| Northeast Jiangxi ophiolite melange is located at the junction of Yangtze plate and Cathaysian plate.It is one of the few Neoproterozoic Ophiolites in Southeast China.It contains important information about the tectonic evolution of Jiangnan orogenic belt and even Precambrian in South China.In this study,we selected the Zhang Shudun-Xiwan OPHIOLITIC MELANGE belt in Northeast Jiangxi Province as the research object.First,we collected and sorted out the previous research results systematically.Then we went to Zhang Shudun-Xiwan area in De Xing City,Jiangxi Province to carry out field route survey,typical profile survey and outcrop scale lithologic analysis.Finally,we carried out petrology,chronology and geochemical survey on the samples from Zhang Shudun and Xiwan.The purpose of this study is to find out the age of the formation of Zhang Shudun-Xiwan ophiolite,to determine the geochemical characteristics of gabbro and basalt in the melange,to explore the tectonic background of their formation,to enrich the research data of this area,and to provide new evidence for the genesis and tectonic evolution of rocks.The main results of this study are as follows:?1?The Zhang Shudun-Xiwan ophiolite melange belt is mainly composed of serpentine body and gabbro body.The original sequence of ophiolite suite has been structurally dismembered and has obvious structural emplacement characteristics.It is in contact with the late Proterozoic shallow metamorphic sedimentary rock series in the ductile shear zone,and the basic ultrabasic rock block is in the mylonitic schist of the surrounding rock.?2?the U-Pb dating of 206Pb/238U zircon is between 920±10Ma and 1046±11 Ma,in which the weighted average age of zircon is 982.9±6 Ma?MSWD=2.8?,which represents the emplacement age of gabbro.The Zhang Shudun-Xiwan ophiolite was formed in the early Neoproterozoic.?3?the basalts in the Zhang Shudun ophiolite melange are characterized by low k,Mg,medium Ti,high Na,Al,etc.the samples in the SiO2-Nb/Y classification diagram fall in the subalkaline basalt,the samples in the SiO2-TFeO/MgO diagram fall in the tholeiite series,and the Zhang Shudun basalt belongs to the subalkaline tholeiite series.The total alkali content of gabbro in Xiwan ophiolite melange is relatively high,and the samples in SiO2-Na2O+K2O diagram are all on the alkaline gabbro,which is alkaline gabbro.?4?The trace element distribution pattern of gabbros and basalts in Zhang Shudun-Xiwan ophiolite melange is similar to that of E-MORB,which is probably the result of partial melting of mantle wedge caused by fluid metasomatism produced by plate subduction.?5?the total REE content of gabbro and basalt in Zhang Shudun-Xiwan ophiolite melange is 58.59×10-6?73.35×10-6,LREE/HREE ratio is 2.48?3.15,?La/Yb?N ratio is 1.82?2.66,which has the positive anomaly of EU and the distribution curve and REE composition similar to the enriched oceanic ridge basalt?E-MORB?.?6?The U-Pb dating,major elements,trace elements and rare earth elements test results show that the Zhang Shudun-Xiwan ophiolite was formed in the mid ocean ridge environment and originated from the depleted mantle.The subduction zone fluid metasomatized the mantle wedge and was affected by the contamination of terrigenous materials.The Zhang Shudun-Xiwan ophiolite melange has experienced the evolution of oceanic crust?1100-970 Ma?,subduction?970-870 Ma?,collision?870-800 Ma?and post collision?800 Ma?. |
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