Calcite U–Pb dating of altered ancient oceanic crust in the North Pamir, Central Asia

Abstract

Abstract. The North Pamir, part of the western syntax of the India–Asia collision zone, preserves remnants of a poorly understood Paleozoic intra-oceanic subduction zone. To constrain the age of this ancient ocean floor, we analyzed calcite phases in vesicular basalt and basaltic volcanic breccia with U–Pb geochronology using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Dating of radial fibrous to equant spary calcite yielded three meaningful Visean–Serpukhovian ages. Rare-earth elements and yttrium (REE + Y) data reveal that the basaltic host rock of the calcite and oxidizing seawater are major sources of trace elements during calcite precipitation. U–Pb ages seem to be independent of REE + Y concentrations. Our results demonstrate the potential of calcite dating to constrain the age of ancient ocean floors. We challenge the hypothesis that a continuous early Paleozoic Kunlun Terrane extended from northern Tibet into the North Pamir.

Spatiotemporal relationship between hydrocarbon fluid and sandstone‐hosted uranium deposits in the Qianjiadian area, Songliao Basin

“…Eventually, a low intercept 238 U/ 206 Pb age of 65.93 ± 3.35 Ma, similar to the age obtained from SL20‐10 sample, was determined (Figure 5c). The initial 207 Pb/ 206 Pb value was 0.778 ± 0.013, and the MSWD value of 5.6 also indicates good reliability for the age determination (Rembe et al, 2022).…”

“…Compared with previous methods, the newly established method exhibits numerous advantages, including high precision, high spatial resolution, high efficiency, convenient sample preparation, low consumption and low test background (Jin et al, 2021; Wu et al, 2022). Consequently, it is widely employed in various geological fields to determine the formation age of carbonate minerals, study diagenetic process, investigate fault and hydrothermal activities and explore the evolution of oil–gas reservoirs (Amidon et al, 2022; Ganade et al, 2022; Lan et al, 2023; Rembe et al, 2022). In this study, we focus on the red‐variegated Upper Cretaceous Qingshankou Formation of the Dalin uranium deposit in the Qianjiadian area of the Songliao basin.…”

Geochronology, Geochemistry, and Geodynamic Implications of Permo-Triassic Back-Arc Basin Successions in the North Pamir, Central Asia

“…We also investigated a Permian deformed felsic sill in the Markansu valley, Permian andesitic to dacitic rocks in the upper Bieertuokuoyi valley, and a variety of Middle to Upper Triassic volcanic rocks in the Oytag and Gez valleys (Figure 4). The Permian units unconformably overlie Carboniferous (Hercynian) island arcrelated rocks, identified as mainly basaltic to andesitic lava flows and tuffs and associated epiclastic rocks and intruded Carboniferous plagiogranites [9,16,31]. In the Qimgan valley, two calcite U-Pb ages from the Permian strata and one zircon U-Pb age of a crosscutting aplitic dike temporally constrain the deposition of Permian strata to between 260 and 250 Ma [9].…”

“…The Pamir has been subdivided into 3 major tectonic units, the North, Central, and South Pamir [2,6,15], separated by intervening suture zones (Figure 2). The North Pamir is composed of rocks associated with a Carboniferous oceanic arc that accreted to the Paleo-Asian margin in the late Carboniferous to Permian due to closure of a part of the Paleo-Tethys [3,4,9,16]. This process, along with the closure of the Turkestan Ocean, further north, is regarded as the Hercynian orogeny in Central Asia [8,17].…”

“…The Carboniferous volcanic arc of the North Pamir can be subdivided into the eastern Oytag segment, with more primitive island arc volcanic rocks and associated plagiogranites (tonalites and trondhjemites), and the western Darvaz segment, comprising pre-Carboniferous metasedimentary rocks in the Kurguvad-Faizabad zone (also named the Kurguvad block) and Carboniferous basalts and associated granodioritic rocks of continental arc affinity [3,9,16,31,32]. The Carboniferous volcanic arc system accreted in the late Carboniferous to early Permian [9].…”