Hot subduction in the middle Jurassic and partial melting of oceanic crust in Chilean Patagonia
Hot subduction in the middle Jurassic and partial melting of oceanic crust in Chilean Patagonia
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DOI：
10.1016/j.gr.2016.10.007
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发表时间：
2017-02
影响因子：
6.1
通讯作者：
S. Angiboust;T. Hyppolito;J. Glodny;A. Cambeses;A. Garcia‐Casco;Mauricio Calderón Nettle;Caetano Juliani
中科院分区：
文献类型：
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作者：
S. Angiboust;T. Hyppolito;J. Glodny;A. Cambeses;A. Garcia‐Casco;Mauricio Calderón Nettle;Caetano Juliani
在智利巴塔哥尼亚的迭戈德阿尔马格罗岛上，暴露出中生代俯冲高压（HP）增生杂岩的罕见遗迹。我们在这里专注于Lazaro单元，一个连贯的片的洋壳暴露在这个岛上，已首先受到高温（HT）变质，其次是低温变形事件（LT）。它的压力-温度-时间（P-T-t）的演变重建使用现场和岩相观察，相位关系，热压和地质年代学。首次报道了在新体中，在由石榴子石（含钛铁矿出溶体）、透辉石、奥长质熔体、钠长石、斜长石±绿帘石组成的镁铁质岩石中，残留了一次原生角闪岩-高压麻粒岩相事件，表明P-T峰值条件为1.1- 1.3GPa，c. 750 °C。在等压冷却至c时，这一T峰共生体被白云母-辉长岩-阳起石组合完全覆盖。450摄氏度变质沉积岩中锆石变质边的U-Pb定年结果表明，HT事件的均一年龄为162 ± 2 Ma。两个含石榴子石的样品的Sm-Nd年龄分别为163 ± 2 Ma和163 ± 18 Ma。叠加LT变形的变质沉积岩的多矿物Rb-Sr定年表明，120和80 Ma之间的逆行剪切。我们的研究结果表明，在拉扎罗单元的HT事件发生在大约160-165 Ma，巴塔哥尼亚岩侵位开始之前不久。Lazaro单元报告的俯冲洋壳部分熔融与冈瓦纳大陆西缘沿着热俯冲的早期阶段有关。Lazaro单位保持在C。沿俯冲界面沿着40 km深度> 80 Ma，记录了直至上白垩统的俯冲通道环境的变形和长期冷却。
Rare remnants of a Mesozoic subduction high pressure (HP) accretionary complex are exposed on Diego de Almagro Island in Chilean Patagonia. We herein focus on the Lazaro unit, a coherent slice of oceanic crust exposed on this island that has been first affected by high temperature (HT) metamorphism followed by a lower temperature deformation event (LT). Its Pressure-Temperature-time (P-T-t) evolution is reconstructed using field and petrographic observations, phase relations, thermobarometry and geochronology. Remnants of a primary amphibolite to HP granulite-facies event in mafic rocks comprising garnet (with ilmenite exsolutions), diopside, trondhjemitic melt, pargasite, plagioclase ± epidote are reported for the first time in neosomes, indicating peak P-T conditions of 1.1–1.3 GPa and c. 750 °C. This peak T paragenesis has been thoroughly overprinted by a phengite-chlorite-actinolite assemblage during isobaric cooling down to c. 450 °C. U-Pb dating of zircon metamorphic rims from a metasedimentary rock yielded a homogeneous age population of 162 ± 2 Ma for the HT event. Sm-Nd dating of two peritectic garnet-bearing samples yield ages of 163 ± 2 Ma and 163 ± 18 Ma for the HT event. Multi-mineral Rb-Sr dating of a metasedimentary rock overprinted by LT deformation suggests retrograde shearing between 120 and 80 Ma. Our results show that the HT event in the Lazaro unit took place at around 160–165 Ma, shortly before the onset of Patagonian Batholith emplacement. Partial melting of subducted oceanic crust reported in the Lazaro unit is related to the early stages of hot subduction along the Gondwana western margin. The Lazaro unit remained at c. 40 km depth along the subduction interface for > 80 Ma, recording the deformation and long-term cooling of the subduction channel environment until the upper Cretaceous.