Geochemistry And Tectonic Significance Of Malic-ultramafic Rocks Of Wengeng Region In Urad Middle Banner Of The Inner Mongolia

Wengeng region in Urad Middle Banner of the Inner Mongolia emerges a strip ofmafic-ultramafic complex zone which is less than10km width and expands100km towardNEE and NWW directions. This mafic-ultramafic complex zone is constituted by more thanone basic-ultrabasic complex rocks and its tectonic is located in the northern margin of theNorth China plate at a distance of100km north from Rhon ophiolitic melange belt. Thistwo rock zones form the mafic-ultramafic complex zone and possess more importantmeaning in the tectonic directing.Ultrabasic complex rock outcropping in Wengeng region is shown most in zonalstructure and the later formed ultrabasic rocks invade into the former mafic facies thuscompose the nucleus of zone. Lithological association is consist of ultrabasic rocks such asserpentinized dunite、coarse-grained serpentinized peridotite、medium to coarse grainedsubamphiboled pyroxenolite、hornblende pyroxenolite and mafic rocks such as hyperite、norite、amphibolite gabbro and fine-grained subamphiboled gabbro. The major elementsof MgO、 CaO、Al₂O₃、K₂O+Na₂O、TFeO、MnO and transition elements Cr is well relatedand possessing the character of allite weathered and silicon depleted; Trace elements inprimitive mantle normalized diagram appears the same evolution regular;Rare earth elements and transition element primitive mantle normalized diagram showcontinuous characteristic in which the curve of Rare earth and excessive elements of theultrabasic rocks is relatively smooth， having the trait of initial mantle; Rare earth elementsin the mafic rocks in the standardized diagram was right-wing explaining the fractionationof light rare earths elements and heavy rare earth elements. The transition elements Ni、Crobviously show the ‘W’ shape of loss having the trait of partial melting of primitivemantle;the value of⁸⁷Sr/⁸⁶Sr is between0.706592-0.70719，which scope is small and thespecific value is large;The specific value of⁴³Nd/¹⁴⁴Nd is between0.51191and0.51225，which shows low value possessing the characteristic of enriched mantle. Most rocks inWengeng igneous complex belong to Calc-alkaline magmatic evolution sequence，anothersmall amount of igneous complex belong to tholeiitic evolutionary sequence. The value ofLa/Nb and La/Sm、（La/Nb）_N-（Th/Ta）_Nand Pb isotopic characteristics of igneouscomplex show it suffered crustal contamination which is most from the upper crust when itemplaced. In the tectonic discrimination diagrams of different trace element， the samples are mainly distributed in and around arc volcanic rocks. The constructor property issqueezed environment In the case of dive.formation and evolution process of miscellaneous magma is as below: in theenvironment of the ancient Asian ocean plate subduction to the North China plate， theprimitive mantle was partial melting and Diapir rising as the subducting oceanic crustheating dehydration. Thus it forms the volcanic arc basic-ultrabasic igneous complexwhich is contaminated with the upper crust bringing by the subducting plate.