Structural setting of the Apennine－Maghrebian thrust belt

The Apennine-Maghrebian fold-and-thrust belt devel-oped from the latest Cretaceous to Early Pleistocene at the subduction-collisional boundary between the Euro-pean and the westward-subducted Ionian and Adria plates. Large parts of the Mesozoic oceanic lithosphere were subducted during an Alpine phase from the Late Cretaceous to Middle Eocene. The chain developed through the deformation of major paleogeographic internal domains (tectono-sedimentary sequences of the Ligurian-Piedmont Ocean) and external domains (sedi-mentary sequences derived from the deformation of the continental Adria-African passive mareinL The continu-ity of the Apennine chain is abruptly interrupted in the Calabrian Arc by the extensive klippe of Kabylo-Calabrian crystalline exotic terranes, derived from deformation of the European passive margin.Major complexities (sharp deflections in the arcuate configuration of the thrust belt, out-of-sequence propagation of the thrusts) are referred to contrasting rheology and differential buoyancy of the subducted lithosphere (transitional from conti-nental to oceanic) and consequent differential roll-back of the Adria plate margin, and to competence contrasts in the Mesozoic stratigraphic sequences,where multiple décollement horizons at different stratigraphic levels may have favored significant differential shortening.From the Late Miocene, the geometry of the thrust belt was strongly modified by extensional fault-ing, volcanic activity, crustal thinning and formation of oceanic crust correlated with the development of the Tyrrhenian Basin.     

A new interpretation for the interference zone between the southern Brasília belt and the central Ribeira belt,SE Brazil

In southeastern Brazil, the Neoproterozoic NNW–SSE trending southern Brasília belt is apparently truncated by the ENE–WSW central Ribeira belt. Different interpretations in the literature of the transition between these two belts motivated detailed mapping and additional age dating along the contact zone. The result is a new interpretation presented in this paper. The southern Brasília belt resulted from E-W collision between the active margin of the Paranapanema paleocontinent, on the western side, now forming the Socorro-Guaxupé Nappe, with the passive margin of the São Francisco paleocontinent on the eastern side. The collision produced an east vergent nappe stack, the Andrelândia Nappe System, along the suture. At its southern extreme the Brasília belt was thought to be cut off by a shear zone, the “Rio Jaguari mylonites”, at the contact with the Embu terrane, pertaining to the Central Ribeira belt. Our detailed mapping revealed that the transition between the Socorro-Guaxupé Nappe (Brasília belt) and the Embu terrane (Ribeira belt) is not a fault but rather a gradational transition that does not strictly coincide with the Rio Jaguari mylonites. A typical Cordilleran type magmatic arc batholith of the Socorro-Guaxupé Nappe with an age of ca. 640 Ma intrudes biotite schists of the Embu terrane and the age of zircon grains from three samples of metasedimentary rocks, one to the south, one to the north and one along the mylonite zone, show a similar pattern of derivation from a Rhyacian source area with rims of 670–600 Ma interpreted as metamorphic overgrowth. We dated by LA-MC-ICPMS laser ablation (U–Pb) zircon grains from a calc-alkaline granite, the Serra do Quebra-Cangalha Batholith, located within the Embu terrane at a distance of about 40 km south of the contact with the Socorro Nappe, yielding an age of 680 ± 13 Ma. This age indicates that the Embu terrane was part of the upper plate (Socorro-Guaxupé Nappe) by this time. Detailed mapping indicates that the mylonite zone is not a plate boundary because motion along it is maximum a few tens of kilometres and the same litho-stratigraphic units are present on either side. Based on these arguments, the new interpretation is that the Embu terrane is the continuation of the Socorro-Guaxupé Nappe and therefore also part of the active margin of the Paranapanema paleocontinent. The Brasília belt is preserved even further within the central Ribeira belt than previously envisaged.     

Several distinct tectono-metamorphic slices in the Cycladic eclogite–blueschist belt,Greece

Several relatively thin tectono-metamorphic slices have been recognized in the Cycladic eclogite–blueschist belt, through detailed studies on Ios, Sifnos, Syros, and Tinos. A sequence of distinct metamorphic mineral growth events has been documented. These recur in each tectonic slice, although individual slices are dominated by different events. To constrain the timing of these processes, the method of asymptotes and limits has been used to reanalyze published ⁴⁰Ar/³⁹Ar apparent age spectra. This reanalysis supports the concept that there were separate and quite distinct high-pressure metamorphic mineral growth events, and allows potential constraints as to the timing of some of these events to be developed. M_1B eclogite-facies metamorphism is estimated to have occurred at some time in the period 53–49 Ma, the M_1C blueschist-facies metamorphic event at some time in the period 44–38 Ma, and the M_1D transitional blueschist-facies metamorphic event is estimated to have occurred at some time in the period 35–30 Ma. A kinematic model is proposed to explain the geometry of a thinly sliced tectono-metamorphic stratigraphy, as observed, and the reason as to why individual tectonic slices in this ‘tectono-metamorphic stratigraphy’ should display distinctive patterns of fabrics and micro-structures, as well as characteristic temperature-time curves as inferred by ⁴⁰Ar/³⁹Ar geochronology.     

Protoliths of the 3.8–3.7 Ga Isua greenstone belt,West Greenland

The Isua greenstone belt (Fig. 1) contains the oldest known, relatively well preserved, metavolcanic and metasedimentary rocks on Earth. The rocks are all deformed and many were substantially altered by metasomatism, but both the deformation and metasomatism were heterogeneous. Transitional stages can be seen from relatively well preserved primary volcanic and sedimentary structures to schists in which all primary features have been obliterated. Likewise different kinds, and different episodes, of metasomatic alteration can be seen that produced a diversity of different compositions and metamorphic mineral assemblages from similar protoliths. New geological mapping has traced out gradations between the best preserved protoliths and their diverse deformed and metasomatised equivalents. By this means, the primary nature of the schists that make up most of the Isua greenstone belt was reinterpreted, and a new map that better portrays the primary nature of the rocks has been produced. The previously mapped stratigraphy was found to be of little value in understanding the geology. Stratigraphic units were defined by different and diverse criteria, such as current composition, structure, metamorphic texture, and inferred protoliths. Much of this stratigraphy represents a misinterpretation of the primary nature of the rocks. The new work indicates that most of the Isua greenstone belt consists of fault-bounded rock packages, mainly derived from basaltic and high-Mg basaltic pillow lava and pillow lava breccia, chert–BIF, and a minor component of clastic sedimentary rocks derived from chert and basaltic volcanic rocks. A previously mapped, extensive, unit of felsic volcanic rocks was found to be derived from metasomatised basaltic pillow lava and pillow breccia intruded by numerous sheets of tonalite.     

Isotopic-geochronological systems in metamorphic rocks: Pon’goma Island,Belomorian mobile belt

Several isotopic methods (U-Pb, Sm-Nd, Rb-Sr, and K-Ar) were applied to different rock-forming and accessory minerals to decipher the chronology of events in a separate segment of the Belomorian mobile belt. Enderbites intruded supracrustal rocks at 2.73 Ga and granodiorites were emplaced at 2.41 Ga. Immediately afterwrads, a permeable schistosity zone was formed along the enderbite-granodiorite contact. Isotopic data indicate that this zone served as a pathway for heat and fluid. The retrograde stage of regional metamorphism and subsequent cooling continued from 1.89 Ga till ～ 1.46 Ga.The cooling rate of the Pon’goma Island rocks is similar to that of other Precambrian complexes and amounted to ～1.5⁰/Ma, which is consistent with previous data on the northern segment of the Belomorian belt. Based on isotopic geochronological data, two tectonometamorphic scenarios can be proposed for the evolution of the Belomorian belt. The first scenario suggests long-term regional metamorphism, i.e., lengthy residence of the Archean and Lower Proterozoic rocks at a significant depth and high temperatures. Geochronological data for different systems (U-Pb, Sm-Nd, Rb-Sr, and K-Ar) suggest Caledonian hydrothermal cryptometamorphic processes. However the rocks of this age are absent from the study area.     

A Plate-Tectonic Model for the Evolution of the Daqingshan Granulite belt in Inner Mongolia

One of the most important events in the early geological evolutionary history of the Earthwas the wide occurrence of granulite belts at the end of the Archaean in the world, whichmeans a possible transformation of evolution mechanism of the crust. More and more geo-     

A greenstone belt in southeast Tibet: An accreted middle–late Permian oceanic plateau

Studies of accreted oceanic plateau sections provide crucial information on their structures, compositions, and origins. We investigate the petrogenesis of ultramafic–mafic rocks in the Tangjia–Sumdo greenstone belt of southeast Tibet using petrography, whole-rock geochemistry, and U-Pb zircon geochronology. These rocks are divided into four groups based on geochemical characteristics that include depleted and tholeiitic mafic rocks, transitional mafic rocks, enriched and alkaline mafic rocks, and picritic ultramafic rocks. Depleted and tholeiitic mafic rocks have the oldest crystallization ages (～272 Ma), followed by picritic ultramafic rocks (～270 Ma), transitional mafic rocks (267–254 Ma), and enriched and alkaline mafic rocks (252–250 Ma). Hafnium and neodymium isotope ratios of depleted and tholeiitic mafic rocks (ε_Hf(t) = +13.1–+16.9; ε_Nd(t) = +6.9–+7.1), transitional mafic rocks (ε_Hf(t) = +1.8–+16.9; ε_Nd(t) = +0.8–+5.5), enriched and alkaline mafic rocks (ε_Hf(t) = +0.5–+5.4; ε_Nd(t) = ?1.5 to +1.9) and picritic ultramafic rocks (ε_Hf(t) = +14.9–+17.2; ε_Nd(t) = +7.8–+9.0) are similar to those of N-MORB, E-MORB, OIB and depleted-type picritic mafic rocks in other oceanic plateaus, respectively. The geochemical characteristics of the depleted and tholeiitic mafic rocks suggest that they formed by partial melting of depleted spinel lherzolite in a mid-ocean ridge setting, whereas the picritic ultramafic rocks suggest a high degree of partial melting of depleted lherzolite in a hot mantle plume head. The transitional mafic rocks formed by partial melting of moderately enriched garnet lherzolite. The youngest rocks (enriched and alkaline mafic rocks) formed by partial melting of a more enriched garnet lherzolite (compared to transitional mafic rocks) at relatively low temperatures. We propose that the depleted and tholeiitic mafic rocks represent normal oceanic crust of the Sumdo Paleo-Tethys Ocean and the transitional mafic rocks, enriched and alkaline mafic rocks and picritic ultramafic rocks are the fragments of the oceanic plateau, which were related to middle–late Permian mantle plume activity in the Sumdo Paleo-Tethys Ocean. We further suggest that the majority of the Tangjia–Sumdo greenstone belt represents a middle–late Permian oceanic plateau that reflects a previously unrecognized middle–late Permian mantle plume.     

Permo-Triassic intermediate–felsic magmatism of the Truong Son belt,eastern margin of Indochina

Permo-Triassic intermediate–felsic magmatism is developed along the Truong Son fold belt, located in the eastern margin of the Indochina Block. It comprises a succession of the active continental margin associations: calc-alkaline volcano-plutonic associations (272–248 Ma), peraluminous granites (259–245 Ma), and subalkaline felsic volcano-plutonic associations (younger than 245 Ma). Detailed study of geochemical characteristics such as trace elements (LILE, REE, HFSE) and isotopes (Sr, Nd, Pb) indicates that they are homogeneous and that they are products of the Palaeotethys subduction process in relation to Indochina (IC)/North Vietnam–South China (NV–SC) amalgamation (S.L. Chung et al., Abstr., GEOSEA 98, Malaysia, 1998, pp. 17–19). The Indosinian characteristics are represented by mantle–crust interaction in magma generation, controlled by their emplacement localities in relation to the Kontum Uplift. The spatial and temporal evolution of Permo-Triassic magmatism allows reconstructing the geodynamic history of the Indosinian orogeny. It confirms that this event ended in Early to Middle Triassic (246–240 Ma, after C. Lepvrier et al., Tectonophysics 393 (2004) 87–118).     

Ore fluid geochemistry of the Jinlongshan Carlintype gold ore belt in Shaanxi Province, China

THEJINLONGSHANGOLDOREBELTINZHEN’ANCOUN TY,SOUTHERNSHAANXIPROVINCE,ISLOCATEDINTHEWEST ERNQINLINGGOLDPROVINCE(NO.16INFIG.1;CHEN YANJINGETAL.,2004).ITWASDISCOVEREDINTHEDEVO NIANSTRATAINTHELATE1980S).ITSGEOLOGICALSETTING ANDMETALLOGENICEVOLUTIONARESIMILARTOT…     

Diamondiferous Archean rocks of the Olondo greenstone belt (western Aldan–Stanovoy shield)

Diamond from metaultramafic rocks of the Mesoarchean (2.96–3.0 Ga) Olondo greenstone belt, located in the western Aldan–Stanovoy shield, has been studied. Diamonds occur in lenses of olivine–serpentine–talc rocks within metaultramafic rocks of intrusive habit, whose composition corresponds to peridotite komatiites. All diamonds from the metaultramafic rocks are crystal fragments 0.3 to 0.5 mm in size. Morphological examination has revealed laminar octahedra, their transitional forms to dodecahedroids, crystals with polycentric faces, and spinel twins. The crystals vary in photoluminescence color: dark blue, green, yellow, red, or albescent. Characteristic absorption bands in crystals point to nitrogen impurities in the form of A and B1 defects and tabular B2 defects. The crystals studied belong to the IaA/B type, common among natural diamonds. The overall nitrogen content varies from < 100 to 3800 ppm. The relative content of nitrogen in B1 centers varies from 0 to 94%, pointing to long stay in the mantle. The carbon isotope ratio in the diamonds, ¹³C = ? 26‰, is indicative of involvement of subducted crust matter in diamond formation in the Archean.     

Tectonics and metallogeny of the Khakandzha ore district in the Okhotsk–Chukotka volcanic belt

The data on the structure, geodynamics, and metallogeny of the Khakandzha ore district in northwestern Okhotsk region are analyzed and the two main factors responsible for the localization of ore deposits are defined. The magmatic factor controls the confinement of the ore district to the tectono-magmatic structure of the central type (source of ore matter), which determines the concentric zoning patterns in the distribution of ore mineralization. The tectonic factor determines the confinement of the ore districts, deposits, and ore occurrences of the region to the meridional left-lateral shear structure, which controls the magma and fluid distribution. Local extension (transtension) in this structure against the background of general lateral compression (transpression) provided tectonic environments most favorable for ore accumulation.     

First data on late vendian granitoid magmatism of the Northwestern Sayan–Yenisei accretionary belt

Late Vendian (540–550 Ma) U–Pb age was established for zircon from postcollisional granites of the Osinovsky Massif located among island-arc complexes of the Isakovka terrane in the northwestern Sayan–Yenisei accretionary belt. The granites were formed 150 Ma after the formation of the host island-arc complexes and 50–60 Ma after the beginning of their accretion to the Siberian Craton. These events mark the final stage of the Neoproterozoic history of the Yenisei Ridge related to the end of accretion of oceanic fragments and the beginning of the Caledonian Orogeny. The granites are subalkaline leucoractic Na–K rocks enriched in Rb, U, and Th. The petrogeochemical and Sm–Nd isotope data (T_Nd(DM)-2st = 1490–1650 Ma and ε_Nd(T) from–2.5 to–4.4) indicate that their source was highly differentiated continental crust of the SW margin of the Siberian Craton. Therefore, the host Late Riphean island-arc complexes were thrust over the craton margin for distance significantly exceeding the size of the Osinovsky Massif.     

Carbonate dykes associated with Arch˦an lode-Au mineralisation,Barberton greenstone belt,South Africa

Carbonate dykes, exposed within the Barberton greenstone belt, display geochemical signatures similar to altered carbonatite. The trace element signature normalised to primordial mantle, and the chondrite-normalised REE trends of the Ulundi Dyke display geochemical similarities to carbonatites. In addition, stable isotope results from the Ulundi Dyke (δ¹³C_{whole rock} and δ¹⁸O_{whole rock} range from -3.7 to -4.9‰ and 12.8 to 13.2‰, respectively) are similar to values found for samples of wall rock and vein carbonate from Arch˦an Au-quartz-carbonate-sulphide vein systems studied in the Barberton greenstone belt. Although the data do not plot in the field of primary igneous carbonatite, they are similar to data of deuterically-altered carbonatite. These associations strengthen the deduction that Iode-Au mineralised fractures and shear zones in the Barberton greenstone belt were open to mantle-tapping fundamental faults.     

Geochemistry of Adakitic Rocks and Cu-Au Mineralization in the Tianzishan Region, West Qinling orogenic belt

Please refer to the attachment(s) for more details     

An Eocene magmatic belt across central Tibet: mantle subduction triggered by the Indian collision?

Mountain domes rising to ≈ 6600 m along Tibet's Tanggula range herald the Eocene intrusion of calcalkaline granites into terranes accreted much earlier. Together with coeval, cogenetic volcanics, such intrusives, which have similar crystallization and cooling ages, may be part of an ESE-trending belt cutting central Tibet in half. This magmatic belt may have marked a former northern boundary of the plateau, testifying to S-directed subduction of the Asian mantle. Such subduction would have developed soon after India's collision but long before the rise of the plateau's present rims, along one of central Tibet's Mesozoic sutures.     

Evolution of a tertiary volcanogenic trough in SW Turkey — The Alakaya basins of the Lycien belt

Field study of several stratigraphic sections from allochthonous thrust fault slices of SW Turkey reveal that a deeply subsiding volcanogenic trough, the Alakaya basin existed during Paleocene-Middle Eocene times along the Lycian belt. The Alakaya basin was located along a tectonically active zone of weakness between two relatively stable tectonic terrains, the Menderes massif to the northwest and the Beydaglari continental platform to the southeast. The basin was underlain by continental substratum. All known outcrops of the Alakaya sediments overlie platform carbonates of Cretaceous age that correlate with the Beydaglari shelf sediments. The generation of the volcanogenic Alakaya basin reflects a tensional period that culminated in Middle Eocene when basic volcanic activity took place. The tensional stage was replaced by a compressional regime in Late Eocene and large scale overthrust faulting took place. The Alakaya basin was closed when the Tefenni nappe from the north was emplaced on its sediments in Late Eocene. The Alakaya sediments overlying the Tefenni nappe and underlying the Cretaceous platform carbonates moved southeastward over a hundred kilometers onto the autochthonous sediments of the Beydaglari terrain in Miocene time. The Alakaya basin is analogous to the Maden basin of SE Turkey thrust fault belt. Both basins were located along tectonically active belts. The main stage of basin subsidence and volcanism was in Middle Eocene. Closure of both basins by large scale thrust faulting was in Late Eocene. The creation and destruction of the volcanogenic Alakaya basin may be related to the regional adjustments in plate motions in Paleocene-Eocene times.

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Zusammenfassung Geländestudien einiger stratigraphischer Profile von allochthonen Überschiebungspaketen in der SW Türkei zeigen, daß ein tief abgesunkener vulkanogener Trog, das Alakaya Becken, während des Paläozäns und Mittel Eozäns entlang der Lyzischen Zone bestand. Das Alakaya Becken lag innerhalb einer tektonisch aktiven Schwächezone zwischen zwei relativ stabilen tektonischen Terrains, dem Menderes Massiv im NW und der Beydaglari Kontinentalplattform im SE. Das Becken besaß eine kontinentale Unterlage. Alle bekannten Aufschlüsse mit Alakaya Sedimenten lagern über kretazischen Plattformkarbonaten, die sich mit den Beydaglaria Schelfsedimenten korrelieren lassen. Die Entwicklung des vulkanogenen Alakaya Bekkens spiegelt eine Spannungsperiode wieder, die im Mittel Eozän mit basischem Vulkanismus kulminierte. Diese Periode der Zugspannung wurde im späten Eozän von einer kompressiven Beanspruchung abgelöst, welche zu großmaßstäblichen Überschiebungen führte. Das Alakaya Becken wurde geschlossen, als auf Grund der späteozänen Platznahme die aus dem Norden stammende Tefenni Decke auf deren Sedimenten zu liegen kam. Die Alakaya Sedimente zusammen mit der überlagernden Tefenni Decke und den unterlagernden kretazischen Plattformkarbonaten wurden während des Miozäns über einhundert Kilometer südostwärts auf die autochthonen Sedimente des Beydaglari Terrains überschoben. Das Alakaya Becken ist ein Analogon zu dem Maden Becken der SE Türkischen Überschiebungszone. Beide Becken lagen entlang tektonisch aktiver Zonen. Während des Mittel Miozäns war das Hauptstadium der Beckensubsidenz und des Vulkanismus. Das Schließen der Becken mittels großmaßstäblicher Überschiebung fand in beiden Fällen im späten Eozän statt. Die Bildung und der Zerfall des vulkanogenen Alakaya Beckens scheint mit den regionalen Anpassungen an die Plattenbewegung während des Paläozäns und Eozäns verbunden zu sein.

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Résumé L'étude de terrain de plusieurs coupes stratigraphiques dans les lames charriées de l'allochtone du sud-ouest de la Turquie révèle l'existence, du Paléocène à l'Eocène moyen, d'une fosse volcanogénique fortement subsidente: le bassin d'Alakaya, situé le long de la chaîne lycienne. Ce bassin d'Alakaya s'est localisé le long d'une zone de faiblesse tectoniquement active, entre deux blocs relativement stables: le massif de Menderes au nord-ouest et la plate-forme continentale de Beydaglari au sud-est. Le bassin repose sur un substratum continental. Dans tous les affleurements connus, les sédiments d'Alakaya surmontent des carbonates de plateforme d'âge Crétacé, corrélables aux sédiments de shelf de Beydaglari. La genèse du bassin volcanogène d'Alakaya reflète une période d'extension dont le maximum se situe à l'Eocène moyen, lors de l'apparition d'une activité volcanique basique. A la phase distensive a succédé, à l'Eocène supérieur, un régime compressif marqué par des charriages de grande échelle. Le bassin d'Alakaya était fermé au moment où la nappe de Tefenni, venant du nord, s'est mise en place sur ses sédiments, à l'Eocène supérieur. Au Miocène, l'ensemble formé par la plate-forme carbonatée crétacée sous-jacente, les sédiments dAlakaya et la nappe de Tefenni surincombante a été transporté d'une centaine de km vers le sud-est sur les sédiments autochtones de Beydaglari. Le bassin d'Alakaya est analogue au bassin de Maden de la ceinture charriée du sud-est de la Turquie. Tous deux se sont localisés le long de zônes tectoniques actives. Leur phase culminante de subsidence et de volcanisme se situe à l'Eocène moyen. Dans les deux cas, les bassins ont été formés à l'Eocène supérieur par un charriage à grande échelle. La formation et la destruction du bassin d'Alakaya semblent pouvoir être rattachées aux ajustements régionaux dans les mouvements des plaques au Paléocène-Eocène.

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Delineation of fresh aquifers in tannery belt for sustainable development — A case study from southern India

The tannery effluents discharged by the existing units on either side of the Palar river at Ambur town (known for tannery industry), has resulted in vertical and lateral spread of pollution. The study area of 55.3 km² is situated on a granitic terrain of Archaean age with undulating topography and hillocks. The shallow aquifers, in flood plain and valley fills of the river are highly polluted (with EC: 15340 μS/cm) by tannery effluents making groundwater unfit for any use, hence the local population (20000) face health hazards and shortage of potable water. Hydrogeological, geophysical and in-situ groundwater quality measurement were carried out to demarcate fresh groundwater zones and to delineate lateral and vertical extent of pollution. The results show, brackish aquifer was characterized by low order of resistivity (<20 Ω-m) with a thickness of 8.5 to 28 m located in the flood plains, valley fills, and partially in hard rock formations, whereas the fresh water aquifer resistivity varying from 23 to 216 Ω-m in hard rock. Further, these results were correlated with the water quality data and Ground Penetrating Radar (GPR) signals. The integrated studies revealed that pollution due to tannery effluents has spread over an area of 33.4 km² (60.4 %) on either side of the river and only a small area of 21.9 km² (39.6 %) was identified as fresh groundwater zone, which has to be conserved and exploited in sustainable manner for future generations.     

The Malpica–Lamego Line: a major crustal-scale shear zone in the Variscan belt of Iberia

The Malpica–Lamego Line (MLL) is a deformation zone in the Variscan belt of NW Iberia (NW Spain and N Portugal) that runs parallel to the chain for at least 275 km, bearing I-type granodiorite plutons along most of its length. The MLL affects previous structures by which high pressure and ophiolitic rocks were exhumed and emplaced on the Iberian plate during earlier deformation phases. Correlation and reconstruction of the stratigraphy of these sheets or tectonic units at both sides of the shear zone allows a preliminary estimate of the accumulated vertical and horizontal offsets after the tectonic activity of the fault. The value of the separations, of crustal-scale proportions, reaches a maximum 15 km of vertical offset that decreases gradually to the south. The structural record found in the rocks indicates a strike-slip regime that, in general, does not fit the geometry of the offsets. We suggest that the MLL went through two different stages during the same orogenic cycle: a first dip-slip episode, a reverse faulting event, overprinted by a later strike-slip reactivation.