma age for a basaltic andesite, 353 ± 8 Ma for a gabbro, and 317.1 ± 9 Ma for a diorite were obtained in this study. Both unmetamorphosed basic rocks and eclogites carry geochemical signatures of plume‐derived seamounts that were influenced by their respective mantle source. Taken together with previously published age data, the spatial and temporal features of these Atbashi rocks indicate the timing and sequence of formation, subduction, and extrusion of the South Tianshan oceanic remnants in the Early/Middle Devonian to Late Triassic. The integrated data indicate the existence of a seamount chain composed of Early/Middle Devonian–Late Triassic seamounts in the Atbashi Complex. The paleogeographic pattern and analysis of these fragments derived from the ocean‐type seamounts enable the reconstruction of tectonic models of that portray, magmatism, mantle‐derived plumes, subduction and exhumation of this Devonian–Triassic ocean floor.

Radiolarian age and geochemistry of cherts from the Atbashi accretionary complex, Kyrgyz South Tianshan

“…First, the tectonic setting of the South Tianshan Ocean was previously considered to be a small, short‐lived basin, based either on the short age span of Devonian conodonts in a mélange (Alekseev et al, 2007) or on geochemical studies of an ophiolitic mélange (Charvet, Shu, & Laurent‐Charvet, 2007; Jourdon et al, 2017). Our new radiolarians indicate a late Early Carboniferous that is consistent with the Late Permian or even Early to Mid‐Triassic isotopic ages of ultrahigh‐pressure components in the Atbashi Complex (Sang et al, 2017, 2018; Sang, Xiao, & Windley, 2020). This confirms that the South Tianshan accretionary complex contains components of different age.…”

“…This confirms that the South Tianshan accretionary complex contains components of different age. Our chert samples are closely associated with basic magmatic rocks with N-MORB (mid-ocean ridge basalt) characteristics (Sang et al, 2018(Sang et al, , 2020. The banded chert sample that yielded a late Early Carboniferous age has the same strike as nearby pelagic sediments (Sang et al, 2018), which suggests a common hemipelagic environment.…”

Accretionary tectonics, deep structures and metallogeny of southern Altaids

“…The detection of a chain of accreted seamounts and further reconstruction of the multiple accretions of ancient seamounts are very challenging jobs in modern orogenic anatomy. A combined analysis of geochronology and geochemistry is employed on the basic eclogitic rocks from the Atbashi accretionary complex in the Kyrgyz South Tianshan, in the research undertaken by Sang, Xiao and Windley (, this issue). The existence of a seamount chain composed of Early/Middle Devonian‐Late Triassic seamounts in the Atbashi Complex was identified in the research.…”

Age and Petrogenesis of the Gabbros from Tajik South Tianshan: Implications for Early Paleozoic Geodynamic Evolution of the Southwestern Central Asian Orogenic Belt

“…A microcontinent with pre-Cambrian basement was inferred to exist in the South Tianshan, according to the outcrop of Paleozoic shallowmarine limestones [27,67,68]. On the other hand, some Early Paleozoic and Late Paleozoic carbonate rocks (caps) and associated OIB-like rocks in the northern and central parts of the South Tianshan were linked to Paleozoic accretion of seamounts and/or oceanic plateau [37,69,70]. The HP/UHP metamorphic rocks related to the subduction and closure of the Turkestan Ocean were exposed in the Atbashi and Zeravshan areas.…”