Oman Ophiolite: Petrological and Geochemical Investigation of Fast-Spreading Crust Formation Processes

Abstract:

We undertook a detailed field campaign in the Wadi Gideah, which is located in the Wadi-Tayin Massif in the southern part of the Oman Ophiolite, to sample a complete section of fast-spreading oceanic crust. Our concept of performing different analytical and structural investigations on the same samples enabled us to create a coherent data set. The thickness of the layered and virtually undeformed oceanic crust, containing pillow lavas and sheeted dikes as well as varitextured, foliated and layered gabbros resting on a relatively thin MOHO transition zone, was recalculated to approximately 6km. Here we present our data focusing on the petrological and geochemical logs obtained. Samples from the layered gabbro sequence show modal compositions of ~50 vol% plagioclase, ~40 vol% clinopyroxene and ~10 vol% olivine in average. The samples from the foliated gabbro sequence display a slightly higher amount of plagioclase. In very few samples up to 20 vol% of orthopyroxene is present. The layered gabbro sequence display Mg# 71-82 for olivine, Mg# 75-83 for clinopyroxene and An% in plagioclase of 71-93 mol%. The foliated gabbro sequence display Mg# 67-79 for olivine, Mg# 76-85 for clinopyroxene and An% in plagioclase of 58-85 mol%. The varitextured gabbro sequence display Mg# 74-80 for clinopyroxene and An% 59-86 in plagioclase mol%. The generally evolving trends in mineral major element composition from bottom to top of the profile are also observed for bulk rock major and trace element data. The average Sr⁸⁷/Sr⁸⁶ ratio is 0.7033 ± 0.0002 for the entire foliated and layered gabbro with significantly higher values for samples from fault zones cutting the gabbros at all crustal level which here are interpreted as possible hydrothermal pathways for cooling of the deep crust. We calculated the Wadi Gideah bulk crust composition and modeled possible fractionation paths, implying significant crystallization in the deep crust.