Birth, life, and demise of the Andean–syn‐collisional Gissar arc: Late Paleozoic tectono‐magmatic‐metamorphic evolution of the southwestern Tian Shan, Tajikistan

Abstract

The amalgamation of the Central Asian Orogenic Belt in the southwestern Tian Shan in Tajikistan is represented by tectono‐magmatic‐metamorphic processes that accompanied late Paleozoic ocean closure and collision between the Karakum‐Tarim and Kazakh‐Kyrgyz terranes. Integrated U‐Pb geochronology, thermobarometry, pseudosection modeling, and Hf geochemistry constrain the timing and petro‐tectonic nature of these processes. The Gissar batholith and the Garm massif represent an eastward, along‐strike increase in paleodepth from upper‐batholith (~21–7 km) to arc‐root (~36–19 km) levels of the Andean–syn‐collisional Gissar arc, which developed from ~323–288 Ma in two stages: (i) Andean, I‐type granitoid magmatism from ~323–306 Ma due to northward subduction of the Gissar back‐arc ocean basin under the Gissar microcontinent, which was immediately followed by (ii) syn‐collisional, I‐S‐type granitoid magmatism in the Gissar batholith and the Garm massif from ~304–288 Ma due to northward subduction/underthrusting of Karakum marginal‐continental crust under the Gissar microcontinent. A rapid isotopic pull‐up from ~288–286 Ma signals the onset of juvenile, alkaline‐syenitic, post‐collisional magmatism by ~280 Ma, which was driven by delamination of the Gissar arclogite root and consequent convective asthenospheric upwelling. Whereas M–HT/LP prograde metamorphism in the Garm massif (650–750°C/6–7 kbar) from ~310–288 Ma was associated with subduction‐magma inundation and crustal thickening, HT/LP heating and decompression to peak‐metamorphic temperatures (~800–820°C/6–4 kbar) at ~288 ± 6 Ma was driven by the transmission of a post‐collisional, mantle‐derived heat wave through the Garm‐massif crust.

Final Assembly of the Southwestern Central Asian Orogenic Belt as Constrained by the Evolution of the South Tianshan Orogen: Links With Gondwana and Pangea

“…Therefore, these data reveal that the final suturing of the southwestern CAOB was achieved by northward subduction of the South Tianshan Ocean and subsequent collision of the CTB and the Karakum-Tarim cratons at~320 Ma. Notably, recent studies suggest that a trench-arc-back-arc basin system developed in the northern Karakum during Carboniferous times Worthington et al, 2017), which differs from the here suggested tectonic evolution that favors a transition of the northern Tarim Craton from a trench-arc-back-arc system to a passive margin at~390-380 Ma.…”

The Tajik Basin: A composite record of sedimentary basin evolution in response to tectonics in the Pamir

“…No significant exposures of magmatic rocks younger than ca. 250 Ma exist in the westernmost Tian Shan (Käßner et al, ; Worthington et al, ). Older, Paleozoic zircon U–Pb age populations could have been derived from either the Tian Shan or the Pamir Mountains.…”

“…Basement in the Tajik Basin consists of Proterozoic to Paleozoic continental crust that was accreted onto Asia during the late Carboniferous to early Permian (Burtman & Molnar, ; Schwab et al, ). Carboniferous to Permian igneous and metamorphic rocks associated with this subduction–accretion event are widely exposed in the westernmost Tian Shan Worthington et al, ) (Figure b). Permian and Triassic sedimentary rocks are locally present on the Tajik Basin margins and are thought to be locally present at depth (Nikolaev, ) (Figure b).…”

“…The westernmost Tian Shan is part of the Central Asian Orogenic Belt and is chiefly comprised of Permian igneous and metamorphic rocks associated with the Gissar arc and by late Paleozoic metavolcanic and metasedimentary rocks associated with the Zaravshan subduction–accretion complex (Figure b) (Käßner et al, ; Worthington et al, ). Uplift and erosion of the western Tian Shan began during the early Miocene and has accelerated since ca.…”

Source-to-sink dynamics in the Kyrgyz Tien Shan from the Jurassic to the Paleogene: Insights from sedimentological and detrital zircon U-Pb analyses

“…2). In the MTS and NTS, Pennsylvanian -Early Permian ages are mainly reported from the Chatkal-Kurama mountain ranges and Hercynian granitoids also occur to a minor extent in mountain ranges adjacent to the Naryn and Issyk-Kul basins (Alekseev et al, 2009;Glorie et al, 2010;De Grave et al, 2011;Seltmann et al, 2011;Macaulay et al, 2016 and references therein;Konopelko et al, 2017b;Worthington et al, 2017) (Fig. 2).…”