Volcanic Rocks In The Ximemi Taiwan, Xinjiang Province

Traditionally, the volcanic rock strata of the Xiemisitai area in West Junggar is attributed to Devonian to Carboniferous. The attribution is mainly based on regional stratigraphic correlation, which lacks conclusive scientific evidence. This paper reports the two profiles of the volcanic rock strata and a detailed description of the main volcanic rock types exposed in this area. According to the unconformity contact, rock assemblages and alteration characteristics of volcanic rocks, they can be divided into two sets of volcanic rocks of different eras. On this basis, this paper provides the typical volcanic zircons U-Pb dating results and puts forward that the age(423.6-394.1Ma) of volcanic rocks in Xiemisitai area belong to the late Silurian-early Devonian instead of middle-late Devonian-Carboniferous. The late Silurian is mainly composed of andesite, dacite and mix a small amount of volcanic tuff and altered sandstone. The Middle Devonian is consists of andesitic-dacitic volcanic clastic rock with a large number of glutenite. The stratigraphic occurrence forms a monocline structure with an overall south-dipping. In addition, the tectonic attribution and the continuity of time and space of volcanic rock in the region have discussed which infer that the volcanic rock strata of Xiemisitai is the product of late Silurian Boshchekul-Chingiz magmatic arc stretches eastward from East Kazakhstan into China, which can be combined with the volcanic strata on both east and west side to constitute a suit of continuous volcanic strata of late Silurian-middle Devonian.The Xiemisitai Paleozoic volcanic rocks most have Si O2>56%,high Al2O3 content, high potassium calcium alkaline and aluminum-peraluminous characteristics. In Harker diagrams main elements Ti O2、Al2O、Ca O、Mg O and TFe O show the tendency of negative correlation with Si O2. The LREE slightly enrichment relative to HREE in the volcanic rocks,while the extent of the Eu anomalies is unconspicuous.The large-ion lithophile elements(LILE,Rb,K) have positive anomalies, the high field-strength dement(HFSE,Nb,Ta and Ti)have negative anomalies and the tectonic discrimination diagrams all indicate the volcanic rocks are belongs to subduction zone. Together with the reported ages of volcanic rocks(435Ma-391Ma),we infer that the volcanic rock strata of Xiemisitai is the product of Early Palaeozoic Boshchekul-Chingiz magmatic arc stretches eastward from East Kazakhstan into China together with a small amount of Late Palaeozoic Zharma-Saur magmatic arc. The Xiemisitai volcanic rocks are origin form mantle partial melting caused by oceanic lithosphere subduction. The magma mix with continental crust material due to the assimilation contamination or crust melt in he rising progress and experienced crystallization differentiation.Magma origin depth of about 8 km-33 km, and late Paleozoic volcanic magma origin depth is slightly deeper than the early Paleozoic magma.