Zircon U-Pb age and Hf-O isotope evidence for Paleoproterozoic metamorphic event in South China
Zircon U-Pb age and Hf-O isotope evidence for Paleoproterozoic metamorphic event in South China
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DOI：
10.1016/j.precamres.2006.08.009
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发表时间：
2006-12
影响因子：
3.8
通讯作者：
Shao‐Bing Zhang;Yong Zheng;Y. Wu;Zi‐Fu Zhao;Shan Gao;Fu-Yuan Wu
中科院分区：
文献类型：
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作者：
Shao‐Bing Zhang;Yong Zheng;Y. Wu;Zi‐Fu Zhao;Shan Gao;Fu-Yuan Wu
认识大陆板块化与全球构造事件的关系，对于认识大陆地壳的形成和演化至关重要。古元古代是世界上发生大规模构造岩浆活动的重要时代，但它们是否也影响了华南最古老的大陆，一直是个令人困惑的问题。为了揭示华南古元古代事件的性质，对华南唯一出露的太古宙微大陆-空岭古陆的变质沉积物和斜长角闪岩进行了锆石U-Pb定年、Hf和O同位素联合研究。U-Pb年龄为1.97±0.03Ga，Th/U比值为0.01-0.14，表明该年龄为古元古代变质事件的记录。变质沉积物中石英和角闪岩中石榴石的δ 18 O值分别为1.11 ‰和1.88 ‰，表明其源区经历了壳上循环。变质岩中锆石的Hf（t）值约为-6.5，模式年龄约为3.0Ga，表明其源区为太古代。因此，华南地区对古元古代全球性构造事件的响应是太古宙陆核的改造。与空岭太古代岩石相比，古元古代变质沉积岩中K2 O/Na 2 O、稀土元素及其它微量元素的变化明显。这被解释为反映了太古代-元古代边界上地壳成分的变化。对扬子地块古元古代的年代学研究表明，扬子地块北部发生了变质作用和岩浆活动，而南部仅发生了岩浆活动。变质作用和岩浆活动都与扬子陆块统一基底的形成有关。这提供了该克拉通形成与古元古代全球构造岩浆作用之间的地球动力学联系，标志着哥伦比亚超大陆组装期间弧-陆碰撞造山作用的大陆增生。
To understand the connection between continental cratonization and global tectonothermal event is essential for recognizing the formation and evolution of continental crust. Paleoproterozoic is an important era with occurrence of megascale tectonomagmatism in the world, but it has been intriguing whether they also influenced the oldest continent in South China. In order to decipher the nature of Paleoproterozoic event in South China, a combined study of zircon U-Pb dating, Hf and O isotope analyses was carried out for metasediments and amphibolite from the Kongling terrane, the only Archean microcontinent outcropped in South China. U-Pb ages of 1.97±0.03Ga were obtained with low Th/U ratios of 0.01–0.14, indicating that the ages are a record of Paleoproterozoic metamorphic event. δ18O values of ∼11‰ and ∼8‰ were measured for quartz from the metasediments and garnet from the amphibolite, respectively, suggesting that their sources experienced supracrustal recycling. ɛHf(t) values of about −6.5 and model Hf ages of about 3.0Ga were acquired for zircons from the metapelites, suggesting an Archean source. Thus a response to the Paleoproterozoic global tectonothermal event in South China is reworking of Archean continental nucleus. Compared with Archean rocks at Kongling, abrupt changes in K2O/Na2O, REE and other trace elements are observed in the Paleoproterozoic metasedimentary rocks. This is interpreted to reflect a change in upper crustal composition at the Archean–Proterozoic boundary. A survey of Paleoproterozoic ages throughout the Yangtze Block suggests that metamorphic event and subsequent magmatic activity occurred in the north, but only magmatic activity in the south. Both metamorphic and magmatic activities are associated with formation of a unified basement responsible for cratonization of the Yangtze Block. This provides a geodynamic connection between the formation of this craton and the global tectonomagmatism in the Paleoproterozoic, marking continental accretion by arc-continent collision orogeny during assembly of the supercontinent Columbia.