Trending Normal Faults Research Articles

Reduction of environmental risk from capable faults: The case of the Eastern Etna region (eastern Sicily, Italy)

On the eastern flank of Etna volcano, movements along the NNW–SSE trending normal faults of the Timpe system generate recurrent, low magnitude very shallow seismic events that induce noteworthy ground surface effects. The Timpe system is the on-land extension of the Hyblean–Malta fault system, which is the likely source of the 1693 Maw 7.4 earthquake. Frequent creep phenomena occur both associated with seismic events and/or volcanic eruptions, and independent from them. These surface deformations are mainly confined in the eastern sector of the volcano apparatus and result from the interaction between regional tectonics and local volcano-tectonic processes. The widespread diffusion of cultural sites in this region even before the Greek civilisation testifies to the complex relationship of humans with a restless violent nature. Many Greek authors and myths refer to the frightening eruptions and earthquakes of Etna, but, at the same time, Strabo underlines the extreme fertility of the land due to the volcanic ash, and the quality of the local wine. So notwithstanding the evident risk, this region is one of the most densely inhabited regions of Sicily. Coseismic surface ruptures and creep are responsible for damaging effects on buildings, roads, railways and lifelines, including the water supply network. To reduce the environmental risk from faulting, APAT—Italian Agency for Environment Protection and for Technical Services—has compiled a georeferenced database, where capable faults, extract from ITHACA (Italy Hazard from Capable Faults) catalogue, and water supply and other environmentally sensible networks are overlapped to pinpoint zones of expected damage. This tool is fundamental in land planning and during an emergency, as seen during the 2002 Santa Venerina earthquake when the environmental agency needed to quickly verify the integrity of the water distribution and sewage networks.

Active faults, deformation rates and Quaternary paleogeography at Kyparissiakos Gulf (SW Greece) deduced from onshore and offshore data

Kyparissiakos Gulf forms a 45 km long zone located at 70–80 km east from the Hellenic trench with a general direction NNW–SSE. Onshore studies show the existence of several neotectonic horsts and grabens bounded by E–W trending normal faults. Thrust sheets of the underlying Hellenides crop out within the horst areas and younger sediments, mostly Lower Pleistocene, have been deposited in the grabens. The age of the marine sediments is mostly Lower Pleistocene. Throw rate on the normal faults varies between 0.7 and >1.0 mm/yr, accommodating extension in the N–S direction. Subsidence rates during Early Pleistocene are between 0.1 and 0.3 mm/yr, whereas uplift rates during Middle Pleistocene–Present are between 0.18 and 0.50 mm/yr. Offshore data were obtained using bathymetric and air-gun litho-seismic profiles. The shelf has been disrupted by active faults with several meters of throw. Average Holocene throw rates are 0.4–0.6 mm/yr, but in some areas adjacent Filiatra and Olympia values greater than 3 mm/yr are detected. Holocene and Upper Pleistocene marine sediments thicken gradually to the north, as do the marine Lower Pleistocene sediments onshore. A NNW–SSE offshore longitudinal fault parallel to the Kyparissiakos coast with throw rate above 3 mm/yr is the dividing structure between the uplifted coastal area and the present-day gulf. This indicates a major change in paleogeography between Early and Middle Pleistocene. Present-day transition from E–W compression in the Hellenic Trench to E–W extension in the Kyparissiakos Gulf and to N–S extension in Western Peloponnesus is discussed. The development of E–W structures in Western Peloponnesus since Latest Pliocene may be related to the Central Hellenic Shear Zone, which accommodates differential GPS rates between Northern Greece and Southern Peloponnesus.

North-south transfer zones and paleo-morphological reconstruction of the Xylokastro area (Corinth Gulf, Greece)

A large number of studies have documented the structural and sedimentary architecture of the Corinth Gulf, especially the major E–W trending normal faults important in accommodating the main extensional strain and associated growth of the Gilbert fan deltas. However, the role of several N–S oriented structures that crop out at the surface and are detectable at depth by seismic reflection and gravity surveys are not clearly understood. Based on new geological data, collected near Xylokastro, we describe the N–S oriented tectonic activity of this area. The mapped inland faults correspond to off-shore structures identified in re-interpreted seismic lines and appear to have acted as a major transfer zone during the opening of the Corinth Gulf. Reconstruction of the paleo-topography based on sedimentary facies and the environment of clay mineral formation suggest these transfer zones played an important role in controlling both local structural relief and depositional conditions of the Gilbert fan deltas.

The relationships between tectonics and sedimentation in the Late Cretaceous series of the eastern Atlasic Domain (Algeria)

Our study of the Late Cretaceous series in the eastern Atlasic Domain of Algeria is intended to show the geometry of the sedimentary deposits and the sequential palaeogeographic evolution of the region’s basins. The Late Cretaceous series consist of four transgressive–regressive sedimentary megasequences corresponding to 2nd order cycles, noted as I–IV. Each megasequence is made up of three or four sequences that have been correlated with 3rd order cycles. The beginning of megasequences I and II mark a rapid tectonic deepening concomitant with an acceleration of sea-level rise which allowed the deposition of pelagic sediments at their initiation, during the latest Albian and early Turonian times. This tectonism reflects the reactivation of basement faults resulting in extension and block-tilting. The succeeding sequences, showing alternating marls and carbonate beds with benthic facies were deposited in a homoclinal ramp and are indicative of a gradual development of shallow marine conditions. In the megasequences III (Coniacian to Santonian) and IV (Campanian to Maastrichtian) the sequences were wholly deposited on a homoclinal ramp. The major basement faults are NE-SW trending transtensional strike-slip faults, which delimit the margins of the basins, and WNW-ESE and NW-SE trending normal faults that led to block tilting during the Late Cretaceous. Both types of faults strongly influenced palaeogeography and sedimentation. The evolution of the subsidence through the Late Cretaceous shows a progressive sagging of these basins, interrupted by short phases of extension highlighted by accelerations on the subsidence curves. These phases constitute, after the Jurassic extension, a new extensional episode occurring during the latest Albian and Early Turonian, which led to a tilting of basement blocks. The Late Cretaceous extension phases reflect reorientations of the stress in the African plate, during its northeastwardly directed drift, and rifting processes on its northeastern margin. A first compressive phase, which was relatively localized, is registered at the end of the Maastrichtian, leading to palaeogeographic reorganization of the Atlasic basins.

40Ar/39Ar and K–Ar geochronology of magmatic and hydrothermal events in a classic low-suphidation epithermal bonanza deposit: El Peñon, northern Chile

The epithermal El Penon gold–silver deposit consists of quartz–adularia veins emplaced within a late Upper Paleocene rhyolitic dome complex, located in the Paleocene–Lower Eocene Au–Ag belt of northern Chile. Detailed K–Ar and 40Ar/39Ar geochronology on volcano–plutonic rocks and hydrothermal minerals were carried out to constrain magmatic and hydrothermal events. The Paleocene to Lower Eocene magmatism in the El Penon area is confined to a rhomb-shaped basin, which was controlled by N–S trending normal faults and both NE- and NW-trending transtensional fault systems. The earliest products of the basin-filling sequences comprise of Middle to Upper Paleocene (∼59–55 Ma) welded rhyolitic ignimbrites and andesitic to dacitic lavas, with occasional dacitic dome complexes. Later, rhyolitic and dacitic dome complexes (∼55–52 Ma) represent the waning stages of volcanism during the latest Upper Paleocene and the earliest Eocene. Lower Eocene porphyry intrusives (∼48–43 Ma) mark the end of the magmatism in the basin and a change to a compressive tectonomagmatic regime. 40Ar/39Ar geochronology of hydrothermal adularia from the El Penon deposit yields ages between 51.0±0.6 and 53.1±0.5 Ma. These results suggest that mineralization occurred slightly after the emplacement of the El Penon rhyolitic dome at 54.5±0.6 Ma (40Ar/39Ar age) and was closely tied to later dacitic–rhyodacitic bodies of 52 to 53 Ma (K–Ar ages), probably as short-lived pulses related to single volcanic events.

Structural and remote sensing studies of the southern Betsimisaraka Suture, Madagascar

An assessment of the southern Betsimisaraka Suture (B.S.) of southeastern Madagascar using remote sensing and field investigation reveals a complex deformation history. Image processing of Landsat ETM+data and JERS-I Synthetic Aperture Radar (SAR) imagery was integrated with field observations of structural geology and field petrography. The southern B.S. divides the Precambrian basement rocks of Madagascar in two parts. The western part includes Proterozoic rocks whereas the eastern part is an Archean block, named the Masora block. The southern part of the B.S. includes high-grade metamorphic rocks, recording strong deformation and has mineral deposits including chromite, nickel, and emerald, characteristic of oceanic material that is compatible with a suture zone. Large-scale structural features indicate ductile deformation including three generations of folding (F1, F2, and F3) associated with dextral shearing. The first folding event (F1) shows a succession of folds with NE striking axial planes. The second folding event (F2) mainly has north–south striking axial planes and the last event (F3) is represented by mega folds that have ENE–WSW axial plane directions and have NNW and SSE contractional strain patterns. Closure of the Mozambique Ocean between two components of Gondwana sandwiched rocks of the B.S. and formed upright folds and shortening zones which produced N–S trending lineaments. Later dextral movements followed the contraction and formed NW–SE trending lineaments and N–S trending normal faults associated with dextral strike slip faults and fractures.

Interpretation of radon anomalies in seismotectonic and tectonic-gravitational settings: the south-eastern Crati graben (Northern Calabria, Italy)

The study area is located in the south-eastern part of the Crati valley (Northern Calabria, Italy), which is a graben bordered by N–S trending normal faults and crossed by NW–SE normal left-lateral faults. Numerous severe crustal earthquakes have affected the area in historical time. Present-day seismic activity is mainly related to the N–S faults located along the eastern border of the graben. In this area, much seismically induced deep-seated deformation has also been recognised. In the present paper, radon concentrations in soil gas have been measured and compared with (a) lithology, (b) Quaternary faults, (c) historical and instrumental seismicity, and (d) deep-seated deformation. The results highlight the following: (a) There is no evidence of a strong correlation between lithology and the radon anomalies. (b) A clear correlation between the N–S geometry of radon anomalies and the orientation of main fault systems has been recognised, except in the southernmost part of the area, where the radon concentrations are strongly affected by the superposition of the N–S and the NW–SE fault systems. (c) Epicentral zones of instrumental and historical earthquakes correspond to the highest values of radon concentrations, probably indicating recent activated fault segments. In particular, high radon values occur in the zones struck by earthquakes in 1835, 1854, and 1870. (d) Deep-seated gravitational deformation generally coincides with zones characterised by low radon concentrations. In the studied area, the anisotropic distribution of radon concentrations is congruent with the presence of neotectonic features and deep-seated gravitational phenomena. The method used in this study could profitably contribute towards either seismic risk or deep-seated gravitational deformation analyses.

COMPRESSIONAL GROWTH OF THE MINERVA ANTICLINE, OTWAY BASIN, SOUTHEAST AUSTRALIA—EVIDENCE OF OBLIQUE RIFTING

Shipwreck Trough, east-central Otway Basin, evolved through Early Cretaceous to Santonian extension, followed by Campanian–Paleocene and Miocene to Recent pulses of compression.Onshore to offshore correlation of seismic sequences combined with 3D seismic mapping reveals that the Minerva anticline is located above an Early Cretaceous, northeast trending, basement-involved, graben. The graben-forming, northeast and north–south trending faults became largely inactive prior to the end of the Early Cretaceous. During the Turonian to Santonian, the northeast trending Point Ronald anticline and newly formed east–west trending normal faults controlled sediment distribution. The structural style changed in the Campanian as the northeast trending Minerva anticline began to form with a coeval, northwest-trending, axial-perpendicular fault array located along the crest of the fold. The location and orientation of this fault set is consistent with a compressional mechanism for fold growth. Similar compressional folding events during the Miocene–Recent modified and tightened the fold. Isopach maps show that during the Campanian to Maastrichtian, sediment thinned onto the nascent Minerva anticline, but accommodation rate outpaced structural growth, preserving a continuous sedimentary sequence.The timing of compressional fold growth is enigmatic. Campanian–Maastrichtian compression at the Minerva anticline was synchronous with over 10 km of extension accommodated by the Tartwaup–Mussel hingeline, 50 km to the south. Although the compression may be far-field effects associated with Tasman Basin sea floor spreading, we speculate that the Minerva anticline grew by transpression within a larger left-lateral transtensional Shipwreck Trough.

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A systematic compilation and characterisation of many reports of neotectonic crustal deformation in Norway (both on local and regional scales) has identified two neotectonic faults in northern Norway. The Stuoragurra Fault is a large reverse fault in Finnmark County. The Nordmannvikdalen fault is a much smaller normal fault in Troms County. The Stuoragurra postglacial fault can be followed, in several discontinuous sections, for 80 km, in a NE–SW direction. The fault has up to 10 m of displacement. During 1998, two trenches were made across the fault. The hanging wall was seen to be thrust upwards over the footwall, with 7 m vertical displacement evident from displaced glacial contacts. The fault did not penetrate the overlying glacial materials, but rather folded them, forming a blind thrust. Large liquefaction and other deformation structures were found in the glaciofluvial sediments in both trenches. Veins of angular and subangular pebbles from the local bedrock penetrate more than 10 m laterally from the thrust plane and into the sediments in the footwall. It is thought that these veins were injected during the fault activity. The major deformation of the sediments has a décollement plane that continues laterally in the E/B horizon contact of the modern soil on top of the footwall. This may indicate that an initial pedogenesis had taken place before the fault activity occurred, however no macro plant fossils to support this were found in the possible buried soil. Deformational structures seen in the trench can be explained as a result of one major fault event. The Nordmannvikdalen postglacial fault is a NW–SE trending normal fault, dipping to the NE. The fault offsets till on the NW slope of Nordmannvikdalen. The escarpment varies in height from 0.5 to 1.5 m, with a trench often present between the hanging wall and the footwall. The fault locally splits into two subparallel branches, however this is probably only in the glacial overburden. Ground penetrating radar (GPR) profiles show two prominent bedrock reflectors, dipping approximately 40° to the NE. An upward extrapolation of the northernmost reflector through the overburden coincides with the position of the surface scarp. The bedrock is well exposed along a streamed parallel to the GPR profiles. Bedding and foliation cannot be responsible for the reflectors visible in the GPR profiles. Gravitational forces have been ruled out as the origin of the fault. Although both faults probably formed shortly after Weichselian deglaciation, there is evidence that isostatic uplift was not the only force acting. Quaternary tilting of Fennoscandia due to ridge push, or mantle convection, may also play a role in neotectonic activity in Norway.

Tectonic evolution and stress field of the Kymi-Aliveri basin, Evia island, Greece

Stress and strain analysis has been used to reconstruct the post-Oligocene geodynamics of the Kymi-Aliveri basin: The Kymi-Aliveri basin occupies the footwall of the Kymi-Thrust, which formed during the Middle Miocene as a large transpressional structure in the late orogenic stages of the Hellenides. Subsequently, in the Upper Miocene the shape of the basin was strongly modified by an orthogonal system of NE and NW trending normal faults as a result of post orogenic collapse. In the Pliocene and Pleistocene time the basin is a part of the back arc basin, which developed behind the Hellenic Arc. WNW trending normal faults and reactivated faults characterized this tectonic phase.

Neotectonic faulting in northern Norway; the Stuoragurra and Nordmannvikdalen postglacial faults

A systematic compilation and characterisation of many reports of neotectonic crustal deformation in Norway (both on local and regional scales) has identified two neotectonic faults in northern Norway. The Stuoragurra Fault is a large reverse fault in Finnmark County. The Nordmannvikdalen fault is a much smaller normal fault in Troms County. The Stuoragurra postglacial fault can be followed, in several discontinuous sections, for 80 km, in a NE–SW direction. The fault has up to 10 m of displacement. During 1998, two trenches were made across the fault. The hanging wall was seen to be thrust upwards over the footwall, with 7 m vertical displacement evident from displaced glacial contacts. The fault did not penetrate the overlying glacial materials, but rather folded them, forming a blind thrust. Large liquefaction and other deformation structures were found in the glaciofluvial sediments in both trenches. Veins of angular and subangular pebbles from the local bedrock penetrate more than 10 m laterally from the thrust plane and into the sediments in the footwall. It is thought that these veins were injected during the fault activity. The major deformation of the sediments has a décollement plane that continues laterally in the E/B horizon contact of the modern soil on top of the footwall. This may indicate that an initial pedogenesis had taken place before the fault activity occurred, however no macro plant fossils to support this were found in the possible buried soil. Deformational structures seen in the trench can be explained as a result of one major fault event. The Nordmannvikdalen postglacial fault is a NW–SE trending normal fault, dipping to the NE. The fault offsets till on the NW slope of Nordmannvikdalen. The escarpment varies in height from 0.5 to 1.5 m, with a trench often present between the hanging wall and the footwall. The fault locally splits into two subparallel branches, however this is probably only in the glacial overburden. Ground penetrating radar (GPR) profiles show two prominent bedrock reflectors, dipping approximately 40° to the NE. An upward extrapolation of the northernmost reflector through the overburden coincides with the position of the surface scarp. The bedrock is well exposed along a streamed parallel to the GPR profiles. Bedding and foliation cannot be responsible for the reflectors visible in the GPR profiles. Gravitational forces have been ruled out as the origin of the fault. Although both faults probably formed shortly after Weichselian deglaciation, there is evidence that isostatic uplift was not the only force acting. Quaternary tilting of Fennoscandia due to ridge push, or mantle convection, may also play a role in neotectonic activity in Norway.

When Did the Western Anatolian Grabens Begin to Develop?

Abstract To solve a long-lasting controversy on the timing and mechanism of generation of the western Anatolian graben system, new data have been collected from a mapping project in western Anatolia, which reveal that initially north-south trending graben basins were formed under an east-west extensional regime during Early Miocene times. The extensional openings associated with approximately north-south trending oblique slip faults provided access for calc-alkaline, hybrid magmas to reach the surface. A north-south extensional regime began during Late Miocene time. During this period a major breakaway fault was formed. Part of the lower plate was uplifted and cropped out later in the Bozdağ, Horst, and above the upper plate approximately north-south trending cross-grabens were developed. Along these fault systems, alkaline basalt lavas were extruded. The north-south extension was interrupted at the end of Late Miocene or Early Pliocene times, as evidenced by a regional horizontal erosional surface which developed across Neogene rocks, including Upper Miocene-Lower Pliocene strata. This erosion nearly obliterated the previously formed topographic irregularities, including the Bozdağ elevation. Later, the erosional surface was disrupted and the structures which controlled development of the Lower-Upper Miocene rocks were cut by approximately east-west trending normal faults formed by rejuvenated north-south extension. This has led to development of the present-day east-west trending grabens during Plio-Quaternary time.

Kinematics of basin development during the transition from terrane accretion to strike‐slip tectonics. Late Cretaceous‐early Tertiary Cantwell Formation, south central Alaska

The Cantwell basin was formed during Late Cretaceous time in the suture zone between the Wrangellia composite terrane and the former continental margin of southern Alaska. The Late Cretaceous (∼80–70 Ma) lower Cantwell Formation represents the initial fill of this basin and includes ∼4000 m of sedimentary rock. Between Maastrichtian and late Paleocene time (∼70–60 Ma), rocks of the lower Cantwell Formation were deformed by nearly eastwest trending folds and north vergent thrust faults. This deformation can be linked to the northward accretion and suturing of the Wrangellia composite terrane to southern Alaska. During late Paleocene to early Eocene time (∼60–55.5 Ma), at least 2750 m of volcanic rocks of the upper Cantwell Formation were deposited above the folded lower Cantwell Formation. New40Ar/39Ar ages for the upper Cantwell Formation range from 59.8+/−0.2 to 55.5+/−0.2 Ma and reveal that the unconformity between the lower and upper Cantwell Formations represents a 10–20 million year hiatus. Following volcanism the Cantwell Formation was crosscut by northeast trending folds, northwest trending normal faults, north trending left‐lateral slip faults, northeast trending reverse faults, and east trending right‐lateral slip faults. These structures are consistent with northwest‐southeast compression in a zone of right‐lateral simple shear along a fault with the same trend (east‐northeast) as that of the present McKinley strand of the Denali fault system. Cantwell basin kinematics are compatible with an escape tectonics model for south central Alaska whereby the Cantwell basin was formed, folded, and partially uplifted during northward terrane accretion and suturing and was deformed again during the westward transfer of terranes along right‐lateral strike‐slip fault systems.

Surface Geology of Jebel Rawdah, Oman Mountains

ABSTRACT Jebel Rawdah is a west-northwest to east-southeast trending, post-obduction fold located at the western edge of the Hatta Zone of the Northern Oman Mountains. The main syncline plunges about 5 kilometers to the northwest and it is flanked to the west by a minor anticline. The outcrops in the area consist of: (1) allochthonous Semail Ophiolite, consisting of slices of oceanic crust and upper mantle, together with the Haybi Complex of volcanic rocks and associated metamorphics; (2) the parautochthonous Sumeini Group consisting of shelf edge and slope carbonates and clastics; and (3) the post-obduction neoautochthonous clastics and carbonates of the Qahlah, Simsima and Muthaymimah formations (Maastrichtian to Early Tertiary). Two stages of folding were detected in the Jebel Rawdah area. The older folds affect the allochthonous rocks and result from shearing deformation along the westward extension of the Hatta Zone. The younger deformation is manifested in drape folds in the neoautochthonous rocks which was caused by differential vertical movements of fault blocks in the underlying allochthonous rocks. Three sets of faults were observed: (1) northwest-southeast trending vertical to steeply-dipping scissor faults; (b) reverse faults which form flower structures; and (c) northeast-southwest trending normal faults. Field observations, biostratigraphic studies and petrographic examination suggest three stages in the development of the stratigraphic units in Jebel Rawdah. The first stage occurred during the Early Maastrichtian when the Oman Mountains emerged and were subsequently exposed to subaerial erosion. In the second stage a transgression occurred during the gradual subsidence of the area which led to the deposition of the Qahlah Formation in a fluviatile to shallow-marine environment, and the overlying Simsima in a shallow shelf setting. In the final Tertiary stage the Muthaymimah Formation was deposited in a subsiding basin and slope setting.

Tertiary tectonics of the Sea of Okhotsk, Russia: Far‐field effects of the India‐Eurasia collision

A new structural map of the western Sea of Okhotsk, based on grids of multichannel seismic data, provides several new insights into the Tertiary deformation of Asia, especially in regard to the extension of “extrusion” tectonics, linked to the India‐Eurasia collision, into northeastern Asia. The sedimentary basins in this offshore region are the result of two regional shear systems. In the west, the north trending Sakhalin‐Hokkaido dextral fault system transects Sakhalin Island. Accessory structures closely related to its dextral shear include northeast trending normal faults as well as northwest trending en echelon folds and thrusts. The accessory normal faults are predominantly Eocene to lower Miocene and indicate transtensional shear, whereas the folds and thrusts are mostly younger and indicate late Miocene and Pliocene transpression. In the north, an east‐west trending sinistral shear zone enters the sea at its northwest corner; this sinistral shear system links farther west to extensional faults of the early Tertiary Baikal rift. Extending northeastward from the terminus of this sinistral shear zone are a series of long, predominantly northwest dipping listric normal faults that form a large “lazy‐S” shaped pull‐apart basin, the Shantar‐Liziansky basin (SLB). Normal faults in this 500 × 140 km basin accommodate 15 to 20% extension. Extension and related sinistral shear appear to be largely Eocene to Oligocene in age, with lesser later activity. To the northeast of SLB, a further extension of the sinistral shear zone appears to bend northeastward, transecting Pustorets and Penzhina basins and following the course of the older, Mesozoic Mongol‐Okhotsk‐Chukotsk active margin and suture; it possibly reaches as far as the Arctic. As suggested by previous workers, the Baikal rift and its associated sinistral shear zone may be interpreted as by‐products of the India‐Eurasia collision in Eocene time; mapping results included here show that this diffuse sinistral shear system extends much farther to the northeast. The sinistral shear zone is transected by the dextral Sakhalin‐Hokkaido fault zone in the Kashevarov region of central SLB, where a fan of north to northwest striking late Tertiary transpressional fault splays marks the northern termination of the dextral fault zone. Older SLB normal faults are locally deformed, and half grabens are partly inverted, by the slightly younger dextral splays. The two regional fault systems are essentially conjugate, and the pattern of intersection closely resembles that predicted by recent modelling studies of India/Eurasia collision tectonics.

Rift-related Devonian sedimentation and basin development in South China

During Devonian times South China lay to the north of the Palaeo-Tethyan ocean, the boundary being a passive continental margin. A shallow sea covered the southern parts of the continent while northern areas, forming the Huanan Landmass, were emergent. At the beginning of the Devonian most of South China was above sea level. Subsequent transgression from the south gave rise to an irregular coastline with the development of many fault-controlled gulfs. Further transgression led to the development of an epicontinental sea with reefs forming along the margins of the submerged gulfs and black shales deposited within them. By Emsian time a widespread carbonate platform was established, while anoxic deposition continued in the troughs. The marine transgression peaked in the Frasnian Stage. During Famennian time widespread regression occurred and much of South China became once more emergent. Peneplanation of the Huanan Landmass led to the partial infilling of many of the older fault-bounded depressions. Throughout the Devonian the local distribution of sediments was strongly controlled by NE-SW trending transtensional faults that bounded NW-SE trending normal faults. These structures continued to influence sedimentation in the Late Palaeozoic, the Mesozoic and possibly the Tertiary in the offshore Beibu Gulf Basin.

Tectonic Ancestry of Central Montana and Its Influence on Inversion Tectonics: ABSTRACT

Inversion tectonics, where structurally low areas become structurally high, has profound implications for hydrocarbon exploration. Effective exploration depends on understanding structures, timing, and controls on tectonic inversion. In central Montana tectonic inversion occurred three times in Phanerozoic time and reflects Precambrian tectonic trends. Westerly striking, steep foliation in Archean crystalline rocks defines the tectonic grain in basement exposures. The Helena embayment of the Middle Proterozoic Belt Basin formed an east-trending aulacogen extending into the craton in central Montana. Westerly trending fault-blocks of probable Late Proterozoic age formed within the embayment. The trough was tectonically inverted in the Devonian, but was depressed in the Carboniferous, accumulating major thicknesses of Madison Group and Big Snowy Group strata. Tectonic inversion again occurred with rise of the {open_quotes}Belt island{close_quotes} in the Jurassic. The trough was reactivated with a thick accumulation of lower Lower Cretaceous strata. Laramide (Late Cretaceous-early Tertiary) deformation resulted in tectonic inversion with rise of the Little Belt, Big Snowy, and related uplifts. Reactivation with reverse and strike-slip movement occurred on synsedimentary Proterozoic westerly trending normal faults that bounded the Helena embayment. Subsidence was probably related to crustal extension, whereas tectonic inversion and rise is inferred to be caused by crustal shortening.more » West-northwesterly trending en echelon folds that cross central Montana suggest major left shift. The Precambrian structural framework and fabric of the region thus appear to have had major influence on tectonic features that were multiply reactivated in Phanerozoic time.« less

Oblique rifting in Salina, Lipari and Vulcano islands (Aeolian islands, southern Italy)

ABSTRACTA structural analysis carried out on the volcanic products of the islands of Salina, Lipari and Vulcano (Aeolian archipelago) points out that the large‐scale tectonic setting is dominated by NW‐SE trending right‐lateral extensional strike‐slip faults and by N‐S to NE‐SW trending normal faults and fractures. This fault pattern generates pull‐apart type structures, developing between different right‐hand overlapping fault segments and a characteristic extensional imbricate fan geometry at the tip of the major strike‐slip faults. All the structures, representing the surface expression of an active crustal discontinuity which controls the evolutionary history of the magmatism of the three islands, are kinematically compatible with a N100°E extension related to a rifting process affecting southern Italy.

Plio-pleistocene fault movement as evidence for mega-block kinematics within the Hyblean—Malta Plateau, Central Mediterranean

This paper examines the structural kinematics from the late Miocene to recent across the Hyblean—Malta Platform. Seismic data show that the E—W trending North Gozo Graben formed by right-lateral transtension during the Upper Pliocene. Structural mapping on the top of the Miocene in the western half of the Malta Platform shows both compressional and extensional features. The compressional features are generally right-stepping, with en echelon ridges and positive flower structures, all of which support a zone of dextral strike-slip fault movement north of the island of Gozo. This recent episode of transtension has reactivated the older ENE-WSW and NW-SE trending normal faults to create a series of small pull-apart grabens near the islands of Gozo and Malta. By mapping the orientation of these regional faults and timing their relative movement, we have developed a schematic fault block model that attempts to provide a tectonic framework for the Hyblean—Malta Plateau.

Fault‐generated mountain fronts in the central apennines (Central Italy): Geomorphological features and seismotectonic implications

AbstractThe morphotectonic framework of the Central Apennines is given by faulted blocks bounded by normal faults, mostly trending NW–SE, NNW–SSE and NE–SW, which cut previous compressive structures. Such a structural setting is consistent with the focal mechanisms of the earthquakes which often occur in this area.In this paper, three lithologically different normal fault‐generated mountain fronts are analysed in order to assess the relations between their geomorphic features and active tectonics. They border the Norcia depression (Sibillini Mts, Umbria), the Amatrice–Campotosto plateau (Laga Mts, Lazio) and the Fucino basin (Marsica Mts, Abruzzi).The Norcia depression is bounded by a N20°W trending normal fault to the east and by a parallel antithetic fault to the west. The main fault has a 1000 m throw and gives rise to a wide fault escarpment, characterized by: (1) sharp slope breaks due to low angle gravity faults; (2) important paleolandslides; and (3) several fault scarplets on the piedmont belt affecting Quaternary deposits.The Amatrice–Campotosto plateau is delimited by the western slope of Mt Gorzano which runs along a N20°W trending normal fault having a 1500m throw. Minor parallel faults dislocate Quaternary landforms. Large‐scale massmovements also occur here.The Fucino basin was struck by the 1915 Avezzano earthquake (I=XI MCS) which produced extensive surface faulting along two parallel NW trending normal fault escarpments on the eastern border of the basin. There is paleoseismic evidence including buried gravity graben in Late Glacial gravels and tectonic dip‐slip striations on Holocene calcitic crusts covering bedrock normal fault planes.These data suggest that active extensional tectonics plays a major role in the slope morphogenesis of the Central Apennines and they indicate the importance of geomorphic analysis in seismic zonation of this area.