NW-SE Striking Faults Research Articles

Past and present circulation of CO2-bearing fluids in the crystalline Gran Paradiso Massif (Orco Valley, north-western Italian Alps): tectonic and geochemical constraints

In the Orco Valley, inside the Gran Paradiso Massif, 3 main fault systems are present: (a) E–W striking faults dipping at 45–60° to the N, (b) high-angle NW–SE striking faults, and (c) high-angle NE–SW to NNE–SSW striking faults. The E–W striking faults and the interposed NW–SE-faults appear to represent a cogenetic structural association related to a larger scale transtensional shear zone, while the NE–SW faults are probably inherited by an older discontinuous deformation stage. Breccia bodies or veins, mostly consisting of carbonate (siderite–ankerite±calcite)+quartz with sulphide–Au mineralisation, recording a multistage mesothermal evolution, occur along both E–W and NW–SE fault systems. Three water types are recognised: type I, Ca2+–HCO3− waters, with minor SO42−; type II, (Ca2+/Na+)–HCO3− waters varying towards Na+–(HCO3−/Cl−) waters; and type III, Mg2+–HCO3− waters. Type I and type III groundwaters are freshly recharged waters, only slightly exchanged with rocks. Type II includes waters which come into contact with carbonate fracture fillings, and geochemical modelling indicates that dissolution of carbonates along fractures is the main process controlling the groundwater chemistry. These waters evolve in a system open to uprising CO2, and their strongly negative δ13CCO2 suggests a substantial organic component in the CO2 discharge. In the past, CO2-bearing fluids were likely responsible for the formation of Fe-bearing carbonate fracture fillings. The persistence through time of the CO2 flux in the region has important implications for the reconstruction of the Alpine tectonic evolution and deep structure.

Ground deformation of the southern sector of the Aeolian islands volcanic arc from geodetic data

The deformation pattern and the dynamics of the southern sector of the Aeolian archipelago are investigated. A study on the ground deformation, measured over the last 20 years in the trilateration geodetic network between the islands of Vulcano and Lipari, has been conducted. Analysis of the relative displacements and the uniform strain tensor parameters, as well as the comparison between areal dilatation and the vertical variations deduced by precise levelling, allow distinguishing different phases associated both with the regional dynamics and the local volcanic context of the area. These phases, however, appear to be closely interrelated. The analysis of the deformation pattern allows to constrain the predominance of a roughly E–W trending extension and a N–S contraction at a regional scale. This regime is consistent with right-lateral movements along a NW–SE striking fault system.

Bookshelf

Eleven seismic reflection lines recorded by the Italian Petroleum Agency, Azienda Generale Italiana Petroli (AGIP), in 1982–1984 around the flanks of the Somma-Vesuvius complex were utilized for studying its sub-surface structure. A new seismic reflection profile acquired within the Avellino caldera, at the southwestern edge of the Great Cone of Vesuvius, integrates the AGIP seismic dataset. The new reflection profile allows us to delineate two main reflectors. The first reflector may indicate a SW lateral collapse experienced by the volcano, probably between 35 and 11 ka ago. Evidence of this seismic discontinuity was also found on one AGIP line and on some refraction surveys. Other volcanic structures, such as buried adventive craters, dikes and pyroclastic deposits were detected on the eastern side of the volcanic complex. In particular, two shallow undulated reflectors are interpreted as pyroclastic deposits older than the Campanian Ignimbrite (CI). The study confirmed the presence of NW–SE striking faults crosscutting Vesuvius, which probably played a major role in the genesis of the volcano. Finally, evidence of ring faults was found mainly in the northeastern and southeastern sectors of the volcano. These faults yielded a low signal-to-noise area characterized by high lateral heterogeneity and the presence of a large number of fractures, possibly due to the stress field created by collapse of the volcanic structure.

Study of the sub-surface structure of Somma-Vesuvius (Italy) by seismic reflection data

Eleven seismic reflection lines recorded by the Italian Petroleum Agency, Azienda Generale Italiana Petroli (AGIP), in 1982–1984 around the flanks of the Somma-Vesuvius complex were utilized for studying its sub-surface structure. A new seismic reflection profile acquired within the Avellino caldera, at the southwestern edge of the Great Cone of Vesuvius, integrates the AGIP seismic dataset. The new reflection profile allows us to delineate two main reflectors. The first reflector may indicate a SW lateral collapse experienced by the volcano, probably between 35 and 11 ka ago. Evidence of this seismic discontinuity was also found on one AGIP line and on some refraction surveys. Other volcanic structures, such as buried adventive craters, dikes and pyroclastic deposits were detected on the eastern side of the volcanic complex. In particular, two shallow undulated reflectors are interpreted as pyroclastic deposits older than the Campanian Ignimbrite (CI). The study confirmed the presence of NW–SE striking faults crosscutting Vesuvius, which probably played a major role in the genesis of the volcano. Finally, evidence of ring faults was found mainly in the northeastern and southeastern sectors of the volcano. These faults yielded a low signal-to-noise area characterized by high lateral heterogeneity and the presence of a large number of fractures, possibly due to the stress field created by collapse of the volcanic structure.

Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland

Two Archaean supracrustal sequences in the area north-east of Disko Bugt, c. 1950 and c. 800 m in thickness, are dominated by pelitic and semipelitic mica schists, interlayered with basic metavolcanic rocks. A polymict conglomerate occurs locally at the base of one of the sequences. One of the supracrustal sequences has undergone four phases of deformation; the other three phases. In both sequences an early phase, now represented by isoclinal folds, was followed by north-west-directed thrusting. A penetrative deformation represented by upright to steeply inclined folds is only recognised in one of the sequences. Steep, brittle N–S and NW–SE striking faults transect all rock units including late stage dolerites and lamprophyres. Investigation of major- and trace-element geochemistry based on discrimination diagrams for tectonic setting suggests that both metasediments and metavolcanic rocks were deposited in an environment similar to a modern back-arc setting.

Microseismicity and focal mechanisms at the western termination of the North Anatolian Fault and their implications for continental tectonics

For seven weeks, a temporary network of 68 seismological stations was operated in Central Greece, in the region of Thessaly and Evia, located at the western termination of the North Anatolian Fault system. We recorded 510 earthquakes and computed 80 focal mechanisms. Seismic activity is associated with the NE–SW dextral North Aegean Fault, or with very young E–W-striking normal faults that are located around the Gulf of Volos and the Gulf of Lamia. The important NW–SE-striking faults bounding the Pilion, or the basins of Larissa and Karditsa, are not seismically active, suggesting that it is easier to break continental crust, creating new faults perpendicular to the principal stresses, than to reactivate faults that strike obliquely to the principal stress axes

Koroglu caldera, mid-west Anatolia, Turkey: volcanological and magmatological evolution

The Koroglu caldera is a result of the eruption of `Seydiler ignimbrites', which have been emplaced in two sequences known as Lower Seydiler (LS) and Upper Seydiler (US). The Koroglu caldera measures 13 km×18 km, contains a resurgent dome in the center, and produced low aspect ratio ignimbrites, which have been transported up to 50 km away from the source. The ignimbrites show argillaceous weathering which decreases from the bottom towards the top of the deposits. Such a transition (from ignimbrites to reworked tuffs) indicates the development of a lacustrine environment over the ignimbrites. SPOT image analysis shows that tectonic activity continued after the caldera collapse. Two main trends of tectonic elements (NE–SW and NW–SE) have been distinguished, the latter being the younger. A NW–SE-striking fault was used by lamprophyric magmas which were extruded into the post-ignimbrite lacustrine deposits. The lava flows and dikes (trachybasalte, trachyandesite) also occur along the ring fractures of the caldera. The dikes are composed of olivine+phlogopite+Cr-diopside+salite+K-feldspar+Ba-feldspar (hyalophane). The lava flows contain scarce cognate inclusions.

Strike-slip deformation in the Confidence Hills, southern Death Valley fault zone, eastern California, USA

The Confidence Hills form a well exposed, composite, positive flower structure developed in Pliocene to Recent lacustrine and alluvial fan sediments. The structure has developed along the current trace of the southern Death Valley dextral strike-slip fault zone. California, USA. NW–SE-striking fault zones bound the Confidence Hills. In 3D, these fault segments are inferred to link at depth to a common basal fault system. The flower structure is formed by doubly plunging anticlines that roughly parallel the bounding fault segments. Fold development was aided by: (a) the presence of a basal salt deposit and numerous detachment horizons within the sedimentary pile and (b) buttressing and uplift along and against the bounding oblique-slip reverse faults. Structural and palaeomagnetic evidence indicates that the anticlines developed with axial surfaces parallel and sub-parallel to the trace of both fault zones. Folding appears to have initially developed adjacent to and above the southeastern fault segment and then propagated outwards and to the northwest. The latest displacements along the current southern Death Valley fault zone are probably only in the orders of hundreds of metres and as young as 0.9 Ma to Recent. This young fault zone is highly segmented along the length of the floor of southern Death Valley: the high proportion of oblique-slip faulting consistent with the strike-slip zone being immature. The Confidence Hills structure displays close geometric similarities with other natural examples of positive flower structures and to the features found in scaled. analogue sandbox experiments of strike-slip faulting.

Late Cretaceous deformation of the Pieniny Klippen Belt, West Carpathians

The Late Cretaceous position and dynamics of the Pieniny Klippen Belt of the West Carpathians, which lies behind the Palaeogene flysch accretionary prism, are reconstructed. As shown by the reconstruction, based on structural, sedimentological and palaeomagnetic data, the Pieniny Klippen Belt occupied a WNW-ESE to NW-SE trending zone during the Late Cretaceous, which acted as an oblique convergent boundary between the ancestral West Carpathians and the oceanic lithosphere attached to the North European platform. Sediments of the Pieniny Klippen Belt were part of both the mountain belt and foredeep at that time. Known change from pelagic micritic limestone to a flysch sequence is progressively younger seawards in the thrust-slice stack forming the Pieniny Klippen Belt. The syn-sedimentary record includes flysch, olistostrome and wildflysch sediments. Both the NW-SE thrusting along the NE-SW striking faults and dextral strike-slip faulting along the WNW-ESE to NW-SE striking faults were active in the Late Cretaceous in the area of the current Pieniny Klippen Belt.

Recent fault tectonics and their relations to the seismicity of East Germany

The prominent features of the map of recent vertical crustal movements of East Germany are NW-SE striking faults which divide the whole country into tilted blocks. Some of the faults are known from geological mapping, others, especially in Mecklenburg-Vorpommern and Brandenburg are known only from geophysical investigations or are unknown except for geodetic evidence. The recent mobility of all faults was proved by typical geodetic indications. There are almost no conformities with morphologic structures. The movements along these faults are aseismic and creeping. The difference in the velocity of movement between the blocks on either side of the fault is not more than 0.18 mm/yr, and the direction of movement changes after short periods of time (not geological periods). In some cases, the continuation of faults show no recent mobility in the above described sense, but along the fault planes the epicentres of small earthquakes can be found, especially in southwest Saxony (Vogtland). That seems to be an explanation for areas of very low seismicity and for the relationship between recent crustal movements along faults and the seismic activity along faults.