CAJ | 학술논문

近年来在青藏高原南部拉萨地块不断发现的碰撞后钾质和超钾质岩石,对于揭示印度与亚洲大陆碰撞以来高原岩石圈的深部作用与过程发挥了重要作用.分布在拉萨地块西部扎布邪茶卡东岸的钾质和超钾质火山岩主体喷发时代为中新世(约16Ma),出露面积约为400km~2,火山岩持续喷发0.45Ma,估算的喷发速率约为0.26×10~(-3)km~3/a.岩石包括3种类型,第一类(约16Ma)为超钾质的粗面安山岩,SiO_2低(55%～58%),高Fe_2O_3、MgO、TiO_2;第二类(约27Ma)为钾玄质的响岩和粗面岩;第三类是高SiO_2的钾玄质-超钾质粗面岩(SiO_2=59%～64%)和流纹岩(SiO_2=69%).岩石显示轻稀土元素、大离子亲石元素高度富集和部分高场强元素亏损的特征,部分中酸性岩石显示高Sr低Y的埃达克岩的属性.岩石的Sr-Nd-Pb-O同位素组成与拉萨地块典型的超钾质岩石明显不同,显示亲青藏高原北部地球化学省的地球化学特征.扎布耶茶卡不同类型的岩浆代表了碰撞后高原南部岩石圈减薄作用导致的岩石圈不同层次的岩石部分熔融的产物.
근년래재청장고원남부랍살지괴불단발현적팽당후갑질화초갑질암석,대우게시인도여아주대륙팽당이래고원암석권적심부작용여과정발휘료중요작용.분포재랍살지괴서부찰포사다잡동안적갑질화초갑질화산암주체분발시대위중신세(약16Ma),출로면적약위400km~2,화산암지속분발0.45Ma,고산적분발속솔약위0.26×10~(-3)km~3/a.암석포괄3충류형,제일류(약16Ma)위초갑질적조면안산암,SiO_2저(55%～58%),고Fe_2O_3、MgO、TiO_2;제이류(약27Ma)위갑현질적향암화조면암;제삼류시고SiO_2적갑현질-초갑질조면암(SiO_2=59%～64%)화류문암(SiO_2=69%).암석현시경희토원소、대리자친석원소고도부집화부분고장강원소우손적특정,부분중산성암석현시고Sr저Y적애체극암적속성.암석적Sr-Nd-Pb-O동위소조성여랍살지괴전형적초갑질암석명현불동,현시친청장고원북부지구화학성적지구화학특정.찰포야다잡불동류형적암장대표료팽당후고원남부암석권감박작용도치적암석권불동층차적암석부분용융적산물.
The postcollisional potassic and ultrapotassic rocks have been found recently in southern Tibetan plateau, which are important clues in studying the deep processes since India collided with Asia. The volcanic rocks located in the east bank of Zabuye salt lake in western Lhasa terrane were dated to be ～16 Ma, with an area of ～ 400 km~2. The volcano erupted in ～0.45 Ma with an eruption rate of 0.26×10~(-3)km~3/year. Three types of rock were found in the Zabuye volcanics. Type one (～16 Ma) are ultrapotassic trachyan-desite, with lower SiO_2 (55%-58%), high Fe_2O_3, MgO, and TiO_2. Type two (～27 Ma) are shoshonitic phonolite and trachyte. Typethree are shoshonitic and ultrapotassic trachyte (SiO_2=59%-64%) and rhyolites (SiO_2=69%), with high Sr lower Y adakite-affinity. The rocks, as a whole, show enrichment of light rare earth elements (REEs) and large ion lithosphile elements (LILE), and are low in some high field strength elements (HFSEs). The Sr-Nd-Pb-O isotopic composition of the Zabuye rocks differed from the typical ultrapotassic rocks in southern Tibet. Instead, they show similar nature to the rocks from the northern Tibet geochemical province. The Zabuye rocks imply that, they originated from partial melting of different depth of the lithospheric mantle and thickened lower crust that caused by the thinning process in southern Tibet.