Pumpellyite and Coexisting Minerals in Metapelites and Veins From the Federico Units in the Internal Zone of the Rif, Spain

Abstract

Pumpellyite has been found for the first time in phyllites and synfolial veins in Permo-Triassic formations in the Beni Mezala 1 unit, part of the Federico units, Internal Zone of the Rif belt, Spain. Back-scattered images indicate that equilibrium was attained only at the millimeter scale or lower. Two main assemblages were identified in different microdomains: 1) pumpellyite -actinolite -epidote and 2) pumpellyite -muscovite -epidote. Only the second assemblage was identified in phyllites. Chlorite rarely occurs in these rocks, whereas vermiculite is abundant. Epidote is Fe-rich; actinolite contains very low Na and Al, and white mica has a mean Si content of 3.13 atoms per formula unit, all these characteristics being typical of low-pressure conditions. Assemblages in pumpellyite-bearing rocks indicate pressures of ~2 kbar and temperatures of ~250°C, in agreement with the estimates deduced from crystal-chemical parameters of white mica and chlorite from the enclosing pumpellyite-free phyllites. Nevertheless, peak conditions reached ca. 400°C and 5 kbar, as indicated by kyanite-bearing veins from the same area. Two compositionally different populations of pumpellyite occur: (i) a Fe-rich population, coexisting with actinolite, and (ii) an Al-rich population, present in actinolite-free rocks or microdomains. The mineral assemblages and phase compositions were thus mainly controlled by both reaction kinetics and microdomainal variations in composition.soMMaire Nous décrivons pour la première fois la pumpellyite dans les phyllites et les veines concordantes à la foliation des formations permo-triassiques faisant partie de l'unité Beni Mezala 1, une des unités de Federico, zone interne de la ceinture du Rif, en Espagne. Les images d'électrons rétrodiffusés démontrent que l'équilibre n'a été atteint que sur une échelle millimétrique, voire inférieure. Nous décrivons deux assemblages principaux: 1) pumpellyite -actinolite -épidote, et 2) pumpellyite -muscovite -épidote. Seul le second de ces assemblages a été identifié dans les phyllites. La chlorite est rarement développée dans ces roches, tandis que la vermiculite y est abondante. L'épidote est riche en fer, l'actinolite contient de très faibles teneurs en Na et Al, et le mica blanc possède en moyenne une teneur en Si de 3.13 atomes par formule unitaire, toutes ces caractéristiques étant typiques de conditions de faible pression. Les assemblages des roches porteuses de pumpellyite indiquent une pression d'environ 2 kbar et une température d'environ 250°C, ce qui concorde avec les estimés fondés sur la cristallochimie du mica blanc et de la chlorite dans les phyllites encaissantes dépourvues de pumpellyite. Toutefois, les conditions maximales dans la même région auraient atteint environ 400°C et 5 kbar, d'après la présence de veines à kyanite. Nous trouvons deux populations distinctes de § ZeN, e-aN (1974): Prehnite-and pumpellyite-bearing mineral assemblages, west side of Appalachian metamorphic belt, Pennsylvania to Newfoundland. J. Petrol. 15,

Permo-Triassic Clastic Rocks from the Ghomaride Complex and Federico Units (Rif Cordillera, N Morocco): An Example of Diagenetic-Metamorphic Transition

“…This agrees with the estimations deduced from crystal-chemical parameters of white mica (CIS, b) from the enclosing pumpellyite-free phyllites (MG-14 and MG-13, Table 2). Nevertheless, the outstanding presence of kyanite-bearing veins in the same area suggests pressure conditions of 5 kbar [65]. With respect to the temperature conditions, in addition to the CIS values and the presence of minerals as pyrophyllite (T~200 • C, lower anchizonal limit) and paragonite (anchizone and epizone mineral), semi-empirical chlorite thermometers show results for the deepest Federico units that are coherent with the rest of the data.…”

“…Temperature ranges are narrower in samples from the Boquete Anjera unit (250-400 • C) than in Beni Mezala 1 unit (150-350 • C), but in any case, these temperature ranges suggest the genesis of several populations of chlorites during the PTt evolution of the orogen as in the case of dioctahedral micas as it is commented below. In relation to the thermal conditions, the enclosed veins found in the Beni Mezala 1 sequence indicate temperatures of~250 • C and the kyanite-bearing veins in the same area suggest peak conditions of 400 • C [65]. Nevertheless, these estimates in Beni Mezala 1 unit are far from those deduced by Bouybaouène [22] and Bouybaouène et al [24] based on paragenesis with carpholite and talc, and other data relative to the Betic Cordillera [66].…”

“…However, in the deepest Federico units (Boquete Anjera and Beni Mezala units), the presence of 3T mica polytype ( Figure 6) and the wide range of phengitic substitution values (Si from 3 up to more than 3.35 apfu, Figure 13b) indicates the coexistence of mica grains formed under a wider range of pressure. The detailed research carried out by Ruiz-Cruz et al [65] about the petrology of the phyllites and the enclosed veins found in the Beni Mezala 1 sequence showed the presence of pumpellyite-actinolite-epidote in the veins from Permo-Triassic formations, indicating pressures of~2 kbar. This agrees with the estimations deduced from crystal-chemical parameters of white mica (CIS, b) from the enclosing pumpellyite-free phyllites (MG-14 and MG-13, Table 2).…”

The pressure–temperature–time–deformation history of the Beni Mzala unit (Upper Sebtides, Rif belt, Morocco): Refining the Alpine tectono‐metamorphic evolution of the Alboran Domain of the western Mediterranean

“…Regarding the metamorphic signature, the Alpujarride-Sebtide units record a low grade, subduction-type metamorphism on Permian-Triassic protoliths and a high-grade Barrovian-type metamorphism on pre-Alpine protoliths (Azañón & Crespo-Blanc, 2000;Azañón et al, 1998;Bouybaouene et al, 1995;El Maz & Guiraud, 2001;Goffé et al, 1996;Gueydan et al, 2015;Homonnay et al, 2018;Michard et al, 2006;Rodríguez-Ruiz et al, 2019;Ruiz Cruz et al, 2010;Vidal et al, 1999), respectively, with a marked downward increase in the palaeo-temperature gradients, commonly referred to the heat source provided by the intracrustal emplacement of the peridotite bodies (Negro et al, 2006).…”

“…In fact, while several and contrasting tectonic and geodynamic models have been proposed in the literature by the study of the Alboran Domain units (e.g. Azañón & Crespo-Blanc, 2000;Booth-Rea et al, 2005;Frasca et al, 2017;Garrido et al, 2011;Guerrera et al, 2021;Gueydan et al, 2019;Hidas et al, 2013;Hommonay et al, 2018;Mazzoli et al, 2013;Michard et al, 2002;Platt et al, , 2006Platt, Argles, et al, 2003;Platt & Vissers, 1989;Tubía et al, 2004;Van der Wal & Vissers, 1993;Williams & Platt, 2018;Zeck, 1996), still poorly constrained are (a) the timing of Alpine orogenic construction and subduction zone metamorphism in the region and (b) the evolving tectonic/geodynamic regimes driving the Alpine structuration of the Rif-Betic orogen. Both elements hampering a full assessment of the tectonic correlations at regional scale as well as the palaeotectonic reconstructions.…”