大别山碰撞后火山岩的锆石U—Pb年龄和氧同位素组成

大别山碰撞后火山岩的锆石U—Pb年龄和氧同位素组成

夏群科1, 郑永飞1, E.Deloule2

1. 中国科技大学地球和空间科学学院，合肥 230026; 2. 法国国家科研中心岩石学和地球化学研究中心，南锡 BP54501，法国

收稿日期:2003-06-20 修回日期:2003-06-20 出版日期:2003-06-20 发布日期:2003-06-20

U-Pb Ages and Oxygen Isotope Compositions of Zircons from Post-Collisional Volcanic Rocks of Dabieshan

XIA Qun-ke1, ZHENG Yong-fei1, Deloule Etienne2

1. School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China; 2. GRPG-CNRS, BP20, 54501 Vandoeuvre Cedex, France

Received:2003-06-20 Revised:2003-06-20 Online:2003-06-20 Published:2003-06-20

摘要/Abstract

摘要： 利用阴极发光技术(CL)观察了大别山碰撞后玄武岩和安山岩的锆石内部结构，并通过离子探针技术(SIMS)测定了其U—Pb年龄和氧同位素组成。玄武岩中锆石都是直接从玄武质岩浆中结晶的岩浆锆石，其年龄为130±2Ma(1σ)；安山岩中有两种锆石，绝大多数是直接从安山质岩浆中结晶出来的岩浆锆石，年龄为133±3Ma(1σ)，少数是残留的原岩锆石，其年龄有两组：768—805Ma和1827—1873Ma。玄武岩和安山岩的岩浆锆石年龄表明，大别山碰撞后火山岩的主体应形成于130Ma左右，属早白垩世。结合文献资料来看，大别山碰撞后火山岩和侵入岩无论是化学组成、微量元素配分、Sr—Nd同位素比值还是年龄，都是基本一致的，说明火山岩和侵入岩的源区以及成因可能是相同的。玄武岩和安山岩的岩浆结晶年龄一致，暗示着它们之间的可能的成因联系。玄武岩锆石相对于正常地慢亏损^18O(δ^18O＝(4．1±0．6)‰)，说明其岩浆源区可能含有一定数量的俯冲板块断离后进入该区地幔的大别山榴辉岩原岩组分。安山岩中残留的原岩锆石既有扬子板块的年龄信息，又有华北板块的年龄信息，这表明华北和扬子的深部界线可能就在北淮阳。

Abstract: The internal texture of zircons from post-collisional basalt and andesite in Dabieshan have been investigated by cathodoluminescence(CL) imaging，and their U-Pb ages and oxygen isotope compositions have been determined by SIMS(Cameca 1270)．A1l zircons from the basalt give U-Pb ages of 130±2 Ma(1σ) and low δ18O values of(4．1±0．2)‰ ．Magmatic zircons from the andesite yield ages of 133±3 Ma(1σ)and 8180 values of(5．1±0．1)‰ ，and inherited zircons from the andesite show ages in two groups of 768～ 805 Ma and 1 827～ 1 873 Ma,but the Same δ18O values of(6．9±0．1)‰ ．It appears that the post-collisional volcanic rocks in Dabieshan were all crystallized at 130 M a．The chemical compositions ，trace element pattern, Sr-Nd isotopic ratios and zircon ages of post-collisional volcanic rocks from Dabieshan are similar to the intrusive rocks，so that these rocks may possibly share the same source and petrogenesis．Moreover，the same ages of both basalt and andesite imply their possible petrogenetic connections ．Some zircons from the andesite display retrograde zoning，which are considered to be the relict zircons from the protolith．Their inherited ages correspond to characteristic age signatures from the Yangtze Block and the North China Bloc k, respectively．The lowδ18O zircons from the basalt suggest that the source of basalt magma might contain recycled component like low δ18O protolith of the Dabieshan eclogites ．Therefore，the suture of the Yangtze Bloc k an d the North China Block at depth is probably located in the Beihuaiyang region

夏群科, 郑永飞, E.Deloule. 大别山碰撞后火山岩的锆石U—Pb年龄和氧同位素组成[J]. J4.

XIA Qun-ke1, ZHENG Yong-fei1, Deloule Etienne2. U-Pb Ages and Oxygen Isotope Compositions of Zircons from Post-Collisional Volcanic Rocks of Dabieshan[J]. J4.