Age Of The Kimberlitic Explosive Breccia In The Bachu Area, Xinjiang And Its Diagenetic Mechanism Research

Tarim craton is three of China’s ancient craton, has a good vision of diamond mineralization. A setof brecciated ultramafic rocks in the northwest of central uplift in the Wajilita,Tarimbasin,Western China have been found by predecessors. They found the Bachu area of theKimberley rock as rock-tube and dyke-likdistribution. This study through a field geologicalexploration, petrological and mineralogical characteristics under the microscope observation andthe LA-ICP-MS zircon U--Pb dating, elemental geochemical compositions, delved intobrecciated ultramaficiron rocks in the Bachu area to the causes of conditions, which formed in theTarim margin of C-P mantle plume magmatic events genesis.The main understanding at this stage are as follows:1. Field geological study indicated that the Bachu area of the brecciated ultramafic rock asdyke and pipe output, has been found in the rock body above38（32for the dikes, rock tubular6）.Field distribution is mainly affected by the fracture of the NWW and the NEE control.2. The rock LA-ICP-MS zircon U-Pb dating is288.5±2.6Ma, the Bachu brecciatedultramafic rocks formed in the Early Permian. This era and the C-P mantle plume development inTarim are in the same time, indicating that the kimberlitic explosive breccia rock formation maybe related to the Tarim Early Permian mantle plume. The class of alkaline ultrabasic rocksdiagenetic age provides important new information and evidence for the mantle plumemagmatism in the Tarim margin of the Permian.3. The contrast of the brecciated ultramafic rocks in Bachu and the typical kimberlite inconstant and trace element geochemical characteristics are as follows: MgO （6.16%²0.30%） islow, and TFe2O3（14.51%to15.42%） and CaO （9.50%¹9.18%） higher than the correspondingconcentration of the diamond kimberlite; Mg^#values （49.30⁷5.88） lower than the typicalkimberlite Mg^#（80.1to85.9）. The REE distribution patterns and typical of the world thekimberlite basically the same are steeply inclined to the right of a single linear distribution patterns.ΣLREE=221.57×10^-6928.28×10^-6,lowerthantheworldofkimberliteΣLREE=489.8×10^-6720.6×10^-6;（La/Yb） n ratio ranged between13.78to44.80, lower than the typical kimberlite（La/Yb） n ratios （107.6to420.3）.Comprehensive study of the outcome,we proposed that the contrast of the brecciated ultramafic rocks in Bachu and the typical kimberlite, although phenocryst minerals containing alarge number of olivine, phlogopite, apatite phenocrysts and perovskite microcrystals, but pyrope,diopside and other very low in mineral content; enrichment in LREE enrichment is lower than thetypical kimberlite rock found in the Bachu uplift pipe, dyke-like output of the brecciatedultramafic rocks is only some of the compositional characteristics of the kimberlite rock.Theformation of depth should be less than the typical kimberlite, that is not diamond prospectingpotential vision in Kimberley rock, it is recommended to be known as the kimberlitic explosivebreccias. This study is the first obtain rock diagenetic age of288.5±2.6Ma, which reveals theTarim mantle plume before about283Ma have large-scale basaltic lava eruption, with homologyto the early activities of the alkaline ultrabasic magma.