摘要
西藏措勤地区布嘎寺正长岩体地处冈底斯带西段,空间上与大面积中新世钾质火山岩共生,是以中-中粗粒或似斑状霓辉正长岩为主要岩性的中深成侵入体。岩体中正长石的40Ar-39Ar坪年龄和等时线年龄分别为(27.14±0.05)Ma和(27.15±0.04)Ma,代表岩体的结晶年龄。这一年龄数据表明布嘎寺正长岩是整个冈底斯带目前发现的时代最早的后碰撞超钾质碱性系列岩浆岩,暗示拉萨地体内新生代后碰撞陆内钾质-超钾质岩浆作用至晚应始于27 Ma前,且很可能从大约30 Ma前已经发生,而不是目前认为的25 Ma前。该结论对高原南部岩石圈演化及整个高原后碰撞岩浆事件的对比研究提供了更为可靠的时空定位。
The Bugasi syneite body of the Coqen area belongs to a mid-deep intrusion dominated by medium to medium-coarse grained or medium-coarse porphyroid aegirine-augite syenite. It is located in the west segment of Gangdise and intimately associated with the widespread Miocene potassic volcanics. ^40Ar-^39Ar plateau age and isochronal dating of the orthoclase from the syneite body are （27.14±0.05）Ma and （27. 15±0.04）Ma, respectively. They represent the crystalline age of the intrusion. The new data indicate that the Bugasi syneite may be the earliest post-collision uhrapotassic alkaline m agmatic rock found around the southern Tibet Plateau so far, and suggest that the Cenozoic post-collision potassic and uhrapotassic magmatism in the Lhasa block should start from 27 Ma B. P. at latest, and likely started from around 30 Ma B. P. rather than 25 Ma B. P. believed now. The obtained results provide more reliable space-time restriction for the future investigation of lithospheric evolution of the southern Tibet Plateau as well as for the comparative study of post-collision magmatic events over the Tibet Plateau.
出处
《成都理工大学学报（自然科学版）》
CAS
CSCD
北大核心
2009年第2期172-176,共5页
Journal of Chengdu University of Technology: Science & Technology Edition
基金
中国地质调查局资助项目
