Origin of volcanic ash beds across the Permian-Triassic boundary, Daxiakou, South China: Petrology and U-Pb age, trace elements and Hf-isotope composition of zircon
Origin of volcanic ash beds across the Permian-Triassic boundary, Daxiakou, South China: Petrology and U-Pb age, trace elements and Hf-isotope composition of zircon
复制标题
华南大峡口二叠系-三叠系界线火山灰层成因：岩石学及锆石U-Pb年龄、微量元素及Hf同位素组成
DOI：
10.1016/j.chemgeo.2013.09.020
复制
发表时间：
2013-12-18
期刊：
影响因子：
3.9
通讯作者：
Sun, Xiufeng
中科院分区：
文献类型：
--
作者：
Gao, Qiuling;Zhang, Ning;Sun, Xiufeng
摘要中国南方大峡口剖面二叠系-三叠系界线层发育丰富的火山灰层，火山灰蚀变为粘土。火山活动可能在二叠-三叠纪大灭绝中发挥了重要作用，因此了解这些火山灰床的起源非常重要。260号灰层的岩性受晶体碎片模式（66.7%斜长石、7.2%碱性长石和26.1%石英）的限制，表明灰代表英安质火山作用。本文用LA-ICPMS和LA-MC-ICPMS分析了10个火山灰层中锆石的U-Pb年龄、微量元素和Hf同位素组成。锆石可分为岩浆锆石（约97%，227-279 Ma）和继承锆石（约3%，678-2424 Ma）两大类。岩浆锆石的Y，Hf，Th和U的含量和Nb/Ta比值典型的钙碱性火山作用的锆石。岩浆锆石的Hf（t）值变化范围为-10.9 ~+5.3，表明岩浆混合了年轻地壳物质（可能为新元古代）和古老地壳物质（可能为太古代）。252-259-B层Hf同位素组成相对亏损，eHf（t）值为-10.9 ~+5.3，平均值为-5.0--2.5，其余层eHf（t）值为-10.8 ~+4.4（主要为-10.8--3.5），平均为-8.9--6.8，表明在252-259-B层的火山作用中有较多的新生地壳物质的输入。岩浆锆石的Hf同位素和微量元素组成的整合表明，火山活动产生的灰烬发生在沿着收敛大陆边缘在盘古超大陆的形成。这种强烈的火山活动可能在华南二叠纪-三叠纪生物大灭绝中起了重要作用。(C)2013年由Elsevier B. V.出版
Abundant volcanic ash layers, largely altered to clay, characterize the Permian-Triassic boundary beds of the Daxiakou section, South China. Volcanism may have had an important role in the Permian-Triassic mass extinction, so it is important to understand the origin of these ash beds. The lithology of ash bed 260, as constrained by modes of crystal fragments (66.7% plagioclase, 7.2% alkali feldspar, and 26.1% quartz), suggests that the ash represents dacitic volcanism. The U-Pb ages, trace elements and Hf-isotope compositions of zircons from ten ash beds have been analyzed using LA-ICPMS and LA-MC-ICPMS. The zircons can be divided into two groups: magmatic zircons (similar to 97%, 227-279 Ma) and inherited zircons (similar to 3%, 678-2424 Ma). Magmatic zircons have Y, Hf, Th and U contents and Nb/Ta ratios typical of zircons from silicic calc-alkaline volcanism. epsilon(Hf)(t) values of magmatic zircons vary from -10.9 to +5.3, implying magmatic mixing between juvenile crustal material (probably Neoproterozoic in age) and ancient crustalmaterial (probably Archean). Beds 252-259-b have relatively depleted Hf-isotope compositions with eHf(t) values of -10.9-+5.3 and averages of -5.0--2.5, while other beds have eHf(t) values of -10.8-+4.4 (mostly -10.8--3.5) and averages of -8.9--6.8, implying more input of juvenile crustal material in the volcanism of Beds 252-259-b. Integration of the Hf-isotope and trace-element compositions of magmatic zircons suggests that the volcanism producing the ashes took place along the convergent continent margins during the formation of the Pangea supercontinent. This intense silicic volcanism may have played an important role in causing the Permian-Triassic mass extinction in South China. (C) 2013 Published by Elsevier B.V.