Geochronology and Stratigraphy of the Roque Nublo Cycle, Gran Canaria, Canary Islands

Journal ofthe Geological Society, London, Vol. 152, 1995, pp. 807-818, 5 figs, 5 tables. Printed in Northern Ireland Geochronology and stratigraphy of the Roque Nublo Cycle, Gran Canaria, Canary Islands F. J. PEREZ-TORRADO', J. c. CAR RACE DO^ & J. MANGAS' I Departamento Fisica-Geologia, Facultad Ciencias del Mar, ULPGC, PO Box 550, 35080-Las Palmas de Gran Canaria, Canary Islands (Spain) 2Volcanological Station of the Canary Islands, Spanish Research Council (CSIC), PO Box 195, 38080-La Laguna, Tenerife, Canary Islands (Spain) Abstract: The Roque Nublo Cycle, of Pliocene age, is the second main cycle of subaerial volcanic activity in GranCanaria. During this cycle a stratovolcano at least2500111 high developed in the central part of theisland; its volcanic products covered an area of about540 km2. Thedetailed stratigraphy of the Roque Nublo Cycle, together with a magnetostratigraphic study and six new K-Ar dates, which complement 22 previously published ones, have led to the reconstruction of the volcanic history of this cycle in which six main stages have been distinguished. The revised chronology of the Roque Nublo Cycle implies an overlap in age with the earliest rocks of the third cycle of subaerial activity in Gran Canaria. No volcanic hiatus occurred between the second and third cycles, as was previously thought to be the case. Keywords: Canary Islands, stratigraphy, geochronology, stratovolcanoes. Interbedded fossiliferous layers are absent from the volcanic Miocene with an episode of submarine volcanism that sequences of theCanary Islands. Therefore dating the represents 75% of the total volume of the island (Schmincke volcanic formations has been mainly by radiometric (K-Ar) 1982, 1990). The subaerial development of the island can be and, to a lesser extent, palaeomagnetic methods. divided into three main magmatic cycles, called Cycle I or More than a hundred radiometric ages of Gran Canaria Old (Miocene), Cycle I1 orRoque Nublo(Pliocene) and havebeen published since the early 1970s. These have Cycle 111 orRecent (Plio-Quaternary) (Schmincke 1976; mainly been 40K-40Ar (Abdel-Monem et al. 1971; Lietz & McDougall & Schmincke 1976; Araiia & Carracedo 1978; Schmincke 1975; McDougall & Schmincke 1976; Feraud et ITGE 1992). al. 1981; ITGE 1992), andto a lesser extent 4"Ar-'9Ar The Roque Nublo Cycle began at about 5.5 Ma, after a (Bogaard et al. 1988; Clark 1988) and I4C (Nogales & period of volcanic repose of at least 3 Ma following Cycle 1. Schmincke 1969) methods. Twenty two of these, obtained by Atthe beginning of this eruptivereawakening of Gran the 40K-4"Ar method, date lava flows and intrusions of the Canaria,strombolian-type basaltic fissure eruptionswere Roque Nublo Cycle (Table 1). located in thesouthern slopes of the island, producing Despitethe numerous radiometricages published, NW-SE lineations of cindercones and nephelinitic lava several important aspects of the volcanic history of the fields of relatively small surfaceextent. Lateron, the Roque Nublo Cycle remain unclear. For example, the age of volcanic activity was concentrated at the centre of the island the explosive eruptions which generated the Roque Nublo where it remained until the end of the Roque Nublo Cycle breccia deposits andthe age of emplacement of the (Hoernle 1987; Schmincke 1990; P6rez-Torrado 1992). phonolitic plugs stratigraphically located at the end of the During thelatter stage,large amounts of lava flows and cycle are not known. This paper details the stratigraphy and breccia-type pyroclastic deposits(known as Roque Nublo geochronology of theRoque Nublo Cycle, and gives an agglomerates or breccias) were produced. At the end of the evolutionarymodel of this cycle, onthe basis of cycle, endogenous phonolitic plugs were intruded (F6ster et magnetostratigraphy and K-Ar dating. It also demonstrates d. 1968; Anguita 1972, 1973; Schmincke 1976, 1990; Brey & the importance 01 combiningradiometric and mag- Schmincke 1980; Hoernle 1987; Anguita et al. 1989,1991; netostratigraphic methods when dating volcanic formations Pkrez-Torrado 1992). in the Canarian Archipelago. Some of the results discussed The distribution and geometry of theRoque Nublo here have beenpresented previously (Perez-Torrado & deposits, the outwarddips of lava and pyroclastic flow Mangas 1992; PCrez-Torrado et al. 1993). deposits and the radial pattern of a dyke swarm indicates the existence in thecentre of the island of astratovolcano (Roque Nublostratovolcano) (Fig. 1).This stratovolcano Geological framework of the Roque Nublo Cycle may have reached at least 2500 m above sea level (Anguita The Canary Islands, which comprise seven main islands and et al. 1989,1991; PCrez-Torrado 1992; Mehl & Schmincke several islets, are situated in the Atlantic Ocean between N 1992). 27" and N 30" latitudes (Fig. 1). These islands are located on According tothe previously published ages, the time the passive continental margin of the African plate. span of the Roque Nublo Cycle was from 5.5 to 3.4 Ma and Gran Canaria, a nearly circular island with a diameter of the stratovolcano was active from 4.4 to3.4Ma (Abdel- about 40 km and a height of 1949 m, is located in the centre Monem et al. 1971; Lietz & Schmincke 1975; McDougall & of the archipelago.It is the third largest island in surface Schmincke 1976; Feraud et al. 1981; ITGE 1992). These ages area (1532 km'). Its geological history beganduring the imply a relatively long period of volcanic quiescence before 807 Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/152/5/807/4890370/gsjgs.152.5.0807.pdf by guest on 27 September 2021 808 F. J. PEREZ-TORRADO ET AL. Table 1. Summary of the published K-Ar age determinations (whole rock, 40K/40Ar)for the Roque Nublo Group Sample No. Formation Site location andpetrologyReferences sample Age' Age' GP (M 4 (M4(M4 GC53 1 Tirajana? Tephrite. Area of Las Fortalezas, McDougall & Schmincke 3.40 f 0.08 3.49 Barranco de Tirajana. (1976) GC52 2 Tirajana? Tephrite. Just below sample No. 1. McDougall & Schmincke 3.49 f 0.08 3.58 ( 1976) GCU-29A 3 Tirajana? Tephrite. Mesa de las Burras, Abdel-Monem et al. (1971) 3.50 f 0.09 3.59 Barranco de Tirajana. 1155 4 Tenteniguada Phonolite. Risco Blanco volcanic dome. Lietz & Schmincke (1975) 3.65 f 0.18 3.75 3.71 f 0.18 3.81 GC- 105 5 Rincon de Tejeda? Tephrite with hauyne. Dyke north of Abdel-Monem et al. (1971) 3.75 f 0.12 3.85 Tejeda. P4 6 Riscos de Chapin Ankaramite. Barranco de Tenoya. Lietz & Schmincke (1975) 3.77 f 0.08 3.87 P18 7 Riscos de Chapin Ankaramite. Area of Salto del Negro. Lietz & Schmincke (1975) 3.77 f 0.15 3.87 GC65 8 Riscos de Chapin Phonolite. Road C-811, between Tejeda McDougall & Schmincke 3.81 f 0.09 3.91 and San BartolomC de Tirajana. ( 1976) GC1 9 Tenteniguada Phonolite. Volcanic dome of Montaiia McDougall & Schmincke 3.86 * 0.06 3.96 de 10s Brezos. (1976) GC76 10 Riscos de Chapin Alkali basalt. Barranco de Siberio, near McDougall & Schmincke 3.88 f 0.07 3.98 El Chorrillo. (1976) P15 11 Riscos de Chapin Alkali basalt. Barranco de Tirajana, Lietz & Schmincke (1975) 3.96 f 0.10 4.07 east of Aldea Blanca. 950 12 El Tablero Alkali basalt. Montaiia Molinos. Lietz & Schmincke (1975) 3.99 f 0.10 4.10 4.02 f 0.10 4.13 GC-l612901 13 Riscos de Chapin Basanite. Barranco de Quintanilla. ITGE (1992) 4.15 f 0.10 4.15 1419 14 Riscos de Chapin Alkali basalt. Road from Santa Lucia Feraud et al. (1981) 4.29 f 0.10 4.29 to Temisas. P2 15 Riscos de Chapin Alkali basalt pillow-lava. Lomo de 10s Lietz & Schmincke (1975) 4.25 f 0.09 4.36 Ingleses, northwest of Las Palmas. 4.37 f 0.09 4.49 1244 16 Riscos de Chapin Alkali basalt. Lower sequence of Mesa Lietz & Schmincke (1975) 4.38 f 0.09 4.50 del Junquillo. 4.43 f 0.09 4.55 P12 17 El Tablero Olivine nephelinite. El Tablero de Lietz & Schmincke (1975) 4.86 f 0.15 4.99 Maspalomas. GC-l612908 18 El Tablero Basanitic lava related to the Roque ITGE (1992) 5.01 f 0.09 5.01 Bermejo vent. Road C-810 (Agaete-San Nicolb). 799 19 El Tablero Intracanyon nephelinite lava. Las Feraud et al. (1981) 5.07 f 0.10 5.07 Tabladas, north of San Nicol5s de Tolentino. GC25 20 El Tablero Intracanyon olivine nephelinite lava. McDougall & Schmincke 4.95 f 0.13 5.08 Near the end of the Barranco de (1976) Tazartico. GC-l712901 21 El Tablero Basalt. Pino Gordo eruptive vent. ITGE (1992) 5.32 f 0.07 5.32 GC24 22 El Tablero Intracanyon olivine nephelinite lava. McDougall & Schmincke 5.48 f 0.14 5.58 Mouth of the Barranco de Tazartico. ( 1976) Sample, Site location and sample petrology and Age' are taken from the original references. Age', ages recalculated with the Steiger & Jager (1977) standards. No., refers to Fig. 3. GP, geomagnetic polarity (n.d., polarity not determined). the onset of Cycle 111, the most recent period of activity of fraction). K and @Ar analyses were made in duplicate in order to GranCanaria which startedat approximately 3Ma increase the accuracy of the dates. K-Ar ages were calculated using (McDougall & Schmincke 1976, sample GC-71). However, international standards (Steiger & Jager 1977). Ages from other the data of the present work show that Cycles and 111 authorsand laboratorieswere recalculated using these standards I1 (see Table 1). overlap. Determinations of geomagnetic polarities were carried out on lava and pyroclastic flow deposits using flux-gate portable K-Ar ages and magnetic stratigraphy magnetometers in more than twenty detailed stratigraphic sections, including most of the previously dated rocks (see Figs 1 & 2 and Tables 1 & 2).

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