ORIGINAL ARTICLE Olivine and Cr-spinel as indicators of the petrogenesis and partial melting conditions of the high-MgO ultramafic volcanic rocks from NW Ad Dhala Province—Yemen Mukhtar A. Nasher 1 • Murad Ali 1 Received: 7 July 2020 / Revised: 15 December 2020 / Accepted: 12 January 2021 / Published online: 3 February 2021 Ó Science Press and Institute of Geochemistry, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2021 Abstract The high-MgO ultramafic volcanic rocks in the NW Ad Dhala province are classified as meimechite according to the IUGS classification scheme. This province represents the southeastern outcrops of the Yemen Vol- canic Group (YVG), which constitutes part of the Afro- Arabian continental large igneous province (LIP) and located within the boundary of the Afar mantle plume. In this study, we present the chemical compositions of olivine and Cr-spinel in meimechite rocks from Bagah Village in NW Ad Dhala province, aiming to characterize the genesis and partial melting conditions and to estimate the crystal- lization temperatures of these high-MgO rocks. Olivine crystals are characterized by high forsterite, ranges from Mg-rich core (up to Fo 89.69 ) to relatively Fe-rich rim (down to Fo 78.57 ), high CaO, MgO and MnO whereas Cr-spinel crystals have high TiO 2 and Cr# values ranging from 0.49 to 0.63 which indicate that they are crystallized from pri- mary magma and are typical of volcanic olivine and Cr- spinel that formed in intraplate tectonic setting. Olivine and Cr-spinel compositional data and primary melt composi- tion (MgO * 23 wt.%) are compatible with the derivation of studied meimechite rocks from peridotite mantle source by small degrees of partial melting under conditions of high temperature and pressure at great depths, mostly within the garnet stability field. Also, these data provide a compelling indicator for the important role of upwelling Afar mantle plume in the genesis of these high-MgO ultramafic volcanic rocks. Finally, based on the different olivine-liquid equilibrium methods and Al-in-olivine thermometer approach the estimated crystallization tem- perature ranges from 1450 to 1490 °C, and mantle potential temperature (Tp) ranges from 1617 to 1677 °C, at high pressure (3–4.8 GPa). These high temperatures substantiate the existence of the Afar thermal mantle plume and its important role in the genesis of the studied meimechite rocks. Keywords Olivine  Cr-spinel  High-MgO ultramafic volcanic rocks  meimechite  Afro-arabian LIP  Yemen 1 Introduction The Afro-Arabian continental floods province is one of the Phanerozoic large igneous provinces (LIPs) that is covering extensive areas extend from SW Ethiopia to western Yemen and SW Saudi Arabia passing through Djibouti and Eritrea (Fig. 1a). The formation of this continental LIP is associated with the continental rifting and formation of the Red Sea and the Gulf of Aden basins due to the emergence of the Afar mantle plume and the movement of the Arabian plate away from Africa in the NE direction (e.g.Joffe et al. 1987; Mohr et al. 1988; Jestin et al. 1994; Mattash 1994; Al-Kadasi 1994; Davison et al. 1994; Baker et al. 1996a; Chu et al. 1998; Ghebreab 1998; Ukstins et al. 2002, 2005; Bosworth et al. 2005; Mattash et al. 2013). Within the volcanic rocks of the LIPs, the occurrence of high-MgO volcanic rocks such as picrite, ferropicrite, komatiite, and meimechite is relatively uncommon, how- ever, they are reported to be found in many continental LIPs such as the Siberian LIP (e.g., Arndt et al. 1995; Kogarko et al. 2000; Carlson et al. 2006; Elkins-Tanton et al. 2007; Sobolev et al. 2009; Vasil’ev et al. 2014; Ivanov et al. 2018), the Karoo LIP (e.g. Heinonen et al. & Mukhtar A. Nasher mukhtar_nasher@yahoo.com 1 Department of Geology, Faculty of Applied Sciences, Taiz University, Taiz, Yemen 123 Acta Geochim (2021) 40(4):532–556 https://doi.org/10.1007/s11631-021-00454-6