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Tajik Basin and Southwestern Tian Shan, Northwestern India-Asia Collision Zone: 3. Preorogenic to Synorogenic Retro-foreland Basin Evolution in the Eastern Tajik Depression and Linkage to the Pamir Hinterland

Abstract : The Tajik basin archives the orogenic evolution of the Pamir hinterland. Stratigraphic‐sedimentologic observations from Cretaceous‐Pliocene strata along its eastern margin describe the depositional environment and basin‐formation stages in reaction to hinterland exhumation and basin inversion. During the Late Cretaceous‐Eocene (preorogenic stage: ~100–34 Ma), a shallow‐marine to terrestrial basin extended throughout Central Asia. An alluvial plain with influx of conglomerate bodies (Baljuvon Formation) indicates a first pulse of hinterland erosion and foreland‐basin formation in the late Oligocene‐early Miocene (synorogenic stage Ia: ~34–23 Ma). Further hinterland exhumation deposited massive alluvial conglomerates (Khingou Formation) in the early‐middle Miocene (synorogenic stage Ib: ~23–15 Ma). Westward thickening growth strata suggest transformation of the Tajik basin into the Tajik fold‐thrust belt in the middle‐late Miocene (synorogenic stage IIa: ~15–5 Ma). Increased water supply led to the formation of fluvial mega‐fans (Tavildara Formation). Latest Miocene‐Pliocene shortening constructed basin morphology that blocked sediment bypass into the central basin from the east (Karanak Formation), triggering drainage‐system reorganization from transverse to longitudinal sediment transport (synorogenic stage IIb: < ~5 Ma). Accelerated shortening (~27–20 Ma) and foreland‐directed collapse (~23–12 Ma) of Pamir‐plateau crust loaded the foreland and induced synorogenic stages Ia and Ib. Coupling of Indian and Asian cratonic lithospheres and onset of northward and westward delamination/rollback of Asian lithosphere (i.e., lithosphere of the Tajik basin) beneath the Pamir at ~12–11 Ma transformed the Tajik basin into the Tajik fold‐thrust belt (synorogenic stage IIa). The timing of the sedimentologically derived basin reconfiguration matches the thermochronologically derived onset of Tajik‐basin inversion at ~12 Ma.
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Ralf Dedow, Matthias Franz, Adam Szulc, Jörg Schneider, Jan Brückner, et al.. Tajik Basin and Southwestern Tian Shan, Northwestern India-Asia Collision Zone: 3. Preorogenic to Synorogenic Retro-foreland Basin Evolution in the Eastern Tajik Depression and Linkage to the Pamir Hinterland. Tectonics, American Geophysical Union (AGU), 2020, 39 (5), pp.e2019TC005874. ⟨10.1029/2019TC005874⟩. ⟨insu-02873588⟩

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