Central Southern Alps Research Articles

Precollisional development and Cenozoic evolution of the Southalpine retrobelt (European Alps)

The retrobelts of doubly vergent collisional orogens are classically interpreted as late-stage postcollisional features. Here, we integrate literature data with new structural and thermochronological evidence from the European Alps in order to document the precollisional development of the retrobelt segment exposed in the central southern Alps. During the Late Cretaceous, by inversion of inherited extensional faults of Permian age, the Variscan basement of the central southern Alps was stacked southward onto the Permian–Mesozoic cover sequences of the Adria margin. These thrust systems were first deformed within regional-scale antiforms (the “Orobic anticlines”) and then cut by Eocene magmatic bodies. Our apatite fission-track data show that these units were largely structured and exhumed to shallow crustal levels before the intrusion of the Eocene magmatic rocks. Therefore, thrusting and folding in the Alpine retrobelt took place before the final closure of the Alpine Tethys and subsequent continental collision between Adria and Europe. Final exhumation and uplift in the northern part of the Southalpine retrobelt took place under a dextral transpressional regime largely coeval with the right-lateral strike-slip activity along the Insubric fault. In Neogene times, deformation propagated southward, leading to the formation of a frontal thrust belt that is largely buried beneath the Po Plain.

Dichotrachelus pesarinii sp.n., a missing link between the species from the central and the western southern Alps (Coleoptera: Curculionidae: Cyclominae)

A new species of Dichotrachelus associated with Saxifraga caesia is described, D. pesarinii sp.n., and a phylogenetic analysis is carried out based on morphological and molecular mtCOI data. The new species resolved as the sister group of the D. sulcipennis group, whose members are associated with Saxifraga oppositifolia. This placement suggests that this group differentiated in the central southern Alps, and that the new species represents an evolutionary link between the species from the central and eastern southern Alps and those from the western Alps. The evolution of the association of Dichotrachelus with particular Saxifraga species remains contradictory; scenarios are proposed.

Revision of a classic site for Permian tetrapod ichnology (Collio Formation, Trompia and Caffaro valleys, N. Italy), new evidences for the radiation of captorhinomorph footprints

Abstract The recent studies on Permian captorhinomorph (non-diapsid eureptile) footprints from North America, North Africa, and Europe raised the interest on their taxonomic and biostratigraphic significance. They seem to radiate in the late Early Permian, but the scarcity of absolute dating in the classic sections bearing these trace fossils is not helpful in order to unravel their distribution. The continental Collio Formation cropping out extensively in the central Southern Alps of Italy can cover this gap of knowledge, since it preserves a rich testimony of these trace fossils ( Erpetopus , Hyloidichnus , Varanopus ) and it is well-constrained from radiometric datings and fossil content. For this and because of the huge amount of stored but unanalyzed material, a revision was necessary, through careful taxonomic assignations. These taxa are here confirmed and/or identified as being: Amphisauropus kablikae , cf. Batrachichnus isp., Dromopus lacertoides , Erpetopus cassinisi , Hyloidichnus bifurcatus , Limnopus heterodactylus and Varanopus isp. The occurrence of Erpetopus at the base of the Collio Formation (Kungurian base) suggests its minimum age of first appearance in a global context: this is a very important presence in order to build a reliable tetrapod footprint biostratigraphy during the Permian. The quantity of material yielded in the different facies of the Collio and Dosso dei Galli Formations also permit new insights on the paleoenvironments and climatic settings.

Changes in hot spring temperature and hydrogeology of the Alpine Fault hanging wall, New Zealand, induced by distal South Island earthquakes

AbstractThermal springs in the Southern Alps, New Zealand, originate through penetration of fluids into a thermal anomaly generated by rapid uplift and exhumation on the Alpine Fault. Copland hot spring (43.629S, 169.946E) is one of the most vigorously flowing, hottest of the springs, discharging strongly effervescent CO2‐rich 56–58°C water at 6 ± 1 l sec−1. Shaking from the Mw7.8 Dusky Sound (Fiordland) 2009 and Mw7.1 Darfield (Canterbury) 2010 earthquakes, 350 and 180 km from the spring, respectively, resulted in a characteristic approximately 1°C delayed cooling over 5 days. A decrease in conductivity and increase in pH were measured following the Mw7.1 Darfield earthquake. Earthquake‐induced decreases in Cl, Li, B, Na, K, Sr and Ba concentrations and an increase in SO4 concentration reflect higher proportions of shallow‐circulating meteoric fluid mixing in the subsurface. Shaking at amplitudes of approximately 0.5% g Peak Ground Acceleration (PGA) and/or 0.05–0.10 MPa dynamic stress influences Copland hot spring temperature, which did not respond during the Mw6.3 Christchurch 2011 aftershock or other minor earthquakes. Such thresholds should be exceeded every 1–10 years in the central Southern Alps. The characteristic cooling response at low shaking intensities (MM III–IV) and seismic energy densities (approximately 10−1 J m−3) from intermediate‐field distances was independent of variations in spectral frequency, without the need for post‐seismic recovery. Observed temperature and fluid chemistry responses are inferred to reflect subtle changes in the fracture permeability of schist mountains adjacent to the spring. Permanent 10−7–10−6 strains recorded by cGPS reflect opening or generation of fractures, allowing greater quantities of relatively cool near‐surface groundwater to mix with upwelling hot water. Active deformation, tectonic and topographic stress in the Alpine Fault hanging wall, where orographic rainfall, uplift and erosion are extreme, make the Southern Alps hydrothermal system particularly susceptible to earthquake‐induced transient permeability.

Geological-structural map of the Orobic and Porcile thrust junction, central Southern Alps (N Italy)

The central Southern Alps retrobelt was built trough a polyphase tectonic evolution that developed in the hangingwall of the SE-directed Alpine Tethys subduction. In the northern sector of the central Southern Alps the earliest stages of shortening resulted in the inversion of structures inherited from the Permian and Triassic rifting phases, together with southward thrusting and large-scale folding. In the San Marco Pass area (N Italy) the Variscan basement overrides the Permian-Triassic sedimentary cover along regional thrusts. Here the E-W trending Orobic Thrust joins the NE-SE Porcile Thrust. Initial thrusting phases formed greenschist facies mylonites in the basement and S-verging folds in the sedimentary covers. The Porcile line, a feature likely inherited from the Permian extension, was re-activated as a steep mylonite shear zone. Fault activity continued at brittle conditions: cataclastic shear zones overprinted the mylonites. During this phase, shortening was preferentially accommodated along the Orobic Thrust. A final transpressive re-activation observed along both thrusts is linked to the Oligocene activity of the Insubric Fault.

Low‐frequency earthquakes reveal punctuated slow slip on the deep extent of the Alpine Fault, New Zealand

AbstractWe present the first evidence of low‐frequency earthquakes (LFEs) associated with the deep extension of the transpressional Alpine Fault beneath the central Southern Alps of New Zealand. Our database comprises a temporally continuous 36 month‐long catalog of 8760 LFEs within 14 families. To generate this catalog, we first identify 14 primary template LFEs within known periods of seismic tremor and use these templates to detect similar events in an iterative stacking and cross‐correlation routine. The hypocentres of 12 of the 14 LFE families lie within 10 km of the inferred location of the Alpine Fault at depths of approximately 20–30 km, in a zone of high P‐wave attenuation, low P‐wave speeds, and high seismic reflectivity. The LFE catalog consists of persistent, discrete events punctuated by swarm‐like bursts of activity associated with previously and newly identified tremor periods. The magnitudes of the LFEs range between ML – 0.8 and ML 1.8, with an average of ML 0.5. We find that the frequency‐magnitude distribution of the LFE catalog both as a whole and within individual families is not consistent with a power law, but that individual families' frequency‐amplitude distributions approximate an exponential relationship, suggestive of a characteristic length‐scale of failure. We interpret this LFE activity to represent quasi‐continuous slip on the deep extent of the Alpine Fault, with LFEs highlighting asperities within an otherwise steadily creeping region of the fault.

Background and delayed-triggered swarms in the central Southern Alps, South Island, New Zealand

Low-magnitude earthquake swarms (ML ≤ 2.8), consisting of up to 47 events of similar waveforms, have been observed repeatedly in the central Southern Alps, a rapidly uplifting orogen bounded by the transpressive Alpine Fault in the South Island of New Zealand. We compare nine background swarms recorded between November 2008 and April 2010 with five delayed-triggered swarms that occurred after the MW 7.8 Dusky Sound and the MW 7.1 Darfield (Canterbury) earthquakes. The two types of swarms are similar in terms of the magnitudes, depths, focal mechanisms, and interevent times of the constituent microearthquakes, and appear to both involve the rupture of steeply dipping faults in highly fractured crust in a 10 km × 12 km area in the center of the SAMBA network. The delayed-triggered swarms occurred at similar epicentral distances (c. 4.5× the rupture length of the mainshocks) to the Dusky Sound and Darfield earthquakes, commenced shortly after the passage of the surface waves, continued for ∼5 and ∼2 days, respectively, and were followed in each case by a ≥2 day long quiescent period, which may suggest clock-advanced of faults in their failure-cycle. Triggering thresholds of ≥0.01 MPa proposed elsewhere are similar to the dynamic stress changes computed for the Southern Alps (≥0.09 MPa). However, as 98% of the locatable triggered events occurred several hours after the surface waves had passed, the dynamic stress changes associated with the surface waves themselves are unlikely to have triggered the earthquakes directly. Instead, we suggest that the locations and delays of the triggered swarms are more consistent with triggering by pore pressure diffusion.

Spatial analysis of thickness variability applied to an Early Jurassic carbonate platform in the central Southern Alps (Italy): a tool to unravel syn‐sedimentary faulting

AbstractEarly Jurassic syn‐sedimentary extensional tectonics in the central Southern Alps controlled patterns of deposition within the Calcari Grigi carbonate platform. We used variogram maps to gather model‐independent information on the spatial distribution of thicknesses of selected platform units and investigated whether major syn‐sedimentary faults outlined subsiding domains during platform growth. Thicknesses display a spatial organization that suggests that large fault belts, often coincident with exposed Jurassic extensional structures, transected large parts of the platform. The network of four fault systems (trending NNW–SSE and NE–SW) displays orthorhombic symmetry, suggesting non‐Andersonian faulting and a true triaxial strain field with N100°E maximum extension or transfer shear zones connecting major NNW–SSE‐trending extensional faults. In both cases, inherited structures of Permian to Triassic age may have played a primary role in Jurassic faulting. If confirmed throughout the South‐Alpine domain, this arrangement could shed new light on Early Jurassic rifting mechanisms in the Southern Alps.

Calving retreat and proglacial lake growth at Hooker Glacier, Southern Alps, New Zealand

AbstractHooker Glacier in the central Southern Alps of New Zealand has undergone significant downwasting and recession (∼2.14 km) during the last two centuries. High retreat rates (51 m a−1 1986–2001, 43 m a−1 2001–2011) have produced a large (1.22 km2) proglacial lake. We present a retreat scenario for Hooker Glacier. A retreat scenario predicts that the glacier terminus will stabilise >3 km up‐valley of the current lake outlet after 2028 when ice velocity equals calving rate.

The transition between the two major Permian tectono-stratigraphic cycles in the central Southern Alps: results from facies analysis and U/Pb geochronology

The Val Daone Conglomerate (VDC) is a continental clastic unit that crops out eastwards of the central Southern Alps, from the NE sector of the Collio Basin to the W as far as the Tione Basin to the E. This significant but as yet relatively unknown formation lies just above the regional unconformity that marks the boundary between the two Permian major tectono-sedimentary cycles (TSU1 and TSU2) and grades upwards paraconformably (?) to the fluvial red beds of Verrucano Lombardo/Val Gardena Sandstone, generally associated with Late Permian times. Recent palynological investigations on the VDC suggested a Guadalupian age (late Roadian–early Wordian), owing to the remarkable presence of diversified pollen associations; therefore, this sedimentary unit is to date the first one ascribed, on a palaeontological basis, to the Middle Permian in the entire Southern Alps domain. A detailed facies analysis of VDC shows deposition in amalgamated alluvial fan-braided and fluvial environments with wide channels and longitudinal bars. In its type area and Val Rendena, the VDC rests unconformably above the last volcanic episode of the TSU1. LA ICP-MS U–Pb dating on zircon from two samples of such topmost Lower Permian volcanic rocks, known as Ponte Murandin dacitic lava and Malga Plan rhyodacitic Ignimbrites (Tione Basin), provided Concordia ages of 278 ± 2 Ma (MSWD = 0.01) and 279 ± 2 Ma (MSWD = 0.16), respectively. As well as allowing us to better define the duration of the time gap between the two Permian megacycles in the central Southern Alps in almost 10 Ma, these radiometric age determinations are also significant because they enable us to regionally link the coeval volcanic bodies which crop out in the Collio Basin to the SW and in the “Athesian Volcanic Group” to the NE, respectively.

Potentially active faults in the rapidly eroding landscape adjacent to the Alpine Fault, central Southern Alps, New Zealand

Potentially active faults are exposed in the steep glaciated topography of the central Southern Alps, New Zealand, immediately adjacent to the Alpine Fault plate boundary. Four major faults exposed along the flanks of three of the highest mountain ranges strike 10–23 km (potentially 40 km) NNE oblique to the Alpine Fault, dipping 57° ± 12° NW in the opposite direction. Youngest discernable motions were reverse dip‐slip, accommodating both margin‐perpendicular shortening and dextral margin‐parallel components of plate motion. Kinematic analysis yields a compression axis (295/10° ± 9° trend or plunge) equivalent to the contemporary shortening determined from seismological and geodetic studies, suggesting the faults may be active, although definitive evidence for recent movement or single event displacements is lacking. There are 106 other potentially active faults mapped in central Southern Alps with strike lengths 4–73 km. Earthquake parameters were assigned from fault trace lengths and historical earthquake statistics, indicating potential for MW 5.5–7.4 earthquakes at recurrence intervals of 1000–10,000 years. Such long recurrence intervals are consistent with the faults having little surface expression, with rapid erosion of these seismically agitated mountains erasing any evidence of surface rupture during periods between earthquakes. The central Southern Alps faults exemplify the difficulty in fully deciphering long‐term (e.g., Holocene or Quaternary) records of seismicity in tectonically active regions with rapidly evolving landscapes. Although there may be little evidence of surface ruptures remaining in the landscape, the faults are still an important potential source of earthquakes and seismic hazard.

Differential compaction and early rock fracturing in high‐relief carbonate platforms: numerical modelling of a Triassic case study (Esino Limestone, Central Southern Alps, Italy)

AbstractNumerical models were used to investigate the effects of differential compaction on strain development and early fracturing in an early cemented high‐relief Triassic carbonate platform prograding onto basinal sediments, whose thickness increases basinward. Results show that basinal sediment compaction induces stretching of internal platform and slope strata in prograding platforms. When sediments are early cemented, such extensional strain is accommodated by the generation of syndepositional fractures. The amount of stretching is predicted to increase from the oldest to the youngest layers, due to the thickening of the compactable basinal sequences towards the external parts of the platform. Stretching is also controlled by the characteristics of the basin: the thicker and the more compactable the basinal sediments, the larger will be the stretching. Numerical modelling has been applied to the Ladinian–Early Carnian carbonate platform of the Esino Limestone (Central Southern Alps of Italy). This case study is favourable for numerical modelling, as it is well exposed and both its internal geometry (inner platform, reef and prograding clinostratified slope deposits) and the relationship with the adjacent basin can be fully reconstructed, as the Alpine tectonic overprint is weak in the study area. Evidence for early fracturing (fractures filled by fibrous cements coeval with the platform development) is described and the location, orientation and width of the fractures measured. The fractures are mainly steeply dipping and oriented perpendicularly to the direction of progradation of the platform, mimicking local platform‐margin trends. The integration of numerical models with field data gives the opportunity to quantify the extension triggered by differential compaction and predict the possible distribution of early fractures in carbonate platforms of known geometry and thickness, whereas the interpretation of early fractures as the effects of differential compaction can be supported or rejected by the comparison with the results of ad hoc numerical modelling.

Microseismicity and stress in the vicinity of the Alpine Fault, central Southern Alps, New Zealand

We investigate present‐day microseismicity associated with the central Alpine Fault and the zone of active deformation and uplift in the central Southern Alps. Using 14 months of data, robust hypocenter locations have been obtained for ∼1800 earthquakes of magnitudes between −0.3 and 4.2. We derived a magnitude scale with a frequency‐dependent attenuation factor, γ(f) = γ0f, where γ0 = 1.89 ± 0.02 × 10−3 s/km, that enables magnitudes to be calculated consistently for earthquakes of different sizes and frequency contents. The maximum depth of the seismicity varies systematically with distance from the Alpine Fault, from 10 ± 2 km near the fault to 8 ± 2 km within 20 km and 15 ± 2 km further southeast. This distribution correlates with lateral variations in crustal resistivity: earthquake hypocenters are concentrated in areas of strong resistivity gradients and restricted to depths of resistivities >100 Ωm. Rocks at greater depth are too hot, too fluid‐saturated, or too weak to produce detectable earthquakes. Focal mechanism solutions computed for 211 earthquakes (ML > 0.44) exhibit predominantly strike‐slip mechanisms. We obtain a maximum horizontal compressive stress direction of 115 ± 10° from focal mechanism inversion. This azimuth is consistent with findings from elsewhere in the central and northern South Island, and indicates a uniform crustal stress field despite pronounced variations in crustal structure and topographic relief. Our stress estimates suggest that the Alpine Fault (with a mean strike of 055°) is poorly oriented in an Andersonian sense but that individual thrust and strike‐slip segments of the fault's surface trace have close to optimal orientations.

Rheological constraints on quartz derived from scaling relationships and numerical models of sheared brittle-ductile quartz veins, central Southern Alps, New Zealand

The mechanical properties of quartz strongly influence the strength of continental crust, but natural examples to constrain quartz rheology are rare. Here, brittle-ductile fault arrays in the Southern Alps, New Zealand, provide a natural laboratory into the rheology of quartz rocks. The faults formed in the hanging wall of the Alpine Fault during the late Cenozoic at ≥21 km depth. They are near-vertical, extend over tens of metres, strike sub-parallel to the Alpine Fault, and displace quartzofeldspathic metagreywacke through predominantly brittle processes. They also displace centimetre-thick quartz veins that are discordant to the dominant schist foliation with variably ductile to brittle slip. We use field-observed geometrical scaling relationships related to the sheared quartz veins and interactions between brittle faults and ductilely deforming quartz veins that intersect them to produce a set of viable numerical models. Quartz rheology is modelled by linear or power law creep, and the material parameters extracted for the quartz veins, together with viscous and brittle strength ratios between vein quartz and schist. The results indicate that under the prevailing deformation conditions, the dominant deformation mechanism in the quartz veins was dislocation creep resulting in a non-linear quartz rheology.

Allanite behaviour during incipient melting in the southern Central Alps

The response of allanite to incipient melting was investigated in migmatites from the Tertiary Barrovian-type sequence of the Central Alps (southern Switzerland, northern Italy). Inheritance and new mineral growth were recorded in composite allanite grains sampled from meta-granitoids and leucosomes. Ion microprobe (SHRIMP) dating of high Th/U allanite cores in meta-granitoids yield Permian ages consistent with magmatic crystallisation dating protolith intrusion. In contrast, low Th/U allanite overgrowths and weakly-zoned allanite in meta-granitoids and leucosomes yield Alpine U–Pb intercept ages between 30±4 and 20±5Ma; these date allanite formation during the Barrovian cycle. Major and accessory mineral REE compositions suggest that Alpine allanite crystallised in the presence of a low-temperature melt. Whereas new zircon growth is rare in the migmatites, allanite readily recorded growth during the Alpine cycle. Allanite U–Th–Pb isotopes may therefore present a complementary approach to zircon for dating low-temperature partial melting, where the preservation of allanite is aided by low LREE solubility in hydrous granitic melt. The Th–Pb age is preferred to date high-Th magmatic allanite, however the U–Pb and Th–Pb ages of allanite overgrowths may differ (by up to 25%), and this demands a comparison of both U–Pb and Th–Pb isotopic systems to obtain a best estimate for the timing of low-Th allanite crystallisation. Protolith allanite preserves a substantial memory of its initial age in spite of upper amphibolite facies re-working during migmatisation (T=620–700°C), which places strong constraints on Pb closure temperature. Magmatic allanite contains <30% of initial (non-radiogenic) Pb, allanite in migmatites is characterised by an initial Pb of 20–70%, and subsolidus allanite has >60% of initial Pb. Therefore, the initial Pb may be useful as a sensor for the amount of melt present during allanite formation. The Pb isotope composition of allanite overgrowths indicates ⩽5% inherited radiogenic Pb from precursor allanite, which suggests efficient redistribution and homogenisation of Pb isotopes during the Alpine partial melting period.

Syn-thrust deformation across a transverse zone: the Grem–Vedra fault system (central Southern Alps, N Italy)

The lateral continuity of the E–W trending thrust sheets developed within the Lower to Middle Triassic cover of the central Southern Alps (Orobic belt) is disturbed by the occurrence of several N–S trending transverse zones, such as the poorly known Grem–Vedra Transverse Zone (GVTZ). The GVTZ developed during the emplacement of the up to six S-verging thrust sheets consisting of Lower to Middle Triassic units, occurring immediately south of the Orobic Anticlines. The transverse zone, active during thrust emplacement related to the early Alpine compressions which pre-date the Adamello intrusion, includes three major vertical shear zones, the Grem, Pezzel and Zuccone faults. The major structure of the transverse zone is the dextral Grem fault, forming a deep lateral ramp between thrust sheets 3 and 5. A similar evolution also occurred along the Zuccone and Pezzel faults, which show a left-lateral displacement of syn-thrust folds. The Grem fault was later reactivated as an oblique tear fault during the emplacement of the Orobic Anticlines, due to back-thrusting along out-of-sequence thrust surfaces (Clusone fault). Transpressional deformations along the fault zone are recorded by the rotation of major syn-thrust folds, which also suggest a horizontal offset close to 0.5 km. Records of the first stage of evolution of the Grem fault are better preserved along its northern segment, and structural relationships suggest that it propagated southward and downward in the growing thrust stack. The study of the meso and megascopic structures developed along the GVTZ constrains the evolution of the transverse zone, illustrating the complex deformational phenomena occurring in a transpressional regime. The GVTZ probably reflects the existence of pre-existing tectonic lineaments with a similar orientation. Evidence of pre-existing structures are not preserved in the exposed units, nevertheless the N–S extensional fault systems that characterize the Norian to Jurassic rifting history of the Lombardian basin are valid candidates.

Controls on mass balance sensitivity of maritime glaciers in the Southern Alps, New Zealand: The role of debris cover

The “mass balance sensitivity” of a glacier provides a means for assessing its response to future warming and contribution to sea level rise. Many studies have concluded that the first‐order control on mass balance sensitivity is climatic, where higher‐precipitation (and less continental) glaciers are most sensitive while lower‐precipitation (and more continental) glaciers are least sensitive. The Southern Alps in New Zealand experience a limited range of continentality (9–13 K) but strong gradients in precipitation (2.5–11 m a−1). Using an energy balance model applied on a regional scale we find that the central Southern Alps glaciers are very sensitive to temperature change (1.9 m w.e. a−1 K−1, with a range of −1.1 to −4.0 m w.e. a−1 K−1) and that an 82% increase in precipitation is required to offset a 1 K warming. Spatial variations in mass balance sensitivity cannot be simply explained as a function of precipitation. Topographic effects are important, and we find that debris cover reduces mass balance sensitivity. Mass balance amplitude, which takes into account debris cover, hypsometry and other topographic characteristics, is a better predictor of mass balance sensitivity than precipitation. The mass balance gradient is almost as good a predictor indicating that hypsometry is not a necessary component of sensitivity calculations. Estimating mass balance sensitivity as a function of mass balance gradient allows for parameterizations of mass balance sensitivity based on glacier inventory data. This provides a simple and robust way to assess glacier mass balance sensitivity on a global scale, which may refine future predictions of valley glacier melt and its contribution to sea level rise.

Spatial and temporal variability of annual glacier equilibrium line altitudes in the Southern Alps, New Zealand

Assessments of the contribution of meltwater to sea-level rise from mountain glaciers cannot presently account for the considerable spatial inter-catchment and temporal inter-annual variations in annual net glacier mass balance. We therefore analyse annual equilibrium line altitudes (ELAs) to infer the controls on annual net glacier mass-balance variability for 34 glaciers in the central Southern Alps, New Zealand. Elevation, curvature and mean solar radiation receipt (both direct and indirect) during the ablation season can in combination account for up to 95% of the (temporal) variability in the long term ELA and up to c. 85% for a given year. It appears that long-term glacier net mass balance in the Southern Alps is controlled by ablation processes as a function of air temperature which decreases with elevation, and shortwave radiation which causes a positive feedback in ablation by reducing snow and ice cover and increasing albedo. In detail however, the degree to which local topographic variables can explain the differences in (i) the patterns and (ii) in the magnitudes of departures from the trend varies considerably from year to year and across the study region. At least 15–35% of annual ELA temporal variability is apparently associated with regional weather patterns. Our basic quantification of the interaction on multiple scales of topographic influences on annual ELA and ELAo (steady-state ELA) has implications for understanding inter- and intra-catchment variability in glacier responses to climatic change.

Hydrothermal dolomitization in platform and basin carbonate successions during thrusting: A hydrocarbon reservoir analogue (Mesozoic of Venetian Southern Alps, Italy)

The Early Jurassic dolomitized carbonates in the Venetian Alp, represent a surface analogue of the hydrocarbon exploration targets in Adriatic offshore and Po Plain, Italy. Dolomitization affected the carbonate platform of Monte Zugna Formation (Lower Jurassic) and the Neptunian dikes breccia in the pelagic Maiolica Formation (Uppermost Jurassic–Lower Cretaceous) improving the poro-perm characteristics. Petrography, stable isotope, strontium isotope ratio, trace element and fluid inclusion analyses were carried out on samples from the Monte Grappa Anticline, which is the direct analogue for subsurface. The petrographic analyses showed a first pervasive, replacement dolomitization phase (D1) followed by volumetrically less important dolomite cement precipitation phases (D2, D3, DS). The same, quite wide range of oxygen isotope (−9 to −2‰ V-PDB) is observed in all dolomite types. The δ 13C range is in the positive field of marine derived carbonate (from +0.5 to +3.2‰ PDB). The trace element analysis showed a slight enrichment in Fe and Mn contents in the Monte Zugna dolostones with respect the original limestone. The same dolomite precipitation temperature (up to 105 °C Th) was observed in the replacement and cement dolomites, suggesting a unique dolomitization event. This temperature, largely higher than the maximum burial temperature (about 50 °C), supports a hydrothermal origin of the dolomitizing fluids, which had a seawater to brackish composition. The data collected suggest a hydrothermal dolomitization occurring during to the South Alpine thrusting according to the “squeegee model”. The interpretation is consistent with the dolomitization model proposed for similar Jurassic successions in the Central Southern Alps. This study indicates that the deformed foreland and thrust fold belts carbonates in Po Plain and Adriatic offshore are suitable to be dolomitized, and therefore reflect an efficient hydrocarbon exploration play.

Large-scale progradation, demise and rebirth of a high-relief carbonate platform (Triassic, Lombardy Southern Alps, Italy)

The Upper Anisian to Early Carnian succession of the Middle Val Brembana–Pegherolo Massif (Central Southern Alps of Italy) records a complete depositional cycle from platform inception to growth, demise and rebirth. The depositional architecture of this system reflects different evolutionary stages: an inception stage which postdates a previous drowning of an Anisian carbonate platform with progradation of the carbonate platform from the nucleation areas, an aggradational stage with increasing water depth in the basins, a progradational stage where steep slopes composed of margin-derived breccias develop and a final crisis corresponding to the subaerial exposure of the platform top, followed by the deposition of shales in the basin before the rebirth of a different type of carbonate factory. The record of this evolution reflects the effects of the change in accommodation space (interplay of subsidence and eustacy), which controls the type and storage sites of the sediments produced by the carbonate factory. The effects of the changes in accommodation space are recorded in the shallow water platform as well as in the intraplatform basins, where the sediments, delivered at different rates from the platform top are stored. As a consequence, the aggradational stage corresponds to reduced sedimentation in the basins (i.e. sediments are stored on the platform top) whereas during progradation resedimented limestones are more common in the basin. Subaerial exposure rapidly halted the carbonate production on the platform top, while a major input of shales (probably reflecting a climate change and/or lowering of the base level) is recorded in the basin, where shales onlap the slope of the previous carbonate system. The rebirth of the carbonate factory after subaerial exposure of the platform top is characterized by a different composition of the carbonate factory, probably reflecting changes of the environmental conditions. The step-by-step recording of the evolution of the carbonate system represents a unique opportunity to record a seismic-scale complete evolutionary cycle of a carbonate system in its different sub-environments, from the platform top to the basin.