Journal
GEOCHIMICA ET COSMOCHIMICA ACTA
Volume 331, Issue -, Pages 35-47Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.gca.2022.06.002
Keywords
Canary Islands; Ocean island basalt; Lavas; Xenoliths; Helium; Neon; Argon
Categories
Funding
- NSF Petrology and Geochemistry program [NSF EAR 1447130, EAR 1918322, EAR 0439122]
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The noble gas isotope systematics of ocean island basalts suggest relatively undegassed and primitive mantle sources. The Canary Islands lavas confirm the dominance of gas-rich mantle sources in ocean island basalts.
Noble gas isotope systematics of ocean island basalts (OIB) provide evidence for relatively undegassed and primitive mantle sources. These OIB sources partly derive from the deep mantle by virtue of their distinctiveness from mid-ocean ridge basalts (MORB), which dominantly sample upper mantle. New helium, neon and argon isotope data are presented for Canary Islands lavas, carbonatites and cumulate and mantle xenoliths confirming He-3/He-4 ratios that are the same or lower than MORB, but that are heterogeneous (similar to 3-9.5R(A)) within and between islands in the archipelago. Neon and Ar isotope systematics for lavas are mostly within the range of air compositions. Harzburgite xenoliths from Lanzarote, which are interpreted to represent ancient refractory mantle residues, have distinct He-Ne-Ar isotope systematics from lavas or cumulate xenoliths. The harzburgites are characterized by forsteritic olivine (>Fo(91)) with uniformly low-He-3/He-4 (6.6 +/- 0.2RA), high Ar-40/Ar-36 (630-4900), and have Ne isotope compositions that range between air values or that are similar or more nucleogenic than depleted MORB mantle (DMM). Similar refractory mantle peridotites have been discovered as xenoliths at other OIB localities and are likely to be distinct from continental lithospheric mantle. Refractory mantle (RM), which by virtue of its high melting temperature is difficult to partially melt, may be a significant component in the convecting mantle and has potential to impart a cryptic noble gas signature to partial melts in intraplate, divergent and convergent margin settings. In this sense, RM may represent a 'sixth mantle component' after DMM, high-mu (high U-238/Pb-204; HIMU), enriched mantle endmembers (EMI, EMII) and the 'focus zone' (FOZO). An RM-type component may be presented in the older eastern Canary Islands and possibly in recent rejuvenated volcanism from Teide (Tenerife). Canary Island intraplate volcanism samples multiple mantle components, confirming that the most gas-rich mantle sources involved in magmatism dominate OIB noble gas compositions. (C) 2022 The Author. Published by Elsevier Ltd.
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