The Petrogenesis Of Magmatic Rocks In The Shaquanzi Fe(-Cu) Deposit Area, Eastern Tian Shan, Xinjiang

The Eastern Tianshan, the eastern part of the Tianshan belt, is a key area for understanding the Paleozoic evolution of the Central Asian Orogenic Belt(CAOB) because of complicated crustal accretionary and collisional processes with intense crustal-mantle interaction during the Late Paleozoic period. The Aqishan-Yamansu belt, one of the main tectonic units between Yamansu fault and Aqikekuduke fault, is an important polymetallic belt in China and host numerous Fe(-Cu) deposits or occurrences(eg., Yamansu, Shaquanzi, Shungfengshan and Heifengshan, etc). The Shaquanzi Fe-Cu deposit, located at the Aqishan-Yamansu belt of eastern Tianshan, is one of deposits hosted in Paleozoic volcanic rocks. The deposit occurs in the second and third lithologic sections of the Dikaner Formation consisting of volcanic rocks intercalated with sedimentary rocks. The iron mineralization also occurs at contact zone between diorite-porphyrite and wallrocks.In this paper, we present the petrographic, zircon U-Pb geochronological and geochemical analyses on Dikaner Formation rhyolite, basalt and diorite-porphyrite in the Shaquanzi Fe-Cu ore district. We endeavor to constrain their dynamic mechanism and Paleozoic geological evolution history of the Eastern Tianshan. Some conclusions had been drawn:(1) LA-ICP-MS analyses of zircons with well-defined oscillatory zoning yielded mean 206Pb/238 U ages of 320.8±1.7Ma and 323.5±1.7Ma, respectively, indicating they were formed during late Early Carboniferous to early Late Carboniferous. They also restricted that the deposits hosted in the Dikaner Formation were formed after 320 Ma.(2) The LA-ICP-MS zircon U-Pb analyse on diorite yielded mean 206Pb/238 U ages of 282.5-276.3Ma, which was formed on Early Permian.(3) The rhyolite and diorite-porphyrite have different magma sources although they formed in the same period magmatism. The rhyolite samples belong to calcalkaline series with high Na2 O contents and display obvious positive anomaly of Th, U and K with negative anomaly of Ba, Sr, P, Ti and Eu(0.40~0.46). The zircons from rhyolite have high εHf(t) values(+6.28~+15.51), indicating a source dominated by juvenile crustal materials. The characteristics of elements geochemical of dioriteporphyrite indicate that they origins from mantle wedge modified by fluids from subducted materials.(4) The regional geology and geochemical evidence indicate that the Dikaner Formation volcanic rocks and diorite-porphyrite were the products of island arc magmatism during the late stage of subduction.(5) The Paleozoic Asia Ocean had been closed in the Early Permian.