Development of large north-facing folds and their relation to crustal extension in
the Alborán domain (Alpujarras region, Betic Cordilleras, Spain)
Miguel Orozcoa, Francisco M. Alonso-Chavesb and Fernando Nietoa
a
Instituto Andaluz de Ciencias de la Tierra, CSIC–Universidad de Granada, Granada, 18002,
Spain
b
Departamento de Geología, Universidad de Huelva, La Rábida, Huelva, 21819, Spain
Abstract
Detailed research in the eastern part of the Alpujarras region, Betic Cordilleras, has revealed
the existence of large recumbent fold structures involving lithological sequences previously
considered to belong to different tectonic units. We have reconstructed a large, complex fold
structure (which can be followed axially for over 50 km) based on a careful revision of the
boundaries between lithological formations, a structural analysis of the carbonate and
metapelite sequences, and the use of mineralogical techniques such as measurements of d001
basal spacing of phengite, paragonite and chlorite, determinations of the illite ‘crystallinity' index
(IC) and b0 parameters of mica and chlorite. Structural field data described in this paper include
gently dipping axial plane cleavage surfaces, common occurrence of gently dipping boudinage
and pinch-and-swell structures and associated sub-orthogonal stretching lineation, similarity in
orientation of this stretching lineation with the slip direction of the low-angle normal faults, and
close association between north-facing recumbent folds and top-to-the-north low-angle normal
faults (the slip direction of the faults being broadly perpendicular to the fold axes). These
features clearly indicate that extensional processes played a decisive role in the generation of
the Alpujarras large recumbent folds. The development of these recumbent folds probably
occurred during the Early to Middle Miocene extensional tectonics that affected the Betic
Cordilleras. The formation of large-scale folds in association with normal faulting is consistent
with the P–T paths and geochronological data established for the Alpujarride region.
Author Keywords: extension; north-facing folds; Alborán domain; Alpujarras region; Betic
Cordilleras; Spain
1. Introduction
The relationship between recumbent fold generation and crustal-scale extension was discussed
by different authors for the Basin and Range province (e.g. Davis, 1975; Davis and Coney,
1979; Compton, 1980; Malavieille, 1987). Less attention has been devoted to development of
large folds by extension of overthickened crust. As pointed out by Dewey (1988), “lithospheric
extension is sited, preferentially, along orogenic belts because they have thicker continental
crust, contain structural inhomogeneities, and suffer extensional orogenic collapse caused by
body forces resulting from isostatically compensated elevation and sharp elevation gradients”.
Froitzheim (1992) interpreted kilometric-scale second generation folds in the Austroalpine
nappes of the Alps as resulting from crustal extension affecting steeply inclined layering.
North-dipping extensional structures were first recognized in the Higher Himalayas by Burg et
al. (1984). There, a north-directed detachment juxtaposes slightly metamorphosed rocks of the
Tibetan sequence against older highly metamorphosed gneisses and Miocene granites of the
Greater Himalayan sequence. Burchfiel and Royden (1985) first suggested that the movement
on the Main Central Thrust and on the extensional detachment of southern Tibet might have
been broadly contemporaneous. Crustal-scale folds in the hanging wall of the ‘South Tibetan
detachment system' (Burchfiel et al., 1992) have been attributed to gravitational sliding or
collapse associated with northeastward displacement on the detachment (Caby et al., 1983;
Burchfiel et al., 1992). Large folds, developed above the Annapurna detachment fault (Brown
and Nazarchuk, 1993) and the Chame detachment (Coleman, 1996) in central Nepal, which are
presumed to be correlated with the South Tibetan detachment system in southern Tibet, can
also be a result of normal-sense shearing related to a detachment system. Burg et al. (1996)
show that, in the Kohistan arc (northwest Pakistan), “horizontal extension of an active orogenic
wedge may produce widespread collapse folding as much as ductile normal faulting”.
The Alpujarras region, south of Sierra Nevada (Betic Cordilleras), has traditionally been
considered as a ‘nappe (thrust sheet) region' (e.g., Westerveld, 1929; Aldaya, 1969; Jacquin,
1970; Orozco, 1972). Nevertheless, recently most of the contacts between tectonic units in the
Alpujárride domain have been reinterpreted as low-angle normal faults and extensional
detachments (García-Dueñas et al., 1992; Crespo-Blanc et al., 1994). The low-angle normal
faults in the Berja region have been dated as Early to Middle Miocene (Langhian to
Serravallian) in age, as inferred from the relationships between the faults and the Miocene
deposits (Mayoral et al., 1994), which is consistent with the existence of Early and Mid-Miocene
major rifting episodes contributing to the development of the Alborán Sea (Comas et al., 1992).
The evidence presented in this paper, from the region of the eastern Alpujarras, allows the
reconstruction of very large fold structures which have not been described until now. The
analysis of the internal structure of the carbonate and metapelitic sequences as well as the
mineralogical study (electron microprobe and XRD, including IC and d001 of muscovite and
paragonite) led us to the recognition of a large fold, which involves lithologic assemblages
previously considered as belonging to different tectonic units (Fig. 1). The structure is formed by
a large north-facing recumbent fold, the Rio Grande anticline (Orozco et al., 1997), of which the
core is occupied by chloritoid-bearing chlorite schists. Both the overturned (geometrically lower)
and the normal (higher) limbs are made up of phyllite, with carbonate sequences in the
stratigraphically higher part. The limestones and dolostones of the normal limb show two
synclinal structures — the Alquería syncline and the Alhamedilla syncline — at its southern end.
The former (the northernmost) is probably not very important as it does not seem to extend
much further east: it could be considered as a subsidiary fold of the Rio Grande anticline.
However, the latter (the Alhamedilla syncline) must be very important, as it causes a polarity
inversion and extends all along the southern border of the Sierra de Gádor (see Fig. 1B and Fig.
2, sections I–I′ and II–II′), some 50 km.
Large north-facing recumbent folds found in the Alpujarride domain of the Betic orogen have
generally been related with a contractional nappe-stacking episode (Balanyá et al., 1987;
Simancas and Campos, 1993) predating the Early to Middle Miocene extension (García-Dueñas
et al., 1992; Crespo-Blanc et al., 1994). Nevertheless, Platt (1982) and Vissers et al. (1995) had
suggested that the emplacement of the ‘Aguilón fold-nappe', Sierra Alhamilla, took place by
gravity spreading. This paper shows that the large folds existing in the Alpujarride domain can
be reinterpreted as extensional in origin, their development being connected with the event that
produced the low-angle normal faults and extensional detachments in Miocene times. This
conclusion is based on the analysis of the relationships between recumbent folds and
extension-related structures, including low-angle normal faults, stretching lineations and
boudinage structures.
2. Geological setting
Two major tectonic complexes are distinguished in the Alpujarras region, a lower one, the
Nevado–Filabride complex and an upper ensemble termed the Alpujarride (nappe) complex.
The third main tectonic ensemble of the internal Betics, the Malaguide complex, is represented
in the Alpujarras region by only a few small outcrops situated west and north of Sierra de Gádor
(Fig. 1B).
Recognition of the extensional character of the boundary between the Alpujarrides and the
Nevado–Filabrides (Platt, 1982; Aldaya et al., 1984; Platt et al., 1984; García-Dueñas et al.,
1986García-Dueñas et al., 1988; Platt and Behrmann, 1986; Galindo-Zaldivar et al., 1989;
Tubía et al., 1992) led to a revision of the areas and to a reinterpretation of the structure in
different parts of the orogen. Crespo-Blanc et al. (1994) reinterpreted most of the boundaries
previously considered to be thrust surfaces as low-angle normal faults and extensional
detachments and, in the region of the Alpujarras, defined the ‘Contraviesa Normal Fault System'
(with a north-northwestwards transport direction), which formed during an extensional episode
in the late Burdigalian to early Langhian (Mayoral et al., 1994). Therefore, the so-called
‘Alpujarride nappes' are reinterpreted as extensional units bounded by low-angle normal faults.
In the eastern Alpujarras four extensional tectonic units are distinguished (Crespo-Blanc et al.,
1994). These units correspond respectively (from the structurally lowest to highest) to the LújarGádor, Escalate, Salobreña and Adra units of Azañón et al. (1994) (Fig. 1A). The lowermost
unit, Lújar, shows a thick carbonate succession dated as Middle to Late Triassic overlying
(through some metres of calc-schists which serve as transitional layers) undated phyllites and
metaquartzites attributed to the Permo–Triassic. According to Orozco (1972) and Aldaya et al.
(1983), the carbonate sequence of this unit crops out in the west of the study area, in the ‘Turón
window', and also makes up most of the Sierra de Gádor mountain massif as well as the
southern part of a small mountain situated southeast of Berja, the Sierra Alhamedilla (Fig. 1B
and Fig. 2, section I–I′). The Turón limestones (Lújar unit) are overlain to the south by a
sequence of low-grade Permo–Triassic phyllites which supposedly belong to a new tectonic
element: the Escalate unit. This latter is, in turn, overlain by the Salobreña unit, which is
composed, from bottom to top, of pre-Permian micaschists and metaquartzites of low to medium
metamorphic grade, phyllites, and a carbonate formation. According to Aldaya (1969) and
Cuevas (1988), west and north of Adra the Murtas limestones are overlain by a new tectonic
element composed mainly of low- to high-grade micaschists: the Adra nappe (Fig. 1A).
3. Large folds and associated structures in the Adra–Berja–Dalías area
3.1. Field data
It was assumed that four independent tectonic elements, i.e. extensional units, are represented
in the Adra–Berja–Dalías area. Nevertheless, we have carried out a careful revision of the area
including a detailed study of structures within the different lithological formations, and especially
of the contacts between them, together with an analysis of the relationships of various
structures including folds, foliations, low-angle faults, and stretching lineation. We also carried
out a methodical study using mineralogical techniques on samples collected along a N–S
section between the southern border of the Turón antiform and a point in the neighbourhood of
Adra (see Fig. 1B). This revision has revealed the existence of large overturned recumbent
folds which are (from north to south and from bottom to top) the Rio Grande anticline (Orozco et
al., 1997), the Alquería syncline and the (Sierra) Alhamedilla syncline which tectonically overlies
the Alquería syncline along a low-angle normal fault (Fig. 1B and Fig. 2, I–I′). A description of
the main observational data leading to the new interpretation of the area is given below.
The field study of the Turón area (Fig. 1B) reveals that the southern boundary between the
Lújar limestones and the overlying phyllites (which supposedly belong to the Escalate unit) is
gradational. Close to the contact there are thin phyllite layers between the limestone and calcschist beds. Furthermore, within the phyllites directly overlying the limestone formation,
carbonate intercalations occur. Both within the limestone formation and in the overlying
phyllites, asymmetrical minor folds and relationships between the ‘principal' foliation (Sp) and
the axial-plane ‘crenulation' cleavage (Sc) are visible, consistent with the existence of a
southern overturned limb of a major syncline. Fig. 3a shows a gradual transition from the
underlying limestones and calc-schists to the overlying phyllites. Also shown are structural
criteria such as the relationship between the steeply dipping Sp and the low-dipping Sc surfaces
and the existence of ‘Z' asymmetrical folds, all consistent with the existence of an overturned
limb.
A polarity inversion in the Lújar limestones had already been reported by Gervilla et al. (1985),
who established the inversion of the Turón carbonate sequence on the basis of lithostratigraphic
criteria such as stromatolite morphology and geopetal features (e.g. internal sediments in
fenestral cavities). Balanyá et al. (1987), using structural criteria as evidence, also referred to
the existence of an inversion in the limestone of the southern part of the Turón antiform.
Nevertheless, the (supposedly) tectonic character of the boundary with the overlying phyllites
was never questioned by Balanyá et al. (1987) or Crespo-Blanc et al. (1994). In fact, in CrespoBlanc et al. (1994) this entire boundary was considered as a low-angle normal fault folded
during the Late Miocene compressional episode. The gradational nature of the southern part of
the Turón antiform does not preclude that, in other sites, e.g. north of Berja (see Crespo-Blanc
et al., 1994, fig. 4), the boundary between the geometrically lower limestones and the overlying
phyllites is a true low-angle normal fault which probably has a ramp-flat geometry, cutting
downwards to the north through metapelites into the underlying (overturned) limestones (see
Fig. 1B, east of Turón).
In the phyllite-metaquartzites, south of the Turón carbonate rocks, the dip of the principal
foliation ranges between 30° and 50° SSE and that of the crenulation cleavage usually ranges
between 10° and 35° southwards (Fig. 1B, Fig. 3a and Fig. 4, plots 1 and 2). Nevertheless, the
effect of the Late Miocene compressional episode which in places steepened the formerly
gently S-dipping surfaces must be taken into account. Asymmetrical small-scale folds (Fig. 3b
and Fig. 4 plot 3) and Sp–Sc relationships are consistent with a position within an overturned
limb of a large syn-Sc north-facing anticline. Although normal-limb type relationships are also
found locally, the overall configuration of the metapelites (phyllites and overlying schists) agrees
well with the presence of a recumbent anticline, and in fact it will be shown (see Section 3.2)
that the metamorphic grade decreases towards the geometrically lowest part (the boundary
between the phyllites and the underlying Turón limestones). Another lithological boundary which
has been carefully examined occurs between the phyllites and the overlying micaschists,
assumed to belong to a different tectonic unit (the ‘Salobreña' unit of Azañón et al., 1994). In
fact, it is a significant question whether the phyllites and overlying micaschists belong to
different tectonic units or not. In the first case, the metamorphic grade within each of them
would be expected to increase towards the north (i.e., the higher-grade schists of the base of
the ‘Salobreña' unit would tectonically overlie the lowest-grade phyllites of the upper part of the
‘Escalate' unit). Nevertheless, the new mineralogical data included in this work preclude that
interpretation.
In the southern part of the schist band and in the overlying phyllites (Fig. 2, I–I′) the Sp surfaces
usually have a gentler dip, between 25° and 45° towards the south, while those of the Sc are
usually steeper (Fig. 1B), which is in agreement with the general normal-limb type geometry
corresponding to the southern flank of the Rio Grande anticline. Overlying the mentioned above
phyllites, 0.5 km west of La Alquería (see Fig. 1B), a sequence of limestones and dolostones
crops out. This forms the upper part of the (presumed) ‘Salobreña unit'. The internal structure of
the carbonate sequence in this area shows a recumbent syncline, here named the La Alquería
syncline, with an overturned southern limb (Fig. 2, I–I′). The synclinal structure, which can be
followed northeastwards across the Rio Grande (Fig. 1B), rests on the underlying phyllites along
a top-to-the-north low-angle normal fault. Both the fault and the axial plane of the fold presently
dip to the south but the dip of the fold axial plane is steeper (Fig. 2, I–I′). Inversion of the
southern limb of the syncline is also revealed by minor structures in the phyllites overlying the
carbonate rocks in the south (see Fig. 1B, west and east of La Alquería, Fig. 3c). Moreover, the
study of metapelite samples collected between this boundary and a point in the neighbourhood
of Adra reveals that the metamorphic grade is very low (all samples can be classified as
‘phyllite') (see Fig. 1B and Table 1), which contradicts previous interpretations (Cuevas, 1988)
that considered them as chloritoid- and garnet-schists belonging to the ‘Adra nappe'. Actually,
the garnet-bearing schists crop out some hundred metres west-northwest of Adra, but not along
the Rio Grande river-course.
In the southeasternmost part of the section (Fig. 2, I–I′ and Fig. 3c) a new north-facing
overturned syncline is shown, the Alhamedilla syncline named after the Sierra Alhamedilla (a
small mountain south of Berja). This structure was described in Balanyá et al. (1987), although
it was considered to be the core of a recumbent syncline whose overturned limb contained the
Turón limestones. This syncline was supposed to have overthrust the limestones of the Murtas
(= ‘Salobreña') nappe (Balanyá et al., 1987) through a (reverse) fault postdating the nappe
tectonics, which would have emplaced the lower folded ‘Lújar' nappe onto the higher
‘Salobreña' one. This fault is here interpreted as a low-angle normal fault descending towards
the north that places the Alhamedilla syncline, with its underlying phyllites, onto the Alquería
syncline situated in a more northerly and lower position (Fig. 2, I–I′). Therefore, the prolongation
of the Alhamedilla syncline towards the west should probably be sought south of Adra, below
the sea.
3.2. Mineralogical data
3.2.1. Methods
In addition to field analysis, mineralogical techniques were employed to verify the results of the
structural study. Clean unaltered samples were obtained from well below the surface and away
from joints in rocks to avoid near-surface weathering. They were gently washed and crushed
and oriented aggregates were prepared for XRD (X-ray diffraction) analysis. Fractions under 2
mm were separated and white mica ‘crystallinity' indices (i.e. IC) were measured, as
recommended by the IGCP 294 IC working group (Kisch, 1991). Mineral composition was
determined from XRD diagrams and optical study of thin sections. Special condition XRD
diagrams were obtained for the b0 parameter, d001 spacing and IC measurements of
phyllosilicates:
(1) The b0 parameters of mica and chlorite were obtained from uncovered thin sections in which
the areas richest in phyllosilicates were optically selected. Thin sections were cut normal to the
mean cleavage of phyllosilicates, thus reducing or avoiding the effect of reflections other than
(060), used for the b0 parameter measure (Guidotti and Sassi, 1976; Frey, 1987). The quartz
peak (211) of the sample itself was used as internal standard.
(2) The d001 basal spacings of chlorite, phengite and paragonite were measured on oriented
aggregates using the quartz peak (100) of the sample itself as internal standard. Peak (005)
was used for both micas and (004) for chlorite. The Philips diffractometer MAX routine which
locates the maximum of a peak after static measurements of intensities, was employed for all
the measurements.
The measured values of IC were converted to internationally comparable data (C.I.S.) by means
of the equation: Our data = 0.674 C.I.S. data + 0.052, obtained using the interlaboratory
standards of Warr and Rice (1994).
Chlorite was analysed with a Camebax SX-50 automated electron microprobe from the
Scientific Instrument Center at the University of Granada, in the wavelength dispersive mode
under the following conditions: acceleration voltage 20 kV; probe current 15 nA; electron beam
diameter 7 mm. Albite, orthoclase, periclase, wollastonite, and synthetic oxides (Al 2O3, Fe2O3
and MnTiO3) were employed as standards.
3.2.2. Physical meaning of the XRD parameters
The illite ‘crystallinity' index (IC) is the half-height width of the basal XRD-peak of white mica.
Among other minor factors, it depends on the crystalline-domain size of the white micas and is
therefore directly related to temperature. Since other geological factors may affect crystalline
size, this parameter cannot be used as a real geothermometer, but it has been extensively
employed for qualitative distinctions between diagenesis, anchizone and epizone. Kisch (1987)
carried out a general correlation with other grade criteria in low-grade and very low-grade
metamorphism.
The basal spacing (d001) of white micas is strongly affected by the relative proportions of K and
Na. The existence of a wide miscibility gap between muscovite, the K-rich mica and paragonite,
the Na-rich one, is a well-known fact. Therefore, when the composition of the system is
adequate, two different basal spacings (10 Å and 9.6 Å) may be recognized in the XRD
diagrams. The width of the miscibility gap is a function of temperature, muscovite becoming
richer in Na and paragonite in K as the temperature increases. As a consequence, the d001 of
muscovite becomes lower and the d001 of paragonite higher with increasing temperature.
Nevertheless, the d001 of muscovite is also very sensitive to other solid solutions in mica, such
as the phengite content (Guidotti, 1984), or to the presence of minor quantities of NH 4+ (Juster
et al., 1987), F− (Robert et al., 1993), or OH → O− substitution (Ackermann et al., 1993). As a
matter of fact, a lack of negative correlation between the d001 of muscovite and paragonite has
been found in our samples (r=0.578). The importance of other solid solutions in paragonite,
apart from K → Na, is comparatively very low and thus the d001 of paragonite must be
considered as a good indicator of temperature.
The b0 parameter of muscovite depends quite exclusively on the phengite substitution of mica.
As this chemical character is related to pressure, the b0 parameter has been used as a semiquantitative geobarometer (Guidotti and Sassi, 1986). The absence of a limiting assemblage is
the main problem of this approach (Massone and Schereyer, 1987), but as in many geological
terrains no other criteria exist for the estimation of pressure.
3.2.3. Results
The mineralogical study was carried out in a series of samples collected along a north–south
section in the western part of the area (see location in Fig. 1B). Special attention was paid to the
boundaries between lithological formations, including those between the (supposed) different
tectonic units. XRD analyses and the optical study of samples from metapelitic formations
previously attributed to different tectonic units show that phengite, paragonite, chlorite, quartz,
feldspar (albite) and haematite are present in most of these samples. Carbonates (calcite and
dolomite) are not uncommon. Chloritoid has also been found in schist samples and in phyllites
neighbouring the schists (Table 1).
Microscopic study also reveals the presence of a golden to reddish-brown pleochroic
phyllosilicate in some samples. This mineral was classified as biotite in former studies of the
zone (Orozco, 1972; Aldaya et al., 1983). However, microprobe analysis actually shows the
‘biotite' to be chlorite, practically identical in composition to the green chlorite coexisting in the
same sample (see Table 2), perhaps with a slightly higher content (in the case of ‘red' chlorite)
of interlayer cations (K, Na, Ca). Moreover, the oxide sum is systematically slightly lower in red
chlorite than in green chlorite, which may be interpreted as a higher content in water and/or
structural OH. These results are consistent with those obtained by Mellini et al. (1991) and Nieto
et al. (1994) in rocks from the Nevado–Filabride and Malaguide complexes, respectively.
According to these authors, the presence of the red chlorite is a consequence of a process of
retrograde alteration which would have given rise to the formation of dioctahedral smectite,
appearing interlayered with trioctahedral chlorite. The phyllosilicates of the red slates
(Malaguide complex) are so small that they cannot be recognized under the microscope;
however, the textural characteristics of the chlorite-to-smectite alteration, described by means of
HRTEM, can also be seen in the Nevado–Filabride complex micaschists, where the green
chlorite–red chlorite intergrowth is clearly recognizable by optical microscopy. Therefore, the
existence of red chlorite is interpreted, not as a result of prograde metamorphism, but as a
product of a probably much younger alteration (retrograde diagenesis, according to Nieto and
Peacor, unpublished data), a process which could hypothetically be related to the Miocene
extensional event referred to in different parts of the cordillera (e.g. García-Dueñas et al., 1992;
Crespo-Blanc et al., 1994).
The average size of the quartz grains in the northern phyllite band, from the underlying Turón
limestones in the north to the overlying chloritoid schists in the south, stays below 0.04 mm up
to some 2 km south of the boundary with the underlying limestones, but becomes coarser (up to
0.2 mm) approaching the overlying micaschists. The mean quartz grain size in the latter is
always over 0.1 mm and may reach 0.5 mm. In the phyllites south of the micaschists there is yet
another decrease in grain size, which is generally below 0.04 mm.
The IC measurements of phengite in each sample are given in Fig. 5A. Disregarding two or
three deviations (samples 1, 4, 10) likely due either to instrumental error or definition or to
structural reasons (the presence of decametric folds within the northern phyllite band or the
possible existence of faults which could bring into contact previously separated (phyllite) rocks),
there is a clear trend towards progressive crystallinity (lower indices) from the first samples,
collected near the boundary with the underlying limestones, up to sample number 13 (chloritoidbearing chlorite schists), collected in the inner core of the recumbent anticline. Another
decrease in crystallinity occurs from this point southwards, which is consistent with the transition
towards upper stratigraphic levels in the normal anticlinal limb. Moreover, if other parameters
are taken into account, such as the d001 of phengite (Fig. 5B), the steady increase from sample
ALQ-8 (phyllite) up to ALQ-13 (schist from the fold core) and the subsequent symmetric
decrease from ALQ-13 up to ALQ-19 (phyllite of the southern band) reveal the existence of a
gradational transition between phyllite and schist and are also consistent with the existence of
the fold. As mentioned in Section 3.2.1, the d001 of phengite depends on various series of solid
solutions of the mica formula and it is very difficult to evaluate the relative influence of each of
them, particularly when the differences are small. Therefore, although geothermobarometric
conclusions cannot be reached from the evolution of this parameter, the geometry of its
variation must reflect that of the fold in the rocks, irrespective of its physical cause. In addition,
the existence of a gradational change phyllite–schist is also supported by the mineralogical
data, including the change in grain size (see above). Moreover, the presence of chloritoid is not
limited to the schist band, as this mineral has been found in the phyllites neighbouring the
schists as well (see Table 1 and Fig. 5).
The existence of an anticlinal core may also be suspected from the relationships between the IC
and d001 of paragonite (Fig. 5C). As explained in Section 3.2.1, both parameters are
temperature-dependent, and a clear linear relation is evidenced. The highest temperatures
correspond to samples situated at the bottom right of the graph. Extreme values occur in
samples 14 and 12 (the existence of paragonite has not been recognized in sample 13),
belonging to the innermost part of the fold core. In the upper left part of the graph are found
samples of higher stratigraphic position belonging to the overturned and the normal limbs of the
fold. Finally, the two samples reflecting the lowest temperatures come from the more distant
positions in the fold both in the overturned and the normal fold limb.
4. Prolongation of the fold structures in the eastern Alpujarras region
4.1. Evidence supporting the prolongation of the Rio Grande anticline to the north of
Berja
As set forth above, the existence of polarity inversion in the carbonate rocks of the western and
southern parts of the so-called ‘Turón window' is evidenced by stratigraphic and structural
criteria. Crespo-Blanc et al. (1994) reported that the antiform shape of the ‘Turón window'
developed during the Late Miocene and that the top-to-the-north ‘Contraviesa extensional
system' was folded during this Late Miocene contractional event. Nevertheless, detailed
research carried out in this work has revealed the gradational nature of parts of the boundary
(mainly the southern and western parts) between the phyllites and the underlying limestones.
Furthermore, the analysis of structural criteria, such as the Sp–Sc geometric relationships,
carried out in the limestones, confirm that a polarity inversion also exists in the limestones of the
northern limb of the Turón antiform (see Fig. 4, plot 4 and Fig. 2, I–I′). In fact, as shown in Fig. 4,
plot 4, the average dip of the Sc surfaces in the northern limb of the antiform is steeper than that
of the Sp ones, which is consistent with the refolding of the overturned flank of the large Rio
Grande recumbent anticline. Therefore, the Turón antiform is a downward-facing anticline.
However, tectonically overlying these reversed limestones, through a low-angle normal fault, the
phyllites and carbonate rocks of the normal limb of the Rio Grande anticline can be seen (Fig. 2,
I–I′). Hence, it may be inferred that the fault has cut across the core of the (Rio Grande)
anticline and micaschists and phyllites part of its overturned limb. This brought the normal limb
(i.e. phyllites and overlying limestones of the Gádor mountain) into contact with the overturned
limestones of the middle and northern parts of the Turón antiform structure (see Fig. 2, I–I′).
Therefore, the fold amplitude clearly exceeds 12 to 14 km, as inferred from the position of the
northernmost outcrops of overturned limestones near Turón. However, it could be much higher
if the outcrop of limestones situated 4 km southwest of Laujar de Andarax (bounded by tectonic
contacts from the neighbouring overlying phyllites) and the narrow band of chlorite quartzschists situated south of it (see Fig. 1B) are considered to represent part of the overturned limb
of the Rio Grande fold.
4.2. Eastward lateral extension of the Alhamedilla syncline inversion
The inversion caused by the Alhamedilla recumbent syncline (see Fig. 1B and 2, I–I′ and II–II′)
has affected most of the southern part of the Sierra de Gádor. Many indicators of overturnedlimb-type relationships can be seen both in the limestones and in the overlying phyllites
between the southern Sierra Alhamedilla, east of Adra (Fig. 1B, Fig. 2, section I–I′, and Fig. 3c),
and the neighbourhood of Enix, in eastern Sierra de Gádor (Fig. 1B, Fig. 4, plots 6 and 7, and
Fig. 6). The mean attitude of the principal foliation (Sp), along the southern part of the Sierra de
Gádor massif, is steeper than that of the crenulation cleavage (Sc) (Fig. 7a and b). Although the
large synformal structure can only rarely be seen directly, very good examples of reverse-limb
relationships can be found locally at many sites: e.g. in the phyllites and underlying limestones
in southern Sierra Alhamedilla (see Fig. 1B and Fig. 3d), or south of Dalías, along the Dalías–El
Ejido road (Fig. 1B, Fig. 4, plot 5), or in the areas east (Fig. 4, plot 6) and west (Fig. 4, plot 7
and Fig. 6) of Félix. The axes of the small-scale folds usually trend between N70°E and E–W,
although some variation exists (Fig. 7f). The Sp–Sc geometric relationship in the limestones
(and even in the overlying phyllites) and small asymmetrical folds observed locally, are usually
consistent with a reverse limb-type relationship. Wherever these kinds of structures are seen
along the southern border of the mountain massif, they show a similar overturned-limb
relationship.
Over the southern overturned limb of the Alhamedilla syncline, a top-to-the-north low-angle
normal fault superimposes a phyllite and carbonate tectonic sheet (Fig. 2, sections I–I′ and II–
II′), represented by outcrops of the southernmost Sierra Alhamedilla (Fig. 1B), and observed
towards the east in the large outcrop of phyllite and overlying limestones in the Félix–Enix area
(Fig. 1B). In the eastern part of Sierra de Gádor (Fig. 1B and Fig. 6), the fault surface between
the underlying overturned sequence (mostly carbonate rocks, although overturned phyllites can
also be seen) and the overlying tectonic sheet formed by phyllites at its base, and limestones
and dolomites at the top, present gentle SSE dips (generally <10°). It may be locally higher and
changes in strike from the mean value (N70–80°E) also occur, probably due to the Late
Miocene folding. The fault in the Felix–Enix area most likely belongs to the ‘Contraviesa Normal
Fault system' (Crespo-Blanc et al., 1994), as it shows the same sense of displacement towards
the NNW inferred from the geometrical relationships between the fault surface and the mean dip
of the underlying carbonate sequence, which is generally towards the south and steeper than
the fault surface one. Evidence supporting the normal character of the fault derives mainly from
the fact that the fracture surface cuts, from south to north, progressively geometrically lower
members of the overturned Sierra de Gádor carbonate sequence. To restore the different
surfaces to their position when the fault developed, the effects of the Miocene folding leading to
the large antiformal structure of Sierra de Gádor must be discounted. Along the fault and in the
underlying overturned sequence there occur carbonate breccias and even mylonitic rocks, such
as the gypsum-mylonites which have developed foliation, boudinage and fractured bodies of
dolostones.
Underlying the fault, as pointed out above, the limestones (and locally, the overlying phyllites)
that constitute the southernmost part of the Sierra de Gádor mountain massif and the adjoining
Sierra Alhamedilla show overturned-limb relationships in many places. Thus, in the Enix
roadcut, 1.5 km northeast of the intersection with the Felix road the geometrical relationship
between the 40–50° S–SSE dipping Sp surfaces and the 15–20° S–SSE dipping crenulation
cleavage (Sc) can be clearly seen (Fig. 1B, Fig. 4, plot 6, and Fig. 6). Asymmetrical minor folds,
with axes trending N60°–N70°E, whose short- to long-limb relationships are consistent with the
overturned limb of a large north-facing fold, are also visible in the outcrop. Evidence of the
lateral continuity of this inversion can be found 2 km west of the former point, in the limestones
directly underlying the large phyllite outcrop of Félix, along the road to the village. Moreover, 2
km west of Félix (Fig. 1B), new evidence of the overturned attitude of the limestone layers can
be seen (see Fig. 1B, Fig. 4, plot 7, and Fig. 8b). Therefore, the axial continuity of the
Alhamedilla recumbent fold for nearly 50 km (from Adra to Enix) is reasonably well established.
The above-mentioned recumbent fold locally shows the effect of superimposed folding, seen 2
km west of Félix (Fig. 1B, site of plot 7). In the side cut of a path joining the village of Felix with
the western part of the Sierra de Gádor massif, good examples of decametric-sized folds with
axes plunging 15–20° SW and an associated axial plane cleavage (Sc 2) dipping 60–70° SE can
be seen (Fig. 8a and b). Nevertheless, in the southern limb of the southernmost antiform
structure (Fig. 8b) another cleavage surface, not consistent with the antiform in question, is
present. In fact, this cleavage (Sc1) dips only 10–20° towards the ESE, while the southern limb
of the antiform structure dips over 30° SE. Considering that the phyllites overlying the
limestones crop out approximately 200 m east of this point, as well as the evidence referred to
in the preceding paragraphs, the interpretation proposed here assumes the existence of a
previous large recumbent fold (the Alhamedilla syncline) with low-dipping axial plane cleavage,
which would have been re-folded by the NE-trending folds shown in Fig. 8a.
The small klippes of schists and/or phyllites and of Malaguide materials, which usually occupy
narrow Late Miocene synforms (see Fig. 1B, SE Ugíjar and 6 km east of Laujar de Andarax and
Fig. 2, section II–II′), represent remnants of uppermost (Alpujarride and Malaguide) extensional
sheets. The klippes are delimited from the underlying Gádor limestones by folded low-angle
normal faults (Crespo-Blanc et al., 1994) (Fig. 2, II–II′). These listric normal faults probably dip
northwards, cutting across the Alhamedilla recumbent syncline, and part of the (Gádor)
carbonate sequence, which constitutes the normal limb of the Rio Grande anticline. The
thinning of the Gádor limestones towards the west has also been favoured by top-to-the-west
low-angle normal faulting (Crespo-Blanc et al., 1994).
5. Discussion
The recumbent folds of the Alpujarras described in this paper (and probably most of the northfacing recumbent folds found in other parts of the Alpujarride domain) can be consistently
explained in terms of gravity-driven extensional tectonics, as proposed by Platt (1982) in the
‘Aguilón nappe' in the Sierra Alhamilla. This assertion is mainly based on a series of
observations and agrees well with the P–T paths and the geochronological data existing for the
Alpujarrides. The main arguments are summarized below.
(1) Low-angle normal faults probably developed in relation to the folding. The carbonate rocks
of the normal limb of the Rio Grande anticline are situated on the underlying phyllites through a
low-angle normal fault, which displaced them roughly northwards, approximating the Alquería
syncline to the (Rio Grande) anticlinal core (Fig. 2, I–I′). The low-angle normal fault has probably
cut across the core and part of the overturned limb of the Rio Grande anticline, because north of
the Turón antiform (which has refolded the Rio Grande anticline), the low-angle fault brings the
normal limb of the Rio Grande anticline (phyllites and overlying limestones of Gádor) into direct
contact with the reversed limestones of the overturned limb (Fig. 2, I–I′).
Overlying both the Alquería and the Alhamedilla synclines are new low-angle normal faults
cutting across the limestones and phyllites of the overturned limbs in a clear footwall ramp
relationship. This type of geometrical relationship of south-dipping overturned limestone layers
overlain by a top-to-the-north normal fault (although presently dipping south) which cuts across
the layers, emplacing a plate composed of phyllites (lower part) and carbonate rocks (upper
part) can be seen at different points of the southern slope of the Sierra de Gádor and especially
in the Felix–Enix area, over 25 km east of Dalías (see Fig. 1B). The large extension of
sequence polarity inversion in the southern part of Sierra de Gádor and the size of the
(minimum) fold wavelength provide an indication of the huge dimensions of the fold structures.
The small klippes in the northern part of the area (Fig. 1B), overlying the Gádor limestones,
represent remnants of the highest Alpujarride and Malaguide sheets, tectonically underlain by
extensional listric faults, similar to those existing in the southernmost Sierra de Gádor.
(2) The slip direction of the low-angle normal faults belonging to the ‘Contraviesa extensional
system' (Fig. 7e) forms a sharp angle (close to 90°) with the mean trend of the fold axes (Fig. 4,
plot 3, and Fig. 7f). The close association of folds and low-angle normal faults suggests a
common origin. As explained above, and as may be inferred from the cross-section in Fig. 2, I–
I′, fold axial surfaces usually dip ‘against' the fault planes, although presently both surfaces dip
south. If the faults are restored to their attitude before the Late Miocene contractional event until
fault surfaces dip gently northwards, then the axial plane of the folds would dip southwards
towards the zone of provenance as shown in Fig. 9a. Two synformal structures (possibly
downward-facing anticlines) are superimposed on one another by a SW-dipping fault. The fault
plane carries slickensides with directions from N210°E to N268°E. This fault probably belongs to
the Serravallian extensional system, which shows a WSW transport direction (García-Dueñas et
al., 1992). Note that the front portion of the fault is deflected upwards (see Fig. 9a and b).
Locally, small-scale folds have developed in the limbs of the synforms (Fig. 9b). These
asymmetrical folds, with axes subperpendicular to the fault striations, are consistent with the
fault kinematics, involving relative lowering of the hanging wall towards the southwest.
Another example of the relationship between folds and low-angle normal faults is the case of
the Sierra de Baza (north of Sierra Nevada). There Crespo-Blanc (1995) has described the
existence of top-to-the-south low-angle normal faults which belong to the same extensional
episode that gave rise to the above-defined (Crespo-Blanc et al., 1994) Contraviesa Normal
Fault System (south of Sierra Nevada), although with an opposite sense of movement. Taking
into account the well-established existence of large south-facing recumbent folds in the
Alpujarride units cropping out north of the Sierra Nevada range (Comas et al., 1979; Delgado et
al., 1980), we can reasonably expect a relationship between these south-facing recumbent folds
and the southwards low-angle normal faults. This, in turn, strongly supports an extensional
origin of the folds as wherever the normal faults change in dip and transport sense, to the south,
the facing direction of the folds also changes to the south.
(3) Foliation surfaces, especially Sc crenulation surfaces parallel to the recumbent fold axialplanes, are subhorizontal to gently dipping (see diagrams in Fig. 4 and Fig. 7). In fact, although
the current disposition of the low-angle normal faults varies (due to the effect of the Late
Miocene folds), the geometric relationships indicate that the fault descends northwards. If we
tentatively assume, given the listric nature of the faults, an original variable dip of 15°–5°
(northwards) and rotate certain crustal segments, removing the effects of the Late Miocene
folding until the fault acquires the supposed original position, we can reconstruct the relative
postures of other structural elements (Sp, Sc, axial planes of the folds) when the fault
developed.
Although it is not easy to make a reliable restoration, due to the existence of various folding
directions during the Late Miocene (see Crespo-Blanc et al., 1994), a tentative reconstruction is
as follows. For the case of the Turón Late Miocene antiform, within the northern limb the fault
surface shows a footwall flat-type relationship, while in the southern one the fault cuts across
the core of an older recumbent fold (see Fig. 2, I–I′). If a very shallow ( 5°?) northward dip is
assumed for the (northern) flat portion of the fault, the restored (overturned) Sp surfaces
underneath the fault would gently dip toward the north, while the restored Sc surfaces would
also dip northwards, although at a steeper angle. Restoration of the southern limb of the Turón
antiform, by rotating it up to a 5° northwards dip, brings the Rio Grande anticline axial surface to
a northwards gently dipping position.
For other recumbent folds (e.g., the Alhamedilla syncline, which causes the inversion of the
entire southern part of the Sierra de Gádor), the results are not exactly the same (e.g. the
restored axial plane of the Alhamedilla recumbent syncline would probably be subhorizontal), as
they depend on the geometry of the low-angle normal faults with respect to reference surfaces
Sp and Sc (Fig. 7a and b). Also, given the listric nature of the faults, there may have been a
clockwise rotation in the hanging wall. The previous dip towards the north of the abovementioned surfaces may therefore have been greater (or have been subhorizontal in those
cases where the restored surfaces dip southwards). This is not consistent with the existence of
lateral compression as the cause of the recumbent folds, as suggested by some authors (e.g.
Azañón et al., 1997). The (assumed) gently dipping attitude of Sc surfaces during the
development of the folds does not necessarily require the folded surface (Sp) to have been
steeply dipping before the folding event, particularly if the extensional deformation also involved
a large component of horizontal (or nearly horizontal) shear.
One important point concerning the Sp–Sc relationship is not only the assumed former
disposition of the Sp surfaces but how to explain the current attitude of the Sc ones. In fact, in
the eastern Alpujarras Sc is usually a very gently dipping surface (Fig. 7b), especially when the
effects of the Late Miocene folding are eliminated. Boudinage and pinch-and-swell structures
and associated very gently dipping stretching lineation as well as steeply dipping cross-joints
are common in the lower part of the carbonate sequence (Fig. 10). These structures probably
developed in relation to both the Sp and Sc surfaces. Boudin-necking lines and steeply dipping
joints are perpendicular to the stretching lineation (Fig. 10c). All these structures are consistent
with extension along subhorizontal to gently dipping planes. The extension direction derived
from stretching lineation diagrams (Fig. 7c and d) is generally NNW–SSE. The existence of a
more or less continuous extensional shearing event (following a crustal thickening one) during
which both Sp and Sc were generated, may be surmised. This is more consistent with the
observation from different parts of the chain, where Sp and Sc are sometimes difficult to
distinguish; in other sites, two crenulation cleavages can be observed. The study of the
metamorphism, which also shows continuity in the crystallisation of the mineralogical
assemblages from the onset of Sp development (syn-Sp) up to the end of Sc development
(post-Sc), following a decompression path (e.g. Platt et al., 1996), is also in agreement with this
proposal.
(4) An extensional-type hypothesis is consistent with the existing P–T path for the Alpujarride
rocks (Azañón and Alonso-Chaves, 1996; García-Casco and Torres-Roldán, 1996; Platt et al.,
1996). For instance, the P–T paths inferred for the Permo–Triassic schists in the region of
Sierra Tejeda, ca. 80 km west of Berja (Azañón and Alonso-Chaves, 1996), indicate an initial
high-pressure metamorphic event (10–12 kbar, 525–650°C), followed by continuous
decompression under nearly isothermal conditions during which the main foliation (Sp)
developed. A temperature of 500–550°C at low pressures (3–4 kbar) can be estimated for the
end of Sp development. Afterwards, under similar P–T conditions, (recumbent) folding and
crenulation cleavage (Sc) were generated (Azañón and Alonso-Chaves, 1996). According to
Azañón and Alonso-Chaves (1996), although the recumbent folds and the associated
crenulation cleavage were generated during a nappe-stacking contractional event, no pressure
increase during the development of Sc or postdating it is recorded. A decrease in pressure
between the onset of Sp development and the generation of Sc, or even postdating it (as shown
by the P–T path), could not be explained by a contractive event. Our proposal favouring an
extensional origin for the folds is consistent with a continuous pressure decrease, as inferred
from the petrological data.
(5) Although detailed fabric dating remains to be done, the existing data consistently point to
19±1 Ma as the closure age for several isotopic systems in metamorphic rocks of the Alpujarride
complex (e.g. Zeck et al., 1992; Monié et al., 1994). According to García-Casco and TorresRoldán (1996), cooling has proceeded at a very fast rate, given the very narrow range (19±1
Ma) in which the ages obtained from different minerals and methods cluster. These data are in
good agreement with the palaeontological ages of transgressive marine sediments that overlie
the Malaguide complex (González-Donoso et al., 1982). In connection with the P–T path for
each of the areas investigated, these data have been explained as the result of uplift and
tectonic unroofing in the final stage of development of the Cordillera (Zeck et al., 1992),
considering the Alpujarrides as a ‘collapsed' terrane, related to very rapid extension at the end
of the Alpine orogeny (Monié et al., 1994). As the mineralogical assemblage associated with the
Sc development seems to postdate any other important metamorphic association, it can
reasonably be assumed that a relationship exists between the previously mentioned extensional
process and the development of the recumbent folds (and associated axial-plane cleavage).
6. Conclusions
The data presented in this paper reveal the existence of large recumbent folds in the Alpujarras
region. These folds involve lithological sequences previously considered to belong to different
tectonic units. From structural field data, e.g. a close association between north-facing folds and
top-to-the-north low-angle normal faults, the gently dipping axial plane surface, and the
similarity in orientation of the stretching lineation with the slip direction of the low-angle normal
faults, it is concluded that the development of the large folds of the Alpujarras took place in
relation to crustal extension processes. The folding may have taken place in relation to
movement of an overlying gliding plate (i.e. Malaguide sheet) which was also undergoing
extension and thinning associated with faulting (Fig. 11).
Nevertheless, any attempt at reconstruction, including the location of the area where northward
gravitational collapse took place, must take into account the existence of important extensional
movements (postdating the northwards ones) in a southwest direction during the Serravallian
(e.g., García-Dueñas et al., 1992). Taking into account that the Alpujarride domain is part of the
hanging wall of the main detachment that developed during this extensional episode, implies
that the units that crop out in the region of the Alpujarras were situated in an area roughly east
of the Almería meridian in the early Serravallian. Therefore, the development of structures
associated with N–S (present direction) extension could have taken place as a result of active
extension in the western end of the Mediterranean, which led to crustal thinning and the
opening of the Algerian–Balearic basin in the Early to Middle Miocene.
The results of this work provide new insight into the structural history of the Alborán domain and
clearly support the hypothesis of extensional collapse (Platt and Vissers, 1989) as a kinematic
model to explain the origin and development of the Betic-Rif orogen and the opening of the
Alborán Sea. It is likely that recumbent folding in relation to extensional collapse of previously
thickened crust is a fairly common process of orogenic deformation.
Acknowledgements
We sincerely thank André Michard and John Platt for their useful comments and suggestions.
J.I. Soto, D. Bernoulli and N. Froitzheim who critically reviewed a former version of the
manuscript are also gratefully acknowledged. We thank Christine Laurin for her assistance with
the English version of the manuscript. This study was supported by grants PB95-1219 and
PB92-0020-CO2-01.
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FIGURES
Fig. 1. (A) Major allochthonous tectonic units in the Alpujarras, according to Azañón et al. 1994).
The outlined box indicates location of detailed map (B) presented in this work. (B) Detailed
tectonic map of the eastern Alpujarras showing axial traces of main recumbent folds and lowangle normal faults. Encircled figures refer to stereoplots presented in Fig. 4. Large numbered
stars in the SW corner indicate sample localities keyed to Table 1 as Alq. 1 to Alq. 21.
Fig. 2. Cross-sections showing the main folds. Location shown in Fig. 1B. Sp = principal
(‘metamorphic') foliation. Sc = axial plane crenulation cleavage. I–I′ = Turón–Sierra Alhamedilla
section. Note the large amplitude of the Rio Grande recumbent anticline manifested by the
extension reached by the polarity inversion of the carbonate sequence in the Late Miocene
Turón antiform. II–II′ = section across the western part of Sierra de Gádor. A normal type
sequence polarity consistent with the upper limb of a large north-facing recumbent anticline (Rio
Grande anticline) is shown in most of the section. Note the existence of a recumbent syncline
(Alhamedilla syncline, see section I–I′) in the southernmost part of the section. Note also the
small klippes of uppermost extensional units (Alpujarride and Malaguide) preserved in the cores
of Late Miocene synforms, in the northern part of the section. P = phyllites; S = schists; Mgd =
Malaguides.
Fig. 3. Photographs showing some details of section I–I′. (a) Upside-down phyllite–limestone
boundary. The gradational character of the boundary is evidenced by the existence of calcschists and interlayered phyllite levels neighbouring with the boundary. The Sp–Sc relationships
and the asymmetric small-scale folds are consistent with the inversion of the series. Southern
border of the Turón antiform. L = limestone; Cs = calc-schist; Ph = phyllite; Qz = quartzite. Note
the circled hammer. (b) Asymmetrical small-scale folds in quartzite levels. Overturned limb of
the Rio Grande anticline (see Fig. 2). (c) Sp–Sc relationships and subsidiary folds in phyllites
and quartzites. Southern limb of La Alquería syncline. (d) Steeply dipping main foliation (Sp)
and gently dipping crenulation cleavage (Sc) in phyllites. Overturned limb of the Alhamedilla
syncline.
Fig. 4. Lower-hemisphere, equal-area projections of major fabric elements are shown. Poles to
principal foliation (Sp) indicated by dots, poles to crenulation cleavage (Sc) indicated by
squares, stretching lineation indicated by small filled stars and fold axes indicated by circles.
See location in Fig. 1B.
Fig. 5. (A) IC phengite measurements. A clear trend towards progressive crystallinity from the
first (northernmost) phyllite samples (see Fig. 1B for location) to sample 13 (chloritoid
micaschist), collected in the core of the presumed anticlinal structure, is indicated. (B) Graph
showing the variation d001 of phengite across the phyllite–micaschist boundaries. The
continuous increase in spacing from sample 8 up to sample 13 is consistent with a gradual
change from phyllite towards the overlying (overturned) micaschists. (C) Graph showing the
relationships between IC and d001 of paragonite. The existence of an anticlinal core is consistent
with the linear relationship shown in the graph. The highest temperatures correspond to
samples farther right and in a lower position while the lowest temperature samples of the
overturned and the normal limbs of the anticline are situated farther left and higher.
Fig. 6. Cross-section (III–III′) in the Felix area. See location in Fig. 1B. The Sp–Sc relationship in
the carbonate sequence underlying the fault is clearly consistent with the existence of an
overturned limb of a large recumbent fold (see text). Note the existence of small superimposed
folds in the northwestern part of the section (see Fig. 8).
Fig. 7. Stereonet data, lower hemisphere, equal-area projection. (a) Mean attitude of the
principal foliation (Sp), and (b) the crenulation cleavage (Sc), in southern Sierra de Gádor. (c)
Stretching lineation, Berja–Turón road. (d) Stretching lineation east of Berja. (e) Slip direction
along low-angle normal faults, Sierra de Gádor and neighbouring areas. (f) Fold axes, southern
Sierra de Gádor.
Fig. 8. (a) Northeast-trending folds in the Gádor limestones west of Felix (location in Fig. 1B,
site of plot 7). A steeply dipping axial plane cleavage has developed locally. Arrow indicates the
approximate location of (b). Section length approximately 80 m. (b) Close-up of the southern
limb of the antiform where the steeply dipping (spaced) cleavage, subparallel to the pencil, can
be seen. The existence of another, more closely spaced gently dipping cleavage is clearly
evidenced on the right. The latter cleavage surfaces must have developed in relation with older
large recumbent folds which produced completely reversed flanks ;therefore the folded
limestones shown in the photograph must be upside-down. Permo–Triassic phyllites overlying
the limestones crop out 200 m east of this point (see Fig. 1B).
Fig. 9. (a) Cascade-like folds associated with low-angle normal faults seen from the east. Berja–
El Ejido road, 3 km south of Dalías. The present high dip of the fault and the synform axial plane
is related to the superposed Late Miocene folding. Box indicates the approximate location of (b).
Person in lower left of photo for scale. (b) Close-up of outcrop shown in (a). Note the fault trace
and the development of asymmetric folds and tension joints consistent with the downward
movement of the hanging-wall. Arrow points to slickensides on the fault surface.
Fig. 10. Pinch-and-swell structure and associated stretching lineation. Dolostones and calcschists of the carbonate formation, very close to the boundary with the phyllite sequence. (a)
Example from a locality 4 km northeast of Berja (Fig. 1B, plot 8). (b) Northeast of Dalías (Fig.
1B, site of plot 9). Pencil in left part of photo for scale. (c) Stretching lineation and steeply
dipping cross-joints (great circles) associated to boudinage structures. Lower-hemisphere,
equal-area projection.
Fig. 11. Schematic cross-section illustrating a tentative model for the development of recumbent
folds and associated structures in the Alpujarrides. Mgd = Malaguides. Not to scale.
TABLES
Table 1. Results of XRD analyses
Table 2. Chemical composition of chlorites