The Carboniferous Arc of the North Pamir

Abstract

In this study, we investigate the age and geochemical variability of volcanic arc rocks found in the Chinese, Kyrgyz, and Tajik North Pamir in Central Asia. New geochemical and geochronological data together with compiled data from the literature give a holistic view of an early to mid-Carboniferous intraoceanic arc preserved in the northeastern Pamir. This North Pamir volcanic arc complex involves continental slivers in its western reaches and transforms into a Cordilleran-style collision zone with arc-magmatic rocks. These are hosted in part by Devonian to Carboniferous oceanic crust and the metamorphic Kurguvad basement block of Ediacaran age (maximum deposition age) in Tajikistan. We discuss whether a sliver of Carboniferous subduction-related basalts and intruded tonalites close to the Chinese town of Mazar was part of the same arc. LA-ICP-MS U-Pb dating of zircons, together with whole rock geochemistry derived from tonalitic to granodioritic intrusions, reveals a major Visean to Bashkirian intrusive phase between 340 and 320 Ma ago. This clearly postdates Paleozoic arc-magmatic activity in the West Kunlun by ~100 Ma. This observation, along with geochemical evidence for a more pronounced mantle component in the Carboniferous arc-magmatic rocks of the North Pamir, disagrees with the common model of a continuous Kunlun belt from the West Kunlun into the North Pamir. Moreover, Paleozoic oceanic units younger than and west of the Tarim cratonic crust challenge the idea of a continuous cratonic Tarim-Tajik continent beneath the Pamir.

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

“…The hosting basalt has a flat C1-normalized REE pattern (Boynton, 1984), implying an intra-oceanic arc origin (Jiang et al, 2008;Rembe et al, 2021). We suggest a possible control of the basalt geochemistry on calcite REE patterns; any process altering this signal would significantly change the calcite REE pattern (Debruyne et al, 2016).…”

“…However, corresponding, early Paleozoic geologic events or rock records in the North Pamir have not been reported. Instead, previous works on mafic to intermediate volcanic rocks and granitoids of the North Pamir show major, subduction related, arc magmatic activity in the mid to late Carboniferous (Rembe et al, 2021;Jiang et al, 2008;Ji et al, 2018;Kang et al, 2015). Carboniferous arc magmatic rocks found in the Waqia (Tang et al, 2020) and East Mazar (Li et al, 2006) tectonic slivers, reflect the closure of a remnant ocean basin, whereas major arc magmatic activity was focused on the North Pamir arc further to the west (Figure 6b).…”

“…It changes the mineral composition completely, such that primary igneous textures are obliterated (e.g. epidosites, Honnorez, 2003 (Schwab et al, 2004), and zircon U-Pb ages of ~360 to 314 Ma from island arc granites (Ji et al, 2018;Rembe et al, 2021) (Figure 5).…”

“…show, that calcite U-Pb dating has great potential in constraining the age of oceanic crust, which is usually difficult to date radiometrically. There is a sedimentary hiatus between the Middle Pennsylvanian and the Guadalupian (Rembe et al, 2021 (Wang et al, 2021). (b) Paleogeographic situation in the upper…”

“…The North Pamir arc consists of poorly dated mafic and intermediate volcanics, associated volcaniclastic rocks, and subordinate cherts. A series of leucogranites and granodiorites intruded into the arc between 360 and 314 Ma (Rembe et al, 2021). The green color of the volcanic rocks implies thorough spilitization, making them unsuitable for 40 Ar/ 39 Ar dating.…”