lable at ScienceDirect

Journal of Structural Geology 60 (2014) 97e101

Contents lists avai

Journal of Structural Geology

journal homepage: www.elsevier .com/locate/ jsg

Comment

Comment on: “Localization of deformation and kinematic shift duringthe hot emplacement of the Ronda peridotites (Betic Cordilleras,southern Spain)” by J.M. Tubía, J. Cuevas, and J.J. Esteban, Journal ofStructural Geology 50 (2013), 148e160

Stefano Mazzoli a,*, Agustin Martín-Algarra b

aDipartimento di Scienze della Terra, dell’Ambiente e delle Risorse (DiSTAR), Università di Napoli Federico II, Largo San Marcellino 10,80138 Napoli, NA, ItalybDepartamento de Estratigrafía y Paleontología and IACT-CSIC, Universidad de Granada, 18071 Granada, Spain

a r t i c l e i n f o

Article history:Received 19 August 2013Accepted 19 December 2013Available online 2 January 2014

Keywords:Subcontinental mantleExhumationTranspressionExtrusion

In their excellent paper on the Ronda peridotites (Fig. 1), Tubíaet al. (2013) apply a tectonic model that they describe as “kine-matic shift” to explain the final emplacement of the subcontinentalmantle rocks within the Betic Cordillera. This interpretation isconsistent with the partitioned transpression model previouslypublished by Mazzoli and Martín-Algarra (2011). There we sug-gested that, while a high-T dynamothermal metamorphic aureolerecords coeval orogen-perpendicular foreland-ward thrusting ofthe outer peridotite massif of Sierra Bermeja (Fig. 1) on top of bothlow-P metamorphic rocks of the Guadaiza Unit (Cuevas et al., 2006;Esteban et al., 2008a) and sedimentary successions of the NievesUnit (Martín-Algarra, 1987), a high P-T shear zone occurring at thebase of the inner peridotite massif of Sierra Alpujata (Tubía andCuevas, 1986; Tubía and Gil Ibarguchi, 1991) records orogen-parallel left-lateral shear between the peridotites and the Alpineeclogites of the Ojen Unit. We interpreted these features for the firsttime in terms of deformation partitioning associated with obliqueconvergence during continental subduction and subsequent

DOI of original article: http://dx.doi.org/10.1016/j.jsg.2013.12.012.* Corresponding author.

E-mail address: stefano.mazzoli@unina.it (S. Mazzoli).

0191-8141/$ e see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.jsg.2013.12.013

exhumation involving the coeval activity of kinematically linkedsystems of reverse, strike-slip and ‘normal-sense’ shear zones, thelatter favouring the development of wedge-top sedimentary basins(Fig. 2). Top-to-the-hinterland shear along the contact between theRonda peridotites and overlying crustal rocks is consistent withextrusion of the subcontinental mantle rocks, a concept introducedby Mazzoli and Martín-Algarra (2011) and later applied again byTubía et al. (2013, their figure 10). Although both strike-perpendicular and strike-parallel extension and thinning of thecrustal rocks overlying the peridotites had been documented in aseries of papers (e.g. Van Wees et al., 1992; Balanyà et al., 1997;Argles et al., 1999; Platt et al., 2003) including Tubía (1994),Mazzoli and Martín-Algarra (2011) were the first to reconcilethese processes within a coherent scenario of a rapidly exhumingmantle extrusion wedge coeval with syn- to late-orogenic Miocenesedimentation at uppermost structural levels.

Although Tubía et al. (2013) furnish an excellent description ofthe high-T shear zone exposed within the Guadaiza tectonic win-dow in the interior of the Sierra Bermeja peridotite massif (Fig. 1),they provide a partial and incomplete picture of the relationshipsbetween the Ronda peridotites and their footwall, particularlyconcerning the frontal zone. In fact, in a geological section acrossthewestern peridotitemassif of Sierra Bermeja (their figure 3), theyshow that the high-T dynamothermal metamorphic aureoleoccurring at the base of the ultramafic rocks is breached by steepreverse faults in the frontal part of the massif. According to thisinterpretation, reiterating that by Esteban et al. (2008a, their figure2), the tectonic contact with the Mesozoic-Tertiary sedimentaryrocks of the Nieves Unit in the footwall appears to consist of a late,‘cold’ thrust fault clearly postdating the ‘hot’ emplacement of theRonda peridotites. On the contrary, Mazzoli and Martín-Algarra(2011) demonstrated that the peridotites were still at very hightemperatures as they were emplaced on top of sedimentary rocksas young as late Aquitanian (Nava Breccia Formation; Martín-Algarra and Estevez, 1984; Martín-Algarra, 1987). The Nieves Unitcarbonates exposed in the footwall of the Ronda mantle extrusion

Fig. 1. Tectonic sketch map of the western Betic Cordillera (modified after Mazzoli and Martín-Algarra, 2011). Tectonic transport data for the Sierra Alpujata and Guadaiza areas areafter Tubía and Cuevas (1986), and Esteban et al. (2008a), respectively. Tectonic transport data for the frontal (i.e. northwestern) part of Sierra Bermeja are from Mazzoli and Martín-Algarra (2011).

S. Mazzoli, A. Martín-Algarra / Journal of Structural Geology 60 (2014) 97e10198

wedge are in fact characterized by a strong inverse metamorphicgradient: within a c. 1.5 km thick zone, non-metamorphic lime-stones/dolostones pass to high-grade marbles in contact with theoverlying peridotites. The metamorphic gradient is marked by sil-icate minerals occurring in the marbles, defining a series of zonesvarying in thickness from tens to several hundred metres andcharacterized by the occurrence of (moving towards the perido-tites): (i) talc, (ii) phlogopite, (iii) tremolite, (iv) diopside, and (v)forsterite (Mazzoli andMartín-Algarra, 2011). Extreme deformationgradients and changes in structural styles accompany the meta-morphic gradient. Field structural analysis integrated with petro-logical, microstructural and electron backscatter diffraction (EBSD)textural data from the Nieves Unit document large finite strains

consistent with general shear within the metamorphic aureoleassociated with NW-ward thrusting of the peridotites, whileolivineeclinohumite-bearing assemblages sampled close to thecontact record maximum temperatures above 700 �C (Mazzoliet al., 2013). Therefore, during the Early Miocene, the Ronda peri-dotites were not just emplaced into middle crustal HPeLT to LPeHTmetamorphic units as it is commonly assumed (e.g. Hidas et al.,2013) and as the structural interpretation portrayed in Tubía et al.(2013, their figure 3) would somehow confirm. Rather, high-T pe-ridotites reached shallow crustal levels and, along the leading edgeof the mantle extrusionwedge, were emplaced on top of otherwisenon-metamorphosed Mesozoic-Tertiary sedimentary rocks of theBetic Cordillera. This has major implications for the modes and

Fig. 2. Inferred Early Miocene tectonic setting of the western Betic Cordillera during extrusion of the Ronda mantle wedge at ca. 19 Ma (modified after Mazzoli and Martín-Algarra,2011; compare with figure 8 of Tubía et al., 2013). Important aspects of the model include the coeval occurrence of: (i) foreland-directed thrusting of the Ronda peridotites on top ofthe Nieves Unit and development of a regional overturned syncline (cored by the late Aquitanian Nava Breccia Fm) in the footwall succession; (ii) left-lateral shear between theperidotites and the eclogites of the Ojen Unit; (iii) top-to-the-hinterland shear along the upper peridotite boundary; and (iv) syn-orogenic extension affecting the upper structurallevels of the overriding plate. Here, strongly subsiding basins are being formed and rapidly filled with sediments eroded from nearby reliefs raised above base level, therebyproducing significant Burdigalian sediment accumulations (Viñuela Group).

S. Mazzoli, A. Martín-Algarra / Journal of Structural Geology 60 (2014) 97e101 99

rates of exhumation of the Ronda subcontinental mantle perido-tites during the Early Miocene.

The very interesting new results just published by Tubía et al.(2013) confirm our original 20110 interpretation that partitioningof the deformation into orogen-parallel strike-slip and orogen-perpendicular thrusting resulted in different e though consistente kinematics of Ronda peridotite emplacement, as recorded infootwall crustal units deformed at various P-T conditions (Fig. 2). Inthis context, orogen-parallel wrenching would have dominated inthe deeper, high-P portions of the continental subduction system,whereas orogen-perpendicular thrusting would have characterizedthe shallower, outer parts. At the same time, Burdigalian depositionof the Viñuela Group was occurring in wedge-top basins above therapidly exhumed Malaguide and highest Alpujarride units. Thelatter had been previously subducted (up to latest Aquitanian-earliest Burdigalian time, that is, up to the geochronologicallywell constrained age for the metamorphic peak, dated at ca. 22 Ma,

or 21 � 2 Ma according to Zeck et al. (1989); which was the firstgeochronological study on the Alpujarride metamorphism to takeinto account also the geological significance of the late-orogenicViñuela Group sedimentation). Besides the extensional collapse ofthe Betic Internal Domain nappe stack during the Early Miocene,our 20110 paper also adequately explains high-temperature Alpinemetamorphism within continental crust rocks at deep structurallevels (Alpujarride Complex) during the emplacement of the Rondaperidotites, while coeval sedimentation was taking place in theInternal (Frontal Units and Malaguide Complex) and Flysch Do-mains. These processes occurred during subduction of the FlyschDomain below the Internal Domain at ca. 19 Ma (Fig. 2) andimmediately before continental collision produced the super-position of rocks of the Internal Domain on top of those of theExternal Domain at ca. 17e16 Ma. At variance with Tubía et al.(2013), our model fully takes into account previous and yet validstratigraphic data on the Oligocene-Miocene deposits occurring on

S. Mazzoli, A. Martín-Algarra / Journal of Structural Geology 60 (2014) 97e101100

top of the Internal Domain units (e.g. Guerrera et al., 1993; Martín-Algarra et al., 2000). Indeed, it also provides a coherent geodynamicscenario for the complex and evolving tectono-sedimentary re-gimes during the AquitanianeBurdigalian time interval (23.03e15.94 Ma according to the 2013 International ChronostratigraphicChart): (i) syn-orogenic sedimentation occurred during the latestOligocene-Aquitanian; (ii) coeval development of an accretionaryprism involved the sedimentary cover of the Flysch Domain e itsbasement being subducted below the Internal Domain e whilemarine to continental piggy-back basin sedimentation occurred ontop of the Frontal Units and the Malaguide Complex; (iii) late-orogenic sedimentation took place during the Burdigalian, withthe deposition of the Viñuela Group in wedge-top basins above thecollapsing nappe stack, immediately before continental collision atca. 17e16 Ma (e.g. Martín-Algarra and Estevez, 1984; Aguado et al.,1990; Guerrera et al., 1993; Martín-Algarra et al., 2000).

In Mazzoli and Martín-Algarra (2011) we further suggested thathe overriding plate of the continental subduction system under-went left-lateral wrenching as a result of fault propagation into theoverlying crustal units (Fig. 2), and that a related tectonic inheri-tance is represented by the Monda Fault Zone, a complex, long-lived structure separating the Sierra Bermeja from the SierraAlpujata-Sierra Blanca massifs (Fig. 1). Multiple fault reactivationsare recorded by variable kinematics along different fault strands(Aguado et al., 1990; Sanz de Galdeano and Andreo, 1995; Estebanet al., 2008b) some of which have been active until recent times, asindicated by offset Burdigalian to Pliocene sediments at both ter-minations of the main fault zone. One of such fault strands, knownas Albornoque Fault, is characterized by recente i.e. post-peridotiteexhumation e right-lateral kinematics, as shown by Tubía et al.(2013, their figure 1) and Mazzoli et al. (2013, their figure 2).Although the model by Tubía et al. (2013, their figure 10) impliessinistral shear coeval with frontal thrusting during the EarlyMiocene e therefore being consistent with the partitioned trans-pression model of Mazzoli and Martín-Algarra (2011, their figure 6)e the original tectonic significance of the Monda Fault Zone ap-pears to have been overlooked in a reconstruction emphasizing therole of recent right-lateral motion along the Albornoque Fault. Thelarge amount of sinistral displacement between the Sierra Bermejaand the Sierra Alpujata massifs, which would be further increasedby restoring the dextral displacement along the Albornoque Faultaccording to Tubía et al. (2013), is consistent with oblique plateconvergence. This is hardly compatible with the idea that the shearsense of the Sierra Bermeja metamorphic sole can be taken as agood approximation for the convergence direction between theAfrican and Iberian plates in Tertiary times (Tubía et al., 2013), sincethis would imply that the major left-lateral wrench zone separatingthe Sierra Bermeja from the Sierra Alpujata peridotite massifs wasperpendicular, rather than oblique, to the plate convergence di-rection. A more coherent picture, proposed by Mazzoli and Martín-Algarra (2011), implies that overall northwardmotion of Africawithrespect to Iberia during the Early Miocene resulted in obliqueconvergence across the originally NE trending Meso-Cenozoiccontinental margin segments in the study area (O’Dogherty et al.,2001), with partitioning of the deformation into margin-normal(i.e. top-to-the-NW) thrusting and margin-parallel, sinistralstrike-slip.

As a final remark, it is worth recalling that the Neogene tectonicevents discussed in detail by Mazzoli and Martín-Algarra (2011)and Tubía et al. (2013) represent just the final stages of a long-lasting, complex process that produced the exhumation of theRonda peridotitese the largest outcropping body of subcontinentalmantle rocks on Earth e from diamond facies (>140 km; Davieset al., 1993). Composite tectonic emplacement of the Ronda peri-dotites most probably occurred as a result of a series of geodynamic

events including (e.g. Sánchez-Rodríguez and Gebauer, 2000;Martín-Algarra et al., 2009; Garrido et al., 2011; Hidas et al.,2013): (i) late- to post-Variscan extension; (ii) Mesozoic rifting,break-up of Pangaea and opening of the Tethyan Ocean, (iii)Oligocene back-arc lithospheric extension and (possibly) subse-quent tectonic inversion, and (iv) Early Miocene continental sub-duction associated with oblique plate convergence. The fact thattwo research groups reached, in completely independent ways,similar conclusions on stage (iv) above, is rather remarkable andcertainly encouraging.

Acknowledgements

Financial support was provided by the Projects CGL2012-32169(MCI-DGICYT) and P11-RNM-7067 (JA), by the RNM-208 and RNM-3715 research groups (Junta de Andalucia), and by the University ofNaples Federico II. Constructive comments by JSG Editor CheesPasschier are gratefully acknowledged.

References

Aguado, R., Feinberg, H., Durand-Delga, M., Martín-Algarra, A., Esteras, M., Didon, J.,1990. Nuevos datos sobre la edad de las formaciones miocenas transgresivassobre las Zonas Internas béticas: la formación de San Pedro de Alcántara. Rev. laSoc. Geológica España 3, 79e85.

Argles, T.W., Platt, J.P., Waters, D.J., 1999. Attenuation and excision of a crustalsection during extensional exhumation: the Carratraca Massif, Betic Cordillera,southern Spain. J. Geol. Soc. 156, 149e162.

Balanyà, J.C., García-Dueñas, V., Azañón, J.M., Sánchez-Gómez, M., 1997. Alternatingcontractional and extensional events in the Alpujárride nappes of the AlboranDomain (Betics, Gibraltar Arc). Tectonics 16, 226e238.

Cuevas, J., Esteban, J.J., Tubía, J.M., 2006. Tectonic implications of the granite dykeswarm in the Ronda peridotites (Betic Cordilleras, Southern Spain). J. Geolog.Soc. Lond. 163, 631e640.

Davies, G.R., Nixon, P.H., Pearson, D.G., Obata, M., 1993. Tectonic implications ofgraphitized diamonds from the Ronda, peridotite massif, southern Spain. Ge-ology 21, 471e474.

Esteban, J.J., Cuevas, J., Vegas, N., Tubía, J.M., 2008a. Deformation and kinematics ina melt-bearing shear zone from the Western Betic Cordilleras (Southern Spain).J. Struct. Geol. 30, 380e393.

Esteban, J.J., Cuevas, J., Tubía, J.M., 2008b. Zonación estructural en una zona decizalla en serpentinitas (Falla de Peña Parda, peridotitas de Ronda). Geogaceta45, 19e22.

Garrido, C.J., Gueydan, F., Booth-Rea, G., Precigout, J., Hidas, K., Padrón-Navarta, J.A.,Marchesi, C., 2011. Garnet lherzolite and garnet-spinel mylonite in the Rondaperidotite: vestiges of Oligocene backarc mantle lithospheric extension in thewestern Mediterranean. Geology 39, 927e930. http://dx.doi.org/10.1130/G31760.1.

Guerrera, F., Martín-Algarra, A., Perrone, V., 1993. Late-oligocene-miocene syn-/-late-orogenic successions in Western and Central Mediterranean Chains fromBetic Cordillera to Southern Apennine). Terra Nova 5, 525e544.

Hidas, K., Booth-Rea, G., Garrido, C.J., Martínez-Martínez, J.M., Padrón-Navarta, J.A., Konc, Z., Giaconia, F., Frets, E., Marchesi, C., 2013. Backarcbasin inversion and subcontinental mantle emplacement in the crust:kilometre-scale folding and shearing at the base of the proto-Alboránlithospheric mantle (Betic Cordillera, southern Spain). J. Geol. Soc. 170, 47e55. http://dx.doi.org/10.1144/jgs2011-151.

Martín-Algarra, A., 1987. Evolución geológica alpina del contacto entre las ZonasInternas y las Zonas Externas de la Cordillera Bética (Ph. D. thesis). University ofGranada, p. 1171.

Martín-Algarra, A., Estevez, A., 1984. La brèche de la Nava: dépôt continental syn-chrone de la structuration pendant le Miocène inférieur des Zones Internes del’ouest des Cordillères Bétiques. Comptes Rendus l’Académie Sci. Paris 299,463e466.

Martín-Algarra, A., Mazzoli, S., Perrone, V., Rodríguez-Cañero, R., 2009. Variscantectonics in the Malaguide Complex (Betic Cordillera, Southern Spain): strati-graphic and structural Alpine vs. pre-Alpine constraints from the Ardales area(Province of Malaga). II: structure. J. Geol. 117, 263e284.

Martín-Algarra, A., Messina, A., Perrone, V., Russo, S., Maate, A., Martín-Martín, M.,2000. A Lost Realm in the internal domains of the Betic-Rifian Orogen (Spainand Morocco): evidence from Oligo-Aquitanian Conglomerates and conse-quences for alpine geodynamic evolution. J. Geol. 108, 447e467.

Mazzoli, S., Martín-Algarra, A., 2011. Deformation partitioning during transpres-sional emplacement of a ‘mantle extrusion wedge’: the Ronda peridotites,western Betic Cordillera, Spain. J. Geol. Soc. 168, 373e382. http://dx.doi.org/10.1144/0016-76492010-126.

Mazzoli, S., Martín-Algarra, A., Reddy, S.M., López Sánchez-Vizcaíno, V., Fedele, L.,Noviello, A., 2013. The evolution of the footwall to the Ronda subcontinental

S. Mazzoli, A. Martín-Algarra / Journal of Structural Geology 60 (2014) 97e101 101

mantle peridotites: insights from the Nieves Unit (western Betic Cordillera).J. Geol. Soc. 170, 385e402. http://dx.doi.org/10.1144/jgs2012-105.

O’Dogherty, L., Martín-Algarra, A., Gursky, H.J., Aguado, R., 2001. The Middle Jurassicradiolarites and pelagic limestones of the Nieves Unit (Rondaide Complex, BeticCordillera): Basin starvation in a rifted marginal slope of the western Tethys. Int.J. Earth Sci. (Geol. Rundsch.) 90, 831e846.

Platt, J.P., Argles, T.W., Carter, A., Kelley, S.P., Whitehouse, M.J., Lonergan, L., 2003.Exhumation of the Ronda peridotite and its crustal envelope: constraints fromthermal modelling of a P-T-time array. J. Geol. Soc. 160, 655e676.

Sánchez Rodríguez, L., Gebauer, D., 2000. Mesozoic formation of pyroxenites andgabbros in the Ronda area (southern Spain), followed by Early Miocenesubduction metamorphism and emplacement into the middle crust: U-Pbsensitive high-resolution ion microprobe dating of zircon. Tectonophysics316, 19e44.

Sanz de Galdeano, C., Andreo, B., 1995. Structure of Sierra Blanca (AlpujarrideComplex, West of the Betic Cordillera). Estud. Geológicos 51, 43e55.

Tubía, J.M., 1994. The Ronda peridotites (Los Reales nappe): an example of therelationship between lithospheric thickening by oblique tectonics and late

extensional deformation within the Betic Cordillera (Spain). Tectonophysics238, 381e398.

Tubía, J.M., Cuevas, J., 1986. High-temperature emplacement of the Los Realesperidotite nappe (Betic Cordillera, Spain). J. Struct. Geol. 8, 473e482.

Tubía, J.M., Gil Ibarguchi, I., 1991. Eclogites of the Ojén nappe: a record of subduc-tion in the Alpujárride complex (Betic Cordilleras, southern Spain). J. Geol. Soc.148, 801e804.

Tubía, J.M., Cueva, S.J., Esteban, J.J., 2013. Localization of deformation and kinematicshift during the hot emplacement of the Ronda peridotites (Betic Cordilleras,southern Spain). J. Struct. Geol. 50, 148e160. http://dx.doi.org/10.1016/j.jsg.2012.06.010.

Van Wees, J.D., de Jong, K., Cloeting, S., 1992. Two-dimensional P-T-t modelling andthe dynamics of extension and inversion in the Betic Zone (SE Spain). Tecto-nophysics 203, 305e324.

Zeck, H.P., Albat, F., Hansen, B.T., Torres-Roldan, R.L., García-Casco, A., Martín-Algarra, A., 1989. A 21þ2 Ma. age for the termination of the ductile alpinedeformation in the internal zone of the Betic Cordilleras, South Spain. Tecto-nophysics 169, 215e220.