Inner Mongolia Alxa Bayan Nuru NW Dike Swarm Study In Public Area

Bayan Nuru area in Alxa Zuoqi, Inner Mongolia is located in western part margin of North China craton. It is the combination positions of the North China craton, Tarim plate and Tianshan-Xingmeng orogenic belt. Our study area mainly develops N W-trending, diorite porphyrite veins and grabbro vein. And the plagioclase phenocryst with andesine and labradorite, have zonal structure, which reflected the exists of mag ma mixing.The content of each element oxide of diorite-porphyrite dikes is: SiO2 vayyjing from 58.56% to 62.90%, the content Al2O3 is higher, it is from 16.51% to 16.74%, MgO as 2.64%~3.29%(Mg# 58.73~62.78>45 and high), Na2 O / K2 O ranging from 0.95 to 1.58, the ratio of A/NK is from 1.89 to 1.99. The ratio of A/NCK is from 0.92 to 0.99, σ =2.39~3.78. The diorite-porphyrite dikes are high-K calc-alkaline series ermediate rocks which characterized by high Mg, Na, quasi aluminum.The content of each element oxide of gabbro dikes is: SiO2 49.71%~54.05%, the content of Al2O3 is high, from 15.87% to 17.32% and MgO as 4.40%~6.60%(Mg# 60.51%~64.9%>45 and high), Na2 O / K2 O ratios between 1.62~5.19; the ratio of A/NK is from 1.99 to 2.48. A/NCK ranging from 0.74 to 0.88. The gabbro dikes are high-K calc-alkaline series ermediate rocks which characterized by high Mg, Na, quasi aluminum.The higher REE content in dike, Chondrite-normalized REE patterns shows steep right deviation REE partition type, which displays the similar formation environment and the homologous magma evolution. There exists strong fractionation between LREE and HREE, including relative enrichment in LREE, relative depletion in HREE. The diorite porphyrite veins has Eu depletion(δEu=0.85~ 0.97). Plagioclase residue may exists in source area after the fractional crystallization of plagioclase to a certain extent. The extremely depleted-HREE may result from gamet in source area. Positive Eu anomaly(δEu =1.02~1.07)in grabbro dikes displays the probable residual pyroxene and the hornblende in origin region. And the primitive mantle-normalized graph also show relative enrichment in LILE such as Ba,K, and depletion in HFSE, such as Th, Y, Nb, Ta.According to the petrogeochemical characteristics of Bayan Nur area,we can jud ge that, the dike of this area may have originated from partial melting of thickened l ower crust and may have reacted strongly with surrounded mantle materials,formed by the process of final invasion.Diorite-porphyrite dike and gabbro dike are both intraplate basalt. In combinatio n with regional geological background, it is considered that the dikes on study area ar e intraplate prodcucts. There was a N-S extension, theoretically, it should form northeastern and northwestern dikes, but the northeastern dikes were not developed. Therefore, the final dikes were northwestern.Dikes intruded into the early Permian biotite monzonitic granite. The dating of zircon from dikes determined by LA-ICP-MS yields age of 241.0 + 3.2Ma(MSWD=0,018),the age of the dikes is Middle Triassic.