CAJ | 학술논문

塔里木地块西北缘的阔什布拉克钾长花岗岩富碱(Na_2O+K_2O平均8.36%＞8%),富钾(K_2O/Na_2O=1.27～1.47),准铝质(A/CNK=0.82～0.88),属于高钾钙碱性系列岩浆岩.岩石的稀土含量较高(∑REE=263.90×10~(-6)～445.75×10~(-6)),富集Th、u、Ta、Nb、Hf和Y等高场强元素和大离子亲石元素Rb,具有强的负Eu异常(8Eu=0.003～0.019),富集高不相容元素(Zr+Nb+Ce+Y=368×10~(-6)～531×10~(-6)＞350×10~(-6)),高Ga(Ga/Al×10000=4.17～4.72＞2.6),显示出A型花岗岩的地球化学特征.岩石Th/U比值(平均为3.86)、Nb/Ta比值(平均为12.75)和Rb-Th富集、Ti亏损指示其壳源成因.对花岗岩进行的LA-ICP-MS微区原位锆石U-Pb定年结果表明,花岗岩的结晶侵位年龄为275.4±2.8 Ma.综合西南天山与塔里木盆地早二叠世花岗质岩浆活动的特点,认为早二叠世西南天山的后碰撞岩浆活动不仅在西南天山内部引起了强烈的花岗质岩浆活动,而且对塔里木地块西北边缘的花岗质岩浆活动也有显著的影响.阔什布拉克A型花岗岩也说明西南天山地区的碰撞造山作用在275.4±2.8 Ma之前已经趋于结束,以南天山洋盆为代表的古亚洲洋已基本结束了其演化历史.
탑리목지괴서북연적활십포랍극갑장화강암부감(Na_2O+K_2O평균8.36%＞8%),부갑(K_2O/Na_2O=1.27～1.47),준려질(A/CNK=0.82～0.88),속우고갑개감성계렬암장암.암석적희토함량교고(∑REE=263.90×10~(-6)～445.75×10~(-6)),부집Th、u、Ta、Nb、Hf화Y등고장강원소화대리자친석원소Rb,구유강적부Eu이상(8Eu=0.003～0.019),부집고불상용원소(Zr+Nb+Ce+Y=368×10~(-6)～531×10~(-6)＞350×10~(-6)),고Ga(Ga/Al×10000=4.17～4.72＞2.6),현시출A형화강암적지구화학특정.암석Th/U비치(평균위3.86)、Nb/Ta비치(평균위12.75)화Rb-Th부집、Ti우손지시기각원성인.대화강암진행적LA-ICP-MS미구원위고석U-Pb정년결과표명,화강암적결정침위년령위275.4±2.8 Ma.종합서남천산여탑리목분지조이첩세화강질암장활동적특점,인위조이첩세서남천산적후팽당암장활동불부재서남천산내부인기료강렬적화강질암장활동,이차대탑리목지괴서북변연적화강질암장활동야유현저적영향.활십포랍극A형화강암야설명서남천산지구적팽당조산작용재275.4±2.8 Ma지전이경추우결속,이남천산양분위대표적고아주양이기본결속료기연화역사.
The Kuoshibulak granites located in the northwestern margin of the Tarim Basin are highK calc-alkaline series,and rich in alkali(Na_2O+K_2O averages 8.36%＞8%)and K(K_2O/Na_2O=1.27～1.47),with the A/CNK values between 0.82 and 0.88,which fall into the range of metaluminous rocks.The rocks with large negative Eu anomaly(δEu=0.003～0.019)are also characterized by enrichment of REE(ΣREE=263.90×10~(-6)～445.75×10~(-6)),HFS elements such as Th,U,Nb,Hf,Y,LILE elements such as Rb,highly incompatible elements(Zr+Nb+Ce+Y=368×10~(-6)～531×10~(-6)＞350×10~(-6))and high-Ga(Ga/Al×10 000=4.17～4.72＞2.6).The geochemical features of the rocks are similar to that of A-type granites.Rb-Th richment,Ti-depletion and the elemental ratios of the Kuoshibulak granites,such as the Th/U(averages 3.86),Nb/Ta(averages 12.75)indicate that it probably derived from crustal source.In situ zircon U-Pb LA-ICP-MS dating on the magmatic zircons yielded an age of 275.4±2.8 Ma,representing the emplacement age of the granites.Combined with Early Permian granitoid magmatism in the southwestern Tianshan orogen and Tarim Basin,it is suggested that the Early Permian post-collisional granitoid magmatism occurs not only in the southwestern Tianshan orogen,but also affects remarkably contemporaneous magmatisms in the northwestern margin of the Tarim block.The Kuoshibulak A-type granites also suggested that the collisional orogeny in the southwestern Tianshan probably finished before 275.4±2.8 Ma,and the paleo-Asia ocean represented by the south Tianshan ocean is closed at that time.