Mantle Degassing Through Continental Crust Triggered by Active Faults: The Case of the Baja California Peninsula, Mexico. (17th April 2019)

• Record Type: Journal Article
• Authors: Batista Cruz, Ramón Yosvanis; Rizzo, Andrea Luca; Grassa, Fausto; Bernard Romero, Rubén; González Fernández, Antonio; Kretzschmar, Thomas Gunter; Gómez‐Arias, Efraín
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 20:Number 4(2019)
• Page Start: 1912
• Page End: 1936
• Publication Date: 2019-04-17
• Subjects: Baja California -- magmatic and hydrothermal gases -- 3He/4He -- δ13CCO2 -- mantle degassing -- tectonic; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2018GC007987
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: In this work, we report new chemical and isotopic data ( 3 He/ 4 He, δ 13 CCO2, δ 13 CCH4, and δDCH4 ) from poorly or previously unstudied hydrothermal and magmatic gases that are emitted along the eastern coast of the Baja California Peninsula (BCP). High 3 He/ 4 He values (up to ~7 Ra) characterize the magmatic gases, while lower ratios (≤1.6 Ra) characterize hydrothermal springs. We infer that the mantle beneath the BCP could be Mid‐ocean‐ridge basalt (MORB)‐likes, as in the rift within the Gulf of California, or it may reflect contamination from C‐rich sediment during paleo‐subduction of the Farallon plate. During their ascent, through the crust, mantle/magmatic gases mix with CO2 ‐ and 4 He‐rich fluids, thus forming CO2 ‐rich hydrothermal gases. These hydrothermal gases undergo partial dissolution of CO2 in shallow waters under different temperature and pH conditions, which further modifies their composition. Thermogenic and possibly abiogenic sources of methane are present only in magmatic gases from the BCP. Secondary methane oxidation (microbial/inorganic) processes are proposed for some hydrothermal gases, which are extremely enriched in heavy isotopes. Finally, we argue that the hydrothermal gases that are emitted from the BCP have variable percentages of mantle contribution, indicating the presence of lithospheric faults enhancing the rise of mantle fluids also in areas where volcanism is absent. Key Points: Based on 3 He/ 4 He, the gases emitted from the Baja California Peninsula have two origins: magmatic and hydrothermal The hydrothermal gases contain variable mantle contributions that indicate the presence of active faults The mantle beneath the Baja California Peninsula could be contaminated from subducted C‐rich sediment