TY - JOUR

T1 - Wet magmatic processes during the accretion of the deep crust of the Oman Ophiolite paleoridge

T2 - Phase diagrams and petrological records

AU - Koepke, J.

AU - Feig, S. T.

AU - Berndt, J.

AU - Neave, D. A.

AU - Oman Drilling Project Science Team

N1 - Funding Information: This research used samples and/or data provided by the Oman Drilling Project. The Oman Drilling Project (OmanDP) has been possible through co-mingled funds from the International Continental Scientific Drilling Project (ICDP; Kelemen, Matter, Teagle Lead PIs), the Sloan Foundation – Deep Carbon Observatory (Grant 2014-3-01, Kelemen PI), the National Science Foundation (NSF-EAR-1516300, Kelemen lead PI), NASA – Astrobiology Institute (NNA15BB02A, Templeton PI), the German Research Foundation (DFG: KO 1723/21-1, Koepke PI), the Japanese Society for the Promotion of Science (JSPS no:16H06347, Michibayashi PI; and KAKENHI 16H02742, Takazawa PI), the European Research Council (Adv: no.669972; Jamveit PI), the Swiss National Science Foundation (SNF:20FI21_163073, Früh-Green PI), JAMSTEC, the TAMU-JR Science Operator, and contributions from the Sultanate of Oman Ministry of Regional Municipalities and Water Resources, the Oman Public Authority of Mining, Sultan Qaboos University, CNRS-Univ. Montpellier, Columbia University of New York, and the University of Southampton. This study was funded by DFG projects KO 1723/16-1, 21-1, 25-1, and 27-1. DAN acknowledges support from the Natural Environment Research Council ( NE/T011106/1 ).

PY - 2021/10/20

Y1 - 2021/10/20

N2 - The Oman Ophiolite is regarded as an analogue to modern fast-spreading ocean ridge systems in an environment of subduction zone initiation. In contrast to recent mid-ocean ridge basalts from the East Pacific Rise, parental melts at the Oman paleoridge are assumed to be hydrous in nature. In order to constrain the role of water during magmatic accretion processes in the deep crust at the Oman paleoridge, we evaluated several experimental studies in hydrous tholeiitic systems performed at shallow pressures. We concluded that the wehrlitic phase assemblage (olivine coexisting with clinopyroxene but without plagioclase) is the most significant feature indicative of high prevailing water activities. The stability of the wehrlitic assemblage decreases with decreasing pressure (not stable in the upper plutonic crust) and depends on the chemical system (only stable in primitive MORB systems). We applied these results to plutonic rocks from cores drilled as part of the Oman Drilling Project (OmanDP). A key observation is the presence of coherent wehrlitic layers within the layered gabbro series, which are frequent in the lowermost gabbros (20%), relative sparse in the mid-crust (6%), and absent from the top of the plutonic crust at the dike/gabbro transition. Based on the combined phase relations for hydrous MORB-type systems at shallow pressures, we interpret this as a direct consequence of the presence of a significant water activity during the accretion of the plutonic crust of the Oman paleoridge, and not as a local phenomenon related to variations in temperature or bulk chemistry. These findings have implications for the mechanism of accretion of the lower crust at the Oman paleoridge, supporting a model that significant parts of the plutonic crust were produced by in-situ crystallization of primitive melt sills.

AB - The Oman Ophiolite is regarded as an analogue to modern fast-spreading ocean ridge systems in an environment of subduction zone initiation. In contrast to recent mid-ocean ridge basalts from the East Pacific Rise, parental melts at the Oman paleoridge are assumed to be hydrous in nature. In order to constrain the role of water during magmatic accretion processes in the deep crust at the Oman paleoridge, we evaluated several experimental studies in hydrous tholeiitic systems performed at shallow pressures. We concluded that the wehrlitic phase assemblage (olivine coexisting with clinopyroxene but without plagioclase) is the most significant feature indicative of high prevailing water activities. The stability of the wehrlitic assemblage decreases with decreasing pressure (not stable in the upper plutonic crust) and depends on the chemical system (only stable in primitive MORB systems). We applied these results to plutonic rocks from cores drilled as part of the Oman Drilling Project (OmanDP). A key observation is the presence of coherent wehrlitic layers within the layered gabbro series, which are frequent in the lowermost gabbros (20%), relative sparse in the mid-crust (6%), and absent from the top of the plutonic crust at the dike/gabbro transition. Based on the combined phase relations for hydrous MORB-type systems at shallow pressures, we interpret this as a direct consequence of the presence of a significant water activity during the accretion of the plutonic crust of the Oman paleoridge, and not as a local phenomenon related to variations in temperature or bulk chemistry. These findings have implications for the mechanism of accretion of the lower crust at the Oman paleoridge, supporting a model that significant parts of the plutonic crust were produced by in-situ crystallization of primitive melt sills.

KW - Experimental study

KW - Fast-spreading oceanic crust

KW - Hydrous MORB-systems

KW - Oman Drilling Project

KW - Oman ophiolite

KW - Wehrlites

UR - http://www.scopus.com/inward/record.url?scp=85115016309&partnerID=8YFLogxK

U2 - 10.1016/j.tecto.2021.229051

DO - 10.1016/j.tecto.2021.229051

M3 - Article

AN - SCOPUS:85115016309

VL - 817

JO - TECTONOPHYSICS

JF - TECTONOPHYSICS

SN - 0040-1951

M1 - 229051

ER -