Giulio Viola

The 'Mylonite Zone' (MZ) forms a major, arcuate terrane boundary in the Precambrian Sveconorwegian orogen of SW Scandinavia. SE-directed thrusting along this curvilinear shear zone emplaced the higher-grade Idefjorden Terrane to the west onto the lower-grade Eastern Segment ...

Denudation along the Atlantic passive margin: new insights from apatite fission-track analysis on the ... Africa and South America) from east Gondwana (Australia, Antarctica, India and New Zealand), post ... Modelling of the AFT data along this traverse has to take into account the ...

New structural and geochronological investigations of the “Mylonite Zone” (MZ), an arcuate terrane boundary in southwest Scandinavia, contribute to a refined conceptual model for the Grenvillian–Sveconorwegian tectonic evolution of the Mesoproterozoic Sveconorwegian orogenic belt. During late convergence, around 970 Ma, the MZ acted as a top-to-the-SE thrust that accommodated crustal shortening in the eastern part of the orogen by juxtaposing the Idefjorden Terrane in the hanging wall in the west against the “Eastern Segment” footwall in the east. The eastward vergence of the MZ and of similarly oriented second-order nearby shear zones is interpreted as reflecting late back-thrusting within the overall W-vergent orogeny. Back-thrusting was possibly promoted by the backstop role played by the rigid block formed by the 1810–1650 Ma Transscandinavian Igneous Belt. During subsequent E–W crustal extension, the MZ thrust-related fabrics were reactivated in an extensional fashion with bulk top-to-the-W kinematics. This was triggered by gravitational instabilities resulting from crustal overthickening during the shortening phase. 40Ar-39Ar biotite and white mica ages from a greenschist-facies and extension-related mylonite range between 922 and 860 Ma. This long-lived episode is expressed by extensional structures that evolved continuously from purely ductile to brittle during progressive exhumation of the footwall. The “Eastern Segment” is interpreted as an immature asymmetric core complex, exhumed in the footwall of the extensional MZ, through the antithetic normal displacement of the MZ itself and of the top-to-the-E Sveconorwegian Frontal Deformation Zone farther to the east. The core complex is bound to the north by the transtensional Hammarö Shear Zone, characterized by penetrative constrictional fabrics, interpreted as indicative of an overall transtensional regime.► Structural analysis in the Mesoproterozoic Grenville-Sveconorwegian orogenic belt. ► Build up and collapse of the orogen in southwestern Scandinavia. ► E-vergent back-thrusting in overall west-vergent orogen along the Mylonite Zone. ► Asymmetric core complex development in a Precambrian transtensional regime. ► 40Ar-39Ar biotite and white mica ages record extension between 922 - 860 Ma.

Sandbox experiments with sand and sand-silicone models were performed above a circular strike-slip fault to understand the influence of curvature on the development of second-order faults. Riedel R faults appear already at low displacements in the concave side of the circular plate where they always form more numerous. They are followed by R faults in the convex side and eventually by throughgoing D faults that join the R faults and that develop parallel to the underlying circular fault. The angle between the Riedel faults and the trace of the main circular fault at the surface of the models is c. 26° on the concave side and 15° on the convex side. We infer a larger obliquity of σ1 in the concave side of the circular plate, which corresponds to a larger transpressional component than in the convex side of the main wrench fault due to the more confined volume of deforming sand. In sand experiments, most of the faults root into the underlying strike-slip fault. In sand-silicone experiments instead, the faults form close to the displacement discontinuity in case of a high displacement rate only. Uplifted areas are located all along the main fault in sand experiments. In sand-silicone experiments, they are mostly located in wedges defined by the Riedel faults and the main wrench fault and the width of these uplifted areas appear to be related to the length and activity of the Riedel faults. Our results differ significantly from those of experiments with straight strike-slip faults where strain and second-order faults are symmetrically arranged on both sides of the main fault.► The faults propagate on both sides of circular strike-slip fault although they remain more numerous on the concave side. ► The angle between the R and D fault is always more opened on the concave side of the plate than on the convex side. ► The asymmetry of second-order faults can constitute relevant indications of a circular component along a wrench fault.

The brittle structural history of western South Africa has been investigated by remote sensing and field studies to build a conceptual scheme for its > 500 Ma long evolution. Paleostress tensors were computed from a significant fault-slip dataset and a relative geochronological succession of brittle deformation events was established. This was aided by separating in time faulting events through the usage of Cretaceous weathering horizons, silicified fluvial deposits, paleosols and 77–54 Ma olivine melilitite plugs as time markers. The oldest features recognized formed during four compressional episodes assigned to the Neoproterozoic Pan African evolution. This history is expressed by sub-vertical conjugate fracture sets and fits well the inferences derived from remote sensing. The greatest compressive direction rotated from NW-SE to NNE-SSW and finally to almost E–W. A subsequent ENE-WSW-oriented extensional episode is associated with the local effects of the opening of the Atlantic Ocean and was followed by a second, ca. E–W extensional episode, linked to the well-acknowledged Mid-Cretaceous (115–90 Ma) event of margin uplift. A late Santonian (85–83 Ma) NW-SE compressive paleostress deformed the Late Cretaceous sequences and was in turn followed firstly by a renewed episode of NE-SW extension and later by ca. NNE-SSW Late Maastrichtian (69–65 Ma) shortening. The latter is broadly coeval with the emplacement of the Gamoep magmatic suite. A phase of WNW-ESE Cenozoic extension is assigned to the extensional phase recorded in the Okawango delta, interpreted as reflecting propagation of the East African Rift System into southern Africa. No stress tensor was computed for the present day “Wegener anomaly” stress field, oriented NW-SE. However, in situ stress measurements were used to perform slip tendency analysis, which indicates that, under the currently existing stress conditions, WNW-ESE- and NNW-SSE-striking faults are critically stressed and are the most likely reactivated, in agreement with the present seismicity.►Stress tensor inversion and remote sensing document 500 Myr of brittle evolution. ►Pan African and younger brittle phases due to Mesozoic and Cenozoic evolution. ►Continued fault reactivation controlled accommodation of younger strain increments.

Abstract The Naukluft Thrust forms the floor thrust to the Naukluft Nappe Complex, a far-travelled, nappe stack of the Pan-African Damara belt in Namibia. The thrust tectonostratigraphy comprises three dolomitic components, a calc-mylonite horizon, and a discrete brittle fault. Stable isotope data indicate that the leading edge is characterized by positive δ 13 C values, whereas the trailing edge is characterized by negative δ 13 C values. There is a significant range in the δ 18 O values, over 15‰ in different sections, with the ...

[2] The term ''Pan-African''is widely used to refer to the central part (largely in Africa) of the global orogeny that resulted in the formation of the supercontinent Gondwana between Late Neoproterozoic and Cambrian times [eg, Unrug, 1997]. Although there is general ...

Pan-African high-pressure granulites occur as boudins and layers in the Lurio Belt in north-eastern Mozambique, eastern Africa. Mafic granulites contain the mineral assemblage garnet + clinopyroxene + plagioclase + quartz ± magnesiohastingsite. Garnet porphyroblasts are zoned with increasing almandine and spessartine contents and decreasing grossular and pyrope contents from core (Alm46Prp32Grs21Sps2) to rim (Alm52Prp26Grs19Sps3). This pattern is interpreted as a retrograde diffusion zoning with the preserved core chemistry representing the peak metamorphic composition. Mineral reaction textures occur in the form of monomineralic and composite plagioclase ± orthopyroxene ± amphibole ± biotite ± magnetite coronas around garnet porphyroblasts. Thermobarometry indicates peak metamorphic conditions of up to 1.57 ± 0.14 GPa and 949 ± 92 °C (stage I), corresponding to crustal depths of ∼55 km. Zircon yielded an U–Pb age of 557 ± 16 Ma, inferred to date crystallization of zircon during peak or immediately post-peak metamorphism. Formation of plagioclase + orthopyroxene-bearing coronas surrounding garnet indicates a near-isothermal decompression of the high-pressure granulites to lower pressure granulite facies conditions (stage II). Development of plagioclase + amphibole-coronas enclosing the same garnet porphyroblasts shows subsequent cooling into amphibolite facies conditions (stage III). Symplectitic textures of the corona assemblages indicate rapid decompression. The high-pressure granulite facies metamorphism of the Lurio Belt, followed by near-isothermal decompression and subsequent cooling, is in accordance with a long-lived tectonic history accompanied by high magmatic activity in the Lurio Belt during the late Neoproterozoic–early Palaeozoic East-African–Antarctic orogeny.

Calcite veins are invariably associated with en-echelon kimberlite dyke–fracture arrays. A detailed microstructural study of veining indicates four vein types. Type I stretched or ataxial veins are defined by high aspect ratio calcite fibers that are crystallographically continuous with calcite of the kimberlite matrix wall rock, by elongated phenocrystic phlogopite with sharp crystal terminations centered on contacts between adjacent calcite fibers and by phenocrystic phlogopite that grows or extends across these veins. Type I vein mineralogy indicates syn-dilational crystallization of vein minerals in local tensional areas within the kimberlite. Vein Types II (stretched to syntaxial elongate-blocky) and III (antitaxial) indicate late crystallization vein mineral growth during subsequent or repeated dilation. Calcite fibers in Type I to Type III veins are orthogonal to the contacts of their host dykes regardless of the orientation of vein margins. Type IV calcite veins, with blocky or mosaic/polycrystalline textures, are attributed to minor post-intrusion extension, which was potentially accompanied by repeated kimberlite intrusion within a given dyke array. Syn-crystallization/syn-intrusion Type I veins and an ubiquitous dyke-parallel fracture cleavage, in a zone up to 4 m on either side of dyke contacts, suggest that en-echelon kimberlite dyke–fracture arrays occupied the approximate center of zones of active dilation within the brittle carapace of the upper crust. Type II and III veins indicate that extension or dilation continued, independently of an occupying kimberlite fluid phase, after initial intrusion. Arrested mobile hydrofracturing, under low differential stress within the upper brittle or seismic carapace of the continental crust, followed by repeated dilation of the dyke–fracture system, is proposed as a mechanism for producing the features observed in this study. The conditions constrained in this study indicate passive dyke intrusion into dilating fracture arrays during crustal extension.

The Nampula Block covers over 100,000 km2, making it the largest Mesoproterozoic crustal segment in northern Mozambique and an important component of the Neoproterozoic to Cambrian (Pan-African) East African Orogen. It is bounded in the north by the WSW–ENE trending Lúrio Belt. The oldest rocks (Mocuba Suite) are a polydeformed sequence of upper amphibolite-grade layered grey gneisses and migmatites associated with intrusive trondhjemite-tonalite-granodiorite and granitic orthogneisses. A banded gneiss, interpreted as a meta-volcanic rock, yielded a U-Pb SIMS zircon date of 1127 ± 9 Ma. Metamorphic rims, dated at ca. 1090 Ma, probably grew during a later magmatic phase, represented by the tonalitic Rapale Gneiss, two samples of which were dated at 1095 ± 19 and 1091 ± 14 Ma, respectively. The earliest (D1) deformation that took place at approximately this time, was associated with high grade metamorphism and migmatisation of the Mocuba Suite. The geochemistry of these rocks suggests that they were generated in a juvenile, island-arc setting. The Mocuba Suite is interlayered with extensive belts of meta-pelitic/psammitic, calc-silicate and felsic to mafic meta-volcanic paragneisses termed the Molócuè Group. U-Pb data from detrital zircons from a calc-silicate paragneiss gave a bimodal age distribution at ca. 1100 and 1800 Ma, showing derivation from rocks of the same age as the Mocuba Suite and a Palaeoproterozoic source region. The age of the Molócuè Group has been directly determined by dates of 1092 ± 13 and 1090 ± 22 Ma, obtained from two samples of the leucocratic Mamala Gneiss (meta-felsic volcanics?), one of its major constituent components. The final phase of Mesoproterozoic activity is represented by voluminous plutons and sheet-like bodies of foliated megacrystic granite, augen gneiss and granitic orthogneiss of the Culicui Suite, which have A-type granite geochemical characteristics and are interpreted to have been generated in a late tectonic, extensional setting. Three samples from the suite gave identical ages of ca. 1075 Ma. The Nampula Block was extensively re-worked during the major (D2: Pan-African) collision orogen in Late Neoproterozoic to Cambrian times, when the major regional fabrics were imposed upon the Mesoproterozoic rocks under amphibolite-facies metamorphic conditions. In the dated samples, this orogenic event is represented by metamorphic zircon rim ages of ca. 550 to 500 Ma. The new data indicate that the Mesoproterozoic rocks of the Nampula Block were originally accreted to a Palaeoproterozic crustal Block and the Nampula Block only reached its current position, separated from the other Mesoproterozoic blocks of NE Mozambique by the Lúrio Belt, during Neoproterozoic collision and plate movements. The geological history of the Nampula Block is comparable with that described from other parts of the Mesoproterozoic orogenic belts of the Kalahari craton and helps to constrain an integrated model of their evolution.

Recently discovered mud volcanoes in the Orange Basin, offshore southwestern Africa, denote the existence of neotectonic faults in the submerged continental shelf. Interpretation of seismic lines perpendicular to the trend of the alignment of the mud volcanoes shows flower structures, diagnostic of strike-slip faulting along a N/NNW direction. Analysis at the regional scale of onland neotectonic features in southwestern Africa shows that recent faulting occurred both in central Namibia and Namaqualand, South Africa and that it created both N/NNW- and NW-trending lineaments. It is proposed that the newly discovered offshore neotectonic activity and the onland structures described in this paper represent the structural expression of the same stress field. These structures form a set of conjugate transtensive faults, which constrain the regional horizontal greatest compressive stress in a NW/NNW direction. Such stress orientation, also supported by in situ stress measurements, defines the so-called Wegener stress anomaly, the predominant present-day stress field of southwest Africa. The Wegener anomaly is incompatible with the stress orientation required by plate-scale tectonic constraints, mainly in the form of recently published GPS motion values for the African plate.

Folding of axial plane cleavage can occur during progressive deformation without a change in the overall background flow. Two field examples of upright (Lachlan Fold Belt, SE Australia) and recumbent (Naukluft Nappe Complex, central Namibia) folds are presented, in which strongly refracted pressure solution cleavage in competent layers on the fold limbs is buckled as a result of ongoing fold amplification. Finite element modelling confirms that cleavage refraction on limbs can be sufficient for cleavage planes to be subsequently shortened and therefore folded. Cleavage refraction is unequally developed on opposite limbs of asymmetric folds formed by oblique shortening of a layer in coaxial flow or by folding in a more general shear environment. The differences in finite strain on opposite limbs can be quite marked even when the fold shapes themselves are not obviously asymmetric. For folding in simple shear flow, as specifically modelled here, refraction is only strong on the fold limb that rotates against the imposed sense of shear. In known shear environments, this provides a potential kinematic indicator in folded units at relatively low strain (e.g. in simple shear, γ of around one), where other higher-strain indicators, typical of mylonites, are not yet sufficiently developed or are equivocal.

A new set of zircon and apatite fission-track ages from the Ailao Shan and Day Nui Con Voi (DNCV) metamorphic massifs of the Red River shear zone (RRSZ) and neighboring rocks in northern Vietnam is presented. A complex, along-strike diachronous, denudation history is revealed. The southern sector of the DNCV cooled to about 100 °C by the Late Oligocene, whereas its central compartment was affected by the later thermotectonic evolution of the Song Chay dome to the E of the RRSZ, whose final exhumation occurred during the Early Miocene. The northern sector of the RRSZ is characterized by the 35 Ma Phan Si Pang pre- to synkinematic intrusion. Fission-track ages from a vertical section within the Phan Si Pang granite indicate rapid exhumation and cooling. The Paleozoic tectonic block to the west of the RRSZ (fission-track ages between 40 and 30 Ma) was exhumed and cooled earlier than the fault mylonite belt (fission track ages of 30 Ma and younger) and also than the eastern block. Its structural level is consistent with field observations that suggest the RRSZ in northern Vietnam to be a transtensional system, with a regional NE–SW oriented extension component.

... 3 m/Ma from dolerite sills suggest a strong lithology control on the erosion. ... Since the break-up of Gondwana, Southern Africa has been surrounded by elevated passive margins ... morphology is the result of positive and negative feedback between tectonic uplift and subsidence ...

Zircon and monazite U–Pb data document the geochronology of the felsic crust in the Mozambique Belt in NE Mozambique. Immediately E of Lake Niassa and NW of the Karoo-aged Maniamba Graben, the Ponta Messuli Complex preserves Paleoproterozoic gneisses with granulite-facies metamorphism dated at 1950 ± 15 Ma, and intruded by granite at 1056 ± 11 Ma. This complex has only weak evidence for a Pan-African metamorphism. Between the Maniamba Graben and the WSW–ENE-trending Lurio (shear) Belt, the Unango and Marrupa Complexes consist mainly of felsic orthogneisses dated between 1062 ± 13 and 946 ± 11 Ma, and interlayered with minor paragneisses. In these complexes, an amphibolite- to granulite-facies metamorphism is dated at 953 ± 8 Ma and a nepheline syenite pluton is dated at 799 ± 8 Ma. Pan-African deformation and high-grade metamorphism are more intense and penetrative southwards, towards the Lurio Belt. Amphibolite-facies metamorphism is dated at 555 ± 11 Ma in the Marrupa Complex and amphibolite- to granulite-facies metamorphism between 569 ± 9 and 527 ± 8 Ma in the Unango Complex. Post-collisional felsic plutonism, dated between 549 ± 13 and 486 ± 27 Ma, is uncommon in the Marrupa Complex but common in the Unango Complex. To the south of the Lurio Belt, the Nampula Complex consists of felsic orthogneisses which gave ages ranging from 1123 ± 9 to 1042 ± 9 Ma, interlayered with paragneisses. The Nampula Complex underwent amphibolite-facies metamorphism in the period between 543 ± 23 to 493 ± 8 Ma, and was intruded by voluminous post-collisional granitoid plutons between 511 ± 12 and 508 ± 3 Ma. In a larger context, the Ponta Messuli Complex is regarded as part of the Palaeoproterozoic, Usagaran, Congo-Tanzania Craton foreland of the Pan-African orogen. The Unango, Marrupa and Nampula Complexes were probably formed in an active margin setting during the Mesoproterozoic. The Unango and Marrupa Complexes were assembled on the margin of the Congo-Tanzania Craton during the Irumidian orogeny (ca. 1020–950 Ma), together with terranes in the Southern Irumide Belt. The distinctly older Nampula Complex was more probably linked to the Maud Belt of Antarctica, and peripheral to the Kalahari Craton during the Neoproterozoic. During the Pan-African orogeny, the Marrupa Complex was overlain by NW-directed nappes of the Cabo Delgado Nappe Complex before peak metamorphism at ca. 555 Ma. The nappes include evidence for early Pan-African orogenic events older than 610 Ma, typical for the Eastern Granulites in Tanzania. Crustal thickening at 555 ± 11 Ma is coeval with high-pressure granulite-facies metamorphism along the Lurio Belt at 557 ± 16 Ma. Crustal thickening in NE Mozambique is part of the main Pan-African, Kuunga, orogeny peaking between 570 and 530 Ma, during which the Congo-Tanzania, Kalahari, East Antarctica and India Cratons welded to form Gondwana. Voluminous post-collisional magmatism and metamorphism younger than 530 Ma in the Lurio Belt and the Nampula Complex are taken as evidence of gravitational collapse of the extensive orogenic domain south of the Lurio Belt after ca. 530 Ma. The Lurio Belt may represent a Pan-African suture zone between the Kalahari and Congo-Tanzania Craton.

Sandbox analogue models were used to study the reactivation of a reverse fault in strike–slip and transpressive regimes, for comparison with the evolution of the Giudicarie fault system in the Central Eastern Alps. The Giudicarie system is interpreted as resulting from Late Miocene sinistral transpressive reactivation of an older, Late Oligocene reverse fault. The ‘old’ reverse fault was reproduced as a pre-cut dilatant surface obtained by pulling a stiff metal wire through the model sand layer. The position of the pre-existing fault with respect to the base plate fault accommodating the strike–slip and transpressive faulting phase controlled the extent and geometry of reactivation. The clearest reactivation in a pure strike–slip regime was achieved in experiments where the basal strike–slip fault was immediately below the pre-existing fault plane. This strong reactivation involved lateral extrusion and lateral stepping of secondary faults from the basal fault to the pre-existing reverse fault. In the case of transpression, the most spectacular reactivation was achieved for a convergence angle of 10°. Strongly asymmetric structures developed on either side of the pre-cut dilatant zone. The analogue experiments reproduced very closely the structural features of the Giudicarie fault system, supporting a model involving a twofold tectonic evolution for the Giudicarie fault system, with later reactivation in sinistral transpression of an older reverse fault.

The Neogene kinematics of the Giudicarie fault (part of Periadriatic lineament, NE Italy) have been re-examined using apatite fission-track analysis. Twenty samples were collected along two geological sections; the first one crossing the Tertiary Corno Alto pluton (Adamello batholith) and the Variscan basement (Southalpine domain) adjacent to the South Giudicarie fault, the second one close to the North Giudicarie fault, in the Variscan basement of the Tonale nappe (Austroalpine system). Samples from the southern section show short tracks and ages between 14.7±1.2 Myr and 22.5±2.2 Myr along 1570 m of the profile; samples from the northern profile present long tracks and ages between 11.3±1.3 Myr and 14.7±3.4 Myr along 1225 m of the vertical profile. In the former, the presence of short tracks might indicate either a long permanence of the rocks in the apatite partial annealing zone, or a more complex thermal history; in the latter case we are dealing with rocks which experienced more rapid cooling. The two differing segments of the Giudicarie fault can be explained either as two completely independent tectonic features or, more likely, by hypothesizing a single fault active in its southern and northern parts at different times. Fission track data support a first exhumation of this single fault c. 15 Ma along the North Giudicarie, with a final exhumation towards the south, in the Adamello area, at c. 8–10 Ma (Mid Tortonian). This age fits with the so-called ‘Giudicarie’ phase, during which σ1 in the stress field was orientated N280–290°.

Received 10 June 2005; revised 15 February 2006; accepted 2 March 2006; published 11 August 2006. [1] The southward propagation of the East Africa rift presents an opportunity to study plate boundary formation. We tabulate orientation data which confirm the province of NW-SE ...

Alpine deformation of Austroalpine units south of the Tauern window is dominated by two kinematic regimes. Prior to intrusion of the main Periadriatic plutons at ~30 Ma, the shear sense was sinistral in the current orientation, with a minor north-side-up component. Sinistral shearing locally overprints contact metamorphic porphyroblasts and early Periadriatic dykes. Direct Rb–Sr dating of microsampled synkinematic muscovite gave ages in the range 33–30 Ma, whereas pseudotachylyte locally crosscutting the mylonitic foliation gave an interpreted 40Ar–39Ar age of ~46 Ma. The transition from sinistral to dextral (transpressive) kinematics related to the Periadriatic fault occurred rapidly, between solidification of the earlier dykes and of the main plutons. Subsequent brittle–ductile to brittle faults are compatible with N–S to NNW–SSE shortening and orogen-parallel extension. Antithetic Riedel shears are distinguished from the previous sinistral fabric by their fine-grained quartz microstructures, with local pseudotachylyte formation. One such pseudotachylyte from Speikboden gave a 40Ar–39Ar age of 20 Ma, consistent with pseudotachylyte ages related to the Periadriatic fault. The magnitude of dextral offset on the Periadriatic fault cannot be directly estimated. However, the jump in zircon and apatite fission-track ages establishes that the relative vertical displacement was ~4–5 km since 24 Ma, and that movement continued until at least 13 Ma.

Fault rocks from various segments of the Periadriatic fault system (PAF; Alps) have been directly dated using texturally controlled Rb–Sr microsampling dating applied to mylonites, and both stepwise-heating and laser-ablation 40Ar/39Ar dating applied to pseudotachylytes. The new fault ages place better constraints on tectonic models proposed for the PAF, particularly in its central sector. Along the North Giudicarie fault, Oligocene (E)SE-directed thrusting (29–32 Ma) is currently best explained as accommodation across a cogenetic restraining bend within the Oligocene dextral Tonale-Pustertal fault system. In this case, the limited jump in metamorphic grade observed across the North Giudicarie fault restricts the dextral displacement along the kinematically linked Tonale fault to ~30 km. Dextral displacement between the Tonale and Pustertal faults cannot be transferred via the Peio fault because of both Late Cretaceous fault ages (74–67 Ma) and sinistral transtensive fault kinematics. In combination with other pseudotachylyte ages (62–58 Ma), widespread Late Cretaceous–Paleocene extension is established within the Austroalpine unit, coeval with sedimentation of Gosau Group sediments. Early Miocene pseudotachylyte ages (22–16 Ma) from the Tonale, Pustertal, Jaufen and Passeier faults argue for a period of enhanced fault activity contemporaneous with lateral extrusion of the Eastern Alps. This event coincides with exhumation of the Penninic units and contemporaneous sedimentation within fault-bound basins.