Carboniferous to Permian Tectonic Transition of the North Tianshan Belt (NW China): Insights From an Inverted HT‐LP Metamorphic Sequence in the Harlik Range

The North Tianshan Belt in the southwestern Central Asian Orogenic Belt (CAOB) provides unique insights into crustal evolution and geodynamic processes of accretionary orogeny. Here, we present new structural, thermobarometric and geochronological data from the Xiaopu Metamorphic Complex (XMC) in the eastern North Tianshan. Structural analysis indicates that an initial shortening phase (D1), which produced NW‐SE‐striking folds, was followed by a sinistral transtension (D2). The latter is characterized by syn‐kinematic crystallization of peak mineral assemblages, suggesting an inverted Buchan‐type metamorphic sequence. Subsequent strike‐perpendicular extension (D3) likely facilitated the exhumation of the XMC. Phase modelling and geothermobarometry show a progressive increase in peak temperature from the andalusite–staurolite zone (~580°C) to the sillimanite–migmatite zone (~690°C) at nearly constant pressure (~4 kbar), indicating a high‐temperature and low‐pressure (HT‐LP) thermal regime consistent with an extensional setting. U–Pb dating on zircon, monazite, and apatite indicates that D2 occurred at ~330–310 Ma, coeval with the HT‐LP metamorphism (320–310 Ma), and that D3 occurred at ~285 Ma. Biotite 40 Ar/ 39 Ar dating confirms syn‐/post‐D3 cooling (298–275 Ma). We suggest that magmatic intrusion controlled by transtension at the mid‐crustal level and asymmetric exhumation likely formed the inverted Buchan‐type metamorphic sequence. Our new results, together with regional data, reveal the late Palaeozoic tectono‐metamorphic evolution of the southwestern CAOB, involving arc–arc accretion, back‐arc transtension, and post‐orogenic extension. These processes governed the tectonic transition from shortening to extension in the mid‐crust of arc systems and induced magmatic intrusion and crustal exhumation during the final stages of accretionary orogeny.