GEOGACETA, 59, 2016 New lithologic and structural data of the central and eastern part of Ceuta (Rif Cordillera) Nuevos datos de la litología y de la estructura de los sectores central y oriental de Ceuta (Cordillera Bético-Rifeña) Carlos Sanz de Galdeano1 and María Dolores Ruiz Cruz2 1 Instituto Andaluz de Ciencias de la Tierra (CSIC - Univ. Granada). Facultad de Ciencias. 18071. Granada, Spain. [email protected] 2 Dpto. de Química Inorgánica, Cristalografía y Mineralogía. Facultad de Ciencias. Univ. de Málaga. Campus de Teatinos. 29017. Málaga, Spain. [email protected] ABSTRACT RESUMEN In the central and eastern parts of Ceuta two tectonic units are dif- En los sectores central y oriental de Ceuta se diferencian dos ferentiated: a) the Hacho unit, formed by two groups of orthogneisses unidades: a) la unidad del Hacho, formada por dos grupos de ortogneises which foliation permits to establish the structure: an anticline with a cuya foliación permite establecer su estructura: un anticlinal que tiene periclinal end at its western edge, and b) the Istmo unit, with peridotites una terminación periclinal en su parte occidental, y b) la unidad del Istmo, at the bottom, followed by migmatitic granulites, gneisses, and dark mica con peridotitas en la base seguidas por granulitas migmatíticas, gneises schists. The thrust of the peridotites over the orthogneisses of the Hacho y esquistos oscuros. El cabalgamiento de las peridotitas sobre los unit occurred under fragile conditions. For the first time several types of ortogneises ocurrió en condiciones frágiles. Por primera vez se han rocks, not previously described, have been localized: dark mica schist and localizado afloramientos de rocas no descritos previamente: esquistos phyllites and quartzites, these two last perhaps corresponding to the oscuros y filitas y cuarcitas, estas dos últimas quizás correspondientes a Federico units. With the new data, these units can be better compared, unidades de tipo Federico. Con los datos presentados, estas unidades with those Alpujárride/Sebtide in the sectors of Jubrique-Guadaiza- pueden compararse mejor con las del Alpujárride/Sébtide en los sectores Benahavís. de Jubrique-Guadaiza y Benahavís. Key-words: Alpujarride/Sebtide, peridotites, migmatites, orthogneisses. Palabras clave: Alpujárride/Sébtide, peridotitas, migmatitas, ortogneises. Geogaceta, 59 (2016), 19-22 Fecha de recepción: 1 de junio de 2015 ISSN (versión impresa): 0213-683X Fecha de revisión: 20 de octubre de 2015 ISSN (Internet): 2173-6545 Fecha de aceptación: 27 de noviembre de 2015 Introduction who described the rocks of this area and gneisses for the rocks situated in the cen- named "gneisses oeillés", augen gneisses, tral part of Ceuta (Fig. 1A). Ruiz Cruz et The area of Ceuta (Spain), in the N of to the rocks of the Hacho Mountain. Nev- al. (2011) identified the existence of mi- the Rifian Internal Zone (Fig. 1A), provides ertheless, they did not differentiated units, crodiamonds in the migmatitic granulites a link with equivalent Betic units. In this considering that all this area corre- situated over the serpentinites in the Sar- area, the Sebtide and the Ghomaride com- sponded to the "Ceuta unit". Bernard- chal bay, indicating an old stage of UHP plexes (Alpujárride and Maláguide, re- Griffiths et al. (1977), based on Rb/Sr de- metamorphism. spectively, in the Betics) crop out. Particu- terminations in whole-rock, attributed a The aims of this study are: a) to de- larly, the Sebtide Complex occupies the Variscan age (290±4 Ma) to the or- scribe for the first time new rocks in the central and eastern parts of Ceuta, being thogneisses (this is the name used by central and eastern part of Ceuta that the Ghomaride Complex situated immedi- these authors) of Hacho Mountain. Sán- complete the knowledge of the litho- ately to the west. This area began to be chez-Gómez et al. (1995) and Azañón et logic sequences and permits a better studied during the 19th century and it is al. (2004) described the existence of mica comparison with other areas of the Rif particularly interesting the description of schists enclaves in the area of the Desnar- and the Betics, b) to provide some pre- Dupuy de Lôme and Milans del Boch igado, in the SE of the Hacho Mountain. cisions about the structure, particularly (1917) of "calizas sacaroideas" (saccha- They consider the rocks of this unit as that of the Hacho Mountain, till the mo- roidal limestones) in a quarry in the area migmatites (not as orthogneisses), even ment considered as an undifferentiated of San Amaro now disappeared. More de- passing to form granitoids. They used the mass, and c) to afford new data for the tailed studies were made by later authors, name of Monte Hacho unit, while gave correlations of these units with others in as Durand-Delga and Kornprobst (1963), the names of "Istmo de Ceuta" or "Filali" the Betics. Copyright© 2016 Sociedad Geológica de España / www.geogaceta.com 19 GEOGACETA, 59, 2016 C. Sanz de Galdeano y M.D. Ruiz Cruz Fig. 1.- A) Geologic sketch of the Alpujarride and Malaguide Complexes in the area of the Strait of Gibraltar. The rectangle indicates the position of B. B) New geological map of the central and eastern parts of Ceuta. The location of the cross sections of figure 2B is indicated. Fig. 1.- A) Esquema geológico de los complejos Alpujárride y Maláguide en el área del Estrecho de Gibraltar. El rectángulo indica la posición de B. B) Nuevo mapa geológico de los sectores central y oriental de Ceuta. Se indica la posición de los cortes de la figura 2B. Lithologic series of the As previously indicated, in the Desnari- thogneisses. The estimated thickness of differentiated units gado area (Fig. 1B) many enclaves are pres- this group is about 100 m. ent, in some cases of decametric size. The en- We distinguish two units in the study claves show a typical foliated texture, domi- Istmo unit area, the Hacho unit and the overthrusting nated in some cases by biotite. In other cases, Istmo unit. Their cartographic shapes and the xenoliths represent true restites with vari- The serpentinites/peridotites. They crop lithologic columns can respectively be seen able amounts of pinnitized cordierite, stauro- out only in the Sarchal Bay. These ultramafic in figures 1B and 2A. lite, red biotite, apatite, and garnet. Silliman- rocks have been described by Sánchez- ite is also abundant in some of these bodies, Gómez (1995), among others. Where ser- Hacho unit as a product of the transformation of biotite. pentinites are not tectonically disturbed, the These rocks are locally crossed by acidic foliation is well conserved although no According to Bernard-Griffiths et al. dykes, some of which also contains small en- more than 50 m of thickness are visible. (1977) the rocks forming this unit corre- claves of schists. According to the structure de- The migmatitic granulites. These rocks spond to orthogneisses, although Azañón duced from the foliation, the visible thickness are situated directly over the peridotites and et al. (2004) considers them as migmatites. of this gneissic formation is about 300 m. crop out along more than a kilometre in the But our data agree with the interpretation The upper group of orthogneisses. coast (Fig. 1B). They range from migmatites of the first authors. These rocks are This group occupies the northern part of with banded texture, in which thin leuco- arranged in two groups (Fig. 2A). Hacho Mountain (Fig. 1B). Generally, they somes are derived locally from in situ melt- The lower group of orthogneisses. This form a more subdued relief, the arrange- ing, to rocks with larger leucosomes record- formation includes fine-grained rocks inter- ment in layers is well developed, and gen- ing evidence of melt mobilization. Among preted as derived from rhyolites, which are erally they do not show the porphyritic their minerals, the large garnets and also mainly located in the westernmost part of the texture characterizing the lower group. microdiamond inclusions stand out. The vis- Hacho Mountain; porphyritic granites partic- The rocks consist of dominant magmatic ible thickness is about 20 m.Locally, these ularly located in the central and eastern part phases (e.g. K-feldspar and red biotite). rocks are cross cut by aplitic dykes. of this mountain; and leucocratic meta-gran- Nevertheless, some levels of these rocks The paragneisses. They are situated over ites, located in the innermost zone of the out- also contain grains with textural charac- the migmatites with a short transition be- crop. In general, the rocks contain variably teristics of detrital phases, such as the tween the two types of rocks. The town cov- sized porphyroclasts of K-feldspar, plagio- shape of the grains and the clayed or Fe- ers up the greater part of their outcrops. These clase, quartz, and altered cordierite, and a oxide coatings, suggesting a possible vol- rocks are quite similar to those lying several fine-grained matrix of quartz, white mica, and cano-sedimentary origin. Phases showing km south of Ceuta (in Cabo Negro), and also biotite or chlorite. The rocks are characterized these textural characteristics, such as to those overlying the migmatitic granulites in by the abundance of phases inherited from large fractured garnets and angular the Jubrique zone (in the Alpujarride Complex, the source (restites), such as apatite, zircon, quartz grains have not been identified in in the western Betics) (Fig. 1A). These gneisses and small, corroded garnets. the rocks of the lower group of or- are characterized by the presence of small, 20 Geología Estructural y Tectónica / Structura l Geology and Tectonics New lithological and structural data of the central and eastern part of Ceuta (Rif Cordillera) GEOG ACETA, 59, 2016 Fig. 2.- A) Lithologic sequences of the central and eastern area of Ceuta.