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岩石学报 2011
LA-MC-ICP-MS zircon U-Pb dating of Longxianggai pluton in Dachang of Guangxi and its geological significance
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Abstract:
The Longxianggai pluton is a multiple-intruded in the middle of the Dachang ore field of Guangxi. Although the former researchers had carried out some dating on the rock intruded in some stages, so far systematic chronology study about its multi-stage magmatic intrusions has not done. Based on analyzing the interior structures of zircons by the CL technology, in-situ zircon U-Pb dating was performed with LA-MC-ICP-MS and reliable 206Pb/238U age data in fine-grained zircon were obtained. The results show that Longxianggai pluton was formed in three staged, that is, 103.8~102Ma,96.6~93.86Ma and 91~85.1Ma, and 96.6~93.86Ma is the main magmatic period. In the first stage, medium-fine-grained biotite granite with porphyritic (96.6±2.5Ma) and fine-grained biotite granite with porphyritic (94.3±2.2Ma) was formed. In the second stage, medium-fine-grained equigranular biotite granite (96.1±2.0Ma). In the third stage, the porphyraceous biotite granite (93.86±0.84Ma) was formed. The boundary between the rocks is clear and has no chilled margin, which indicates that magmatism forming Longxiagngai pluton is a continuous pulse process. The formation of zinc-copper ore body and tin-polymetallic ore body is closely related with the second magmatic period of the Longxianggai pluton and the mineralization process was completed in a short time. This information period of the Longxianggai pluton is the same as the large-scale mineralization of 110~80Ma in eastern China, and its digenesis and mineralization may be related to lithosphere extension.
