Tectonic Lineations Research Articles

Performance of geophysical methods in determining fault zone at Darakeh Area (Tehran Province; Iran)

Darakeh area is one of the major areas in terms of seismic hazards in Tehran. The North Tehran Fault has gone through the center of the studied area, thus creating fractures, displacements and folds of layers, forming anticlines and synclines. Considering the old residential texture understanding the tectonic characteristics and locating the hidden faults of the region can be quite useful in providing thematic maps and preventing damages caused by potential earthquakes. Nevertheless, no geophysical studies have been carried out on this area so far. To map the area, three GPR and two electric resistivity profiles were designed based on the identified tectonic lineations and previous seismic studies on the area. Each GPR profile, was 100 m in length and surveyed using a MALA GPR with an unshielded 50-MHz antenna. The geo-electric profiles were surveyed by Wenner-Schlumberger array. The results of the processed profiles demonstrate a severe drop in resistivity in some regions which could be due to the presence of fault zones and potential cavities in the region under study.

Epikarstik Kuşağın Denetiminde Gelişmiş Mağara Örneği Olarak: İkiz İncirli Çengirek (Marmaris - Muğla)

During the cave research in Bozburun Peninsula, it was understood that İkiz İncirli Çengirek (cave), one of the many caves discovered, was formed by speleogenetic processes at the epikarstic zone. The formation of many caves in the Bozburun Peninsula region is due to the numerous weak tectonic lineations, suitable climatic conditions, lithology needed for cave formation, and exposure to long-time denudation. Speleogenetic researches carried out in Turkey ignored the role of the epikarstic zone. İkiz İncirli Çengirek is an excellent example for evaluating the impacts of processes in the epikarstic zone on the speleogenesis of the cave. Tectonic weaknesses occurred as a result of tectonic movements during the İkiz İncirli Çengirek formed through tectonic weaknesses that happened as a result of tectonic movements during the Plio– Pleistocene, provided the necessary conditions for the formation of İkiz İncirli Çengirek Cave at that location. Dripping and water-film action in the epikarstic zone under the control of fluviokarstic processes shaped and deepened the morphological structure of the cave. As a result of favorable environmental conditions, the cave is home to many species of Lyciasalamandra flavimembris, cave grasshoppers belonging to the Dolichopoda sp. genus, and other organisms, such as bats, scorpions, and spiders whose species are yet to be identified.

Strain partitioning and relief segmentation in arcuate fold-and-thrust belts: a case study from the western Betics

Within arcuate orogenic belts, strain is commonly partitioned between arc-parallel stretching and arc-perpendicular shortening. Arc-parallel stretching can be accommodated by arc-oblique strike-slip faults and arc-perpendicular normal faults, whose localization in fault systems may provoke significant along-strike structural relief drops. In this work, we have studied the Ubrique area, located in a frontal segment of the external western Betics (northern branch of the Gibraltar Arc), where one of the most significant relief discontinuities along the orogenic grain is defined. We have found that this discontinuity is determined by two main types of structures: (1) arc-parallel, kilometric-scale folds and reverse faults that control the conformable relief of the fold-and-thrust belt; (2) the tectonic lineation related to the SW segmentation of this relief, which is composed of the Colmenar fault and the Ubrique Normal Fault Zone (UNFZ). This tectonic lineation seems to have localized arc-parallel extension. Qualitative and quantitative geomorphological analyses together with the age of the deformed rocks indicate that these structures have been active from the Tortonian to Holocene. Our results suggest that post-Serravallian outward radial thrusting and arc-parallel stretching accommodate a strain partitioning typical of progressive arcs, thus suggesting that the Gibraltar Arc is still protruding.

Lineations and structural mapping of Io's paterae and mountains: Implications for internal stresses

The mountains of Jupiter's volcanic moon Io are tall, steep, and tectonic in origin, yet their precise modes of formation and their associations with volcanic paterae are not fully understood. Global spatial statistics of paterae and mountains and their associated lineations reveal that both types of features are more common at low latitudes and tectonic lineations have preferred orientations, whereas straight patera margins are randomly oriented. Additionally, structurally controlled lineations tend to cluster with each other, and in areas of high concentrations these tectonic lineations are shorter in length than their global average. These results indicate that global-scale (rather than local or regional) processes are involved in forming Io's tectonic structures, but that the diversity of mountain characteristics and the collapse of paterae adjacent to mountain complexes are more locally controlled. Regional structural mapping of the Hi'iaka, Shamshu, Tohil, and Zal regions reveals Io's mountains reside in large, fault-bounded crustal blocks that have undergone modification through local responses of subsurface structures to variable stresses. Strike-slip motion along reactivated faults led to the formation of transpressional and transtensional features, creating tall peaks and low basins, some of which are now occupied by paterae. We propose Io's mountains result from a combination of crustal stresses involving global and local-scale processes, dominantly volcanic loading and tidal flexing. These stresses sometimes are oriented at oblique angles to pre-existing faults, reactivating them as reverse, normal, or strike-slip faults, modifying the large, cohesive crustal blocks that many of Io's mountains reside in. Further degradation of mountains and burial of faults has occurred from extensive volcanism, mass wasting, gravitational collapse, and erosion by sublimation and sapping of sulfur-rich layers. This model of fault-bounded blocks being modified by global stresses and local structural response accounts for the variation and patterns of mountain sizes, shapes, and orientations, along with their isolation and interactions with other features. It also provides a context for the operation and extent of global and regional stresses in shaping Io's surface.

Pluto: Pits and mantles on uplands north and east of Sputnik Planitia

The highlands region north and east of Sputnik Planitia can be subdivided into seven terrain types based on their physiographic expression. The northern rough uplands are characterized by jagged uplands and broad troughs, and it may contain a deeply-eroded ancient mantle. Dissected terrain has been interpreted to have been eroded by paleo-glaciation. The smooth uplands and pits terrain contains broad, rolling uplands surrounding complexes of pits, some of which contain smooth floors. The uplands are mantled by smooth-surfaced deposits possibly derived from adjacent pits through low-power explosive cryovolcanism or through slow vapor condensation. The eroded smooth uplands appear to have originally been smooth uplands and pits terrain modified by small-scale sublimation pitting. The bright pitted uplands features intricate texturing by reticulate ridges that may have originated by sublimation erosion, volatile condensation, or both. The bladed terrain is characterized by parallel ridges oriented north–south and is discussed in a separate paper. The dark uplands are mantled with reddish deposits that may be atmospherically deposited tholins. Their presence has affected long-term landform evolution. Widespread pit complexes occur on most of the terrain units. Most appear to be associated with tectonic lineations. Some pits are floored by broad expanses of ices, whereas most feature deep, conical depressions. A few pit complexes are enclosed by elevated rims of uncertain origin.

Magnetic fabric variations along the fault related anticlines of Eastern Kachchh, Western India

An investigation of the anisotropy of magnetic susceptibility (AMS) along the Kachchh Mainland Fault (KMF) and South Wagad Fault (SWF) in the eastern Kachchh has been carried out to determine the variation of magnetic fabric in different anticlines. 105 cores drilled from 35 Jurassic sandstone samples collected from both forelimbs and backlimbs of the anticlines are analyzed. The various types of fabrics from the three sites indicate essentially three stages of generation of magnetic fabric. The sedimentary fabric (type I) is affected a) initially by layer parallel shortening, resulting in the development of type-III fabric with oblique to parallel bedding and magnetic foliation, b) later by bedding parallel shear associated with the rotation of limbs resulting in the tectonic fabric type-IV and c) finally by bedding parallel thrusting, dominantly in the backlimbs resulting in the imprint of higher tectonic fabric type-V/VI. About 14% of the sampled sites belong to the sedimentary type-I fabric, 54% to the type-III and 32% show tectonic fabric (type-IV and V/VI). The different stages of fabric evolution are not accompanied by linear increase in the degree of anisotropy, but show construction and destruction of magnetic fabric during the layer parallel shortening to late stage bedding parallel thrusting. The tectonic magnetic lineation orientations are mostly not consistent with the bedding strikes or fold axes. The intermediate fabric lineation direction of NNE–SSW is superimposed by later tectonic lineation with varying orientations of NW–SE in the western end to NNE–SSW to NNW–SSE along the eastern end of KMF. We attribute the variations in shortening direction essentially to the transpressional deformation of the basin in general, and individual anticlines in particular. The variation in slip/propagation ratio along individual segmented faults has resulted in the rotation of fold limbs.

Differential displacement and rotation in thrust fronts: A magnetic, calcite twinning and palinspastic study of the Jones Valley thrust, Alabama, US Appalachians

To test whether a displacement gradient along a curved fault structure requires rotation, we studied the northeast-striking, northwest-verging, large-displacement Jones Valley thrust fault of the Appalachian thrust belt in Alabama. Paleomagnetism, anisotropy of magnetic susceptibility (AMS) and calcite twinning analysis, complemented by balanced cross-sections, were used to evaluate the presence and magnitude of any rotation. Remanence directions from the Silurian Red Mountain Formation reveal a prefolding magnetization acquired in the Pennsylvanian, whereas magnetic analysis shows a strong, bedding-parallel compaction fabric with a tectonic lineation. Paleomagnetic directions and magnetic lineations reveal no relative rotation between the hanging wall and footwall of the thrust fault. Rather than rotation, therefore, we interpret the Jones Valley thrust sheet as a structure that developed in a self-similar fashion, with lateral growth of the fault surface occurring coincident with growth into the foreland.

The origin of tectonic lineation in extensional basins: Combined neutron texture and magnetic analyses on “undeformed” clays

In extensional sedimentary basins fine-grained sediments that appear undeformed at the outcrop scale can carry a magnetic fabric consistent with the regional deformation pattern. The origin of the magnetic lineation, which is often found in extensional basins, is not yet well understood. In clays from extensional basins in southern Italy, the magnetic lineation is tectonically controlled and oriented perpendicular to the main normal faults. A combined analysis of magnetic and mineral fabrics was made to gain insight into the processes that lead to a lineation in extensional settings. Low-field, high-field and low-temperature susceptibility measurements were used to distinguish the ferrimagnetic and paramagnetic contributions to the magnetic susceptibility and its anisotropy. The magnetic anisotropy of the sediments is predominantly carried by paramagnetic phyllosilicates. Neutron texture analysis was used to evaluate the spatial distribution of chlorite basal planes. Results demonstrate that the orientation of the magnetic lineation is related to the spatial distribution of chlorite, lying parallel to the common axis of differently oriented basal planes. A quantitative correlation between the magnetic and rock fabric was made comparing the low- and high-field magnetic anisotropy (AMS, HFA) to the theoretical anisotropy calculated from the chlorite-preferred orientation. A good linear correlation is found between the degree of theoretical anisotropy and the AMS and HFA. Results show that the integrated approach of magnetic and mineral fabric investigations represents a valid alternative tool for detecting grain scale and regional deformation patterns in weakly deformed extensional basins, where macroscopic evidence of deformation is often not visible.

Thermally induced lineations on the asteroid Eros: Evidence of orbit transfer

Several systems of tectonic lineations have been observed on the surface of the asteroid 433 Eros. We suggest that many of these lineations may have resulted from thermal stresses associated with a secular change in surface temperature due to orbit migration. We demonstrate how thermal diffusion can lead to tectonic features and how such features should be oriented with respect to Eros' complex geometry. Comparison to observed lineations suggests that some may be explained by thermal stresses. Such stresses represent a largely unexplored tectonic process on asteroids and could be used to gain rare insight into chaotic orbital dynamics. If correct, our results imply a gross orbital history over the last ∼100 Myr involving slow (>several Myr), inward migration followed by more rapid, outward migration to its present orbit.

Tectonic lineations and frictional faulting on a relatively simple body (Ariel)

Anderson's model of faulting and the Mohr-Coulomb failure criterion can predict the orientations of faults generated in laboratory triaxial compression experiments, but do a much poorer job of explaining the orientations of outcrop- and map-scale faults on Earth. This failure may be due to the structural complexity of the Earth's lithosphere, the failure of laboratory experiments to predict accurately the strength of natural faults, or some fundamental flaw in the model. A simpler environment, such as the lithosphere of an icy satellite, allows us to test whether this model can succeed in less complex settings. A mathematical method is developed to analyze patterns in fracture orientations that can be applied to fractures in the lithospheres of icy satellites. In a initial test of the method, more than 300 lineations on Uranus' satellite Ariel are examined. A nonrandom pattern of lineations is looked for, and the source of the stresses that caused those features and the strength of the material in which they occur are constrained. It is impossible to observe directly the slip on these fractures. However, their orientations are clearly nonrandom and appear to be consistent with Andersonian strike-slip faulting in a relatively weak frictional lithosphere during one or more episodes of tidal flexing.

Morphological, sedimentological and tectonic features of diamante‐m. Carpinoso Marine terrace flight (tyrrhenian coast of northern Calabria, Italy)

AbstractMarine terrace flights resulting from the interaction of Quaternary glacio‐eustatic fluctuations and tectonic uplift are a typical feature of the Tyrrhenian coast of Calabria in Southern Italy; in particular a térrace flight with four orders of terraces is evident in the Diamante area. The lowest terrace levels (fourth order: Diamante‐Cirella terrace) are typified by a calcarenitic deposit with Cladocora caespitosa which give a Th/U age > 300,000 years. The third order terrace has a sedimentary cover formed of a basal discontinuous level of well rounded pebbles which underlies a deeply weathered coarse‐grained sand horizon. The deposit ends with a paleosol locally cut by erosional scours filled by yellowish tuff deposits. The formation of this terrace dates from the Middle Pleistocene. The second order terrace presents a sedimentary cover composed of two generations of soils and is attributed to Middle Pleistocene age. The first order terrace (M. Carpinoso terrace) presents a wave‐cut platform covered by a clastic deposit of marine and continental origin; this deposit consists of superimposed depositional events separated by unconformities, bounded by two diachronous surfaces. The formation of the wave‐cut platform could be related to several sea‐level stands during a long‐lasting slow subsidence phase of the coastal area during the Lower Pleistocene. The uplift following terrace formation displaced the first order terrace most markedly; tectonic lineations controlled the hydrographic pattern and erosion of the surfaces.

The Lega Dembi gold mine: an example of shear zone-hosted mineralization in the Adola greenstone belt, Southern Ethiopia

In the Adola Gold District of Southern Ethiopia the outline of the contacts that separate the greenstone belt and the gneissic terrain defines regional scale ductile to brittle-ductile shear zones. Possibly economic mineralization is found to be controlled by these major shear zones. Mapping out and documenting the movement senses of these major shear zones in detail, therefore, was vital for the prediction of the nature and orientation of the minor structures that are likely to host gold deposits. Structural information combined with identification and mapping of suitable host rocks such as the Lega Dembi schists, can provide a powerful tool in exploration for gold in the Adola area. Such techniques are not only important in mineralized areas such as the Lega Dembi Gold Mine, where some, but not all, mineralized structures have been discovered, but also in unexplored terrains. Mapping at a scale of 1:25,000 resulted in detection of several superposed shearing events with both sinistral and dextral senses of displacement. These shear zones are expressed as ductile, brittle-ductile and brittle types. Study of geometric compatibilities between the structural elements viz., shear zones, tectonic lineations and folds helped in locating the Lega Dembi Gold Mine within a grossly N-S trending major ductile transcurrent sinistral shear zone. This has subsequently been reactivated and overlapped by N-S trending mesoscale shear zones with similar trend but of opposed sense of displacement. The formation of the later dextral shear zones took place under similar ductile conditions within a single but extended phase of deformation, D 2, that generated the reversed motion. Generally D 3 E-W wrench faults with minor WNW-ESE/WSW-ENE trending conjugate pairs and mesoscale D 4N-S/NE-SW trending conjugate systems of brittle to brittle-ductile shear zones have been recognized. Mineralization is hosted by quartz veinlets and stringers that propagated along mesoscale D 2 ductile to brittle-ductile shear zones.

Roque Nublo caldera: a new stratocone caldera in Gran Canaria, Canary Islands

Abstract An inferred elliptic structure 5 × 4 km in diameter, has been identified as the caldera that brought the Roque Nublo Pliocene (5-3.5 Ma.) volcanic cycle in Gran Canaria to an end. This buried caldera, whose morphological expression is no longer evident, is now filled with almost 400 m of interbedded lacustrine sediments and nephelinite lava flows, ashes and tuffs. Mapping of the postcaldera sedimentary layers, which comprise debris-flow lobes, turbiditic sandstones and muds, has permitted the paleogeographic reconstruction of a saucerlike volcanic depression. This has been confirmed by a gravimetric survey, whose data clearly define a double gravity minimum in the area of the inferred caldera. Some postcaldera vents are located near the caldera rim, but most of them define a NW-SE line, across the caldera, which apparently marks an important tectonic lineation. The paucity of remains of Roque Nublo breccias in the caldera infilling suggests a powerful explosive terminal phase for the stratocone, after which the center of the residual edifice collapsed to form the caldera. The very early resumption of activity in the caldera is not a definite proof for a resurgent activity in the area. Whereas the Roque Nublo Formation was formed after a quiescent period of almost four million years on Gran Canaria, this event was soon followed by the third and last cycle of volcanic activity on the island.

Major off-axis hydrothermal activity on the northern Gorda Ridge

The first hydrothermal field on the northern Gorda Ridge, the Sea Cliff hydrothermal field, was discovered and geologic controls of hydrothermal activity in the rift valley were investigated on a dive series using the DSV Sea Cliff. The Sea Cliff hydrothermal field was discovered where predicted at the intersection of axis-oblique and axis-parallel faults at the south end of a linear ridge at mid-depth (2700 m) on on the east wall. Preliminary mapping and sampling of the field reveal: a setting nested on nearly sediment-free fault blocks 300 m above the rift valley floor 2.6 km from the axis; a spectrum of venting types from seeps to black smokers; high conductive heat flow estimated to be equivalent to the convective flux of multiple black smokers through areas of the sea floor sealed by a caprock of clastic breccia primarily derived from basalt with siliceous cement and barite pore fillings; and a vent biota with Juan de Fuca Ridge affinities. These findings demonstrate the importance of off-axis hydrothermal activity and the role of the intersection of tectonic lineations in controlling hydrothermal sites at sea-floor spreading centers.

A comparison of the cratered terrain escarpments on Miranda with the thrust faults on Mercury

Large escarpments on the Uranian satellite Miranda are similar in structure to thrust faults on Mercury result of crustal contraction. The tectonic lineations may be considered evidence of a crustal contraction on Miranda result of differentiation of the satellite.

A high bauxitic surface in the Amazone Territory of Venezuela. Mapping through the Radar-Slar imagery and exploratery examination. Existence d'une haute surface bauxitique en Amazonie vénézuélienne. Première reconnaissance et cartographie à l'aide des images Radar-Slar

During the geomorpho-pedological survey of the Federal Amazone Territory in Venezuela completed in 1983, considerable bauxitic areas were observed in the highlands (between 1000 and 1400 m) of the crystalline mountains at the east and north of this territory. These areas are associated with a specific type of landform. Its characteristic pattern reaveled through the Radar-Slar imagery determined its mapping as well as its frontiers in relation with the other lower polyconvex surfaces. This old erosion surface is distributed along an extensive crescent form of 500 km long and 100 km wide which rises above the large turn of the Upper Orenoque river. It stretches over poorly tectonized and often porphyric granites including alkaline types (Surucucu granites, Paraguaza granites). The field observations evidence a fossil landscape with remarkable uniform aspect. It consists of long interconnected glacis dug out by a rather dense river network with V-shaped narrow valleys in a herring-bone pattern. Locally, the primitive structure has been deeply incised in cuts parallel to the tectonic lineations. The soils are ferrallitic (petroferric gibbsiorthox) with bauxitic hardpan blocks in the upper layer. The alterite is not very well known from a geological point of view. It is possible to recognize three main horizons up to 8 m deep : a mottled clayey, a soft oxic, and a gravelly horizon with bauxitic hardpan blocks. The mineral composition which is qualitatively constant defines the alteration as intergrade between allitization and fermonosiallitization with an early dehydration state of the oxides : much gibbsite, some Al-goethite, a little hematite and boehmite, very little kaolinite. Downslope in the valleys, the allitic evolution is not so pronounced probably due to the proximity of the bedrock : gibbsite, goethite, some more kaolinite and quartz, traces of weathered minerals, absence of hematite and boehmite.

Episodic Rifting and Subsidence in the South China Sea

The South China Sea experienced at least three stages of rifting and two intervening stages of sea-floor spreading since the Early Cretaceous. Its evolution can be described by an episodic model of tectonism, one of thermal cooling and subsidence, pulsed by temporally and spatially confined heating events. Analysis of regional geologic and geophysical data suggests episodes of rifting and associated thermal activities initiated during the Late Cretaceous, the late Eocene, and the late early Miocene. The rift system corresponding to the first episode trends northeast-southwest, whereas those of the second and third trend east-west. These two trends coincide with the orientations of the major tectonic lineations within the basin. Age estimates from heat-flow and bathymetric data suggest the oceanic crust in the Southwest subbasin is considerably older (55 Ma) than that in the Northwest (35-36 Ma) or East (32 Ma) subbasins. The episodic tectonic model is supported by basin subsidence analysis. Subsidence, especially subsidence rate curves derived from the regional well data, demonstrates that unlike a classic Atlantic passive margin, thermal subsidence in the South China Sea was punctuated by rapid subsidence events which are chronologically consistent with the rifting episodes. In terms of hydrocarbon potential, the episodes of rifting and drifting would be conducive to the development of overprinted structures and the deposition of several discrete transgressive packages of source rocks and reservoirs, separated by widespread unconformities. The thermal maturity of sedimentary organic matter affected by episodic rifting and subsidence may be greater than expected on a purely passive margin of equivalent age that had not experienced repeated heating.

Implications of the seismic structure for the orogenic evolution of the Pyrenean Range

The dynamic evolution of the Pyrenees is discussed in the light of geophysical data. Recent deep seismic sounding have revealed the crustal structure of the Pyrenees which is used to test the different evolutionary models proposed until now. The crustal thickness of the Paleozoic Axial Zone (PAZ) and the North Pyrenean Zone (NPZ) differ by more than 10 km, ranging from about 30 km in the NPZ to 40–50 km in the PAZ. The transition from PAZ to the NPZ, identified at the surface as the North Pyrenean Fault (NPF), is sharp at depth and marked by a vertical step, at least in the eastern half of the range. The NPZ is characterized by additional throws and dips of the Moho in the east whereas in the west a heterogeneous middle to lower crust is encountered, with high velocity anomalies. The seismic results suggest that the PAZ and the NPZ belong to different plates, the NPF being the plate boundary. These results are inconsistent with evolutionary models involving lithospheric subduction or crustal doubling and intracratonic rifting with the main tectonic lineations following NNE-SSW directions. They rather suggest that after a period of extension, two main orogenic events took place: a phase involving shearing and thinning which affected mainly the present-day NPZ and a later compressive phase which explains the building up of the chain, the thickening of the crust and the enhancement of a pre-existing difference in crustal thickness between the European and Iberian plates.

Structural features of Precambrian, stratabound sulphide-ore deposits in Finland

Abstract Three sulphide-ore deposits are chosen as characteristic examples from Finland: Outokumpu (Cu-Co-Zn), Vihanti (Zn-Pb-Cu) and Hammaslahti (Cu). They have undergone the same polyphase structural and metamorphic history as the adjacent rocks. They exhibit several common structural features that are of primary importance for an understanding of their geometry and genesis. (1) The earliest structure is a transposed, sedimentary layering SSo = S 1. (2) Deformation accompanied by remobilization, redeposition and recrystallization of sulphides took place in two or three consecutive phases, F 1, F 2 and F 3, (3) Whenever the effect of the third deformational phase was strong, the ore bodies occur in en échelon patterns as a result of the superposition of F 3 structures on pre-existing folds. (4) The shapes of the ore bodies resemble highly elongated, triaxial ellipsoids. The a-axes of the ellipsoids are parallel to the tectonic lineation, and the ab-planes to the axial-plane cleavage of the F 1, F 2 or F 3 fold structures.

Island Arc System in Andaman Sea

A sub-bottom profiler survey of the Andaman Sea was conducted as part of the marine geophysical program of the U. S. Coast and Geodetic Survey during the International Indian Ocean Expedition. The survey lines were run at right angles to the predominantly north-south tectonic lineations of the island arc system. A 20,000-joule sparker, energized every 4 sec, was used as a sound source and was towed about 100 m behind the ship. A 20-hydrophone array received the reflected signals, which were recorded both on a paper strip chart and magnetic tape. The sub-bottom profiler sections and the marine gravity and magnetic measurements augmented knowledge of the geology of the island arc system; the linear structural belts on land were traced through the Andaman Sea by geophysical methods. The structural development of the island arc system from east to west can be traced, based on available continental and marine data. It was possible to delineate the major segments of the island arc system through a distance of 600 nautical mi (1,110 km) in the Andaman Sea, specifically, the foredeep, outer sedimentary island arc, interdeep, inner volcanic arc (and rift valley), and backdeep.