东准噶尔鲍尔羌吉一带热隆伸展构造的厘定

DETERMINATION OF THERMAL-UPLIFT EXTENSIONAL STRUCTURES ALONG BAOERQIANGJI,EAST JUNGGAR

东准噶尔1z25万造山带填图方法研究过程中,在鲍尔羌吉一带发现较为典型的伸展构造,与许志琴等提出的热隆伸展构造有相似之处.其隆升与晚古生代造山后期抬升侵位的花岗岩有关.重熔花岗岩侵位上隆形成“热穹隆”构造,在岩体顶部垂直主应力作用下导致上部地壳伸展减薄,形成以晚古生代花岗岩为核心的伸展构造.

Crustal refusion and intrusion of 揝?type granites possibly occur due to large scale crustal detachment and reversed thrust-contraction. As a result cold crust turned to a thermal one. At centers of deep-fusion granites or refusing and rising old metamorphous complex, thermal uplift structure was formed. The vertical main-strain leads to extension and thinning of the upper crust. The extensional structures include shallow and deep ones. Evidence showing the structures was obtained in 1999 in the Zhifang area of East Junggar near Balikun, covering 220 square kilometers. The core of the structure is composed of Erhuzishan super-unit of refused intrusive granites of early Carboniferous age. The single-Zr Pb/Pb age of granodiorites is 325±48 Ma, and the Rb/Sr age of monzonitic granites is 326±86 Ma. The capping rocks and country rocks are quartz diorites and monzonitic mylonites with zircon 207Pb/206Pb age of 830 Ma. The main detachment surface sits on top of the mylonites, separating from upper metamorphic rocks of the middle Proterozoic. There are two secondary detachment faults, with splitting age of 273 Ma on both southern and northern sides. Subsequent tectonic movement causes the overlapping of metamorphic rocks over Upper Carboniferous and Jurassic rocks.