Breakaway Fault Research Articles

Torn Between Two Plates: Exhumation of the Cer Massif (Internal Dinarides) as a Far‐Field Effect of Carpathian Slab Rollback Inferred From 40Ar/39Ar Dating and Cross Section Balancing

AbstractExtension across the southern Pannonian Basin and the internal Dinarides is characterized by Oligo‐Miocene metamorphic core complexes (MCCs) exhumed along mylonitic low‐angle extensional shear zones. Cer MCC at the transition between Dinarides and Pannonian Basin occupies a structural position within the distal‐most Adriatic thrust sheet and originates from two different tectonic processes: Late Cretaceous‐Paleogene nappe‐stacking during a continent‐continent collision with Adria in a lower plate position, and exhumation related to Miocene extension driven by the Carpathian slab‐rollback. Structural data and a balanced cross section across the Cer massif show linking of the exhuming shear zone to a breakaway fault, which reactivated the early Late Cretaceous most internal nappe contact. Paleozoic greenschist‐to amphibolite‐grade lithologies surround a polyphase intrusion composed of I‐ and S‐type granites and were exhumed along a shear zone characterized by top‐N transport. Thermobarometric analyses indicate an intrusion depth of 7–8 km of the Oligocene I‐type granite; cooling below ∼500°C occurred at 25.4 ± 0.6 Ma (1σ) yielded by 40Ar/39Ar dating of hornblende. Biotite and white mica from this intrusion as well as from the mylonitic shear zone yield 40Ar/39Ar cooling ages of 17–18 Ma independent of the used techniques (in situ laser ablation, single‐grain total fusion, single‐grain step heating, and multi‐grain step heating). White mica from the S‐type granite yield an 40Ar/39Ar cooling age of 16.7 ± 0.1 Ma (1σ). Associated dikes intruding the shear zone were also affected by N‐S extension resulting in the exhumation of the MCC, which was triggered by the opening of the Pannonian back‐arc basin in response to the Carpathian slab‐rollback.

Crustal architecture and rift tectonics across the Visakhapatnam Bay basin, central-east Indian margin: Insights from multichannel seismic and potential field data

The Visakhapatnam Bay (VB) basin is a passive margin rift basin located at the non-basinal segment of the Eastern Continental Margin of India (ECMI) and formed during the rift–drift events associated with the breakup of eastern Gondwanaland. In the present study, integrated analysis of potential field and multi-channel seismic reflection (MCS) data were carried out to understand the rift tectonics, crustal configuration and onshore–offshore structural continuity across this basin. The study revealed the following: (i) crustal models derived through joint gravity-magnetic modelling show limited stretching with 36–40 thick crust below the Eastern Ghat Mobile Belt (EGMB) thinning down to 16–20 km at the Ocean Continent Transition (OCT), (ii) extension of Charnockitic basement associated with the Eastern Ghat Mobile Belt (EGMB) into the offshore region. Comparison of the crustal configuration across the VB basin with that across the adjacent thick sedimentary area of the Krishna–Godavari shows that upper crustal configuration is significantly different in the VB area. The observed limited rift related structuration (horst-graben morphology), the mapped high angle break-away fault with large offset in the seismic data and narrow width (70–90 km) of extended crustal domain in VB basin suggests that this segment acts as transfer zone between Krishna–Godavari and Mahanadi rift zones. Further, long curve-linear trend of magnetic anomalies associated with Pudimadaka Lineament (PKL) demarcate the VB basin from the adjacent Krishna–Godavari rift zone.

SYN-SEDIMENTARY TECTONIC MARKINGS IN THE OLIGOCENE DATÇA-KALE-ACI GÖL BASIN, WESTERN ANATOLIA

In southwest Turkey, the Oligocene sedimentary sequence is located on the Datca-Kale-Aci Gol basin between the Menderes Massif and Lycian nappes. To understand the nature of this basin is important for tectonic models that explain the exhumation of the Menderes massif. In the northeast extension of this basin, the sedimentary sequence is interpreted as alluvial fan, fan-delta, beach, marine input, inner shelf carbonates and offshore deposits. The Oligocene Datca-Kale main breakaway fault bounding the south eastern margin of the basin is represented by Inceler and Aci Gol faults in the study area. The wedge geometry of the sequence thickening towards the Inceler normal fault is an evidence of syn-tectonic deposition. The northwest margin of the basin is controlled by two en-echelon faults. The sedimentary sequence has a wedge geometry thickening towards the normal fault and at the same time its upper layers overlap the fault. As a result, the northeast extension of the Datca-Kale-Aci Gol Oligocene basin is an elongated fjord like depositional area containing the shallow marine environments controlled by normal faults located in its southeast and northwest margins. It was demonstrated that the southeast basin margin limited by the Datca- Kale main breakaway fault performed dominant tectonic control. The similar kinematic indicators that is used for the model explaining the exhumation of the Menderes massif by the upward bending of Datca-Kale main breakaway fault are also observed in the northwest of the basin as top to the north-northeast.

The discovery of a low-angle normal fault in the Taurus Mountains: the İvriz detachment and implications concerning the Cenozoic geology of southern Turkey*

The Ivriz detachment fault has been determined on the southern border of the Ulukisla basin separating the metamorphic Bolkar Group of the Taurus Mountains and the Paleocene-Lower Eocene Halkapinar formation of basin deposits. The fault dips towards the north and has kinematic indicators (asymmetric grain/grain aggregate porphyroclasts, oblique foliation, and S-C fabrics), suggesting a top-to-the-N-NE sense of shearing. The clastic material originating from the Bolkar Group in the sedimentary units of the Ulukisla basin demonstrates that the detachment fault could have been be active during Latest Cretaceous-Eocene times. The Ivriz detachment may have initiated as part of a high-angle breakaway fault (the Aydos main breakaway fault) in the south of the Ulukisla basin. The breakaway fault then rotated to a low-angle normal fault and its northern continuation played an important role in the exhumation of the Central Anatolian Crystalline Complex. This implies that the Upper Cretaceous-Eocene sedimentary basins in central Anatolia were supradetachment basins rather than collision- or arc-related basins as previously suggested.

LATE CENOZOIC EXTENSIONAL TECTONICS IN WESTERN ANATOLIA: EXHUMATION OF THE MENDERES CORE COMPLEX AND FORMATION OF RELATED BASINS

The Aegean region (Western Anatolia, Aegean Sea and Greece) is one of the areas of the earth under the effect of extensional tectonics and includes the typical features of core complexes in this type of region. The Menderes Massif in Western Anatolia was exhumed initially as an asymmetric core complex in the Early Miocene due to extension beginning in the Oligocene and then the central Menderes Massif was further exhumed as a symmetric core complex. This article discusses the exhumation mechanisms of the Menderes Massif and development of surrounding sedimentary basins in light of new findings. The proposed model successfully explains, the location of the Oligocene Kale basin, different movement directions of the Lycian nappes in northern and southern parts of the Datca-Kale Main Breakaway Fault and the top-to- the NNE directed shearing dominantly observed in the whole Menderes Massif.

Testing the Bannock detachment breakaway: Negative results support moderate- to high-angle splay system and domino-style fault block rotation along the Valley fault, southern Portneuf Range, southeastern Idaho, U.S.A.

New geologic mapping, kinematic analysis, and tephrochronologic age correlations were completed in the southern Portneuf Range of southeast Idaho to characterize the Valley fault, a large-offset normal fault interpreted as the breakaway for the regionally extensive Bannock detachment system. The Valley fault separates ∼11.8–7.57 Ma Salt Lake Formation from underlying Neoproterozoic to Cambrian Brigham Group and Cambrian rocks. Three-point problems indicate that the Valley fault strikes north–northwest (NNW) and dips an average of 9° west–southwest (WSW), in stark contrast to previous work, which interpreted the fault as steeply west-dipping. Footwall strata strike NNW and dip 37 ± 11° east–northeast (ENE). Measured bedding-to-fault cutoff angles are, therefore, ∼46 ± 11°. Hanging-wall strata strike NNW and dip 20 ± 5° ENE adjacent to the fault and steepen progressively down -section to ∼70 ± 10° ENE due to the Valley fault's minor listricity and multiple hanging-wall splays. Beneath the Miocene strata, Cambrian hanging-wall bedrock strike NNW and dip 55 ± 10° ENE. Adding a 9° Valley fault dip to these bedding dips yields cutoff angles of 29° to 80° for Miocene strata and 64° for hanging-wall bedrock. Top-to-the-west, dip-slip offset across the Valley fault and its hanging-wall splays—using the Miocene unconformity as a marker—is 13.7 ± 1 km. The older, subhorizontal Mine Hollow fault has 1,000 ± 300 m top-to-the-west normal offset. The initial dip of the Valley fault is interpreted to have been steeper than its present 9° dip. If footwall strata were subhorizontal prior to extension, as indicated by reconstruction of the Miocene unconformity, then the Valley fault had an initial dip of 46 ± 11° WSW based on measured bedding-to-fault angles. Combined with the modern low dip of the Valley fault, these data are interpreted to indicate that the Salt Lake Formation accumulated as growth strata adjacent to the active Valley fault, while the fault as well as footwall and hanging-wall strata tilted northeast through time. The Valley fault's mildly listric shape, the progressive domino-style tilting, and the large amount of total slip suggest that the Valley fault is a Basin-Range normal fault rather than a low-angle breakaway fault for the Bannock detachment system. The preferred model for extension in the region is ∼7 km of uplift and exhumation during two phases of moderate- to high-angle domino-style fault block rotation. First, the Valley fault splays and Mine Hollow fault accommodated 5 km of extension between 11.8 to 9.16 Ma; then the Valley fault accommodated 10 km offset between 9.16 to <7.57 Ma (likely as recent as 5–4 Ma). Our regional cross section and restoration suggest that both the Clifton fault to the west (Bannock detachment) and the Valley fault are two separate faults, each with 13–15 km offset. Reconstruction of these Miocene faults shows that the Mesozoic Paris thrust fault has a preextensional footwall flat length of 30 km, similar to that predicted by other workers.

Constraints on the Emplacement Age of the Heart Mountain Slide, Northwestern Wyoming

The Heart Mountain slide is the largest terrestrial landslide deposit as yet recognized on Earth. The slide covers an area of at least 3400 km2, and the upper-plate rocks include 2–4 km of Paleozoic carbonate and Eocene volcanic rocks thrust out over 45 km of Eocene landscape. The precise age and duration of sliding is critical to emplacement models as well the slide’s effect on regional Eocene river systems. To address the timing issues, we sampled zircons from the basal fluidized layer 2 km from the slide’s breakaway fault (Silver Gate, MT) and 40-km downslope, nearer the slide’s toe (White Mountain, WY). Within this basal layer, we have identified mineral content and features consistent with a partially solidified magma. We interpret these observations to be consistent with the slide catastrophically dismembering an active magma body that mixed with the basal fault layer. The results yield remarkably similar U/Pb zircon crystallization ages at the proximal and distal locations: 48.78 ± 0.51 Ma at Silver Gate (n = 48) and 48.88 ± 0.22 Ma at White Mountain (n = 22). These zircon ages from the basal layer are tightly bracketed using various radiometric ages of Eocene Absaroka volcanic units involved in the movement phase of the slide and those deposited after emplacement, including detrital U/Pb zircon ages from the dissected Crandall Conglomerate river system. Our interpretation of the data is that the slide was catastrophically emplaced at 48.87 ± 0.20 Ma.

Quantifying crustal extension and shortening in the back‐arc region of Northeast Japan

The Northeast Japan (NEJ) arc has experienced strong extension in the early to middle Miocene time and contractive deformation since Pliocene time. We determine the amounts of the Miocene extension and Pliocene contraction along four transects across the NEJ arc by area‐balancing restoration using seismic reflection, gravity, and surface geologic data. We find that the Miocene extension is as much as 31–56 km while the Pliocene‐Quaternary contraction is only 10–15 km. The style of the Miocene extension in the back‐arc region of NEJ is highly asymmetric; the zone of concentrated extension is characterized by a breakaway fault on the west, a rollover basement anticline on the east, and abnormally deep (∼10 km) basins and strongly rotated fault blocks in between, suggesting the existence of a large‐scale detachment fault at a mid‐crustal level beneath the extended zone. We reveal that the Pliocene‐Quaternary contractive surface deformation in the back‐arc region of NEJ resulted principally from positive tectonic inversion of the underlying detachment fault. Previous works have suggested that Andean‐type orogens have often experienced negative and positive inversions alternately in their back‐arc regions. Although the former has been well documented, for example, for the Cenozoic North American Cordillera, the latter has rarely been reported because subsequent contraction has obscured the older structures. Since the NEJ arc is still at an incipient stage and hence its older structures are well preserved, our study provides an important example of positive tectonic inversion of Andean‐type orogens.

Plio-Quaternary development of the Baklan–Dinar graben: implications for cross-graben formation in SW Turkey

Western Turkey is characterized mainly by E–W, NW–SE, and NE–SW-trending grabens. The reverse V-shaped geometry of the Baklan–Dinar graben is formed by coupling of the NE–SW-trending Baklan and the NW–SE-trending Dinar grabens, and is critical to an understanding of the structural evolution of the Aegean region. Its geometry indicates biaxial extension in the region, as proposed in the current literature (e.g. Temiz et al. 1997; Cihan et al. 2003). The Acıgöl and Burdur grabens parallel the axis of the Baklan graben in the south, and these three basins terminate against the Dinar fault. The Baklan Basin is bounded along both margins by the Baklan and Çal left-lateral oblique faults. Basin-fill deposits of the Baklan Basin thicken towards the Dinar fault, and the basin floor dips northeastward. In addition, geomorphological characteristics of the Baklan–Dinar graben indicate that the Dinar fault is relatively more active than the faults of the Baklan Basin. All available morphologic, structural, borehole, and geophysical data from the Baklan–Dinar graben define a cross-graben structure that developed during Plio-Quaternary uniaxial NE-directed extension in SW Turkey. In this framework, the Dinar fault plays the role of a breakaway fault of this formation. The increase in the normal components of the northwestern left-lateral oblique basin-bounding faults of the Baklan Basin is explained by the gradual steepening of the pitch of the slip vectors towards the northeast, because of capturing of the extension by the Dinar breakaway fault.

Cenozoic crustal extension in southeastern Arizona and implications for models of core-complex development

In conventional models of Cordilleran-style metamorphic core-complex development, initial extension occurs along a breakaway fault, which subsequently is deformed into a synform and abandoned in response to isostatic rebound and new faults breaking forward in the dominant transport direction. The Catalina core complex and associated geology in southeastern Arizona have been pointed to as a type example of this model. From southwest to northeast, the region is characterized by the NW–SE trending Tucson basin, the Catalina core complex, the San Pedro trough and the Galiuro Mountains. The Catalina core complex is bounded by the top-to-the-southwest Catalina detachment fault along its southwestern flank and the low-angle, northeast-dipping San Pedro fault along its northeastern flank. The Galiuro Mountains expose non-mylonitic rocks and are separated from the San Pedro trough to the southwest by a system of low- to moderate-angle southwest-dipping normal faults. This Galiuro fault system is widely interpreted to be the breakaway zone for the Catalina core complex. It is inferred to be folded into a synform beneath the San Pedro trough, to resurface to the southwest as the San Pedro fault, and to have been abandoned during slip along the younger Catalina detachment. This study aimed to test this model through analysis of field relations and geochronological age constraints, and reprocessing and interpretation of 2-D seismic reflection data from the Catalina core complex and San Pedro trough. In contrast to predictions of the conventional breakaway zone model, we raise the possibility of a moderate-angle, southwest-dipping detachment fault beneath the San Pedro trough that could extend to mid-crustal depths beneath the eastern flank of the Catalina Mountains. We present an alternative kinematic model in which extension was accommodated by a pair of top-to-the-southwest normal-fault systems (the Catalina and Galiuro detachment faults), with the only major difference between the two being the magnitude of displacement, which was greater for the Catalina detachment.

Neogene brittle detachment faulting on Kos (E Greece): implications for a southern break-away fault of the Menderes metamorphic core complex (western Turkey)

Abstract The southern limit of the Menderes metamorphic core complex has recently been proposed to be formed by an Oligocene–early Miocene top-to-the-north breakaway detachment fault, the Datça–Kahle fault running across the Lycian nappes in southwestern Turkey. Proving a breakaway detachment fault as opposed to a ‘simple’ local high-angle normal fault is generally hampered by absence of a metamorphic contrast between hanging wall and footwall. The island of Kos lies close to the inferred southern breakaway fault. It exposes Permo- Carboniferous anchimetamorphic rocks, intruded and contact-metamorphosed at upper crustal levels by a 12 Ma old monzonite during or close to peak-burial conditions. Here, we show that exhumation of these rocks occurred along a top-to-the-north brittle extensional detachment fault underneath upper Mesozoic and Palaeogene non-metamorphic carbonates after 12 Ma, and that any (undocumented) earlier extension did not lead to significant exhumation of the Permo-Carboniferous rocks. Kos should thus be placed within the Cyclades–Menderes extensional province since 12 Ma. The age of exhumation is younger than the proposed activity of the breakaway fault, the existence of which we cannot corroborate. We conclude that the brittle detachment of Kos cannot be straightforwardly correlated to any ductile-to-brittle detachments of the Menderes or eastern Cycladic metamorphic core complexes further to the north and may represent a relatively isolated structure.

From palaeotectonics to neotectonics in the Neotethys realm: The importance of kinematic decoupling and inherited structural grain in SW Anatolia (Turkey)

In order to asses young, i.e. “neotectonic” fault kinematics and the relation with plate-tectonic processes in SW Turkey we focused on the questions: 1) what produced the structural grain, i.e. how and when are faults generated, 2) what was/is the kinematic behaviour of these faults and 3) during which period(s) were these faults active? Firstly, the distribution of faults has been investigated using a lineament analysis performed on satellite imagery and digital elevation models. We define five main tectonic domains in SW Turkey: 1 and 2) the Northern and Southern Western Anatolian extensional provinces; 3) the eastern Hellenic arc (including Rhodes Island and the submarine Anaximander mountains); 4) The Lycian Taurides and 5) the western limb of the Isparta Angle. Lineament analysis reveals dominance of three lineament groups, i.e. NNE-, ENE-, and WNW-trending, in all identified domains. Variations in the relative importance of lineament groups exist and are attributed to the specific tectonic evolution of each domain. A synthesis of recently published field data shows that the onset of activity of related fault groups is neither synchronous, nor uniform. The “structural grain” for the neotectonic deformation in SW Turkey is formed during the last stage of palaeotectonic deformation (stage 1), which is dominated by the onset of the Menderes Massif exhumation along a top-N major detachment, the Datça break-away fault [Seyitoğlu, G., Işık, V., and Çemen, İ., 2004. Complete Tertiary exhumation history of the Menderes massif, western Turkey: an alternative working hypothesis. Terra Nova, 16, 358–364.], and related SE-ward sliding of the Lycian Nappes in the footwall of this fault. This stage is characterized by spatially variable types of deformation that are delineated by, from NW to SE, the Datça Fault around the Menderes–Lycian contact zone and the Lycian frontal thrust zone, respectively. The kinematic decoupling along these structures explains the co-existence of top-N detachment type extension in the Western Anatolian Extensional province and ongoing nappe emplacement and piggy-back development in the Lycian Taurides. The decoupling also explains the lateral complexity of deformation associated with later neotectonic deformation. From late Miocene onward, stage 2 NNE–SSW extension dominated the Western Anatolian Extensional province, influenced by combined Anatolian extrusion and Hellenic subduction roll-back. Contemporaneously, bidirectional ESE–WNW and NNE–SSW extension controls the Lycian Taurides due to the effects of Hellenic arc expansion superposed on extrusion-roll-back extension. The zone of kinematic decoupling is characterized by structural complexity, with local transpressional features. During stage 3 (post-Late Pliocene), the same types of extension prevail in the Western Anatolian Extensional province and the Lycian Taurides, although a third tectonic regime becomes gradually more important. This regime is associated with a tectonic escape in the Hellenic arc that induced forearc slivers to be sheared of the expanding arc along (mostly) sinistrally displacing ENE-trending strike-slip zones. Several of these zones have been identified in the coastal zones of SW Turkey, either through recent seismicity or field observations and are especially focused in the Lycian Taurides domain. Here, they form what is classically referred to as the Fethiye–Burdur Fault Zone, which becomes gradually penetrated from the SW by oblique- or strike-slip zones, exemplifying the time-transgressive nature of the tectonic escape mechanism. Zones of kinematic decoupling remain persistent throughout the entire Early Miocene–Recent tectonic evolution of SW Turkey and explain the existence of differently deforming tectonic domains.

Evolution and Strain Reorganization within Late Neogene Structural Stepovers Linking the Central Walker Lane and Northern Eastern California Shear Zone, Western Great Basin

Late Neogene deformation between the eastern Sierra Nevada and the central Basin and Range province is localized within a boundary zone that contains the Eastern California shear zone and Walker Lane, and has been characterized by dextral strike-slip to oblique-slip displacement on NNW- to northwest-trending fault systems. At the latitude of the central Sierra Nevada, structures in the northern Eastern California Shear Zone and central Walker Lane are misaligned and have been linked kinematically since the mid-Miocene by a system of extensional stepover structures. The stepovers are localized along an ancient crustal boundary and record a complex deformation history marked by a major reorganization of structural geometry and kinematics in the mid-Pliocene. Displacement transfer was initially taken up by the Silver Peak-Lone Mountain extensional complex that passed motion on the Furnace Creek fault system in the Eastern California shear zone ENE into a system of en echelon transcurrent faults of the central Walker Lane. The Miocene to Pliocene extensional complex was underlain by a northwest-dipping detachment that initiated at 12-8 Ma and continued activity into the early Pliocene. The extensional complex was bound on the west and east by northwest-trending transcurrent structures linked along the southern boundary by a northwest-dipping breakaway fault. To the north, an E-W-trending belt of extensional basins separated the extensional complex from structurally coherent tectonic blocks in the central Walker Lane. Paleomagnetic data from Cenozoic volcanic rocks and Mesozoic intrusions exposed in the upper plate of the extensional complex and sets of Miocene mafic dikes in the lower plate show uniform clockwise vertical-axis rotation of 20° to 30°. Localization of large-magnitude extension and vertical- axis rotation within the stepover formed during nonplane strain deformation characterized by vertical thinning and horizontal components of simple and pure shear operating along a northwest axis. This state of deformation persisted until the extensional complex was abandoned at about 3 Ma. In the late Pliocene, the stepover linking the Eastern California shear zone and central Walker Lane broadened and experienced kinematic reorganization with the onset of the contemporary deformation field. The active displacement transfer system, known as the Mina deflection, is underlain by an array of ENE faults with left-oblique slip that cross-cut and locally reactivated structures of the Silver Peak-Lone Mountain extensional complex. Geodetic velocities, earthquake focal mechanisms, and fault kinematic data reflect the transtensional deformation within the active boundary zone that accommodates northwestward displacement of the Sierra Nevada away from the central Great Basin. Strain is heterogeneously distributed and the eastern and western parts of the boundary zone have experienced wrench-dominated and extension-dominated transtension, respectively. The changes in geometry and kinematics of structural stepovers within the tectonic boundary zone between the Sierra Nevada and central Great Basin indicate that late Neogene deformation was not a steady-state process.

Complete Tertiary exhumation history of the Menderes massif, western Turkey: an alternative working hypothesis

AbstractThe main exhumation of the Menderes massif, western Turkey, occurred along an originally N‐dipping Datça–Kale main breakaway fault that controlled depositions in the Kale and the Gökova basins during the Oligocene – Early Miocene interval. The isostatically controlled upward bending of the main breakaway fault brings the lower plate rocks to the surface. In the Early Miocene, E–W‐trending N‐ and S‐dipping graben‐bounding faults fragmented the exhumed, dome‐shaped massif. The development of half grabens by rolling master fault hinges has allowed further exhumation of the central Menderes massif. After the Pliocene, high‐angle normal faults cut all of the previous structures. This model suggests that the Menderes massif is a single large metamorphic core complex that has experienced a two‐stage exhumation process.

Origin of NE-trending basins in western Turkey

The origin of NE-trending basins and their relation to the E–W-trending grabens in western Turkey have been the subject of long lasting debate. The stratigraphical and structural aspects of the basin fill in the E–W Gediz Graben and in the NE-trending Gördes, Demirci, Selendi and Uşak-Güre basins located immediately to the north of the graben are reassessed here. The Gediz Graben is characterized by two contrasting sedimentary packages that are separated by an angular unconformity. These are: (1) a folded Miocene-Lower Pliocene megasequence, exhumed on the shoulders of the graben; and (2) nearly horizontal Plio-Quaternary sediments. In contrast, the NE-trending basins comprise solely Lower–Middle Miocene sediments and unconformably overlying Quaternary alluvium. The Miocene configuration of different trending basins shows close similarities, and suggests that they started to develop simultaneously during the Early Miocene. Miocene sedimentation in these basins occurred in the hanging-wall of a presently low-angle, north-dipping, major normal fault (detachment fault) that bounds the Gediz Graben to the south, while the metamorphic rocks of the Menderes Massif in the footwall were progressively deformed, uplifted and exhumed. The Miocene sediments in the NE-trending basins were also deformed along broad folds with axes parallel to the basin margins. The extension was therefore partially complemented by a horizontal shortening at high-angle to it, and the basin-bounding faults together with the blocks they bound have rotated around vertical axes. In this scenario, the NE-basins started to develop as ”Aegean type cross-grabens”, and the bounding structures are interpreted as ”rotational accommodation faults” that accommodate differential stretching in the hanging-wall of the major breakaway fault, accompanying the Early Miocene phase of extension in western Turkey. Later, during the neotectonic extensional period commencing in the Pliocene (5 Ma), the margin-bounding high-angle normal faults of the modern E–W Gediz Graben cut and displaced the presently low-angle breakaway fault. Some parts of the NE-trending basins were therefore trapped within the E–W graben and some other parts remained as hanging basins on the footwall of the normal fault, along the northern margin of the Gediz Graben. It is concluded that the classification of basins for the area of the Gediz Graben and those located to its north as ”replacement and revolutionary” structures is still valid. It is also confirmed that the latest Oligocene–Early Miocene back-arc extension and/or orogenic collapse cannot be responsible for the entire history of continental extensional tectonics and the extension in western Turkey is not a continuous event, but occurred in two stages separated by a short period (7–5 Ma); the second being the Plio-Quaternary phase of N-S extension related to the westward escape of the Anatolian block.

Scandinavia's North Atlantic passive margin

The tectonics of the eastern passive margin of the North Atlantic are reexamined. The Scandinavian North Atlantic passive margin includes not only the offshore exploration and basin domain but also large portions of the onshore domains of the Scandinavian Caledonides. Combined information from structural geology, potential field data, regional geology, basin development, and geomorphology made it possible to propose a new definition of the passive margin. The rift shoulder is formed by linked faults defining the present rift flank. These faults are the extensional structures located furthest to the east onshore Norway/Sweden that can be linked to the rifting that led to the formation of the North Atlantic. This innermost boundary fault system (IBF) is formed by a set of normal west dipping crustal faults. It extends over a distance exceeding 2000 km from the North Sea, across the Caledonian mountain belt to the Barents Sea. The passive margin width, between the continent‐ocean boundary and the IBF, ranges from 550 km in the south to over 700 km in mid‐Norway to 165 km north of Lofoten. Rifting and faulting on the IBF started in Permo‐Carboniferous, and a succession of rift phases eventually culminated in continental breakup and the formation of the North Atlantic. Basin development between Permian and Cretaceous was toward the future breakaway fault, but faulting was also active on land from Mesozoic to Present. Onshore‐offshore crustal‐scale cross sections show the geometry of the passive margin, the dip orientation of the major faults and the changes in crustal thickness.

Early extension and associated mafic alkalic volcanism from the southern Basin and Range Province: Geology and petrology of the Rodeo and Nazas volcanic fields, Durango, México

Research Article| June 01, 2001 Early extension and associated mafic alkalic volcanism from the southern Basin and Range Province: Geology and petrology of the Rodeo and Nazas volcanic fields, Durango, México James F. Luhr; James F. Luhr 1Department of Mineral Sciences, NHB-119, Smithsonian Institution, Washington, DC 20560, USA Search for other works by this author on: GSW Google Scholar Christopher D. Henry; Christopher D. Henry 2Nevada Bureau of Mines and Geology, University of Nevada, Reno, Nevada 89557, USA Search for other works by this author on: GSW Google Scholar Todd B. Housh; Todd B. Housh 3Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA Search for other works by this author on: GSW Google Scholar J. Jorge Aranda-Gómez; J. Jorge Aranda-Gómez 4Unidad de Investigación en Ciencias de la Tierra, Instituto de Geología, Universidad Nacional Autonoma de México, Campus Juriquilla, A.P. 1-742, Querétaro, QRO 76001, Mexico Search for other works by this author on: GSW Google Scholar William C. McIntosh William C. McIntosh 5New Mexico Bureau of Mines and Mineral Resources, New Mexico Institute of Mining and Technology, P.O. Box 3398 Campus Station, Socorro, New Mexico 87801, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2001) 113 (6): 760–773. https://doi.org/10.1130/0016-7606(2001)113<0760:EEAAMA>2.0.CO;2 Article history received: 10 Aug 1999 rev-recd: 01 May 2000 accepted: 10 Jul 2000 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation James F. Luhr, Christopher D. Henry, Todd B. Housh, J. Jorge Aranda-Gómez, William C. McIntosh; Early extension and associated mafic alkalic volcanism from the southern Basin and Range Province: Geology and petrology of the Rodeo and Nazas volcanic fields, Durango, México. GSA Bulletin 2001;; 113 (6): 760–773. doi: https://doi.org/10.1130/0016-7606(2001)113<0760:EEAAMA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract East-northeast extension ca. 24 Ma at Rodeo and Nazas, México, was accompanied by eruption of hawaiites, marking some of the earliest intraplate-type mafic alkalic volcanism associated with development of the southern Basin and Range Province. An earlier extensional pulse, 32.3–30.6 Ma, concurrent with subduction- related rhyolitic volcanism of the Sierra Madre Occidental, is the earliest established extension in the southern Basin and Range Province. The Rodeo hawaiites are mostly along or just west of the north- northwest−striking, west-dipping Rodeo fault, a major breakaway fault that separates moderately extended terrane to the west from less extended terrane to the east. Hawaiites and interbedded conglomerates in the Rodeo half graben are flat lying to gently tilted and cut by the Rodeo fault. Underlying Eocene−Oligocene ash-flow tuffs to the west are cut by numerous west- dipping faults and tilted as much as 40°. Nazas hawaiites are also along north-northwest−striking faults but are generally unfaulted.Like other Miocene mafic alkalic volcanic rocks from the southern Basin and Range Province, those from Rodeo and Nazas are characterized by (1) moderately evolved hawaiitic compositions, (2) abundant megacrysts, including sodic plagioclase (An26–51), olivine (∼Fo55), Al-augite (7– 9 wt% Al2O3), and a wide variety of spinels, (3) lack of granulitic or peridotitic xenoliths, (4) variable Cs enrichments, and (5) isotopic compositions that indicate interaction with crust (87Sr/86Sri = 0.7037−0.7041; ϵNd = 4.8−2.8; 206Pb/204Pbi = 18.91−18.77; 207Pb/204Pbi = 15.57−15.60). These observations are consistent with a model whereby Miocene intraplate-type magmas rose slowly through the lithosphere, differentiating and interacting with the crust. The megacrysts are interpreted as disrupted gabbroic bodies, formed by slow cooling of mafic alkalic magmas that stagnated in the lower crust, possibly during the earlier extensional episode. Many of the elemental and isotopic parameters used to probe mantle sources of mafic volcanic rocks have been seriously obscured by crystallization, crustal interaction, and megacryst incorporation, complicating efforts to identify temporal changes in mantle source regions during development of the southern Basin and Range Province. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

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.

Evolution of a large Miocene growth structure in the upper plate of the Whipple detachment fault, northeastern Whipple Mountains, California

AbstractMiocene sedimentary and volcanic rocks in the north‐eastern Whipple Mountains, California, and the north‐western Aubrey Hills, Arizona, accumulated in the upper plate of the Whipple detachment fault during regional extension and slip on the detachment. Miocene rocks in this area can be divided into three sequences: (1) pre‐18.5‐Ma dominantly volcanic rocks; (2) the 18.5‐Ma Peach Springs Tuff; and (3) post‐18.5‐Ma dominantly sedimentary rocks. Important stratigraphic markers in sequence 3 include a 100‐ to 14–0‐m‐thick basalt unit and the voluminous War Eagle landslide, both of which correlate across Lake Havasu from the north‐east Whipple Mountains to the Aurbrey Hills. We divide clastic sedimentary rocks of sequence 3 into three informal members: (3a) conglomerate and sandstone stratigraphically beneath the basalt; (3b) conglomerate and sandstone above the basalt and below the War Eagle landslide; and (3c) conglomerate and sandstone that overlie the War Eagle landslide. Detailed stratigraphic analysis and field mapping reveal dramatic south‐westward thickening of member 3b strata, from about 50 m in the Aubrey Hills to over 1500 m in the north‐east Whipple Mountains. In the north‐east Whipple Mountains, this thick dipping section is overlain by the War Eagle landslide along a major angular unconformity; in the Aubrey Hills the base of the War Eagle landslide is roughly parallel to bedding dips of underlying strata.The above stratigraphic relationships can be explained by syndepositional growth of a rollover monocline by progressive tilting of the hangingwall above a master listric normal fault (Whipple detachment fault). This phase of upper‐plate deformation began shortly after deposition of the basalt and ended prior to emplacement of the War Eagle landslide. Interbedded breccias low in member 3b, about 100 m above the basalt, record the first appearance of mylonitic detritus in the section. Growth of this upper‐plate rollover was thus initiated at about the same time (shortly after deposition of the basalt) that the lower plate of the Whipple detachment fault was first exposed at the earth's surface by tectonic denudation and large‐scale crustal uplift. These events are interpreted to record initiation of a secondary breakaway fault on the north‐east flank of the growing Whipple detachment dome shortly after deposition of the basalt at about 14.5 (±1.0) Ma.

Structural observations adjacent to a large-scale extensional detachment zone in the hinterland of the Norwegian Caledonides

Structural and lithological observations in a N-S traverse across Bremangerlandet, western Norway, demonstrate that the region is separated into two plates by the E-W-striking, S-dipping ductile-brittle Vetvika Shear Zone. The Vetvika Shear Zone places Caledonian high-grade gneisses, with a Precambrian protolith age of the lower plate, in tectonic contact with heterogeneous gneisses of the upper plate. The Vetvika Shear Zone is the uppermost part of the Nordfjord-Sogn Detachment Zone. A gently W-plunging stretching lineation within the S-dipping lower-plate augen gneisses is interpreted as having formed within a several kilometers thick ductile W-dipping extensional shear zone that has undergone later rotation around an E-W axis. A highly attenuated sequence of nappes occur structurally on top of a heterogeneous basement and cover quartzite of the upper plate. Pre-Caledonian structures are preserved locally in the gneissic upper plate basement. The nappes at Bremangerlandet are correlated with the Caledonian Middle and Upper Allochthons, representing Baltic/suspect and exotic terranes, respectively. One large and several medium- to small-scale, brittle, top-to-the-south extensional faults are superimposed on ductile contractional structures in the upper plate. Some of the extensional faults merge downward with the Vetvika Shear Zone. The contractional structures include E-W-trending folds and S-directed thrusts in the cover quartzite, and are superimposed on a pronounced W-E stretching lineation. Conjugate sets of fractures and faults related to E-W extension represent the youngest structures in the upper plate. The Old Red Sandstones (Devonian) of the Hornelen basin rest unconformably on top of extensionally faulted upper plate rocks on Bremangerlandet. The unconformity is partly faulted at Bremanger, and truncated by a regionally extensive late, brittle fault along the basin margin further east. This suggests a long-lived tectonic history for the Vetvika Shear Zone and its eastward continuation, with movement pre- and post-dating the filling of the collapse basin, possibly as an eastward migration of the break-away fault.