SSE Compression Research Articles

Deciphering superimposed Ellesmerian and Eurekan deformation, Piper Pass area, northern Ellesmere Island (Nunavut)

The tectonic evolution in the Piper Pass area in northern Ellesmere Island (Canadian Arctic) is characterized by the superimposition of two major deformational events: the Paleozoic Ellesmerian Orogeny and the Tertiary Eurekan deformation. It is difficult to separate the structures formed during each deformation in the parts of the Canadian Arctic in which the post-Ellesmerian and pre-Eurekan Sverdrup Basin is not preserved (Hazen Fold Belt, Central Ellesmere Fold Belt). In the vicinity of the Lake Hazen Fault Zone in the Piper Pass area, kilometre-scale kink folds, cleavage planes and SSE-directed thrust faults are unconformably overlain by Permian through Tertiary rocks of the Sverdrup Basin, which clearly indicates that they are related to the Ellesmerian Orogeny. However, the steep faults of the Lake Hazen Fault Zone are characterized by possible lateral movements and by NNW–SSE compression that cut through or affect both the pre-Ellesmerian Franklinian strata, as well as the post-Ellesmerian Sverdrup Basin deposits. These structures can clearly be assigned to post-mid Cretaceous movements of the Eurekan deformation. The Piper Pass area is a key area in which it is possible to recognize and distinguish Ellesmerian from Eurekan structures.

Exhumation of high-pressure rocks under continuous compression: a working hypothesis for the southern Hellenides (central Crete, Greece)

Combined kinematic, structural and palaeostress (calcite twinning, fault-slip data) analyses are used to study the exhumation mechanism of the high-pressure rocks exposed on the island of Crete (southern Aegean, Greece). Our study shows that the evolution of windows in central Crete was controlled by two main contractional phases of deformation. The first phase (D1) was related to the ductile-stage of exhumation. NNW–SSE compression during D1 caused layer- and transport-parallel shortening in the upper thrust sheets, resulting in nappe stacking via low-angle thrusting. Synchronously, intracontinental subduction led to high-pressure metamorphism which, however, did not affect the most external parts of the southern Hellenides. Subsequent upward ductile extrusion of high-pressure rocks was characterized by both down-section increase of strain and up-section increase of the pure shear component. The second phase (D2) was associated with the brittle-stage of exhumation. D2 was governed by NNE–SSW compression and involved conspicuous thrust-related folding, considerable tectonic imbrication and formation of a Middle Miocene basin. The major D2-related Psiloritis Thrust cross-cuts the entire nappe pile, and its trajectory partially follows and reworks the D1-related contact between upper and lower (high-pressure) tectonic units. Eduction and doming of the Talea Window was accompanied by gravity sliding of the upper thrust sheets and by out-of-the-syncline thrusting. Late-orogenic collapse also contributed to the exhumation process. Therefore, it seems that the high-pressure rocks of central Crete were exhumed under continuous compression and that the role of extension was previously overestimated.

Late orogenic intramontane basin development: the Granada basin, Betics (southern Spain)

ABSTRACTThe quantitative study of subsidence in the Granada basin, using decompaction and backstripping techniques, and contemporaneous relief development in the surrounding areas, especially in the Sierra Nevada, provides a good case example of the development of an intramontane basin. In the Granada basin, according to the interpretation of the seismic profiles and results of the backstripping analysis, subsidence and sedimentation rates were at a maximum in the late Tortonian and decreased progressively; meanwhile, the neighbouring areas were uplifted forming important relief. Chronostratigraphical revisions of the marine sediments show that the marine incursion that deposited sediments in the Granada basin lasted only 1.3 Ma, between 8.5 and 7.2 Ma. The gradual retreat of the sea in the Granada basin is not attributable to global eustatic fluctuations, but rather to uplift in the Sierra Nevada and its adjacent areas. From latest Tortonian to early Messinian times, the region became continental and the Granada basin acquired its present physiography and was differentiated as such. From the late Tortonian onwards, NNW–SSE compression combined with ENE–WSW extension affected the cordillera. In the Granada basin, extension controlled fault movements. There are two well‐defined fault sets: the first trends 70°N–90°E, with low angle faults (less than 30°) dipping towards the north and south, defining the subsiding areas which have approximately E–W direction; whereas the second set has a NW–SE direction, and cuts and displaces the previous ones, defining the main subsiding areas in the eastern part of the basin. The reinterpretation of seismic profiles reveals that the subsiding axes within the Granada basin persisted from the Tortonian to the present because of continued displacements of the main faults.

Active faults, seismicity and stresses in an internal boundary of a tectonic arc (Campo de Dalías and Níjar, southeastern Betic Cordilleras, Spain)

The Betic-Rif Cordilleras, formed by the interaction of NW–SE convergence between the Eurasian and African plates and the westward motion of their Internal Zones, provide a good example of an active tectonic arc. The Campo de Dalías and Campo de Níjar constitute outcropping sectors of Neogene and Quaternary rocks located in the southeastern border of the Betic Cordilleras and allow us to study the recent deformations developed in the internal border of this tectonic arc. The main active faults with related seismicity, representing a moderate seismic hazard, associated to the southeastern Betic Cordilleras boundary, include high-angle NW–SE-oriented normal faults that affect, at least, the upper part of the crust, a main detachment located at 10 km depth, and probably another detachment at 20 km as well. Seismite structures, recent fault scarps with associated colluvial wedges that deform the drainage network and the alignment of the coastline, indicate that the high-angle faults have been active at least since the Quaternary. Paleostresses determined from microfault analysis in Quaternary deposits generally show an ENE–WSW trend of extension. Present-day earthquake focal mechanisms include normal, strike-slip and reverse faulting. Normal and strike-slip focal mechanisms generally indicate ENE–WSW extension, and strike-slip and reverse focal mechanisms are related to NNW–SSE compression. The maximum horizontal compression has a consistently NNW–SSE trend. The deep activity of detachments and reverse faults determines the NNW–SSE crustal shortening related to the Eurasian–African plate convergence. At surface, however, the predominance of normal faults is probably produced by the increase in the relative weight of the vertical stress axis, which in turn may be related to relief uplift and subsequent horizontal spreading. The internal mountain front boundary of the Betic Cordilleras developed through the activity of a set of structures that is more complex than a typical external mountain front, probably as a consequence of a vertical variable stress field that acted on previously deformed rocks belonging to the Internal Zone of the cordilleras.

Tectonic significance of the present relief of the Betic Cordillera

Tortonian calcarenites of the Betic Cordillera were deposited in coastal or very shallow marine environments and represent an ideal marker for estimating vertical movements from the late Miocene to the Present. A map showing the heights at which these Tortonian marine rocks are situated has a clear correlation with the present relief, indicating that today's relief has been formed since the Tortonian. There is also a good correlation between present relief and the Bouguer anomaly distribution in the Betic Cordillera, as well as with crustal thickness. Likewise, the present relief is directly related to the geodynamic setting of a horizontal N–S to NNW–SSE compression and an almost perpendicular extension, along with isostatic readjustment, existing in the Betic Cordillera from the Tortonian. As a result of these regional stresses, faults and folds have produced notable vertical movements. The highest rates of uplift of the Betic Cordillera coincide with large antiforms, in particular those of the Sierra Nevada and the Sierra Filabres. Several subsiding sectors also exist (for example, the Granada Basin or the Guadalquivir Basin). The foreland Guadalquivir Basin has a complex history because the uplift in its eastern sector and subsidence in the western sector coexisted during the late Tortonian. Today the whole Betic Cordillera is characterized by differential regional uplift, even in the aforementioned subsiding sectors.

Paleostress analysis of the Cretaceous rocks in the eastern margin of the Dead Sea transform, Jordan

This paper presents the first paleostress results from fault-slip data on Cretaceous limestone at the eastern rim of the Dead Sea transform (DST) in Jordan. Stress inversion of fault-slip data is performed using an improved right dieder method, followed by rotational optimization (Delvaux, TENSOR Program). The orientation of the principal stress axes ( σ 1, σ 2 and σ 3) and the ratio of the principal stress differences ( R ) show two main paleostress fields marking two main stress regimes, strike-slip and extensional. The first is characterized by NNW–SSE compression and ENE–WSW extension and related to Middle Miocene-Recent sinistral movement along the Dead Sea transform and the opening of the Red Sea. The second paleostress field is a WNW–ESE compression and NNE–SSW extension restricted to the northern part of the investigated area. This stress field could be associated with the development of the Syrian Arc fold belt which started during the Turonian, or it may be due to an anticlockwise rotation of the first stress field.

Active deformation in the frontal part of the Northern Apennines: insights from the lower Metauro River basin area (northern Marche, Italy) and adjacent Adriatic off-shore

An integration of seismological data with geological and geomorphological information aided by seismic interpretation was performed to characterise the Quaternary tectonic evolution of the Metauro River basin area (northern Marche) and adjacent off-shore sector of the external Northern Apennines. On-shore, along the Adriatic coast, the youngest age of thrusting and folding post-dates the Early-Middle Pliocene, while Pleistocene deposits appear to be, at least in part, not involved in the deformation. Recent (i.e. post-thrusting) tectonic structures have been recognised both in pre-Quaternary substratum rocks and in Upper Quaternary continental deposits (Upper Pleistocene terrace alluvium, Upper Pleistocene–Holocene slope deposits). These faults are all compatible with a WSW–ENE oriented extension. In the Metauro River basin area, preserved flights of stream terraces have been categorised according to the presence or absence of alluvial suites in relationship to each terrace level. Here, based on both the heights above the valley floor and the areal distribution of stream terraces, a generalised vertical tectonic uplift can be inferred, particularly during the Middle–Late Pleistocene. Moreover, the along-valley distribution of stream terraces provides further constraints on the age of thrusting and folding. In fact, the reconstructed terrace-levels are substantially parallel, and no evidence for any significant deformation by fold activity has been recognised. Local deformation displayed by both terrace surfaces and alluvial/slope-waste deposits suggests, instead, the intervening of some minor differential movements associated with the generalised uplift and/or to Middle–Late Pleistocene normal faulting. Their occurrence appears anyhow to be unrelated with the pattern of folds and associated thrusts. The present-day seismic activity of the study area was considered by analysing 83 seismic events that occurred from 1987 to 2000. The epicentre distribution is very scattered, and depths are generally comprised within the first 20 km of the crust, clustering between 0 and 15 km. Most of the events have magnitude <3.0, while only a few of them (12) have magnitude between 3.0 and 4.2. Focal mechanisms were obtained for eight events. The results are complex, showing fault plane solutions of “normal fault”, “thrust fault” and “unknown” types, according to commonly used stress categories. The low level of seismicity and the inhomogeneity of fault plane solutions confirm that, in the study area, this kind of data cannot provide clear constraints with respect to the problem of the occurrence or lack of activity along the thrust front. Finally, the Quaternary marine succession was studied in the northern Adriatic off-shore. Lower Pleistocene deposits appear to be slightly involved in the deformation associated with the frontal thrust of the Apennine chain. In contrast, the upper part of the Quaternary succession is clearly undeformed, showing planar and horizontal reflectors, which seal the most external thrusts of the belt. These data suggest that thrusting at the front of the Northern Apennines ended in Early Pleistocene times. Our integrated results indicate that, since Middle Pleistocene times, the external front of the northern Marche Apennines has been inactive. A generalised uplift has taken place, with subordinate tectonic activity being characterised by ENE–WSW extension and NNW–SSE compression. These main features of the stress field, although with spatial permutations of the principal stress axes, also characterise most of the external Northern Apennines during the whole Middle Pleistocene–Holocene time span.

Miocene to Quaternary deformation in NE Slovenia: complex paleomagnetic and structural study

Combined paleomagnetic and structural research was carried out in the Mura-Zala Basin including the western and southern surrounding hills in northeastern Slovenia. The Mura-Zala Basin was formed due to ENE–WSW trending crustal extension in the late Early Miocene (18.3–16.5 Ma). First, marine sedimentation took place in several more or less confined depressions, then in a unified basin. During thermal subsidence in the late Miocene deltaic to fluvial sediments were deposited. After sedimentation, the southernmost, deepest depression was inverted. Map-scale folds, reverse and strike-slip faults were originated by NNW–SSE compression. This deformation occurred in the latest Miocene–Pliocene and is reflected also in the magnetic fabric (low field susceptibility anisotropy). After this folding, the Karpatian sediments of the Haloze acquired magnetization, then suffered 30° counterclockwise rotation relative to the present north (40° counterclockwise with respect to stable Europe). This Pliocene (Quaternary?) rotation affected a wide area around the Mura-Zala Basin. The latest Miocene to Quaternary folding and subsequent rotation may be connected to the counterclockwise rotation of the Adriatic microplate.

Onshore and offshore compressional tectonics in the eastern Betic Cordillera (SE Spain)

This study concerns the northern terminal splay of the Eastern Betic Shear Zone (Betic Cordillera, SE Spain), where the Bajo Segura Basin lies, and its offshore prolongation along the western Mediterranean margin. We have integrated seismic reflection profiles with gravimetry, seismicity, wells and outcrop data from the Bajo Segura Basin and the Alicante shelf in order to determine the current geodynamic setting of the area. The results indicate that the same compressional structures in Upper Miocene–Quaternary rocks are observed both on- and offshore. In the onshore Bajo Segura Basin, there are ENE–WSW growth folds related to reverse faults in the basement. In the Alicante shelf, the main structure is an ENE–WSW anticlinorium which deforms Upper Miocene–Quaternary syntectonic deposits. These compressional structures are still active at present, as shown by the offshore seismicity. From the structural analysis and focal mechanisms of the earthquakes we conclude that the Bajo Segura Basin and its adjacent shelf have been subject to NNW–SSE compression since Late Miocene until the Present. Folding and reverse faulting of the Upper Miocene–Quaternary sedimentary cover and of its basement have accommodated this compression. The main active structures onshore, located in the Bajo Segura Basin, extend eastwards into the Mediterranean Sea. This fact is interpreted as the Eastern Betic Shear Zone continues offshore to the east.

Triassic–early Liassic extensional systems and their Tertiary inversion, Essaouira Basin (Morocco)

NNE–SSW striking late Triassic–early Liassic half-grabens of the Essaouira Basin and the adjacent High Atlas are linked by roughly EW-striking transfer faults. They are overlain by a wide, considerably less faulted, evaporitic sag basin and extensive basalt flows. A Pre-Pliensbachian unconformity truncates the Triassic–early Liassic sequences on the E and NE margin of the basin and is overlain by a mid-Liassic to Cretaceous platform sequence. In the Cap Sim-Necnafa depression Jurassic and early Cretaceous salt tectonics caused widespread salt withdrawal structures. Tertiary NNW to SSE compression caused the inversion of NE and NNE-striking structures and⧸or the formation of salt anticlines. The same compression formed EW-striking reverse faults and anticlines, suggesting the reactivation of late Triassic–early Liassic transfer faults.

Post-early Messinian counterclockwise rotations on Crete: implications for Late Miocene to Recent kinematics of the southern Hellenic arc

Most geodynamical models for the kinematics of the central Mediterranean recognise that major tectonic rotations must have played an important role during the Neogene. The Hellenic arc is believed to have been subjected to clockwise rotations in the west and counterclockwise rotations in the east, while the southern part (Crete) shows no rotations ( Kissel and Laj, 1988). Many qualitative and quantitative models are based on the idea that Crete did not rotate. We present new palaeomagnetic data which show that post-early Messinian counterclockwise rotations have occurred on Crete. The amount of counterclockwise rotation generally varies between 10° and 20°, but in central Crete much larger rotations (up to ∼40° counterclockwise) were found. Only a few sections did not show any rotation. The anisotropy of magnetic susceptibility (AMS) shows lineations, which are consistently WNW–ESE throughout Crete, indicating post-rotational WNW–ESE extension, or NNE–SSE compression. The observed counterclockwise rotations are consistent with the results of tectonic modelling by Ten Veen and Meijer (1998). The latter study compares the late-Middle Miocene to Recent kinematics with modelled intra-plate stresses for various possible distributions of plate boundary forces. Observations reveal that motion along left-lateral and right-lateral faults occurred during the Pliocene. The model analysis shows these motions to be consistent with transform resistance along the eastern segment of the overriding margin. The counterclockwise block rotations observed by us are probably a consequence of displacements along the left-lateral and right-lateral faults and could reflect a similar tectonic regime that involved transform resistance.