摘要
距中国中山站以南约400 km的格罗夫山是普里兹造山带向南极内陆的延伸部分,其基底地体由约在920—910 Ma期间侵入的镁铁质-长英质火成岩和少量中元古代的沉积岩构成,这些岩石仅在泛非期(约570—500 Ma)经历了单相变质—构造旋回,因此是一个典型的泛非期变质地体。泛非期高峰变质作用并不像前人所认为的那样仅为中低压麻粒岩相,而是高达770—840℃、1.18—1.40 GPa,并在随后经历了近等温减压(约0.6 GPa)的P-T演化过程。大规模的A型紫苏花岗岩和花岗岩在同造山-后造山阶段侵位,并造成了麻粒岩地体近等压降温的P-T轨迹。这些花岗质岩石是由长期富集地幔的底侵物质(碱性玄武质岩石)经部分溶融而形成的。结合相邻地质体的研究资料,我们认为普里兹造山带可能发育在太古宙—格林维尔期基底地体之上,这些基底地体可能与新元古代盖层卷入到了统一的泛非期造山作用过程。在泛非期造山作用过程中,地壳曾被增厚约达40—50 km,而后又经历了厚约20 km的地壳伸展垮塌和剥蚀。所以,普里兹造山带应代表东冈瓦纳陆块内部由板块缝合作用所形成的一条泛非期碰撞造山带。
The Grove Mountains, 400 km south of the Chinese Zhongshan Station, are an inland continuation of the Prydz Belt, East Antarctica. The basement terrane of the Grove Mountains consists of voluminous mafic-felsic intrusives of ca. 920---O10 Ma and a small amount of Mesoproterozoic sedimentary rock. This terrane only experienced a single Pan-African （ ca. 570--500 Ma） tectonometamorphic cycle and is therefore a typical Pan-African metamorphic ter- rane in the Prydz Belt. The Pan-African high-grade metamorphism may have reached peak pressure-temperature （P-T） conditions of 1. 18--1.40 GPa and 770--840~C, rather than low-to medium-pressure granulite facies as previously thought. This peak metamorphism was then followed by a near-isothermal decompression of about 0.6 GPa. Numerous A-type charnockites and granites intruded in the metamorphic terrane during syn- to post-orogenic episodes, which resulted in a late near-isobaric cooling of the terrane. These granitoids were probably generated by partial melting of the underplating materials （ alkaline basaltic rocks） derived from a long-term enriched subconti- nental lithospheric mantle. Coupled with available data from other localities, we infer that the Prydz Belt developed on Archean-Grenvillian basement terranes. Subsequently, these basement terranes and Neoproterozoic cover se- quences may have suffered from the same Pan-African orogenic event. The crust of the Prydz Belt was thickened to around 40--50 kin, followed by about 20 km of exhumation during the Pan-African orogenesis. Accordingly, the Prydz Belt should represent a Pan-African collisional zone as a consequence of the East Gondwana assembly.
出处
《极地研究》
CAS
CSCD
北大核心
2013年第1期7-24,共18页
Chinese Journal of Polar Research
基金
国土资源大调查项目(1212010511505
1212010711509
1212011120176)
国家自然科学基金项目(40072028
40372046
40872052)
国家财政专项(CHINARE2012-02-05)资助
关键词
新元古代基底
泛非期单相变质-构造旋回
同造山-后造山岩浆作用
碰撞造山带
格罗夫山
东南极
Neoproterozoic basement, single Pan-African tectonometamorphic cycle, syn- to post-orogenic mag- matism, collisional zone, Grove Mountains, East Antarctica
