Discovery of the Late Silurian volcanic rocks in the Dazhonghe area, Yunxian-Jinggu volcanic arc belt, western Yunnan, China and its geological significance

作者：Mao XiaoChang; Wang LiQuan; Li Bing; Wang BaoDi; Wang DongBing; Yin FuGuang; Sun ZhiMing

来源：Acta Petrologica Sinica, 2012, 28(5): 1517-1528.

• Yunxian-Jinggu volcanic arc
• Late Silurian volcanic rocks
• Paleo-Tethys ocean
• Dazhonghe area

A suit of Early Paleozoic volcanic rocks was recognized from Dazhonghe area in Yunxian-Jinggu volcanic arc belt. LA-ICPMS U-Pb zircon analyses suggest that the volcanic rocks was dated at 421. 3 +/- 2. 3Ma and 418. 8 +/- 3. 5Ma. The volcanic rocks belong to calc-alkaline serie rocks, with characterized by high Al2O3(12. 73% similar to 16. 63%), Na2O (K2O/Na2O = 0. 56 similar to 0. 99) and high Mg-# (46. 0 similar to 50. 0). Furthermore, they are similar to island arc volcanic rocks of active continental margin, with characterized by enrichment of LREE, weak negative anomaly of Eu, strong negative anomalies of HFSE (Nb, Ta, Ti), positive epsilon(Nd) (t) (3. 86 similar to 4. 39) and high Th/Ta (15 similar to 17). The Late Silurian volcanic rocks in Dazhonghe area were probably generated by fractional crystallization of parent magma or assimilation of shallow crustal materials in the process of magma ascent, which partial melting of the depleted mantle wedge by metasomatism with subduction deposit. Being study in combination with the regional magmatic activities and high-metamorphic events during the same period (410 similar to 420Ma), we suggest that the island arc volcanic rocks were resulted from the eastward subduction of Paleo-Tethys ocean, which provide direct petrology evidences of forward arc and its dynamic mechanism for the formation and evolution of the Late Paleozoic Sanjiang multi-island-arc basin system in the western edge of the Yangtze block.

• 出版日期2012-5
• 单位中国地质大学（北京）; 云南省地质调查局; 成都地质矿产研究所