中国东南极地质考察20年进展与展望

GEOLOGICAL SURVEYS IN EAST ANTARCTICA BY CHINESE EXPEDITIONS OVER THE LAST 20 YEARS: PROGRESS AND PROSPECTS

在1998—2017年期间,我国组织了14次东南极地质考察,将考察的范围从中山站所在的拉斯曼丘陵向外扩展了约400 km,主要包括格罗夫山、埃默里冰架东缘-西南普里兹湾、北查尔斯王子山、布朗山、赖于尔群岛和西福尔丘陵等露岩区。通过大、中比例尺的地质编图和多学科综合研究,取得如下重要进展:(1)确定格罗夫山冰下高地为泛非期(~570—500 Ma)单相变质地体,发现镁铁质和泥质高压麻粒岩并刻画了泛非期造山的精细过程,为普里兹造山带的碰撞造山成因以及冈瓦纳超大陆的多陆块汇聚模型提供了岩石学支撑;(2)论证在印度克拉通与东南极陆块之间存在一个延长>2 000 km的中元古代长寿命大陆岛弧,岛弧岩浆作用从~1 500 Ma一直持续到~1 000 Ma,提出雷纳造山带格林维尔期(~1 000—900 Ma)的构造演化可能经历了从弧陆碰撞到陆陆碰撞的过程;(3)在赖于尔群岛超高温变泥质岩中识别出早期蓝晶石的残留,确定了超高温变质作用顺时针演化的精细P-T轨迹;(4)在西福尔丘陵西南部基性岩墙群中发现了格林维尔期(~960—940 Ma)不均匀麻粒岩化,变质条件达820—870℃、0.84—0.97 GPa,认为西福尔陆块也卷入到印度克拉通与东南极陆块的碰撞造山过程;(5)在西福尔丘陵东南部浅变质冰川漂砾和松散砂中获得~3.5—3.3 Ga的古老锆石U-Pb年龄,推测在西福尔丘陵东南方向存在一个从前未知的古太古代冰下陆块。建议今后在东南极面向印度洋构造域的地质考察要进一步扩展到南查尔斯王子山、内皮尔杂岩和登曼冰川,研究工作的重点仍聚焦在南极大陆如何响应地质历史时期里超级大陆的聚散过程这一关键科学问题上,并可在以下几个方面展开:(1)太古宙古老地壳及陆核的识别与全球对比;(2)格林维尔期造山记录与罗迪尼亚超大陆汇聚;(3)泛非期造山记录与冈瓦纳超大陆汇聚;(4)显生宙冈瓦纳超大陆裂解及陆块分离。通过这些考察和研究工作,可以促使我国对南极地质科学的研究达到国际先进水平。

Fourteen geological surveys in East Antarctica from 1998 to 2017 were organized by the Chinese National Antarctic Research Expedition.The semicircular survey region has a radius of about 400 km from the Chinese Zhongshan Station in the Larsemann Hills.Main bedrock exposures in this area include the Grove Mountains,eastern Amery Ice Shelf-southwestern Prydz Bay,northern Prince Charles Mountains,Mount Brown,Rauer Group,and Vestfold Hills.Based on large-and medium-scale geological mapping and comprehensive multidisciplinary studies,the following has been achieved.(1)The Grove Subglacial Highlands has proven to be metamorphic terrain that experienced only a single Pan-African(~570–500 Ma)tectonometamorphic cycle.High-pressure mafic and pelitic granulites have been discovered from glacial moraines,and the Pan-African orogenic process has been accurately depicted.New data suggest that the Prydz Belt is a collisional zone,supporting a tectonic model that the Gondwana supercontinent was assembled from several continental blocks during Pan-African times.(2)A long-lived Mesoproterozoic continental arc exceed ing>2 000 km occurs between the Indian and East Antarctic cratons.Arc magmatism lasted from^1 500 Ma to^1 000 Ma.It is proposed that the tectonic evolution of the Rayner orogen may involve an arc-continent collision followed by continent-continent collision during the Grenvillian(~1 000– 900 Ma)time.(3)Early kyanite relics have been identified from ultrahigh-temperature metapelites in the Rauer Group,and a precise clockwise P-T path of the ultrahigh-temperature metamorphism has been deduced.(4)Grenvillian(~960–940 Ma)heterogeneous granulitization with P-T conditions of 820–870?C and 0.84–0.97 GPa has been recognized in mafic dyke swarms from the southwestern Vestfold Block,suggesting that this block may have involved the Rayner orogeny during collision between the Indian and East Antarctic cratons.(5)U-Pb zircon ages of^3.5–3.3 Ga have been obtained from weakly metamorphosed glacial boulders and loose sands from moraines around the southeastern margin of Vestfold Hills,on which basis it has been inferred that a possible Paleoarchean continental block exists beneath the ice sheet to the southeast of Vestfold Hills.It is suggested that future geological field investigations in the Indian Ocean sector of Antarctica should extend to the southern Prince Charles Mountains,the Napier Complex,and the Denman Glacier.Research should focus on the response of the Antarctic continent to the assembly and breakup of supercontinents in the geological history of the Earth.It can be carried out in the following aspects:(1)recognition of the Archean continental nuclei and their global correlations,(2)record of the Grenvillian orogeny and assembly of the Rodinia supercontinent,(3)record of the Pan-African orogeny and assembly of the Gondwana Supercontinent,and(4)breakup and dispersion of the supercontinent during the Phanerozoic.Such research will advance China’s research on Antarctic geology to appropriate international standards.