Neoproterozoic anatexis of Archean lithosphere: Geochemical evidence from felsic to mafic intrusions at Xiaofeng in the Yangtze Gorge, South China
Neoproterozoic anatexis of Archean lithosphere: Geochemical evidence from felsic to mafic intrusions at Xiaofeng in the Yangtze Gorge, South China
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DOI：
10.1016/j.precamres.2007.12.003
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发表时间：
2008-06
影响因子：
3.8
通讯作者：
Shao‐Bing Zhang;Yong‐Fei Zheng;Zi‐Fu Zhao;Y. Wu;Honglin Yuan;Fu-Yuan Wu
中科院分区：
文献类型：
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作者：
Shao‐Bing Zhang;Yong‐Fei Zheng;Zi‐Fu Zhao;Y. Wu;Honglin Yuan;Fu-Yuan Wu
对长江峡晓峰新元古代侵入体进行了年代学和地球化学综合研究。研究结果用于对其起源提供约束，并有可能解决有关华南同生火成岩的来源和过程的激烈争论的模型。小峰岩体由长英质-基性岩脉及其围岩花岗岩组成，面积<10km2。它们显示了与太古代崆岭杂岩TTG岩石的侵入关系。锆石U-Pb测年表明岩脉和花岗岩几乎在800±3Ma同时结晶。它们具有相似的 REE 和微量元素分布模式，即 LILE 和 LREE 富集，但 HFSE 贫化。岩脉的全岩εNd(t)值为-9.9至-6.4，锆石εHf(t)值为-12.9至-9.0左右，花岗岩的全岩εNd(t)值为-10.6至-9.2，锆石εHf(t)值为-10.5至-8.3。此外，它们的锆石Hf模型年龄彼此相似，从2.8到3.2Ga。这些结果表明它们均来自中太古代岩石圈的改造，仅在主量元素组成上存在差异。锆石的 δ18O 值为 5.4–6.8‰，典型的 I 型花岗岩。矿物 O 同位素表明岩脉侵入花岗岩期间存在小规模高温水-岩石相互作用。小峰岩体中没有发现新元古代中期岩浆作用期间新生地壳的生长。因此，地幔柱和大洋弧都不是其起源的原因，排除了其岩石成因的地幔柱裂谷和板弧模型。相反，太古代岩石圈的新元古代深熔可以用古元古代弧-大陆碰撞太古宙崆岭杂岩形成的加厚陆内造山带的构造塌陷来解释，但由于罗迪尼亚超大陆分裂之前板块重组引起的岩石圈伸展而使其熔化。这为板块裂谷模型的岩石成因提供了积极的测试。
An integrated study of geochronology and geochemistry was carried out for Neoproterozoic intrusions at Xiaofeng in the Yangtze Gorge. The results are used to provide constraints on their origin, with potential resolution to hotly debated models concerning the source and process of contemporaneous igneous rocks in South China. The Xiaofeng intrusions are composed of felsic–mafic dykes and their wall-rock granitoids in an area of <10km2. They show intrusion relationship to TTG rocks of the Archean Kongling Complex. Zircon U–Pb dating indicates that the dykes and granitoids were crystallized almost contemporaneously at 800±3Ma. They share similar distribution patterns of REE and trace elements, i.e. enrichment in LILE and LREE but depletion in HFSE. The dykes have whole-rock ɛNd(t) values of −9.9 to −6.4 and zircon ɛHf(t) values of about −12.9 to −9.0, and the granitoids have whole-rock ɛNd(t) values of −10.6 to −9.2 and zircon ɛHf(t) values of −10.5 to −8.3. Furthermore, their zircon Hf model ages are similar to each other, from 2.8 to 3.2Ga. These results indicate that they both are derived from reworking of Mesoarchean lithosphere, with the difference only in major element composition. Zircon has δ18O values of 5.4–6.8‰ for them, typical for I-type granite. Mineral O isotopes indicate small-scale high-T water–rock interaction during the intrusion of the dykes into the granitoids. No growth of juvenile crust during the middle Neoproterozoic magmatism is identified to occur in the Xiaofeng intrusions. Thus, neither mantle plume nor oceanic arc is responsible for their origin, ruling out the plume-rift and slab-arc models for their petrogenesis. Instead, the Neoproterozoic anatexis of the Archean lithosphere can be explained by the tectonic collapse of a thickened intracontinental orogen that formed by Paleoproterozoic arc-continent collision to the Archean Kongling Complex, but it became molten due to lithospheric extension in response to plate reorganization prior to breakup of the supercontinent Rodinia. This provides a positive test to the plate-rift model for their petrogenesis.