Introduction Directory UMM :Data Elmu:jurnal:J-a:Journal of Asian Earth Science:Vol18.Issue6.Dec2000:

The Jinshajiang–Ailaoshan Suture Zone, China: tectonostratigraphy, age and evolution Xiaofeng Wang a , I. Metcalfe b, , Ping Jian a , Longqing He a , Chuanshan Wang a a Yichang Institute of Geology and Mineral Resources, CAGS, Yichong, People’s Republic of China b Asia Centre, University of New England, Armidale, Australia Received 12 March 2000; accepted 20 July 2000 Abstract The Jinshajiang Suture Zone is important for enhancing our understanding of the evolution of the Paleo-Tethys and its age, tectonic setting and relationship to the Ailaoshan Suture Zone have long been controversial. Based on integrated tectonic, biostratigraphic, chemostrati- graphic and isotope geochronological studies, four tectono-stratigraphic units can be recognized in the Jinshajiang Suture Zone: the Eaqing Complex, the Jinshajiang Ophiolitic Melange, the Gajinxueshan “Group” and the Zhongxinrong “Group”. Isotope geochronology indicates that the redefined Eaqing Complex, composed of high-grade-metamorphic rocks, might represent the metamorphic basement of the Jinsha- jiang area or a remnant micro-continental fragment. Eaqing Complex protolith rocks are pre-Devonian and probably of Early–Middle Proterozoic age and are correlated with those of the Ailaoshan Complex. Two zircon U–Pb ages of 340 3 and 294 3 Ma ; separately dated from the Shusong and Xuitui plagiogranites within the ophiolitic assemblage, indicate that the Jinshajiang oceanic lithosphere formed in latest Devonian to earliest Carboniferous times. The oceanic lithosphere was formed in association with the opening and spreading of the Jinshajiang oceanic basin, and was contiguous and equivalent to the Ailaoshan oceanic lithosphere preserved in the Shuanggou Ophiolitic Melange in the Ailaoshan Suture Zone; the latter yielded a U–Pb age of 362 41 Ma from plagiogranite. The re-defined Gajinxueshan and Zhongxinrong “groups” are dated as Carboniferous to Permian, and latest Permian to Middle Triassic respectively, on the basis of fossils and U–Pb dating of basic volcanic interbeds. The Gajinxueshan “Group” formed in bathyal slope to neritic shelf environments, and the Zhongxinrong “Group” as bathyal to abyssal turbidites in the Jinshajiang–Ailaoshan back-arc basin. Latest Permian–earliest Middle Triassic synorogenic granitoids, with ages of 238 18 and 227 5–255 8 Ma ; respectively, and an Upper Triassic overlap molasse sequence, indicate a Middle Triassic age for the Jinshajiang–Ailaoshan Suture, formed by collision of the Changdu-Simao Block with South China. q 2000 Elsevier Science Ltd. All rights reserved. Keywords: Jinshajiang; Ailaoshan; Suture zone; Tectonostratigraphy

1. Introduction

Eastern Asia is an amalgamation of allochthonous conti- nental terranes Fig. 1 which had their origin on the margin of Gondwanaland Metcalfe, 1988; Metcalfe, 1996a,b, 1998. The remnants of oceanic basins which once sepa- rated these continental terranes are now preserved along narrow suture zones that form the boundaries between the various allochthonous blocks. Detailed studies of the various suture zones of the region provide much valuable information on the history of the ocean basins they represent and on the tectonic history of the continental blocks they bound. This paper presents new information on the Jinsha- jiang and Ailaoshan suture zones in south-western China Fig. 2, here interpreted to be contiguous, which necessi- tates a reinterpretation of the tectonic history of this region. Metamorphic rocks are widespread in the Jinshajiang– Ailaoshan Suture Zone and represent several huge mixed or accumulated bodies. They comprise mixed and overlap- ping rock bodies or rock blocks of different age and origin, which underwent several episodes of metamorphism and deformation. These huge mixed bodies stretch along both sides of the ophiolitic melange situated in the central part of the suture zone from north to south Fig. 3. Traditional stratigraphic principles are not applicable to these dismem- bered metamorphic rocks. The origin, age and tectonic environment of these rocks, and their relationship to Paleo-Tethys evolution, have long been controversial. This paper presents results of our ongoing studies on the basis of three traverses across the Jinshajiang Suture Zone Ganzhangniuchang-Benjinnong, Zhongza-Changbo and Journal of Asian Earth Sciences 18 2000 675–690 1367-912000 - see front matter q 2000 Elsevier Science Ltd. All rights reserved. PII: S 1 3 6 7 - 9 1 2 0 0 0 0 0 0 3 9 - 0 www.elsevier.nllocatejseaes Corresponding author. Fax: 161-2-67733596. E-mail address: imetcalfmetz.une.edu.au I. Metcalfe. Deqing-Benzilan and two traverses across the Ailaoshan Suture Zone Yakou-Laowangzai and Mojiang-Yuanjiang as well as biostratigraphical, tectonic, chemostratigraphical and isotope geochronological investigations of other areas including Xumai and Shuanggou.

2. Tectonostratigraphic subdivision