Lower Permian In The Southern Margin Of South Tianshan Basaltic Geochemical Characteristics Of Magmatic Rocks And Their Tectonic Significance

South Tianshan orogenic belt lies in the south of Tianshan Mountain Fault Zone, from Chinese Xinjiang and gansu provinces junction to uzbekistan,via kyrgyzstan, tajikistan and kazakhstan.It is an international orogenic belt of Central Asia and a typical representative of the Central Asia type of orogenic belt, and its importance was highlighted as a polymetallic ore belt and saving the important information of the Asian continental formation and evolution. The current data indicated that the Southern margin of South Tianshan had developed typically sedimentary rocks, igneous rocks and tectonic features associated with modulation of post-orogenic.Southern margin of South Tianshan developed many lower Permian volcano rocks. This paper focuses on the research of tectonic significance and geochemical characteristics of the Lower Permian Basalts of Xiaotikanlike Formation in Suxiangeken in Baicheng county in Southern margin of South Tianshan. Basalts of Xiaotikanlike Formation present black-dark gray and amygdaloidal structure, pore structure and thick-bedded blocky structure. Basalts of Xiaotikanlike Formation has porphyritic structure, and phenocrysts chiefly composed of pyroxene and plagioclase.The matrix was intergranular texture and mainly composed of plagioclase and pyroxene. Basalts of Xiaotikanlike Formation unconformably cover in Kang Kelin Group [(C2-P1)k], which was covered the Kurgan group (P2K) with unconformity. Geochemical indicators show the basalts were tholeiitic basalts, the content of Basalt SiO2basically ranged from45.98%to48.43%, RitterMann index δ are2.93, the content of Basalts TiO2ranged from1.52%to1.59%, the content of Basalts Al2O3ranged from14.77%to15.11%, Mg#ranged from53.2to55.8. Basalts show that lower FeOT, MgO, total alkali (Na2O+K2O) and higher CaO, Al2O3. relatively high K, The large ion lithophile elements (LILE), such as Rb, K, U and Ba are enriched. REE curve is harmonious on the whole and a right inclined curve. The light rare earth elements (LREE) are enriched relatively to heavy rare earth elements (HREE). That trace element distribution patterns of Basalts were" humped" showed trace element geochemical characteristics of Basalt with intraplate extensional environment.These results suggest that the tholeiitic basalts are suffered variable crustal contamination and crystallization differentiation.143Nd/144Nd=0.512849±0.000005,87Sr/86Sr=0.706845±0.000014,-10<εNd(t)<0, εSr(t)>0. These data Shows that the parent magma of basalts closely related young crust and proved that Basalts of Xiaotikanlike Formation are subjected to intense crustal contamination. According to the Nd model ages of basalt TDM (1.463279765Ga) inferred that the source rock of Basalts of Xiaotikanlike Formation likely come from the ancient materials of Tianshan orogenic belt. Combined with regional geological research about Early Permian post-collisional granites, we concluded that the basalts in early Permian was in rift of extensional settings. Futher more, in early Permian, the south of south Tianshan is in the stage of modulation of post-orogenic. After the Peripheral foreland basin is elongation settings.