Multi‐Stage Hydrothermal Veins in Layered Gabbro of the Oman Ophiolite: Implications for Focused Fluid Circulation in the Lower Oceanic Crust. Issue 8 (16th August 2021)

• Record Type: Journal Article
• Authors: Zhang, Chao; Koepke, Jürgen; Wolff, Paul Eric; Horn, Ingo; Garbe‐Schönberg, Dieter; Berndt, Jasper
• Is Part Of: Journal of geophysical research. Volume 126:Issue 8(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-08-16
• Subjects: Oman ophiolite -- lower oceanic crust -- layered gabbro -- hydrothermal vein -- hydrous partial melting -- amphibole; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2021JB022349
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: An outcrop in the layered gabbro section from the Wadi Wariyah of the Oman ophiolite has been investigated to provide new insights into the hydrothermal activities that cover a large temperature range in the lower crust at fast‐spreading mid‐ocean ridges. Our observations reveal a complex veining system composed of gabbroic dikes, hydrous mineral (amphibole, epidote, and prehnite) veins and associated alteration, which strongly overprinted the layered gabbros shortly after the solidification of the gabbroic cumulates. The general strike of the veins is roughly perpendicular to the magmatic foliation of the layered gabbro. Mineral‐based geothermometry indicates a wide temperature range (ca. 1, 000−250°C) of hydrothermal activities, spanning from hydrous suprasolidus stage (VHT) through amphibolite facies (HT) and epidote‐amphibolite facies (MT) down to the prehnite‐pumpellyite facies (LT), which induced significant differences in selective element depletion and enrichment as well as in exchange of Sr and O isotopes. A key observation is the omnipresence of relics from a previous temperature stage in a given hydrothermal paragenesis formed at lower temperatures, implying that the same pathways were used for hydrothermal veining in a broad temperature interval spanning about 750°C. Our observations support a model that focused fluid circulations, in the form of combined microcracking (grain boundary spacing) and macrocracking (veining), developed shortly subsequent to the complete solidification of the layered gabbros, which may have facilitated effective cooling for magma crystallization in the lower crust. Plain Language Summary: The hydrothermal cooling process of the oceanic crust at the spreading center is crucial for understanding its accretion mechanism. In this paper, we present new data, which unambiguously indicate that the same pathways are used for hydrothermal cooling across a broad temperature range. The results and the conclusion of our study has the potential to enhance our understanding on the cooling mechanism occurring at the deep crust significantly and will also aid future works of thermal modeling. Key Points: hydrothermal alteration beneath mid‐ocean ridges (MOR) starts at very high temperature The same pathways were used for hydrothermal veining in a broad temperature Petrology and Sr‐O isotopes indicate variable fluid/rock ratios