摘要
位于南秦岭构造带南缘的勉略（勉县—略阳）洋是东古特提斯洋的北侧分支洋盆,在勉县—略阳地区发育有典型的蛇绿岩组合.然而,由于中三叠世晚期开始的碰撞造山作用以及之后陆内变形作用的改造,对于勉略洋盆在构造带东段的裂解和演化过程并不清晰.本文对发育于东南秦岭构造带内的基性岩墙群进行了岩石学、岩石地球化学、同位素年代学等方面的研究.结果表明,基性岩脉以辉长岩、辉绿岩等基性岩为主,其SiO2含量为41.89％～49.75％,属基性—超基性岩类,并具有富钠、高钛的碱性岩特征.岩石的稀土、微量元素和Sr—Nd同位素特征与板内洋岛玄武岩（OIB）特征一致,岩浆源于具有地壳混染的板内洋岛玄武岩型地幔源区.该类基性岩脉顺层侵入到早古生代早期地层中,通过基性岩脉中的锆石SHRIMP测年获得岩脉顺层侵位的时代为晚志留世早期（约422 Ma）.这种岩浆作用很可能与古特提斯洋初始裂解有关,并导致南秦岭构造带内地壳伸展、基性岩浆侵位,该过程与南秦岭构造带北缘的商丹（商南—丹凤）原特提斯洋的消减和陆内俯冲可能相关.
The Mianlüe （Mianxian—Lüieyang） paleo-ocean was the north branch of the Eastern Paleo-Tethys,which was distributed at the southern margin of the Southern Qinling belt,and the typical ophiolite combination was developed in the Mianxian—Lüeyang area.However,due to the transformation of the collision orogenesis since the late of Middle Triassic and later intra-continental deformation effect,the break-up and development of Mianlüe ocean in the east part was not clear.This paper studies the petrological,geochemical,isotopic and geochronological characteristics on the mafic dikes in the Southern Qinling belt.The maric dikes are dominated with the gabbro and diabase.And the content of SiO2 for these dikes were range from 41.89% to 49.75%,which are belonging to the basic—ultra.basic rock type.These dikes were alkaline rock,and characteristics with the rich sodium and high titanium.The REE,trace elements and Sr—Nd isotope characteristics was similar to the within-plate ocean island basalt （OIB） for these mafic dikes,and its magma source was originated from the OIB contamination with the crustal.These mafic dykes intruded in the early Paleozoic strata along the bedding planes,and the zircon SHRIMP dating of the gabbro dikes revealed the emplacement age was early of Late Silurian （～ 422Ma）.These maric dikes representing the Southern Qinling belt experienced the crustal extension and maric magma intruded in the late of early Paleozoic,which represented the initial break-up of the Paleo-Tethyan ocean in the eastern of the Southern Qinling belt,and related to the closure and intracontinental subduction of the Shangdan （Shangnan—Danfeng） Proto-Tethys ocean at the northern margin of the Southern Qinling belt in the late of early Proterozoic.
出处
《地质论评》
CAS
CSCD
北大核心
2014年第6期1437-1452,共16页
Geological Review
基金
国家自然科学基金资助项目(编号41102126
41172184)的成果
