Mineral Geochemical Characteristics And Genetic Mechanism Of Olivine Rocks In Shangnan, Shanxi

Qinling orogenic belt which in central of China is the combination of two continental blocks: North China block and Yangtze block.The Study on Qinling orogenic belt has being a reashrch focus in the geology field.The Shang-Dan fault was suggested to be amainsutureoftheQinling orogeny belt.Songshugouperidotite body located at the northern of Shang-dan fault in Shangnan,.There outcrop of the biggestarea of olivinite rocks in china.The genesis of the rocks has been a matter of dispute for decades.The bone of contention in genesis of the rocks focuses on whether it is a ophiolite association or not. It′s of critical importance for resuming formations and evolution of the Qinling orogenic belt. This paper chooses Songshugou olivinite rocks as the research object, On the basis of field investigations- petrology, geochemistry and mineral trace elements to discusses the genesis of the rocksand analysis their diagenetic tectonic environment anddeduce the forming process of Qinling orogenic belt .Someachievementsareasfollowing:1,The results based upon the field investigation showed that:Songshugou olivinite rocksconsist of dunite, diopside peridotiteanddiopsidite. A typical symme- trical structure has formed from the edge to the interior of the rocks, moving in turn from the dunite intercalated with harzburgite lenses, diopside peridotite, diopsidite and then dunite with diopside strip. Thearea of these rocks reached 20 aquare kilo- meters and dunite exceed 95%.2,The structure of rocks and microscopic characteristics showed that: medium-coarse grain dunite don′thave the characteristic of plastic flow in the upper mantle butrather remnant of mylonitization.3,Changes of Chemical Components of Songshugouolivinite is very narrow,that is to say:composition of the rocks is uniformity. Besides, dunite and harzburgite have higher content in MgO (45.69%-48.27%) and lower content in A12O3(0.05%-0.73%), CaO (0.06%-0.68%),K2O(<0.2%),Na2O (0.01%-0. 18%),TiO2(<0.01%).However, diopside peridotiteshave lower content in MgO (25.74%-27.66%) and higher content in CaO (14.51%-15.24%).4,The REE patterns of Songshugou olivinite rocks are characterizedby LREE enrichment, The pattern of HREE is relatively flat. The rocks rich in incompatible elements (e.g.Ba, U, Sr.) and low in HREE.Mineral geochemistry features shows: Songshugou olivinite rocks have the same origin of magmatic. 5,There is no podiform chromitite in the rocks. Contrasted spinels in Songshugou olivinite rocks with the spinels in different blocks under different tectonic conditions of china,the resultsshowthat spinels′composition in this area is diffident from the composition of spinels which from mantle peridotite belonged to the typical Ophiolite suite and cumulate rocks but same to the composition of spinels in the intrusive complex rocks.6,The characteristic of petrological, element geochemical and composition of spinel, olivine, pyroxene shows that : There are significant differences in Songshugou olivinite rocks and residual mantle rock at the bottom of Ophiolite.The diopside peridotitesveinson the edge of the olivinite rock mass is the product of basic magma formed by fusible components when magmatic activities and tectonism.