Complexity of metasomatic and magmatic processes on crust-mantle boundary beneath the Hebridean terrane - mysterious origin of ultramafic and felsic xenoliths and megacrysts from Loch Roag monchiquite (Lewis Island, Outer Hebrides, UK).

• Main Authors: Buczko, Daniel, Matusiak-Małek, Magdalena, Upton, Brian G. J., Puziewicz, Jacek, Ntaflos, Theodoros, Grégoire, Michel
• Other Authors: Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2022
• Subjects: [SDU]Sciences of the Universe [physics]; Lewis Island; Menzies; North Atlantic
• Online Access: https://insu.hal.science/insu-03669377

International audience The xenolith suite in from Loch Roag (Lewis Island, N Scotland) Eocene (Faithfull et al. 2012, JGS) monchiquite dyke comprises ultramafic, mafic and felsic rocks. The peridotitic xenoliths represent samples of Archean mantle underlying marginal parts of North Atlantic Craton, while the origin of non-peridotitic xenoliths is not clear. The studied xenoliths are anhydrous diorites (plagioclase, clinopyroxene formed after replacing of orthopyroxene, apatite, opaques), syenite (dominating K-feldspar, clinopyroxene, biotite, apatite, spinel) and biotite clinopyroxenites (+apatite), megacrysts are represented by clinopyroxene and K-feldspar, both enclosing inclusions of clinopyroxene, biotite and apatite. Megacrysts of alkaline, Na-rich feldspar associated with corundum and HFSE-bearing minerals have been also described from this locality (Menzies et al., 1986). Clinopyroxene in anhydrous diorites and biotite clinopyroxenites is Al-augite/Al-diopside with Mg#=56-75 and 64-85 (Al=0.2-0.4 a.pfu), respectively, and negative Nb-Ta, Zr-Hf, Sr and Ti anomalies. Plagioclase (An40-25) in diorites is characterized by negative Nb-Ta, Zr-Hf and Ti anomalies. Composition of clinopyroxene (Al, Ti diopside) from syenites, K-feldspar megacrysts and clinopyroxene megacrysts are similar in terms of major elements (Mg#=45-72; Al=0.2-0.5 a.pfu), but the trace element concentration in clinopyroxene from syenite is lower than in other rocks from this group. K-feldspar forming megacrysts and syenite exhibit wide range of compositions (>Or55, An0-10), but the latter one is significantly poorer in trace elements. Composition of apatite in clinopyroxene megacryst imply magmatic origin of the suite (O'Reilly and Griffin, 2000, Lithos). Our study shows that the anhydrous diorites and biotite clinopyroxenites from Loch Roag may be genetically related. Rocks similar to anhydrous diorite occurring in Western Redhills igneous complex from Isle of Skye (Scotland) have been interpreted as late fractionates from deep-seated ...