Probing the Chilean subduction zone at mantle depths: Insights from Patagonian High-Pressure rocks
Final Report Abstract
This project focused on the formation and on the geology of a very remote, poorlyknown island, in Chilean Patagonia: the Diego de Almagro island. This island is one of the very rare exposures of the Mesozoic accretionary subduction complex along the Chilean margin. Understanding its formation is important since it represents a window onto the evolution of the Chilean active margin during the Mesozoic. Our results have shown that the island is composed of a nappe stack of ocean-floor derived slivers that underwent very different pressure-temperature-time paths during burial by subduction under the Chilean margin. These rocks witness of a complex thermal evolution of the subduction zone between Jurassic and Cretaceous times with thermal fluctuations as well as multiple episodes of accretion. We have also identified on the island the youngest and the deepest rocks known in Chile (80 Ma and 60 km depth). Paradoxically, tectonic juxtaposition moved these cold, blueschist facies rocks, in contact with rocks from the same paleo-accretionary system that have been earlier heated up to 750 °C at 40 km depth in the granulite facies at c. 160 Ma. The base of the Chilean accretionary wedge at c. 35-40 km depth remained a favorable site for underplating and duplexing for almost 100 Ma during the Mesozoic. The Diego de Almagro island therefore constitutes an amazing laboratory for imaging the roots of accretionary wedges, their structure and their thermal evolution through millions of years. It also represents a unique opportunity to highlight the geological setting along the SW margin of the Gondwana super-continent and improve our understanding of plate tectonics evolution during Jurassic and Cretaceous times in the Earth’s southern hemisphere.
Publications
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2016. Eclogite-, amphibolite- and blueschist-facies rocks from Diego de Almagro Island (Patagonia): Episodic accretion and thermal evolution of the Chilean subduction interface during the Cretaceous. Lithos, 267, 422-440
Hyppolito, T., Angiboust, S., Juliani, C., Glodny, J., Garcia-Casco, A., Calderon, M. & Chopin, C.
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2017. A hot subduction in the middle Jurassic and partial melting of oceanic crust in Chilean Patagonia. Gondwana Research, 42, 104-125
Angiboust, S., Hyppolito, T., Glodny, J., Cambeses, A., Garcia-Casco, A., Calderon, M. & Juliani, C.
