| The Yao'an alkaline volcano-plutonic complex in Central Yunnan Province is an important part of Jinshajiang-Ailaoshan-Red River alkaline porphyry belt,which is located in the west margin of Yangtze plate as well as the east side of the Jinshajiang-Ailaoshan-Red River zone.Deposit enriched metallogenic materials such as Pb,Ag,Cu,Au,and mineralized in the intra-plate with a special porphyry system,which has attracted increasing attention.However,because of its multifarious and multistage for complex,which lead to pay little attention to study such as emplacement mechanism,temporal and spatial sequence,and geodynamic process.In this paper,problems above have been determined by detailed field work and related experimental analysis such as geological survey for its structural and alteration characteristics,and SHRIMP dating,etc.By doing the research,the following main results have been achieved:?1?The Yao'an alkaline volcano-plutonic complex was mainly consisted by 5phase rocks during the same period,and the complex was formed during the Oligocene.?2?Based on the petrography and profile measurement,one complete volcanic edifice is divided,and the volcanic edifices provide the space as joints,fissure zone,and explosion breccia pipe for the emplaced and mineralized of 3rd phase porphyry rocks.?3?Based on the geological logging of structural,alteration,and mineralization,and another proof such as the Molybdenite and Pyrite Re-Os dating,showing that the polymetallic deposit mineralized is related to the emplacement of alkaline porphyry.The genetic type belongs to subvolcanic hydrothermal type Pb,Ag deposit with middle or low temperature in shallow part,and a porphyry type Cu,Mo mineralized in the deep part.?4?The major and trace element,and Sr-Nd-Hf-O isotope analysis of complex indicate that Yao'an complex was mainly originated from the partial melting of thickened lower crust,but minor residual CLM also input during the magma formed.In other side,the Os isotope values show that the source of metallogenic material was derived from mixed magma which formed in the crust-mantle transition layer.?5?The structure of vines,joints,and fractures in the area show that Yao'an complex underwent tectonic stress field of NNE-SSW trending extend and NWW-SEE trending compressive in Oligence.Thus we proposed that distribution of Yao'an complex is related to the large-scale left strike-slip shear faults in the western margin of Yangtze plate.Continuous converged and extruded by South China plate and Northern Qingtang massif resulting in the kinking of Sanjiang region,expressed by block rotation,extrusion,and shearing in the SE margin of Tibetan Plateau during the post-collision of Indian-Eurasian plate,which causing the lithospheric blocks heated and deformed,and the gravitational instability of the lithosphere increases and eventually leads to the delamination of the CLM,which caused that decompression partial melting of the thickened lower crust and CLM.Some NW-SE trending strike-slip faults and nearly E-W trending secondary extensional tectonic belts in shallow crust were formed during the transition from compressional to extensional setting.For Yao'an area in Yangtze intra-plate,the magma migrated along deep faults and eventually emplaced into E-W trending secondary structural weak zone.Ore fluids which related with phase 3rd porphyry magma precipitated and concentrated in space where as joints fissure zone,and explosion breccia pipe provided by phase 2ndd volcanic events,also where mineralized in contact zone between porphyry and surrounding rocks,and porphyry rock itself.Thus Yao'an alkaline volcano-plutonic complex and a typical porphyry type and hydrothermal type Pb-Ag-Au polymetallic deposit was formed in intra-plate under the collision tectonic background. |
PDF Full Text Request