Metasedimentary xenoliths in the lavas of the Timanfaya eruption (1730–1736, Lanzarote, Canary Islands): metamorphism and contamination processes

• Published in: Geological magazine Vol. 143; no. 2; pp. 181 - 193
• Main Authors: APARICIO, A., BUSTILLO, M. A., GARCIA, R., ARAÑA, V.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.03.2006
• Subjects: assimilation; Atlantic Ocean Islands; basalts; Calcite; Canary Islands; Cenozoic; chemical composition; contact metamorphism; Contamination; Dolomite; eruptions; geochemistry; ICP mass spectra; igneous and metamorphic rocks; igneous rocks; inclusions; Invertebrata; Lanzarote; Lava; Magma; magma contamination; mass spectra; metals; Metamorphic rocks; Metamorphism; metasedimentary rocks; metasedimentary xenoliths; microfossils; mineral composition; Mineralogy; Original Article; P-T conditions; Paleocene; Paleogene; petrography; Petrology; Protista; Radiolaria; rare earths; Sedimentary rocks; Silica; spectra; Tertiary; textures; tholeiitic basalts; tholeiitic composition; Timanfaya; Trace elements; volcanic rocks; volcanism; Volcanoes; X-ray diffraction data; xenoliths; Lanzarote; contact metamorphism; metasedimentary xenoliths; tholeiitic basalts; assimilation
• ISSN: 0016-7568; 1469-5081
• DOI: 10.1017/S0016756806001713

We report on the investigation of contact metamorphism provoked by the emplacement of a shallow magma chamber during the Timanfaya eruption of Lanzarote from 1730 to 1736 AD. The study was carried out on metamorphic xenoliths from basaltic Timanfaya lavas, and shows how the primary basanitic magma was contaminated by sedimentary and metamorphic rocks. Mineralogical and chemical studies allowed the definition of several xenolith types. Silica xenoliths (quartz, tridymite, cristobalite or a mixture of these, constituting more than 50 % of the xenolith) and calc-silicate xenoliths (wollastonite, sometimes the 2M type, diopside, forsterite or mixture of these, constituting more than 50 % of the xenolith) are the most frequent. Other minerals recognized were calcite, dolomite, augite, enstatite, hypersthene, spinel and scapolite. The mineralogy and some textures of the metamorphic forsteritic xenoliths are identical to those found in ultrabasic xenoliths (dunites) and point to a possible metamorphic origin for some of them. Major and trace elements showed a diversity of composition, controlled by the mineralogy. The REE composition of the metamorphic xenoliths is high, compared with the sedimentary xenoliths not affected by metamorphism. The mineral assemblages define metamorphic facies of low, medium and high grade, depending on the distance of the sedimentary rocks from the magma chamber border. The IGPETWIN-MIXING program was used to verify the contamination process, taking the xenoliths as representative of the sedimentary/metamorphic rocks that were melted. The results indicated that sedimentary/metamorphic rock contamination of a basanitic magma can produce tholeiitic compositions.