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The late Cenozoic Kongur Shan extensional system lies along the northeastern margin of the Pamir at the western end of the Himalayan-Tibetan orogen, accommodating east-west extension in the Pamir. At the northern end of the extensional system, the Kongur Shan normal fault juxtaposes medium-to high-grade metamorphic rocks in both its hanging wall and footwall, which record several Mesozoic to Cenozoic tectonic events. Schists within the hanging wall preserve a Buchan metamorphic sequence, dated as Late Triassic to Early Jurassic (230-200 Ma) from monazite inclusions in garnet. Metamorphic ages overlap with U-Pb zircon ages from local granite bodies and are interpreted to be the result of regional arc magmatism created by subduction of the Paleo-Tethys ocean. The northern portion of the footwall of the extensional system exposes an upper-amphibolite-facies unit (~650 °C, 8 kbar), which structurally overlies a lowgrade metagraywacke unit. The high-grade unit records late Early Cretaceous crustal thickening at ca. 125-110 Ma, followed by emplacement over the low-grade metagraywacke along a north-northeast-directed thrust prior to ca. 100 Ma. Together these results indicate signifi cant middle Cretaceous crustal thickening and shortening in the northern Pamir prior to the Indo-Asian collision. A third Late Miocene (ca. 9 Ma) amphibolite-facies metamorphic event (~650-700 °C, 8 kbar) is recorded in footwall gneisses of the Kongur Shan massif. North of the Kongur Shan massif, rapid cooling in the footwall beginning at 7-8 Ma is interpreted to date the initiation of exhumation along the Kongur Shan normal fault. A minimum of 34 km of east-west extension is inferred along the Kongur Shan massif based on the magnitude of exhumation since the Late Miocene (~29 km) and the present dip of the Kongur Shan normal fault (~40°). Field observations and interpretation of satellite images along the southernmost segment of the Kongur Shan extensional system indicate that the magnitude of late Cenozoic east-west extension decreases signifi cantly toward the south. This observation is inconsistent with models in which east-west extension in the Pamir is driven by northward propagation of the right-slip Karakoram fault, suggesting instead that extension is driven by vertical extrusion due to topographic collapse, radial thrusting along the Main Pamir Thrust, or oroclinal bending of the entire Pamir region.

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We report four late Palaeozoic zircon sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages for granitic plutons from the Inner Mongolia Palaeo-uplift on the northern margin of the North China block. These cast a new light on the poorly understood tectonic history of the northern margin of the North China block and the Central Asian Orogenic Belt during the late Palaeozoic. The plutons have for a long time been considered to belong to the early Precambrian basement of the North China block. Our new SHRIMP U-Pb zircon dating of four plutons at Longhua, Daguangding, Boluonuo and Hushiha has yielded intrusive ages of 311 AE 2 Ma, 324 AE 6 Ma, 302 AE 4 Ma and 310 AE 5 Ma, respectively. Geochemical data suggest that these granitoids have a calc-alkaline, subduction-related I-type signature, indicating the existence of an Andean-style continental arc along the northern margin of the North China block during the late Palaeozoic. Our results also indicate that the Palaeo-Asian Ocean still existed during latest Carboniferous-earliest Permian time, and that the final collision between the southern Mongolia composite terranes and the North China block occurred later than c. 290 Ma. We suggest that the northern margin of the North China block was an active continental margin and the Inner Mongolia Palaeo-uplift is a deeply exhumed mid-crustal 'root' of a late Palaeozoic Andean-style continental arc.

Recent zircon dating identified several late Carboniferous to early Permian hornblende gabbro-diorite-quartz diorite-granodiorite-tonalite-granite plutons in lithological assemblages at the northern margin of the North China Block (NCB) that were previously regarded as Archaean to Palaeoproterozoic. Our geochronological results indicate that emplacement of these plutons was a continuous process during the late Carboniferous to early Permian, from 324 ± 6 to 274 ± 6 Ma, and lasted for at least 50 Ma. In this paper, the early Permian components with compositions from gabbro to granite within the intrusive complex were studied. The early Permian plutons exhibit calc-alkaline or high-K calc-alkaline, metaluminous geochemical features and highly variable SiO 2 contents. They have no significant Eu anomaly in their REE patterns, and in primitive-mantle-normalized spidergrams they display depletion in Th, U, Nb, Ta, P and Ti, and enrichment in Ba, K, Pb and Sr. The granitoid bodies within these plutons display I-type and adakitic geochemical signatures. The early Permian rocks exhibit low whole-rock initial 87 Sr/ 86 Sr ratios from 0.70520 to 0.70615 and have negative whole-rock e Nd (t) values ranging from -17.4 to -9.3 and zircon e Hf(t) values of -23.2 to -10.5. The gabbros exhibit higher e Nd (t) values from -11.1 to -9.3 and e Hf (t) values from -16.5 to -10.5, and one granodiorite exhibits an even lower e Nd (t) value of -17.4 and zircon e Hf (t) values of -23.2 to -15.1. Geochemical, Sr-Nd and in situ zircon Hf isotopic compositions suggest that the hornblende gabbros were derived from a metasomatized lithospheric mantle, and the diorite and quartz diorite were generated from a gabbroic magma by fractional crystallization, coupled with differential assimilation of ancient lower crustal material. The granodiorite was likely derived from partial melting of ancient lower crust with involvement of some mantle components. Involvement of both lithospheric mantle and ancient lower crust in the generation of the early Permian plutons indicates strong crust-mantle interaction in the northern NCB. Petrological associations as well as geochemical and Sr-Nd-Hf isotopic results show that the early Permian plutons were emplaced along an Andean-type active continental margin during southward subduction of the Palaeo-Asian oceanic plate beneath the NCB. Integration of our results with previously published data for late Carboniferous and late Permian to middle Triassic intrusions suggests that the continental arc on the northern margin of the NCB existed for at least 50 Ma during the late Palaeozoic, and final amalgamation of the Mongolian arc terranes with the northern NCB likely occurred during a period from *270 to *250 Ma, i.e, in the late Permian to earliest Triassic.Electronic supplementary material The online version of this article (

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