Research On Ancient Arc-basain System Of Kangguertage In Eastern Tianshan, Xinjiang

Tectonically, the Kangguertage is a very important area to understand its metallogenic background and the tectonic evolution of eastern Tianshan section in Central Asia Oregon. However, there are lots of disputes and controversy on the tectonic setting and metallogenic background of the Kangguertage in eastern Tianshan, because of the uncertainty of Kangguertage Ophiolite. Through the research for rock assembly including metamorphic peridotite, cumulate peridotite, gabbro, plagiogranite, diabase, basalt, form south and southwest Kangguertage, we confirm that this rock sequence is a typical ophiolite suit. Harzburgite serpentinized (metaperidolite), serpentinized pyroxenite, altered grabbro in Kangguertage ophiolite are similar to the corresponding rocks in Troodos ophiolite, all low in K. MgO/ (MgO+TFeO) ratios of metamorphic peridotite ranges in 0.83—0.87, and TiO₂ (Wt%) is 0.02%, which is consistent with metamorphic peridotite in SSZ-type ophiolite. Geochemistry of basalt and diabase demonstrates they are of MORB characteristic, with Nb negative anomaly, and the environment discriminations suggest that the ophiolite may form in a SSZ-type back-arc basin serves behind a intra-oceanic arc. The radiolarian silicalite, have Al₂O₃/(Al₂O₃+Fe₂O₃) average ratios at 0.047, MnO/TiO₂ value 0.93, Ce negative anomaly and Ce/Ce^* equal to 0.548 and La_n/Ce_n ratio 1.661, indicating that the tectonic environment of radiolarian silicalite relate closely to MOR. The SHRIMP Zircon dating of gabbro (494±10 (2σ) Ma) suggest it is of Late-Cambrian to Early-Ordovician age. The ¹⁴³Nd/¹⁴⁴Nd ratios of gabbro, basalt, plagiogranite and keratophyre range in 0.512842⁰.513328, ε_Nd(t) are +5.7⁺10.5, which indicate that Kangguertage ophiolite derived from a depleted mantle, did not suffered_from obvious crustal contamination and possess similar Nd isotopic composition with Jungger terrane. (⁸⁷Sr/⁸⁶Sr)_i ratio ranges in0.703475-0.704923, which is comparable with form fresh basalts the modern oceanic ridge. Information and data mentioned above indicate that Kangguertage ophiolite is ancient oceanic crust relics of Paleozoic Northern Tianshan Ocean. Research on the Early-Paleozoic to Late-Paleozoic granites in the north of Kangguertage faults shows that the granites are all sodium rocks for calc-alkaline series;Trace elements study indicates that they formed in island arc environment at active continental margin;the granites demonstrate low 87Sr/86Sr isotopic ratios (Isr=0.7033⁰.7040) and high eNd(t) values (+9.4⁺7.2) , which are consistent with the subduction-related volcanic rocks(andesites) in western U.S, and Sierra Nevada and Peninsular Ranges Cretaceous quartz diorites in California, suggesting that the forming of granites is related to the melting of subducted oceanic crust. All these characteristics indicate that research area experienced the process, from rifting-ocean basin open, oceanic crust subduction, ocean basin to closure, a whole trench-arc-basin system in Paleozoic. The Kangguertage deep fault is the ocean basin closure belt, which may be the suture zone of Tarim block and Kazakstan-Jungger block exposed in Kangguertage area. The definition of trench-arc-basin system and suture zone in the research area provide a substantial evidence for this area's metallogenic tectonic background.