Final amalgamation of the Tianshan and Junggar orogenic collage in the southwestern Central Asian Orogenic Belt: Constraints on the closure of the Paleo-Asian Ocean

OIB-type rocks within West Junggar ophiolitic mélanges: Evidence for the accretion of seamounts

We report two newly identified Ordovician ophiolite belts in west Junggar, NW China:
 Tajin–Tarbahatai–Kujibai–Honguleleng (TTKH) and Tangbale–Baijiantan–Baikouquan (TBB)
 ophiolitic belts. These two ophiolitic belts provide constraints for the Palaeozoic
 reconstruction of Central Asia and the geological evolution of this region. The TTKH and
 TBB ophiolitic belts are dismembered parts of different ophiolitic belts which represent
 relics of Ordovician oceanic floor; they subducted to the north under the
 Chingiz–Tarbahatai arc and to the south under the Junggar plate, respectively. The
 Baijiantan–Baikouquan ophiolite melanges comprise the major part of the TBB. Flat rare
 Earth element (REE) patterns with positive Eu anomalies and insignificant depletion of
 high-field-strength elements (HFSE) relative to melts of primitive mantle suggest a
 mid-ocean-ridge basalt (MORB) origin for the metagabbro. Lherzolite samples define a Sm–Nd
 isotopic isochron with age of 474 Ma and
 ɛ Nd( t ) of +8.9. Lherzolite samples with
 positive ɛ Nd( t ) values of +8.8 to +9.1 and
 initial 87 Sr/ 86 Sr ratios of 0.7037–0.7040 are rather homogeneous in
 Sr–Nd isotopic composition, whereas metagabbro samples show wider Sr–Nd isotopic
 compositional ranges with ɛ Nd( t ) of +5.9 to
 +11.0. The Sm–Nd isotopic isochron age ( c. 380 Ma) for garnet amphibolite
 samples, consistent with a zircon U–Pb age ( c. 385 Ma) for metagabbro,
 represents a magmatic event prior to subduction. Thermodynamic calculations for garnet
 amphibolite yield a clockwise pressure–temperature path with peak metamorphic condition of
 c. 15 kbar and 520–560°C at 342 Ma, indicating a subduction-channel
 setting. The Rb–Sr isochron ages (335 Ma, 333 Ma) for metagabbro represent a metamorphic
 event during exhumation.

/pdf/geology-and-geochemistry-of-the-baijiantan-baikouquan-20b0e1tjw2.pdf

Geology and geochemistry of the Baijiantan-Baikouquan ophiolitic mélanges: implications for geological evolution of west Junggar, Xinjiang, NW China

Spatial–temporal framework for the closure of the Junggar Ocean in central Asia: New SIMS zircon U–Pb ages of the ophiolitic mélange and collisional igneous rocks in the Zhifang area, East Junggar

The Junggar–Balkhash Ocean was a major branch of the southern Paleo-Asian Ocean. The timing of its closure is important for understanding the history of the Central Asian Orogenic Belt. New sedimentological and geochronological data from the Late Paleozoic volcano-sedimentary sequences in the Barleik Mountains of West Junggar, NW China, help to constrain the closure time of the Junggar–Balkhash Ocean. Tielieketi Formation (Fm) is dominated by littoral sediments, but its upper glauconite-bearing sandstone is interpreted to deposit rapidly in a shallow-water shelf setting. By contrast, Heishantou Fm consists chiefly of volcanic rocks, conformably overlying or in fault contact with Tielieketi Fm. Molaoba Fm is composed of parallel-stratified fine sandstone and sandy conglomerate with graded bedding, typical of non-marine, fluvial deposition. This formation unconformably overlies the Tielieketi and Heishantou formations and is conformably covered by Kalagang Fm characterized by a continental bimodal volcanic association. The youngest U–Pb ages of detrital zircons from sandstones and zircon U–Pb ages from volcanic rocks suggest that the Tielieketi, Heishantou, Molaoba, and Kalagang formations were deposited during the Famennian–Tournaisian, Tournaisian–early Bashkirian, Gzhelian, and Asselian–Sakmarian, respectively. The absence of upper Bashkirian to Kasimovian was likely caused by tectonic uplifting of the West Junggar terrane. This is compatible with the occurrence of coeval stitching plutons in the West Junggar and adjacent areas. The Junggar–Balkhash Ocean should be finally closed before the Gzhelian, slightly later or concurrent with that of other ocean domains of the southern Paleo-Asian Ocean.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017TC004606

Closure Time of the Junggar-Balkhash Ocean: Constraints From Late Paleozoic Volcano-Sedimentary Sequences in the Barleik Mountains, West Junggar, NW China

Recently, new geochronological data and geological observations including the discovery of garnet amphibolite, Ordovician micro-fossils, unconformable contact between the ophiolitic melange related flysch and the Devonian to Early Carboniferous terrestrial volcano-sedimentary strata provide critical evidences for Paleo-environmental reconstruction in the western Junggar (Xinjiang, China). Two different geological layers could be clearly identified: the Early Paleozoic metamorphic terrane mainly consists of ophiolitic melange and flysch, and the Late Paleozoic volcano-sedimentary units lying on the ophiolitic melange and flysch. Both of these layers were intruded by granitic to dioritic magma during the Late Carboniferous to Early Permian period. Based on these data, a new geological map for the western Junggar has been compiled, which is essential not only for better understanding of the geological evolution but also for exploration of mineral resources.

/pdf/a-new-geological-map-of-the-western-junggar-north-xinjiang-3m1y3htp9b.pdf

A New Geological Map of the Western Junggar, North Xinjiang (NW China): Implications for Paleoenvironmental Reconstruction

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Geology and geochemistry of the Baijiantan-Baikouquan ophiolitic mélanges: implications for geological evolution of west Junggar, Xinjiang, NW China

A New Geological Map of the Western Junggar, North Xinjiang (NW China): Implications for Paleoenvironmental Reconstruction