Along‐axis magmatic system in the northern Oman ophiolite: Implications of compositional variation of the sheeted dike complex

Abstract

[1] Along-axis variations for 70 km from the northern propagating tip at Wadi Fizh to the southern margin of the Hilti block in the northern Oman ophiolite are studied on the basis of bulk rock and pyroxene compositions of the sheeted dike complex. Less evolved dikes with tight compositions predominate at the segment center (Wadi Thuqbah-Ays area), while dikes with much broader compositions occur at both northern and southern ends. The appearance of highly evolved rocks at the segment margin suggests more intensive fractional crystallization at the margin. Paradoxically, primitive rocks occur at both ends, indicating processes other than simple crystallization. These features are interpreted as follows: a more steady state melt lens at the segment center would result in less evolved melts with tight compositions, and a smaller melt lens at the segment margin due to cooler conditions would result in two melts, evolved melts ascribed to a more closed system fractional crystallization, and primitive melts emplaced from depths without stagnancy in the melt lens. Zr/Nb and Y/Nb ratios of the bulk analyses are constant over the whole segment, indicating a comparatively uniform source along the segment. For quantitative considerations, 26 analyses were selected from 125 analyses. Na 8.0 and Ti 8.0 values are lower at the segment center than at the north and south parts. Partial melting degrees are estimated to be about 20% at the center and 16% at the segment boundary, respectively. This is consistent with clinopyroxene compositions of the sheeted dike complex and layered gabbros. The pyroxenes are lower in Na 2 O at the segment center than those at the segment margin as compared with the same Mg#, suggesting independently a higher degree of partial melting at the segment center. The trace element contents of the sheeted dike complex show MORB signatures. However, the Ti 8.0 and Si 8.0 of the sheeted dike complex are lower and slightly higher than modern N-MORBs, respectively. This implies that the source mantle beneath paleo-ridges which produced the Oman ophiolite was different from those of modern mid-ocean ridges.

Crustal diopsidites from the northern Oman ophiolite: Evidence for hydrothermal circulation through suboceanic Moho

“…1). We can observe sharp gabbro/peridotite transition along Wadi Fizh in the northern Oman ophiolite (e.g., Uesugi et al, 2003;Akizawa and Arai, 2009), which reveals excellent exposures of crust -mantle rocks formed at a segment margin of a spreading ridge (Miyashita et al, 2003). Dark brown chlorite rocks were formed in isotropic gabbros, which are located just below the sheeted dike complex along Wadi Bani Umar in the Fizh block of the northern Oman ophiolite (Yoshitake et al, 2009).…”

Root zone of the sheeted dike complex in the Oman ophiolite

“…They were mapped as ''late intrusive'' [Lippard et al, 1986; Ministry of Petroleum and Minerals, 1986], encompassing, wehrlites and gabbronorites, uralitic gabbros, diorites and tronjhemites, the last one making up magmatic breccias with diabase dikes. Olivine gabbros have not been reported among these intrusions These ''late intrusive'' have been related to domains where accretion was under the influence of major tectonic and magmatic activity related to ridge propagation [Juteau et al, 1988;MacLeod and Rothery, 1992;Nicolas and Boudier, 1995;Boudier et al, 2000;Adachi and Miyashita, 2003;Miyashita et al, 2003;Umino et al, 2003]. Here, they are referred to as domains of ''ridge segmentation'' and opposed to domains where the accretion should have been steady state, called here ''normal'' domains, considering their continuity and homogeneity.…”

Geology and petrology of the plutonic complexes in the Wadi Fizh area: Multiple magmatic events and segment structure in the northern Oman ophiolite

“…The analyses are shown in Table 2 except for dolerite dikes which are tabulated by Miyashita et al [2003] together with dolerite analyses from extensive areas. The analytical method for major and minor elements is after Takahashi and Shuto [1997].…”