Evidence for a Moist to Wet Source Transition Throughout the Oman‐UAE Ophiolite, and Implications for the Geodynamic History

Abstract

The Oman-United Arab Emirates (UAE) ophiolite represents the largest and best-preserved fragment of obducted oceanic lithosphere in the world. However, debate continues regarding its geodynamic history. This debate is in part a consequence of the lateral variability in the later stage magmatic units, with arc signatures considered to be well developed in the north of the ophiolite but less so in the south. In this study, we investigate later stage intrusions in the central and southern part of the ophiolite. These intrusions vary from wehrlite to gabbro and tonalite and crosscut all levels of the main ophiolite sequence from the mantle peridotites up to the sheeted dike complex. They are characterized by the presence of magmatic amphibole, low TiO 2 (<1 wt%), document an enrichment in Th, Sr, and Ba, depletion of Y and Dy, and decreasing Dy/Yb and Dy/Dy* with increased fractionation. These data record hydrous fractionation with a significant role for amphibole, which is comparable to many arc-type magmas. The relative Nb and light rare earth element ((La/Yb)n chon < 1) depletion and coupled Nd and Hf isotope variations indicate the same (but depleted) Indian mid-ocean ridge basalts-type mantle source as the main ophiolite sequence. More radiogenic Pb isotope compositions of plagioclase imply the addition of a fluid component likely derived from sediments or altered oceanic crust. These intrusions occur across larger areas than previously reported, implying the entire ophiolite formed in a setting characterized by arc-type magmas, such as a suprasubduction zone setting.

Ocean crust accretion along a high-temperature detachment fault in the Oman ophiolite: A structural and petrological study of the Bahla massif

“…The tectonic setting (subduction-related basins vs. more open ocean ridge segments) during the igneous accretion of the Oman ophiolite is a long-standing debate (e.g. Coleman, 1981;Pallister and Hopson, 1981;Hopson et al, 1981;Pearce et al, 1981;Searle et al, 2004;Gray et al, 2005;Ishikawa et al, 2005;Boudier and Nicolas, 2007;Warren et al, 2007, MacLeod et al, 2013De Graaf et al, 2019;Agard et al, 2020). Plate tectonic reconstructions, imprecise during the Cretaceous normal magnetic superchron, are of little help to solve this specific problem (Granot et al, 2012).…”

“…"P1 vs. P2") for the emplacement and crystallization of the two plutonic series is difficult to determine at the global scale, authors working on different outcrops and different lithologies reaching contrasted conclusions (e.g. Benoit et al, 1999;Python and Ceuleneer, 2003;Haase et al, 2016;Goodenough et al, 2014;Rospabé et al, 2017;De Graaf et al, 2019).…”

Wet magmatic processes during the accretion of the deep crust of the Oman Ophiolite paleoridge: Phase diagrams and petrological records

“…Zircon dating has revealed that the paleocrust formed ~95 Ma ago under fast-spreading conditions with a half-spreading rate of 50 -100 mm/yr (Rioux et al, 2012). In contrast with the contemporary fast-spreading mid-ocean ridges such as the EPR, field relations and geochemical results suggest a polygenetic origin for the Oman ophiolite (e.g., de Graaff et al, 2019). The first magmatic phase produced the socalled V1 lavas and related gabbros that are very similar to the modern EPR, except that the parental MORB melts show enhanced water contents due to the influence of the regional subduction initiation (e.g., MacLeod et al, 2013).…”

A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence

“…A growing body of geochemical and geochronological evidence indicates that the crustal sequences of many Tethyan ophiolites -including the Oman-U.A.E. (Semail) example -formed in response to upper-plate extension during the initiation of lower-plate subduction and roll back Dilek et al, 2007;Dilek and Furnes, 2009;Guilmette et al, 2018;Ishikawa et al, 2002;MacLeod et al, 2013;Metcalf and Shervais, 2008;Rollinson, 2009;Rollinson and Adetunji, 2015;Shafaii Moghadam et al, T. M. Belgrano et al: A revised map of volcanic units in the Oman ophiolite 2013; Stern and Bloomer, 1992). These findings have led to reinterpretation of many ophiolites as counterparts to difficult-to-access magmatic records of subduction initiation preserved in submarine forearcs and arc basement ("protoarcs"; Stern et al, 2012;Stern and Bloomer, 1992;Whattam and Stern, 2011).…”