Structural Geological Data Research Articles

The kinematics of a transition from subduction to strike‐slip: An example from the central New Zealand plate boundary

We develop a kinematic model for the transition from subduction beneath the North Island, New Zealand, to strike‐slip in the South Island, constrained by GPS velocities and active fault slip data. To interpret these data, we use an approach that inverts the kinematic data for poles of rotation of tectonic blocks and the degree of interseismic coupling on faults in the region. Convergence related to the Hikurangi subduction margin becomes very low offshore of the northern South Island, indicating that in this region the majority of the relative plate motion has been transferred onto faults within the upper plate, as suggested by previous studies. This result has implications for understanding the likely extent of subduction interface earthquake rupture in central New Zealand. Easterly trending strike slip faults (such as the Boo Boo fault) are the key features that facilitate the transfer of strike‐slip motion from the northern South Island faults further north into the southern North Island and onto the Hikurangi subduction thrust. Our results also indicate that the transition from rapid forearc rotation adjacent to the Hikurangi subduction margin to a strike‐slip dominated plate boundary (with negligible vertical‐axis rotation) in the South Island occurs via a crustal‐scale hinge or kink in the upper plate, compatible with paleomagnetic and structural geological data. Despite the ongoing tectonic evolution of the central New Zealand region, our study highlights a remarkable consistency between data sets spanning decades (GPS), thousands of years (active faulting data), and millions of years (paleomagnetic data and bedrock structure).

Evidence for a two‐phase Palmer Land event from crosscutting structural relationships and emplacement timing of the Lassiter Coast Intrusive Suite, Antarctic Peninsula: Implications for mid‐Cretaceous Southern Ocean plate configuration

New analysis of the relationships between geological structural data and radiometric ages for the Lassiter Coast Intrusive Suite indicate that the collisional mid‐Cretaceous Palmer Land Event orogeny in the Antarctic Peninsula has had two kinematic phases, forming an intersection orocline, one of which can be related to Cretaceous Southern Ocean plate motions. Both are compressional phases along the Eastern Palmer Land Shear Zone: Phase 1 occurred at ∼107 Ma with a principal paleostrain axis of 341°, and is best expressed in southern Palmer Land although evident elsewhere on the Antarctic Peninsula; Phase 2 occurred at ∼103 Ma with a principal paleostrain axis of 259.5°, but is confined to between 68°S and 74°S. A peak in Lassiter Coast Intrusive Suite magma emplacement rate was coeval with Phase 1, whereas Phase 2 may have coincided with a lull. During Phase 1, the allochthonous Central and Western Domain terranes may have been transported to the Gondwana margin, represented by the para‐autochthonous Eastern Domain, on board the Phoenix plate or on board the South American plate. The variable provenance indicators from the Central and Western terranes can be cited to support either, or a combination, of these scenarios. The convergence direction evident from Phase 2 structures cannot easily be reproduced in regional plate kinematic models. This, and the localized evidence for superposition of Phase 2 structures on Phase 1 structures suggests that Phase 2 is unlikely to have occurred solely in response to changes in the kinematics of the large plates considered.

Re-Evaluations of Seismic Hazard of Syria

Seismic Hazard analysis requires geologic, seismologic and geophysical data to be applied in a certain area. There are several studies were established to estimate the seismic hazard of Syria. In this study, the authors integrated the historical, instrumental seismological data, the structural-geological data of Syria and the subsurface tectonic map of Syria to re-evaluate the seismic hazard of Syria. The current research introduces new seismic source models which were not used before. The source models were chosen according to the structural and tectonic setting of the study area. The recurrence relationship was applied for each source for obtaining the regression coefficients related to each seismic source. Finally, the seismic hazard maps were plotted for (50, 100, 200, 475, and 1000) return periods by using Poisson probabilistic method. Regarding with theses resulted maps, there is obvious increase of the seismicity from the eastern parts of Syria to the western parts which reaches to its maximum value in El-Ghab region.

Neogene and Quaternary development of the Turiec Basin and landscape in its catchment: a tentative mass balance model

Neogene and Quaternary development of the Turiec Basin and landscape in its catchment: a tentative mass balance modelThe development of the Turiec Basin and landscape evolution in its catchment has been reconstructed by methods of geological research (structural geology, sedimentology, paleoecology, and geochronological data) as well as by geophysics and geomorphology. The basin and its surrounding mountains were a subject of a mass balance study during periods of tectonic activity, accompanied by considerable altitudinal differentiation of relief and also during quiet periods, characterized by a development of planation surfaces in the mountains. The coarse clastic alluvial fans deposited beneath the offshore pelitic sediments document the rapid Middle Miocene uplift of mountains on the margin of the Turiec Basin. The Late Miocene finegrained sedimentation represents the main fill of this basin and its origin was associated with the formation of planation surfaces in the surrounding mountains. The rapid uplift of the western and northern parts of the catchment area during the latest Miocene and Early Pliocene times further generated the deposition of coarse-grained alluvial fans. The Late Pliocene basin inversion, due to uplift of the whole Western Carpathians mountain chain, was associated with the formation of the Early Quaternary pediment and ultimately with the formation of the Turiec river terrace systems.

Convergent plate margin dynamics: New perspectives from structural geology, geophysics and geodynamic modelling

Convergent plate margins occur when two adjoining tectonic plates come together to form either a subduction zone, where at least one of the converging plates is oceanic and plunges beneath the other into the mantle, or a collision zone, where two continents or a continent and a magmatic arc collide. Convergent plate margins are arguably the most complicated and dynamic plate boundaries on Earth and have been the subject of many investigations and discussions since the advent of plate tectonic theory. This paper provides a historical background and a review of the development of geological and geodynamic theories on convergent plate margins. Furthermore, it discusses some of the recent advances that have been made in the fields of structural geology, geophysics and geodynamics, which are fundamental to our understanding of this phenomenon. These include: (1) the finding that plates and plate boundaries move at comparable velocities across the globe; (2) the emerging consensus that subducted slabs are between two to three orders of magnitude stronger than the ambient upper mantle; (3) the importance of lateral slab edges, slab tearing and toroidal mantle flow patterns for the evolution of subduction zones; and (4) clear evidence from mantle tomography that slabs can penetrate into the lower mantle. Still, many first-order problems regarding the geodynamic processes that operate at convergent margins remain to be solved. These include subduction zone initiation and the time of inception of plate tectonics, and with it convergent plate margins, on Earth. Fundamental problems in orogenesis include the mechanism that initiated Andean mountain building at the South American subduction zone, the potential episodicity of mountain building with multiple cycles of shortening and extension, and the principal driving force behind the construction of massive mountain belts such as the Himalayas–Tibet and the Andes. Fundamental questions in subduction dynamics regard the partitioning of subduction into a trench and plate component, and the distribution of energy dissipation in the system. In seismic imaging, challenges include improving resolution at mid to lower mantle depth in order to properly understand the fate of slabs, and better constraining the 3-D flow-related anisotropic structure in the surrounding mantle. Future insights into such fundamental problems and into the regional and global dynamics of convergent plate margins will likely be obtained from integrating spatio-temporal data, structural geological data, geophysical data and plate kinematic data into plate tectonic reconstructions and three-dimensional geodynamic models of progressive deformation.

Deformation of Stromboli Volcano (Italy) during the 2007 eruption revealed by radar interferometry, numerical modelling and structural geological field data

The activity of Stromboli volcano is characterized by very low energy explosions, occurring every 10–15 min, throwing out lava above the crater rim. During 2007, the volcano showed an anomalous activity in which new effusive vents developed (27 February and 9 March) and a major explosion took place on 15 March. This paper presents an integrated study based on a structural geological field survey, interferometric radar monitoring and numerical modelling on the deformations of the upper NW flank of the volcano (Sciara del Fuoco — SdF). The field survey carried out during the 2007 events shows the development of mainly NE-striking fissures and fractures on the northern part of the upper SdF. In January 2007, the ground-based synthetic aperture radar (GB-InSAR), installed on the flank of the SdF, showed a progressive acceleration of movement on the NE crater preceding the eruption of 27 February 2007. By the first half of February, the acceleration also involved the upper portion of the SdF and on 27 February the eruption started with the opening of new vents and deformation rates higher than the measurement capability of the radar device. On 8–9 March 2007, the GB-InSAR highlighted the formation of a bulge on the NW sector of the SdF, preceding the opening of an additional vent. To understand the deformation pattern recorded during the eruption, a numerical simulation was carried out by using the FLAC 3D code. Based on the integration of all the data, the deformations observed in the pre-effusive phase (before 27 February) seem to be related to the intrusion of a SW–NE striking dyke. The bulging recorded before the 9 March vent opening is instead to be associated with the intrusion of a sub-horizontal sill.

End-Permian to mid-Triassic termination of the accretionary processes of the southern Altaids: implications for the geodynamic evolution, Phanerozoic continental growth, and metallogeny of Central Asia

The Altaids is one of the largest accretionary orogenic collages in the world with the highest rate of Phanerozoic continental growth and significant metallogenic importance. It is widely accepted that subduction-related orogenesis of the Altaids started in the late Precambrian and gradually migrated southward (present coordinates). However, it is uncertain when and how the building of the Altaids was finally completed. Based on structural geology, geochemical, geochronological, and paleomagnetic data, this paper presents late Paleozoic to early Mesozoic accretionary tectonics of two key areas, North Xinjiang in the west and Inner Mongolia in the east, together with neighboring Mongolia. The late Paleozoic tectonics of North Xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of Siberia and its final amalgamation with the passive margin of Tarim, which may have lasted to the end-Permian to early/mid-Triassic. In contrast, in Inner Mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of Siberia and the northern active margin of the North China craton, which may have lasted to the mid-Triassic. The final products of the long-lived accretionary processes in the southern Altaids include late Paleozoic to Permian arcs, late Paleozoic to mid-Triassic accretionary wedges composed of radiolarian cherts, pillow lavas, and ophiolitic fragments, and high-pressure/ultrahigh-pressure metamorphic rocks. Permian Alaskan-type zoned mafic-ultramafic complexes intruded along some major faults of the Tien Shan. We define a new Tarim suture zone immediately north of the Tarim craton that is probably now buried below the Tien Shan as a result of northward subduction of the Tarim block in the Cenozoic. The docking of the Tarim and North China cratons against the southern active margin of Siberia in the end-Permian to mid-Triassic resulted in the final closure of the Paleoasian Ocean and terminated the accretionary orogenesis of the southern Altaids in this part of Central Asia. This complex geodynamic evolution led to formation of giant metal deposits in Central Asia and to substantial continental growth.

Digital Mapping of Fractures in the Mesozoic Newark Basin, New Jersey: Developing a Geological Framework for Interpreting Movement of Groundwater Contaminants

Abstract A computer-based (digital) approach is used by the New Jersey Geological Survey for analyzing and characterizing the geological framework of fractured bedrock aquifers using outcrop data. The structural geologic data are managed and analyzed using custom personal-computer software. Outcrop locations are built as ARC/INFO Geographic Information Systems point coverages that are used to plot geo-referenced fracture orientations and fracture-spacing symbols. Fracture analysis is based on designating structural domains for faulted, folded, and regionally oriented panels of bedrock and conducting domain-overlap analysis. The regional fracture coverages are made available to the public in digital form to facilitate the evaluation of groundwater pollution sites using geographic information systems. The study area covers parts of two tectonic fault blocks in the central part of the Mesozoic Newark basin in New Jersey. Fractures are grouped into bed-parallel and other (nonbedding) fracture sets for analyzing their distribution, orientation, spacing, and spatial variability relative to mapped faults and folds. Bed-parallel fractures are most frequently aligned subparallel to the faults bordering the basin on its northwestern margin. Nonmineralized nonbedding fractures display more variability and are frequently aligned subparallel to intrabasin faults. The strike of nonbedding fractures systematically varies across the region to reflect the strike of nearby faults; the fractures are less commonly oriented across bedding strike or at moderate angles to fault strike. Nonbedding fractures display the most variability in strike where bedding is gently warped and folded. Fold traces are frequently aligned approximately normal to fault strike. The most frequently mapped nonbedding fracture sets in the central part of the Newark basin have interfracture spacing from 4 to 20 cm. The distance between nonbedding fractures oriented subparallel to a major fault generally decreases toward the fault. A fracture density of > 50 nonbedding, subparallel fractures/meter is usually restricted to within 2 km of a major intrabasin fault in the Newark basin.

Discovery of a huge sector collapse at the Nisyros volcano, Greece, by on-land and offshore geological-structural data

This study uses on-land and offshore geological and structural data to demonstrate that a huge lateral collapse involved the SE flank of Nisyros volcano. The collapse beheaded the summit part of the volcano and also involved the submarine portion of the slope, producing a large debris avalanche deposit with a volume of about 1 km 3 which has been recognized on the sea floor. On-land, stratigraphic and structural data indicate that a thick succession of lava flows (Nikia lavas) was emplaced in a huge horseshoe-shaped depression open seaward and extending below the sea. The magma-feeding system in the volcano, pre-dating and following the collapse, was structurally influenced by a dominant NE–SW direction, which is perpendicular to the newly-recognised sector collapse. The NE–SW structural trend is consistent with the regional tectonic structures found offshore around Nisyros and with the related NW–SE extension direction. We suggest that the lateral magma pressure produced by repeated magma injections along tectonic discontinuities contributed to destabilise the volcano flank. The occurrence of a pyroclastic deposit that mantled the scar left by the collapse suggests that a magma batch might have been injected inside the volcano and triggered the collapse. The lavas of the pre-collapse edifice have been deposited in alternating submarine and subaerial environments, suggesting that vertical movements might also be a major triggering mechanism for large lateral collapses. Recognition of this phenomenon is particularly important in recent/active island or coastal volcanoes, as it can trigger tsunamis.

Three-dimensional seismo-tectonic imaging: An example from the Southern California Transverse Ranges

We present a new technique to image deformation, 3D seismo-tectonic imaging, which juxtaposes instantaneous and accumulated deformation by combining earthquake and structural geology data. We test the technique using three independent data sets. We find concordance between the predicted finite deformation field and related instantaneous deformation surfaces inferred from aftershock and background seismicity data as well as structure imaged by seismic reflection data. These results indicate that: [1] The 1994 Northridge event ruptured a transverse, high-angle reverse fault linking two EW striking listric thrust systems, the Pico and Oak Ridge. The rupture terminated on the thrusts and was capped by a north dipping, forward-breaking imbricate of the Santa Susana Fault. [2] The Los Angeles Seismic Zone is a region of thrusting associated with the development of a new mountain front forming south of the present one represented by the Santa Monica Anticline. The thrust is rooted on a mid-crustal ramp forming beneath the Los Angeles basin. We conclude that seismo-tectonic imaging by linking earthquake data to an empirically based quantitative description of the finite deformation field provides a new and fruitful method for integrating geological and seismological data.

Sedimentary provenance and palaeoenvironment of the Baixo Araguaia Supergroup: constraints on the palaeogeographical evolution of the Araguaia Belt and assembly of West Gondwana

Abstract Provenance studies on metasedimentary rocks of the Baixo Araguaia Supergroup of the Brasiliano Araguaia Belt, central Brazil, yield 207 Pb/ 206 Pb zircon evaporation ages for detrital zircons from quartzites concentrated around 1000–1200 Ma and 2800–2900 Ma; Sm–Nd T DM model ages of schists and phyllites scatter around 1600–1700 Ma. Facies analysis of low-grade metasedimentary rocks from drill cores suggests a sedimentary environment of basin floor and lower- to upper-slope turbidites. Nearby sources are indicated by the textural and mineralogical immaturity; together with structural geological data indicating tectonic transport of the supracrustal pile towards the NW, this suggests probable provenance from the southeastern portion of the Araguaia Belt and not from the Amazonian Craton as usually believed. The Goiás Massif, Goiás Magmatic Arc, São Francisco Craton and Paranapanema block are considered to be the best candidates. They may have formed a larger continental mass during West Gondwana amalgamation, prior to their collision with the Amazonian Craton to form the Araguaia Belt. Final timing of this collision is constrained by c . 550 Ma syntectonic granites. Similar ages for high-grade gneisses in the Rokelide Belt suggest coeval collision and coetaneous metamorphism of the Araguaia and Rokelide belts, but more geological and geophysical data are required for a decisive correlation between these belts.

The role of glacitectonic rafting and comminution in the production of subglacial tills: examples from southwest Ireland and Antarctica

Sedimentological and structural geological data from two sites in southwest Ireland and Antarctica provide evidence for the formation of subglacial till by the brecciation and crushing of bedrock rafts. Up‐sequence transitions, from undisturbed bedrock, to deformed bedrock, to crushed and brecciated bedrock, to massive matrix‐supported till with far‐travelled erratics, represent a process‐form continuum of till production. Initially, bedrock fragments and rafts up to several metres in length are liberated from the substrate by glacitectonic thrusting and plucking. These rafts are then crushed to produce the matrix of a till. Such products are commonly referred to as comminution tills, although the original definition focused primarily on the second phase of the process (crushing of bedrock rafts and fragments) as well as abrasion of bedrock. Data from Ireland and Antarctica indicate that rafting of bedrock is an essential part of the process of till formation. This process is facilitated by weak sedimentary bedrock, which can be displaced along joints and bedding planes to form rafts that are then incorporated into the ‘proto‐till’ prior to being crushed subglacially. Our field data suggest that bedrock failure and displacement of such rafts can occur to depths of 3 m. The occurrence of erratics in the uppermost part of the till demonstrates that the glacier effectively mixes far‐travelled and local materials.

A new concept of the junction nature of the Caspian Sea basin and Mugodzhar

[1] A new version of the collision of mobile belt with suboceanic plate is discussed by the example of the relations between collision structures of the southern termination of Ural (Mugodzhar) and preorogenic structures of the Caspian Sea basin located in the inner angle of the East-European platform. Structural geological and geophysical data are given and analyzed. The suture character of Hercynian boundary structures is revealed in the junction zone of Mugodzhar and the Caspian Sea basin.

Geodynamic evolution of the lithosphere of the Sea of Okhotsk region from geophysical data

The tectonic structure and anomalous distributions of geophysical fields of the Sea of Okhotsk region are considered; the lack of reliable data on the age of the lithosphere beneath basins of various origins in the Sea of Okhotsk is noted. Model calculations based on geological and geophysical data yielded an age of 65 Ma (the Cretaceous-Paleocene boundary) for the Central Okhotsk rise underlain by the continental lithosphere. This estimate agrees with the age (the end of the Cretaceous) derived from seismostratigraphic data. A comparative analysis of theoretical and measured heat fluxes in the Akademii Nauk Rise, underlain by a thinned continental crust, is performed. The analysis points to a higher (by 20%) value of the measured thermal background of the rise, which is consistent with a high negative gradient of gravity anomalies in this area. Calculations yielded an age of 36 Ma (the Early Oligocene) and a lithosphere thickness of 50 km for the South Okhotsk depression, whose seafloor was formed by processes of backarc spreading. The estimated age of the depression is supported by kinematic data on the region; the calculated thickness of the lithosphere coincides with the value estimated from data of magnetotelluric sounding here. This indicates that the formation time (36 Ma) of the South Okhotsk depression was estimated correctly. Numerical modeling performed for the determination of the basement age of rifting basins in the Sea of Okhotsk gave the following estimates: 18 Ma (the Early Miocene) for the Deryugin basin, 12 Ma (the Middle Miocene) for the TINRO basin, and 23 Ma (the Late Oligocene) for the West Kamchatka trough. These estimates agree with the formation time (Oligocene-Quaternary) of the sedimentary cover in rifting basins of the Sea of Okhotsk derived from geological and geophysical data. Model temperature estimates are obtained for lithologic and stratigraphic boundaries of the sedimentary cover in the Deryugin and TINRO basins and the West Kamchatka trough; the temperature analysis indicates that the latter two structures are promising for oil and hydrocarbon gas generation; the West Kamchatka trough possesses better reservoir properties compared to the TINRO and Deryugin basins. The latter is promising for the generation of hydrocarbon gas. Paleogeodynamic reconstructions of the Sea of Okhotsk region evolution are obtained for times of 90, 66, and 36 Ma on the basis of kinematic, geomagnetic, structural, tectonic, geothermal, and other geological and geophysical data.

Impact of neotectonics on the record of glacier and sea level fluctuations, strait of magellan, southern chile

ABSTRACT. This paper presents evidence for a neotectonic influence on Late Pleistocene/Holocene records of environmental change in the southern Strait of Magellan. We concentrate on one site, Puerto del Hambre, a key location for reconstructing palaeoenvironmental change in southernmost South America. We report geomorphological, structural geological, seismic and topographic data that all show the site has been affected by postglacial faulting. There is also indirect evidence from the site stratigraphy that the site has been displaced. Also, recent faulting explains some of the puzzles associated with interpretation of the palaeoenvironmental record at Puerto del Hambre. The implication of this work is that neotectonic faulting had a pervasive influence in the southern part of the Strait of Magellan and southernmost Tierra del Fuego, and thus affects glacial or sea level reconstructions in the area.

Resistivity and ground-penetrating radar images of fractures in a crystalline aquifer: a case study in Caiçara farm—NE Brazil

Current hydrogeological research in NE Brazil aims to better understand factors controlling storage and percolation of ground water in crystalline terrains, due to the fact that a large proportion (about 60%) of this region is formed by igneous and metamorphic rocks. As part of this effort, we present an integrated geophysical–geological study of a fractured bedrock aquifer located in the Caiçara farm, near Equador city, Rio Grande do Norte State, NE Brazil. Pumped wells in this site present very different yields, in spite of short distance of only 20 m. The main lithologies of the site are quartzite and micaschist. Combined interpretation of geophysical images (Resistivity and Ground Penetrating Radar—GPR) and field structural geologic data revealed that the fractured bedrock aquifer is composed of three sets of discontinuities: SW-dipping subhorizontal joints, parallel to the ductile fabric of the country rocks which are probably release joints; NE-dipping subhorizontal fractures, oblique to ductile trend; and subvertical fractures which are orthogonally distributed along N–S and E–W directions. Important subvertical fracture zones occur at a regular spacing of about tens of meters. Fractures in the E–W direction are relatively open, as compared to fractures in the N–S direction. Probably, E–W fractures were opened by the current neotectonic stress regime in NE Brazil, which is controlled by E–W compression and N–S extension. It was possible to rank the hydrogeologic potentiality of water well siting as a function of fracture density and proximity to recharge zones, in this way explaining why wells could present very different yield results on the site. The most favorable places for well siting are intersections of subvertical fracture zones located near drainage because highly fractured zones could be, in this way, connected with recharge zones mainly in alluvial deposits. On the other hand, the least favorable places for well siting lie outside subvertical fractures and far from recharge zones. Intermediate hydrogeological potentialities occur in two cases: at a point near the recharge zone but where there is a low density of fractures, or at point far from the recharge zone but where there is a high density of fractures.

Resistivity and ground-penetrating radar images of fractures in a crystalline aquifer: a case study in Caiçara farm—NE Brazil

Current hydrogeological research in NE Brazil aims to better understand factors controlling storage and percolation of ground water in crystalline terrains, due to the fact that a large proportion (about 60%) of this region is formed by igneous and metamorphic rocks. As part of this effort, we present an integrated geophysical–geological study of a fractured bedrock aquifer located in the Caiçara farm, near Equador city, Rio Grande do Norte State, NE Brazil. Pumped wells in this site present very different yields, in spite of short distance of only 20 m. The main lithologies of the site are quartzite and micaschist. Combined interpretation of geophysical images (Resistivity and Ground Penetrating Radar—GPR) and field structural geologic data revealed that the fractured bedrock aquifer is composed of three sets of discontinuities: SW-dipping subhorizontal joints, parallel to the ductile fabric of the country rocks which are probably release joints; NE-dipping subhorizontal fractures, oblique to ductile trend; and subvertical fractures which are orthogonally distributed along N–S and E–W directions. Important subvertical fracture zones occur at a regular spacing of about tens of meters. Fractures in the E–W direction are relatively open, as compared to fractures in the N–S direction. Probably, E–W fractures were opened by the current neotectonic stress regime in NE Brazil, which is controlled by E–W compression and N–S extension. It was possible to rank the hydrogeologic potentiality of water well siting as a function of fracture density and proximity to recharge zones, in this way explaining why wells could present very different yield results on the site. The most favorable places for well siting are intersections of subvertical fracture zones located near drainage because highly fractured zones could be, in this way, connected with recharge zones mainly in alluvial deposits. On the other hand, the least favorable places for well siting lie outside subvertical fractures and far from recharge zones. Intermediate hydrogeological potentialities occur in two cases: at a point near the recharge zone but where there is a low density of fractures, or at point far from the recharge zone but where there is a high density of fractures.

THE GEOLOGICAL FEATURES OF LIGURIAN SEA - NORTHERN APENNINES - ADRIATIC FORELAND FROM CROP SEISMIC DATA

The structure and the geodynamics of the Northern Apennines, and of the Tyrrhenian and Balearic basins is reconstructed and discussed using deep seismic reflection data from the Italian CROP project. Three profiles cross the Northern Tyrrhenian Sea (CROP M12A), the Northern Apennines (CROP03) and the Adriatic Sea (CROP M16). Lines CROPM10 and M11 cross the northern Balearic Basin, the Ligurian Sea and the Corsica-Sardinia block while line CROP M12B crosses longitudinally the Corsica Basin. Profile interpretation allows imaging E-verging lithospheric-scale contractional structures superposing the Corsica-Sardinia block onto the western margin of Adria Plate (lines CROP M10, M11, M12B) and the Corsica Basin characteristically located above this collision zone. Interpretation of seismic profiles (CROP M10, M11, M12A) has also allowed identifying a culmination of the asthenosphere top in the northern Tyrrhenian Basin. This culmination strikes in a roughly NNW direction and above it nucleate most of the Tyrrhenian extensional structures. The oceanic crust, the architecture of the sedimentary fill and the geometry of the margins of the northern Balearic Basin are imaged in the western part of profiles CROP M10 and M11. Profiles interpretation supports that the Northern Apennines are characterised by a dominant compressional style expressed by a well developed thrust system and shear planes. Crustal extension generally assumed to affect the whole Tuscan Apennines area is instead mainly restricted to the Tyrrhenian Basin where major extensional features mostly reactivate early compressive lithospheric structures. Such a tectonic picture derived from deep seismic profile interpretation is in good agreement with the surface geological-structural data carried out in the hinterland basins and the axial thrust belt along line CROP03. Migration toward the east of compression resulted in major thrusts displacing the Moho beneath the Northern Apennines watershed. The deformation of this lithospheric-scale thrust system propagated far in the foreland and controlled the deposition and sedimentation in the easternmost Pliocene-Quaternary foredeep basin (line CROP M16). During this stage, the Tyrrhenian Basin has been developing in the innermost sectors of the chain.

Miocene to Present kinematics of the NW-Alps: evidences from remote sensing, structural analysis, seismotectonics and thermochronology

At the end of their Cretaceous–Tertiary subduction-collision history, the Alps underwent a complex brittle reworking. An integrated study has been undertaken in order to explain the Miocene to Present kinematic evolution of the north-western Alps. Data from remote sensing, structural geology, seismotectonics and thermochronology have been analysed and compared. Remote sensing and structural analysis evidence that the Pennine-Graian nappe stack constitutes a continuous block, characterised by high-strain border-zones and by a quite homogenous internal deformation. The border-zones of this block are: (i) the normal SW-dipping Simplon fault; (ii) the broad dextral strike-slip system, constituted by the Rhone and Chamonix lines and by the Penninic and Briançonnais reactivated frontal thrusts, and, to the SE of the block, (iii) the recently discovered sinistral strike-slip Ospizio Sottile fault. A complex network of faults and fractures dissects the Pennine-Graian block, the most important being the E–W striking Aosta-Ranzola fault system. Even if these faults do not generally show large displacements in the Miocene, they constitute an important strain marker, since they have a regular frequency and indicate a general NE–SW extension of the block. Seismicity is mainly concentrated along the strike-slip border-zones and focal plane solutions generally agree with surface data (within discussed errors). Thermochronology indicates that, from the Late Miocene onwards, no major changes took place in the exhumation pattern, and hence in the overall kinematics. This evidence supports the general agreement between present-day deformation (seismotectonic data) and kinematics in the recent-past (structural geology data). Different tectonic reconstructions are checked with the discussed data set. In the authors’ opinion, the SW-ward orogen-parallel escape model better explain the presented body of structural, seismotectonic and thermochronology evidences.

The Erlangen geological and mineralogical software collection

The Erlangen Geology Website offers a collection of computer programs written by members of our department for solving geological and mineralogical problems. The programs are small applications for settling time calculation ( Centrifuge, Atterberg) or X-ray data conversion and processing ( Theta, Qfact) as well as complex analysis tools. Winfit! is a program for profile analysis of X-ray reflections by peak fitting that can also be used to obtain size and strain information on the sample investigated. Crossbed is a tool for plotting and back rotation of crossbed measurements for palaeocurrent analysis. WinTek handles structural geology data, plots projections, rotates datasets, counts and produces filled contour lines. Winstruct can be used for simulating 001-diffraction patterns from clay minerals. It allows incorporation of varying chemistry, different atomic positions, instrumental parameters, particle orientation and particle size into the calculations. Convolution of the calculated patterns with a broadening function models instrumental contribution to peak breadth. The site is completed by a collection of links to software from other authors. Some of this software is described on the Web page. Additionally there is a Web-searchable database that contains information about the programs listed on this site supplemented by entries and links to software available on other Web-Sites. Software authors can add their programs, including a short description and key-words, as well as URLs of homepages and download facilities by a Web-form. On submission, the database is updated immediately.