TY - JOUR

T1 - Quantifying the Axial Magma Lens Dynamics at the Roof of Oceanic Magma Reservoirs (Dike/Gabbro Transition)

T2 - Oman Drilling Project GT3 Site Survey

AU - France, Lydéric

AU - Lombard, Maéva

AU - Nicollet, Christian

AU - Berthod, Carole

AU - Debret, Baptiste

AU - Koepke, Juergen

AU - Ildefonse, Benoit

AU - Toussaint, Aurore

N1 - Funding Information: This study relies on field campaigns conducted thanks to the hospitality of the Omani people, and the Directory of Minerals at the Ministry of Commerce and Industry of the Sultanate of Oman. The authors thank Françoise Boudier for her help in the field, and for many discussions related to the root zone of the SDC. Adolphe Nicolas is also thanked for his help in the field, and several advices related to field work in the Oman ophiolite. Mathilde Cannat, Fabrice Fontaine, and Javier Escartin are thanked for discussions related to hydrothermal vents. This study greatly benefited from thorough reviews by Milena Marjanovic, an anonymous reviewer, the associate Editor, and the Editor, whom the authors gratefully thank. Christophe Nevado & Doriane Delmas are thanked for their high quality thin sections. This research was supported by the Région Lorraine ('soutien aux projets de recherche' program), and by CNRS-INSU program SYSTER, and IODP-France. This is CRPG contribution 2753. Open access funding enabled and organized by Projekt DEAL.

PY - 2021/5/10

Y1 - 2021/5/10

N2 - At oceanic spreading centers, the interactions between the igneous system that builds the crust, and the hydrothermal system that cools it govern the plumbing system architecture and its thermokinetic evolution. At fast-spreading centers, most of those interactions occur around the axial magma lens (AML) that feeds the upper crust, and possibly part of the underlying mushy igneous reservoir. Heat extracted from crystallizing AML is transferred through a conductive boundary layer to the overlying hydrothermal system. Quantifying the AML physical and thermal evolutions and its interactions with hydrothermal system is therefore essential to understand oceanic accretion. Those general issues were the rationale of drilling ICDP OmanDP Hole GT3A, and we present herein the geological, structural, and petrological data that were used as a site survey to select its location. GT3 area enables observations in three dimensions of fossilized AMLs and overlying dikes. The new field data and corresponding mineral compositions are used together with thermokinetic and thermodynamic models to deliver an integrated dynamic model for the AML/hydrothermal system interactions. Results attest that the isotropic gabbro interval is composite, with gabbro bodies intruding and reheating both gabbros and dikes (up to 1,040°C). We show that AMLs should be considered as transient igneous bodies that likely crystallize from primitive MORBs in decades, releasing heat to the intruded hosts, and feeding high temperature vents on the seafloor. We show for the first time that the thermal gradient recorded in AML roof is consistent with the heat fluxes reported at active hydrothermal vents.

AB - At oceanic spreading centers, the interactions between the igneous system that builds the crust, and the hydrothermal system that cools it govern the plumbing system architecture and its thermokinetic evolution. At fast-spreading centers, most of those interactions occur around the axial magma lens (AML) that feeds the upper crust, and possibly part of the underlying mushy igneous reservoir. Heat extracted from crystallizing AML is transferred through a conductive boundary layer to the overlying hydrothermal system. Quantifying the AML physical and thermal evolutions and its interactions with hydrothermal system is therefore essential to understand oceanic accretion. Those general issues were the rationale of drilling ICDP OmanDP Hole GT3A, and we present herein the geological, structural, and petrological data that were used as a site survey to select its location. GT3 area enables observations in three dimensions of fossilized AMLs and overlying dikes. The new field data and corresponding mineral compositions are used together with thermokinetic and thermodynamic models to deliver an integrated dynamic model for the AML/hydrothermal system interactions. Results attest that the isotropic gabbro interval is composite, with gabbro bodies intruding and reheating both gabbros and dikes (up to 1,040°C). We show that AMLs should be considered as transient igneous bodies that likely crystallize from primitive MORBs in decades, releasing heat to the intruded hosts, and feeding high temperature vents on the seafloor. We show for the first time that the thermal gradient recorded in AML roof is consistent with the heat fluxes reported at active hydrothermal vents.

KW - fast-spreading oceanic centers

KW - gabbros

KW - granoblastic dikes

KW - heat flux

KW - magma chamber

UR - http://www.scopus.com/inward/record.url?scp=85106885820&partnerID=8YFLogxK

U2 - 10.1029/2020JB021496

DO - 10.1029/2020JB021496

M3 - Article

AN - SCOPUS:85106885820

VL - 126

JO - Journal of Geophysical Research: Solid Earth

JF - Journal of Geophysical Research: Solid Earth

SN - 2169-9313

IS - 5

M1 - e2020JB021496

ER -