Mantle-derived xenoliths from the Cumbre Vieja 2021 lava flows: insights on the composition of the lithosphere beneath La Palma (Canary Islands)
Authors: Ntaflos Theodoros , Casetta Federico , Sandoval-Velasquez Andrès , Rizzo Andrea Luca , Aiuppa Alessandro , Alonso Mar , Padron Eleazar , Pankhurst Matthew , Perez Nemesio 
Published: March 2022

&lt;p&gt;Small, cm-sized ultramafic xenoliths have been reported from the opening phase of the 2021 eruption at Cumbre Vieja, where clinopyroxene aggregates, sometimes amphibole, olivine and/or magnetite-bearing (Pankhurst et al., 2021), likely represent early fractionation products and/or relics of mush-like systems located beneath the volcanic edifice.&lt;/p&gt;&lt;p&gt;Detailed sampling of the lavas produced during the intermediate-late eruptive phase (November 9&lt;sup&gt;th&lt;/sup&gt;) revealed the existence, in the massive portion of the flows, of a 1 cm sized dunitic xenolith with protogranular to partly recrystallized texture. The internal portion of the xenolith is composed of Fo&lt;sub&gt;88-89&lt;/sub&gt; olivine (0.33-0.34 wt% NiO), Ti-Al-poor clinopyroxene (Mg# = 87-92; Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; &lt;1.7 wt%; TiO&lt;sub&gt;2&lt;/sub&gt; &lt;0.5 wt%), Cr-rich spinel and rare Mg-rich orthopyroxene (Mg# = 88-91; Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; from 0.4-0.5 to 1.7-1.9 wt%). Textural and chemical data (Fe-Mg distribution) indicate that olivine, orthopyroxene and clinopyroxene are not far from equilibrium. Preliminary calculations show that the equilibrium T recorded by the xenolith ranges from 950 to 1070&amp;#176;C, with good consistency between results obtained from olivine-spinel and orthopyroxene-clinopyroxene pairs. Silica oversaturated interstitial glasses (SiO&lt;sub&gt;2&lt;/sub&gt;= 67 wt%) were found in the partly recrystallized part of the xenolith.&lt;/p&gt;&lt;p&gt;Part of the coarse-grained xenolith forms a corona of fine-grained and worm-like association of, olivine, orthopyroxene, clinopyroxene and spinel. Both parts are surrounded by a continuous narrow external zone consisting of Ti-magnetite and sub-euhedral greenish Ti-augite, which is in contact with the host basalt. The composition of olivine and orthopyroxene in the corona keeps getting more Fe-rich towards the external zone whereas the clinopyroxene changes gradually from Ti-free to Ti-bearing diopside.&lt;/p&gt;&lt;p&gt;The small xenolith recovered from the November 9&lt;sup&gt;th&lt;/sup&gt; lava flow is apparently a mantle-derived xenolith similar to those from the Duraznero 1949 eruption described by Kl&amp;#252;gel (1998), and those from the San Antonio 1677 eruption described by Neumann &amp; Wulff-Pedersen, 1997. &amp;#160;On the way to surface, the mantle xenolith likely reacted with basaltic melts to form the first corona. These processes presumably took place in depths between 0.10-0.12 GPa as can be inferred by the presence of silica oversaturated glasses (Neumann &amp; Wulff-Pedersen, 1997). The external zone probably formed as the result of a late-stage stagnation of the host magma at sub-crustal depths, as suggested by the compositional similarity between the clinopyroxene-spinel assemblage and the phenocrysts in the matrix.&lt;/p&gt;&lt;p&gt;&lt;em&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; &lt;/em&gt;&lt;/p&gt;&lt;p&gt;&lt;em&gt;Kl&amp;#252;ger, A. (1998). Reactions between mantle xenoliths and host magma beneath La Palma (Canary Islands: constraints on magma ascent rates and crustal reservoirs. Contrib Mineral Petrol 131:238-257&lt;/em&gt;&lt;/p&gt;&lt;p&gt;&lt;em&gt;Neumann, E.-R. and E. Wulff-Pedersen (1997). &lt;/em&gt;&lt;em&gt;The Origin of Highly Silicic Glass in Mantle Xenoliths from the Canary Island. Journal of Petrology 32: 1515-1539&lt;/em&gt;&lt;/p&gt;&lt;p&gt;&lt;em&gt;Pankhurst, M. J., et al., (2021). Petrology of the opening eruptive phase of the 2021 Cumbre Vieja eruption, La Palma, Canary Islands. Volcanica: 5(1), 1&amp;#8211;10&lt;/em&gt;&lt;/p&gt;