中文摘要：

甘肃西秦岭地区存在钾霞橄黄长岩和钾质粗面玄武岩（钾玄岩）两类钾质火山岩，出露在甘肃西秦岭礼县、宕昌县等，地理坐标大致相当于104°20′～104°50′E，33°30′～34°10′N。钾霞橄黄长岩是一种不含斜长石，但普遍含有高钛金云母、黄长石、白榴石、霞石的岩石，全岩化学成分具低SiO2和Al2O3，富TiO2、CaO、MgO和高K/Na、高Mg^#值的特征；钾质粗面玄武岩（钾玄岩）含有大量斜长石但是缺乏高钛金云母、黄长石、白榴石和霞石，全岩化学中SiO2、Al2O3明显高于前者，而TiO2、CaO、MgO、K/Na和Mg^#值要比钾霞橄黄长岩低。钾霞橄黄长岩的全岩K/Ar和金云母单矿物的39^Ar/^40Ar同位素定年落在7.1～23Ma，而钾玄岩的全岩39^Ar/^40Ar同位素定年落在9Ma左右，因此它们同为中新世产物。两类钾质火山岩具有相似的富集不相容元素和轻稀土的特征。两类钾质火山岩的初始87^Sr/86^Sr分别在0.70403～0.70749和0.70412～0.70522；143^Nd/144^Nd分别在0.51274～0.51294和0.51265～0.51276；εNd分别在1.12～5.95和0.3～2.3。206^Pb/204^Pb、207^Pb/204^Pb和208^Pb/204^Pb分别落到18.3746～18.9986、15.529～15.6693和38.4971～39.4144。在火山岩源区示踪的143^Nd/144^Nd-87^Sr/86^Sr，207^Pb/204^Pb-206^Pb/204^Pb，208^Pb/204^Pb-206^Pb/204^Pb，143^Nd/144^Nd-206^Pb/204^Pb，87^Sr/86^Sr-206^Pb/204^Pb和Ba/Nb-La/Nb图解中，一致显示两类钾质火山岩具有与OIB相似的地球化学特征，源区可能与地幔柱有关，并具有EM1、DMM和HIMU端员混合特征。结合前人对该区深部地球物理和断裂构造的研究，论证了火山岩的起源与成因，指出作为对印度—欧亚大陆强烈碰撞的吸收与调节，高原下软流圈地幔流沿400km界面向北东方向的侧向流动以及西秦岭周边克拉通块体的阻挡，是形成西秦岭断裂系左行走滑特征和巨大拉分盆地的主要原因，也是导致西秦岭新生代两类钾质火山?

英文摘要：

Two types of Cenozoic potassic volcanic rocks, kamafugite and potassic trachybasalt, were recognized in Lixian and Dangchang counties in West Qinling, Gansu Province （N104°20′- N104°50′ , E33°30′- E34°10′）. The first type, kamafugite, is plagioclase-free, consisted of Ti-rich phlogopite, melilite, leucite and nephelite. They have lower contents of SiO2 and Al2O3, but have high TiO2, CaO, MgO contents and K/Na and Mg^# ratio whereas the second type, potassic trachybasalt, is abundant in plagioclase and contains no phlogopite, melilite, leucite and nephelite. They have higher SiO2, Al2O3, （Na2O＋K2O）, and lower TiO2, CaO, MgO, and K/Na and Mg^# , in comparision to the first type of rocks. The whole rock K/Ar and phlogopite 39^Ar/^40 Ar ages of kamafugite range from 7.1 to 23 Ma, and the potassic trachybasalt yields the whole rock 39^Ar/^40 Ar age of 49 Ma. They are both Miocene magmatism. Both kamafugite and potassic trachybasalt are enriched in incompatible trace elements and LREE. The kamafugite （87^ Sr/^86 Sr= 0. 704 03-0. 707 49, 143^Nd/ ^144Nd=0. 512 74-0. 512 94, εNd=1. 12-5.95） and the potassic trachybasalt （87^Sr/^86Sr=0. 704 12-0. 705 22, 143^Nd/144^Nd=0. 512 65-0. 512 76, εNd=1. 12-5. 95） have similar Pb isotopic compositions （206^Pb/204^Pb= 8. 374 6-18. 998 6, 207^Pb/204^ Pb= 15. 529-5. 669 3, 208^Pb/204^ Pb=38. 497 1-39. 414） and both show plume-related OIB-like features, suggesting a possible mixture of the geochemical end-members of EM1, DMM and HIMU. Combining the available regional geological and geophysical research, the petrogenesis of the magmatism was studied. As a response and absorption to the India-Asia collision, the northeastward flow of the asthenosphere beneath the Tibetan Plateau along the 400 km depth interface was blocked by the North China craton, and caused a systemic sequences in West Qinling Region, including the strike-slip fault systems and pull-apart basins in the shallow crust and the origin of the two-type magmatism in this work in deep litho