Late Cretaceous‐Tertiary tectonics of the southwest Pacific: Insights from U‐Pb sensitive, high‐resolution ion microprobe (SHRIMP) dating of eclogite facies rocks from New Caledonia
Late Cretaceous‐Tertiary tectonics of the southwest Pacific: Insights from U‐Pb sensitive, high‐resolution ion microprobe (SHRIMP) dating of eclogite facies rocks from New Caledonia
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DOI：
10.1029/2004tc001709
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发表时间：
2005-06
期刊：
影响因子：
4.2
通讯作者：
C. Spandler;D. Rubatto;J. Hermann
中科院分区：
文献类型：
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作者：
C. Spandler;D. Rubatto;J. Hermann
我们提出了新喀里多尼亚北部榴辉岩相样品中锆石的新 U-Pb 敏感高分辨率离子微探针 (SHRIMP) 年代数据，这对西南太平洋地区晚白垩世至始新世的构造演化具有重要影响。两种高压变泥岩含有分区锆石晶体。这些晶体的核心代表了继承的岩浆锆石颗粒，两个样本的年龄均为 85 Ma。变质镁铁质堆积岩和长英质变沉积岩中的火成锆石域的年代也为 55 Ma。沉积成因岩石中年龄一致的火成锆石表明，岩浆作用后不久，沉积物是从有限的来源区域发生的。因此，榴辉岩相岩石的原岩被认为形成于85~55Ma之间的弧后盆地。这一时期与新喀里多尼亚西部未变质的波亚地体的年龄相匹配，并为这两个地体之间的直接联系提供了进一步的证据。在变泥岩中，横切岩心振荡分区的不规则锆石边缘具有较低的微量元素和 Th/U 含量，并含有高压矿物包裹体，这提供了这些锆石边缘在榴辉岩相变质作用过程中形成的证据。因此，从这些边缘获得的 44.1 ± 0.9 Ma 和 44.5 ± 1.2 Ma 年龄代表与弧后盆地俯冲有关的埋藏。有人认为，在最年轻的沉积物沉积后不久，俯冲作用就在 55 Ma 开始，并在 44 Ma 尝试俯冲大陆地壳（现在称为诺福克海岭）期间停止。因此，产生高压岩石的俯冲系统最多只能运行 11 m.y。并且会相对较热。峰值变质作用的 44 Ma 年龄限制也明显早于新喀里多尼亚超镁铁质推覆体的仰冲时间（10 m.y.），从而忽略了仰冲作用和高压变质作用之间的任何联系。将我们的结果与之前记录的地质数据相结合，我们提出了新喀里多尼亚地质发展的修订模型，其中涉及始新世期间的多次压缩和伸展。
We present new U‐Pb sensitive, high‐resolution ion microprobe (SHRIMP) dates for zircon from eclogite facies samples from northern New Caledonia, which have important consequences for the Late Cretaceous to Eocene tectonic evolution of the southwest Pacific region. Two high‐pressure metapelites contain zoned zircon crystals. Cores of these crystals represent inherited magmatic zircon grains, which yield an age of 85 Ma in both samples. Igneous zircon domains from a metamorphosed mafic cumulate and a felsic metasedimentary rock were also dated at 55 Ma. The igneous zircon of uniform age in rocks of sedimentary origin indicates that sedimentation took place from a restricted source area soon after magmatism. Therefore the protoliths of the eclogite facies rocks are considered to have formed between 85 and 55 Ma in a back‐arc basin. This time period matches the age of the unmetamorphosed Poya Terrane of western New Caledonia and provides further evidence for a direct link between the two terranes. In the metapelites, irregular zircon rims that cross cut the oscillatory zoning of the cores have low trace element and Th/U contents and contain inclusions of high‐pressure minerals providing evidence that these zircon rims formed during eclogite facies metamorphism. Therefore the 44.1 ± 0.9 Ma and 44.5 ± 1.2 Ma ages obtained from these rims represent burial related to subduction of the back‐arc basin. It is suggested that subduction initiated soon after deposition of the youngest sediments at 55 Ma and stopped at 44 Ma during attempted subduction of continental crust, now represented as the Norfolk Ridge. Therefore the subduction system that produced the high‐pressure rocks could only have operated for a maximum of 11 m.y. and would have been relatively hot. The 44 Ma age constraint for peak metamorphism also significantly predates (by 10 m.y.) the timing of obduction of the New Caledonia Ultramafic Nappe, discounting any link between obduction and high‐pressure metamorphism. Combining our results with previously documented geological data, we present a revised model for the geological development of New Caledonia, which involves multiple episodes of compression and extension during the Eocene.