Detrital zircon ages: Improving interpretation via Nd and Hf isotopic data
Detrital zircon ages: Improving interpretation via Nd and Hf isotopic data
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DOI：
10.1016/j.chemgeo.2009.01.029
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发表时间：
2009-05
期刊：
影响因子：
3.9
通讯作者：
K. Howard;M. Hand;K. Barovich;A. Reid;B. Wade;E. Belousova
中科院分区：
文献类型：
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作者：
K. Howard;M. Hand;K. Barovich;A. Reid;B. Wade;E. Belousova
大部分沉积物源研究利用沉积体系和潜在物源区碎屑锆石年龄模式或“条形码”的相似性来解释古地理环境。虽然这种只考虑年龄的方法通常被认为是有效的，但它是有限的，因为锆石生长事件的时间可能并不是特定地形所特有的，重要的成岩事件可能与少量的锆石生长有关。在很大程度上，可以通过使用额外的同位素数据集，如Sm-ND和Lu-Hf来克服这些限制，这些数据集提供了关于源区地壳演化的信息，并允许与沉积成套资料进行比较。例如，澳大利亚南部Gawler克拉通东部古元古代变质沉积岩中碎屑锆石的年龄谱实际上与Gawler克拉通相邻较老区域的主要锆石生长年表相同，初步表明它是物源区。然而，全岩Nd同位素数据表明，先前存在的原始Gawler克拉通在同位素上过于地壳演化(εND(1850年Ma)−10)，为相对较年轻的变质沉积单元(εND(1850Ma)−1至−5)提供了大部分沉积物。此外，变质沉积岩(εHf(2000 Ma)+2~+5)中约2000 Ma碎屑锆石的锆石Hf同位素组成明显比邻近高勒克拉通(εHf(2000 Ma)−2~−5)中的2000 Ma岩石年轻。块状岩石ND和Hf锆石数据的组合表明，尽管克拉通内碎屑锆石年龄和锆石结晶事件之间存在惊人的相似性，但Gawler克拉通不是一个可行的变质沉积包源区。
The bulk of sedimentary provenance studies use similarities in the detrital zircon age patterns or “barcodes” in sedimentary systems and potential source regions to make interpretations about palaeogeographic settings. While this “age-only” approach is generally considered to be effective, it is limiting because the timing of zircon growth events may not be unique to specific terrains and important rock forming events may be associated with little zircon growth. To a significant extent these limitations can be overcome by employing additional isotopic data sets such as Sm–Nd and Lu–Hf that provide information on the crustal evolution of the source region, and allow comparisons with sedimentary packages. As an example, the age spectra of detrital zircons in Palaeoproterozoic metasedimentary rocks in the eastern Gawler Craton in southern Australia are virtually identical to the dominant zircon growth timelines in adjacent older domains of the Gawler Craton, presenting a prima facie case that it was the source region. However, whole rock Nd isotopic data indicate that the pre-existing proto Gawler Craton was isotopically too crustally evolved (εNd (1850 Ma)−10) to have supplied the bulk of the sediment to the relatively more juvenile metasedimentary units (εNd (1850 Ma)−1 to −5). In addition, zircon Hf isotopic compositions from ca 2000 Ma detrital zircons in the metasedimentary rocks (εHf (2000 Ma)+2 to +5) are significantly more juvenile than 2000 Ma rocks in the adjacent Gawler Craton (εHf (2000 Ma)−2 to −5). The combination of bulk rock Nd and Hf zircon data suggest that the Gawler Craton is not a viable source region for the metasedimentary packages, despite the striking similarity between detrital zircon ages and zircon crystallisation events within the craton.