【摘要】：內(nèi)蒙古渣爾泰地區(qū)處于華北地臺西北部,其分布的中生代火山巖劃分為兩大類,形成于兩個噴發(fā)旋回。早白堊世早期噴發(fā)旋回以中基性火山巖為主,沿近東西向的深大斷裂呈北東東向裂隙式噴發(fā);晚期噴發(fā)旋回以酸性火山巖為主,沿近南北向斷裂帶呈裂隙-中心式噴發(fā)。中基性火山巖主要為橄欖玄武粗安巖和安粗巖,其SiO_2介于49.65%~56.64%;酸性火山巖包括次火山巖、火山碎屑巖、火山熔巖,其Si O2介于73.18%~83.82%;兩者組成典型的寬雙峰火山巖。中基性火山巖富堿(Na_2O+K_2O=6.70%~7.47%)、高Ti(TiO_2=2.29%~3.55%)、Fe,相對貧Ca、Mg,富含大離子親石元素(LILE)(Rb、Ba),輕稀土相對富集,輕、重稀土元素分餾明顯,LREE/HREE=4.50~6.47,(La/Yb)N=4.17~8.85,具微弱的負(fù)Eu異常(δEu=0.67~0.96),具有與洋島玄武巖(OIB)相似的地球化學(xué)特征,其巖漿來源于交代富集的軟流圈地幔,巖漿上升過程中地殼組分混染較少。酸性火山巖富Si、高K,貧Ca、Mg、Fe、Ti,富含大離子親石元素(LILE)(Rb、Th、U)和高場強元素(HFSE)(Nb、Ta、Zr、Hf),富集輕稀土,LREE/HREE=2.91~14.3,輕、重稀土分餾明顯,(La/Yb)N=2.53~28.4,(La/Sm)N=1.16~4.57,(Gd/Yb)N=1.22~5.04,負(fù)Eu異常明顯(δEu=0.02~0.25),具有A型流紋巖的特征,為幔源巖漿底侵,使上覆的先存地殼巖石發(fā)生部分熔融的產(chǎn)物。結(jié)合區(qū)域地質(zhì)背景,認(rèn)為研究區(qū)雙峰式火山巖形成于西伯利亞板塊與華北板塊碰撞造山期后陸內(nèi)拉張的構(gòu)造環(huán)境。
[Abstract]:The area of Jiltai, Inner Mongolia, is located in the northwest of the North China platform. The Mesozoic volcanic rocks are divided into two types, which are formed in two eruptive cycles. In the early Cretaceous, the middle basic volcanic rocks were the main eruptive cycles, and the deep faults along the near east-west direction were in the north-east-west fracture type, while the late eruption cycles were mainly acidic volcanic rocks, and the near-north-south fault zones were fissured-central eruptions. The middle basic volcanic rocks are mainly olivine-Black Tortoise trachyandesite and their SiO_2 is between 49.65% and 56.64%, while acidic volcanic rocks include subvolcanic rocks, pyroclastic rocks and volcanic lava, and their Si O2 is 73.18% and 83.82%, respectively. The two constitute typical wide bimodal volcanic rocks. The middle basic volcanic rocks are alkali-rich (Na_2O K 鈮，

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