Chronostratigraphy of Gran Canaria

Abstract

A chronostratigraphy of Miocene/Pliocene volcanism on Gran Canaria (Canary Islands) has been established by single-crystal 40Ar/39Ar laser dating of feldspar crystals from 58 samples of welded ignimbrites, lava flows, fallout tephra layers, and intrusive rocks. All subaerially exposed volcanic and intrusive rocks of Gran Canaria were emplaced within the last 14.5 Ma, comprising three major magmatic/volcanic cycles. The subaerial Miocene evolution started with the rapid formation (<0.5 Ma) of the exposed, mildly alkalic shield basalts. The basaltic shield phase ended between 14.04 ?? 0.10 Ma and 13.95 ?? 0.02 Ma and was followed by a 0.6-m.y. magmatism of trachytic to rhyolitic composition (Mogan Group). Single-crystal 40Ar/39Ar laser dating shows that the ash flows erupted at intervals of 0.03-0.04 m.y., with peak eruption rates as much as 2000 km3/m.y. during the initial stages of silicic magma production (Lower Mogan Formation). High-precision ages have been determined for major, widespread lithostratigraphic markers of the Mogan Group, such as ignimbrite P1 (13.95 ?? 0.02 Ma), ignimbrite X (13.71 ?? 0.02 Ma), ignimbrite D (13.44 ?? 0.01 Ma), and ignimbrite E (13.37 ?? 0.03 Ma). After the rhyolitic stage, >500 km3 of silica-undersaturated nepheline trachyphonolitic ash flows, lava flows, and fallout tephra, as well as rare basanite and nephelinite dikes and lavas were erupted between 13.29 Ma and 13.04 Ma (Montana Horno Formation) and 12.43 Ma and 9.85 Ma (Fataga Group). This stage was accompanied and followed by intrusive syenites and a large cone sheet swarm in the central caldera complex, lasting until at least 8.28 Ma. Following a major, nearly nonvolcanic hiatus lasting ~4.7 m.y. (Las Palmas Formation), eruptions resumed with the local emplacement of small volumes of nephelinites, basanites, and tholeiites at ~5 to 4.5 Ma, with peak activity and eruptions of highly evolved phonolite magma between 4.15 and 3.78 Ma (Roque Nublo Group).