Using hafnium and oxygen isotopes in zircons to unravel the record of crustal evolution
Using hafnium and oxygen isotopes in zircons to unravel the record of crustal evolution
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DOI：
10.1016/j.chemgeo.2005.09.018
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发表时间：
2006-02-28
期刊：
影响因子：
3.9
通讯作者：
Kemp, AIS
中科院分区：
文献类型：
--
作者：
Hawkesworth, CJ;Kemp, AIS
U-Pb、Lu-Hf和O同位素及微量元素含量原位分析技术的发展，使大陆地壳起源和演化以及花岗岩成因的模拟方法发生了革命性的变化。关键是要获得有代表性的样品，越来越多的人认为，这些样品最好由锆石提供。在岩浆岩中，它们可能是继承的或在寄主岩浆的演化过程中结晶出来的，在沉积物中，它们可能是来自大陆地壳广大地区的碎屑。原位Hf同位素比现在常规测量亚单位精度的激光烧蚀ICP-MS。微量元素含量广泛地限制了岩浆的构造环境，锆石结晶，Hf同位素反映了新的地壳何时从地幔中产生，和0同位素是敏感的低温过程，如在侵蚀和沉积。一个综合的方法的潜力进行了探讨与新的数据从拉克伦褶皱带在澳大利亚东南部。花岗岩中的继承（岩浆前）锆石和周围奥陶纪变质沉积岩中的碎屑锆石产生非常相似的信息。结晶年龄谱以450-600 Ma和0.9- 1.2Ga的峰值为主，而Hf模式年龄值为6180（<6.5ppm）的锆石则属于1.7-1.9和2.9- 3.1Ga两个较窄的年龄范围。由于这些地壳形成峰与主要锆石结晶年龄不匹配，因此450-600 Ma和0.9-1.2 Ga时期基本上是该地区地壳分异而不是生长的时期。此外，具有高δ O-18值（大于6.5ppm）的锆石的Hf模式年龄峰值约为1.8- 2.0Ga，接近奥陶纪变质沉积岩的Nd模式年龄。Hf，0同位素和微量元素的锆石从两个I型花岗岩套房从Lachlan褶皱带的变化突出了地幔的贡献，在这些花岗岩的产生，当地壳成分是局部熔融的变质沉积岩的存在。从整个岩石成分中获得的这种具体信息很少，但它是更真实的花岗岩成因模型、更好地约束热预算以及更深入地了解大陆地壳特定部分演化的先决条件。(c)2005 Elsevier B. V.保留所有权利。
The development of improved techniques for the in situ analysis of U-Pb, Lu-Hf and O isotopes and of trace element contents has revolutionized approaches to modeling the origins and evolution of the continental crust, and the petrogenesis of granite. The key has been to obtain representative samples, and it is increasingly accepted that these are best provided by zircons. In magmatic rocks they may be inherited or have crystallized in the evolution of the host magma, and in sediments they may be detrital from broad areas in the continental crust. In situ Hf isotope ratios are now routinely measured with sub-epsilon unit precision by laser ablation ICP-MS. Trace element contents broadly constrain the tectonic setting of the magmas from which the zircons crystallized, Hf isotopes reflect when new crust was generated from the mantle, and 0 isotopes are sensitive to low temperature processes, as in erosion and sedimentation. The potential of an integrated approach is explored with new data from the Lachlan Fold Belt in southeast Australia. Inherited (pre-magmatic) zircons in the granites and detrital zircons in the surrounding Ordovician metasedimentary rocks yield very similar information. Their crystallisation age spectra are dominated by peaks at 450-600 Ma and 0.9-1.2 Ga, however the Hf model ages of zircons with broadly mantle-like 6 180 values (< 6.5 parts per thousand) fall into two relatively narrow age ranges, c 1.7-1.9 and 2.9-3.1 Ga. Since such crustal formation peaks do not match those registering the predominant zircon crystallisation ages, the 450-600 Ma and 0.9-1.2 Ga periods are essentially times of crustal differentiation, rather than growth, in this region. Furthermore, the Hf model ages of zircons with high delta O-18 values (greater than 6.5 parts per thousand) peak at about 1.8-2.0 Ga, close to the Nd model ages of the Ordovician metasedimentary rocks. Variations in Hf, 0 isotopes and trace elements in zircons from two I-type granite suites from the Lachlan Fold Belt highlight the presence of mantle contributions in the generation of these granites, and when the crustal component is a partial melt of the local metasedimentary rocks. Little of such specific information is available from the whole rock compositions, and yet it is a prerequisite for more physically realistic models for granite petrogenesis, better constrained thermal budgets, and much greater insight into the evolution of particular segments of continental crust. (c) 2005 Elsevier B.V. All rights reserved.