昌宁-孟连缝合带泥盆系温泉组沉积物源及其对古特提斯洋早期演化的限定  

Provenance of Devonian Wenquan Formation from Changning-Menglian Suture Zone and Its Implication for Early Evolution of Paleo-Tethys

作　　者：甘正勤 冯庆来[1] 孟龙龙 聂小妹 Gan Zhengqin;Feng Qinglai;Meng Longlong;Nie Xiaomei(School of Earth Sciences,China University of Geosciences,Wuhan 430074,China;College of Marine Science and Technology,China University of Geosciences,Wuhan 430074,China)

机构地区：[1]中国地质大学地球科学学院,湖北武汉430074 [2]中国地质大学海洋学院,湖北武汉430074

出　　处：《地球科学》2024年第10期3499-3515,共17页Earth Science

基　　金：国家自然科学基金项目(No.41672222)。

摘　　要：昌宁-孟连特提斯洋是古特提斯洋的主洋盆,传统观点认为它形成于泥盆纪,近期有学者提出它形成于早古生代,目前学术界对其形成时间与过程认识不一.研究的样品采自昌宁-孟连缝合带西亚带温泉组,5件样品的碎屑锆石年代学结果显示出相似的特征,表现为一个~440 Ma的主要峰值和~960 Ma的次要峰值,同时发育~600 Ma、~780 Ma、~1100 Ma、~2500 Ma的弱峰值.年龄~440 Ma左右的锆石颗粒较为自形、且岩浆震荡环带显著,锆石原位ε_(Hf)(t)值分布在-11.9~+7.2之间.结合砂岩薄片中发现的安山岩岩屑,综合区域岩浆事件对比,该年龄物源是缝合带东部的早古生代岩浆事件.而年龄大于500 Ma的锆石颗粒磨圆较好,环带不发育,物源来自冈瓦纳.作为保山地块东缘的被动大陆边缘沉积,温泉组却接收到了东部大陆边缘的碎屑物质,这表明泥盆纪昌宁-孟连特提斯洋的沉积盆地规模较小,无法阻隔来自东部大陆边缘的碎屑物质,古特提斯处于裂谷盆地演化阶段,而不是具有较大规模的特提斯洋盆.The Changning-Menglian suture zone is the main ocean of the Paleo-Tethys which is considered to be opened in the Devonian according to previous studies.Recently,some scholars put forward that it was formed in the Early Paleozoic.It is a controversial topic that when and how it opened.In this paper,samples were collected from the oldest strata Wenquan Formation within the suture zone,detrital zircon chronology of them obtain similar characteristics,showing two distinctive age peaks at~440 Ma and~980 Ma with other age population around 600 Ma,780 Ma,1100 Ma,2500 Ma,respectively.Zircons with~440 Ma have better crystalline morphology and more prominent magmatic oscillation zones,as well as a wide range of Lu-Hf isotopic compositions with in-situε_(Hf)(t)values from-11.9 to+7.2.Zircons comprising the major age peak at~440 Ma are from the andesite dominant volcanic arc in the Lincang block and western Simao block,while is supported by the andesitic fragment in thin sections.Zircons forming the secondary age peak at~960 Ma come from the Gondwana.Zircons whose age larger than 500 Ma have rounded shape come from long distance transportation or resediments from Pre-Devonian sandstone.To sum up,the Lincang and Simao blocks located to the east of the suture zone are the main provenance of Wenquan Formation,while the Gondwana and Baoshan block contributes a small number of debris,based on sedimentology,petrology and detrital zircon chronology.The Wenquan Formation deposited on the west side of the Paleo-Tethyan ophiolites,but it received detrital materials from the opposite continental margin.Thus,the main Paleo-Tethyan Ocean basin was not broad enough to cut off the transport of detrital materials.It was a narrow basin in the Devonian during the rifting stage,rather than a mature,broad pelagic oceanic basin.

关 键 词：碎屑锆石年代学 昌宁-孟连缝合带 古特提斯洋 物源分析 碎屑锆石Hf同位素 构造地质学 

分 类 号：P547[天文地球—构造地质学]