Episodicity of structural flow in an active subduction system, new insights from mud volcano's carbonate veins – Scientific Ocean drilling expedition IODP 366

Abstract : This study's goal is to understand the structural events and episodes of fluid flow recorded in calcium carbonate precipitation sampled in Mariana forearc serpentine mud volcanoes. Those active mounts provide a unique window to deep structural and fluid flow events affecting the subduction channel mélange zone and the subducted Pacific Plate. To build a conceptual model of vein precipitations from the subduction zone to the mud volcanoes edifice, we unravelled the origin, timing, and mechanisms of those precipitations with a multidisciplinary study of calcium carbonate veins, from samples drilled in the flank of Fantangisña Seamount during the International Ocean Discovery Program (IODP) Expedition 366. Structural analysis of the carbonate vein network revealed stages of precipitation and dissolution. The most ancient calcium carbonate minerals underwent high tectonic stress and several degrees of silicification. U-Pb dates ranged from Early Cretaceous to present day, recording potential pre-convergence events and calibrating an episodic building of the Mariana mud volcanoes from the start of the convergence to present day. The UCC-normalized LREE pattern, 87Sr/86Sr ratios ranging from 0.704977 to 0.705798 and δ18O signature 18.7 to 19.8 (‰, V-SMOW) of the veins indicate a mixed origin of the precipitated fluids influenced by the serpentine mud signature. Those mud volcanoes were episodically built from the start of the subduction to present day in function of the forearc tectonic activity. They are complex systems internally composed of a fault network providing multiple circulation pathways that can be successively opened or closed.