Residence time of S-type anatectic magmas beneath the Neogene Volcanic Province of SE Spain: a zircon and monazite SHRIMP study

Abstract

Zircon and monazite from three restitic enclaves and one host dacite have been dated by ion microprobe (SHRIMP), with the aim of characterising their Miocene history and defining the timing relationships between crustal melting and eruption in the high-K calc-alkaline volcanics of the Neogene Volcanic Province of SE Spain. The studied samples are from the volcanic edifices of El Joyazo (Cerro del Hoyazo) and Mazarro´n. Zircons in the enclaves are characterized by a thin euhedral rim overgrowing a detrital core. The corerim boundary is marked by tiny glass inclusions of S-type granitic composition, which attest to the growth of zircon rims during a crustal melting event. At El Joyazo, where lavas erupted at 6.3 Ma (Zeck and Williams 2002), U-Pb ages of zircon overgrowths define an age of anatexis of 9.63±0.26 Ma (95% c.l.), in agreement with monazite ages of 9.74±0.21 Ma (95% c.l.). At Mazarro´n, the age of anatexis provided by monazite at 9.13±0.18 Ma (95% c.l.) overlaps with that of melt-precipitated zircon in the host dacite, dated at 9.06±0.53 Ma (95% c.l.). These results indicate that after partial melting, the enclaves and the syngenetic S-type melts resided at depth for >3 m.y. at El Joyazo. Compared with the results from Mazarro´n, the long residence time obtained at El Joyazo is probably due to the greater depth of melting (c. 25 km vs. c. 15 km). At such depth, corresponding to the Miocene palaeo-Moho, the more ductile regime of the crust is likely to have favoured magma ponding. The thermal anomaly beneath the Neogene Volcanic Province, which generated the S-type crustal melts, is today visible from geophysical data and can be traced back to the Lower Miocene. As a consequence, residence times longer than determined in this work may be expected.

Armouring effect on Sr-Nd isotopes during disequilibrium crustal melting: the case study of frozen migmatites from El Hoyazo and Mazarron, SE Spain

“…850 C) for ca. 3 Myr at El Hoyazo and ,0.8 Myr at Mazarrón (Cesare et al, 2003a). These two different timescales are likely to resemble the generation of granites s.l.…”

“…% anatectic melt from a graphitic metapelite protolith (Cesare et al, 1997). As determined by SHRIMP U-Pb dating on zircon, the eruption age for El Hoyazo high-K calc-alkaline dacite is 6.33 AE 0.15 Ma (Zeck & Williams, 2002) whereas for Mazarrón dacite is 9.06 AE 0.53 Ma (Cesare et al, 2003a). U-Pb age dating of zircon and monazite has also been performed on the restitic xenoliths enclosed in the lavas of El Hoyazo and Mazarrón in order to determine the age of anatexis.…”

“…U-Pb age dating of zircon and monazite has also been performed on the restitic xenoliths enclosed in the lavas of El Hoyazo and Mazarrón in order to determine the age of anatexis. At El Hoyazo, Cesare et al (2003a) found zircon overgrowths and monazite with melt inclusions providing an age of anatexis of 9.63 AE 0.26 Ma, i.e., 3 Myr before the extrusion of the dacite. Conversely, at Mazarrón partial melting of the hosted crustal xenoliths was dated at 9.13 AE 0.18 Ma, coeval with the eruption age of the dacites.…”

Age of anatexis in the crustal footwall of the Ronda peridotites, S Spain

“…Confusion or lack of information on the relationships between radiometric ages and major mineral growth produces a great uncertainty in the P-T-time path and, hence, in the tectonic interpretation of polymetamorphic terrains. In the case of accessory minerals, the link between ages and metamorphic mineral assemblages can be achieved by different approaches, such as: (i) combined ages of accessory mineral and P-T data from garnet, through the study of mineral inclusions in the garnet and the partitioning of REE between garnet and the accessory minerals (Harley and Kelly, 2007;Hermann and Rubatto, 2003;Rubatto, 2002;Whitehouse and Platt, 2003); (ii) in situ dating of accessory minerals that show well-defined microstructural relationships with major mineral assemblages (Williams and Jercinovic, 2012); (iii) dating of accessory minerals that can be linked to particular metamorphic reactions (Janots et al, 2009); and (iv) relating microstructures and ages of accessory minerals with variation in metamorphic grade in the host rock Williams, 2001) or directly with melt inclusions (Cesare et al, 2003.…”

Melt inclusions in migmatites and granulites

“…The arrangement of MI in minerals from the studied samples is commonly indicative of a primary trapping: zonal arrangement dominates in garnet and spinel ( Figure 5A), where inclusions are commonly located in the core of crystals. In zircon, inclusions are distributed in a very thin annulus separating a detrital core from the syn-anatectic overgrowth (Cesare et al, 2003b. In other hosts, especially plagioclase, MI occur throughout the mineral ( Figure 5B, C) and may be so abundant to impart to the crystal a cloudy appearance.…”