bluuebunny/crossref_metadata_2025_split huggingface dataset:
The structure of the Calabro-Sicilian Arc: result of a post-orogenic intra-plate deformation
Authors: Wezel Forese Carlo 
Published: May 2008

Summary
Morphotectonic and geological data show that this arc constitutes a post-orogenic ring-like system concentric round the Marsili ‘backarc’ basin. Peripheral concentric features comprise the ‘Aeolian andesitic ring’ and the arcuate troughs and ridges characteristic of the ‘forearc’ region. The Hyblean horst-like plateau and the Strait of Sicily represent the block-faulted foreland of the Sicilian segment of the Calabro-Sicilian Arc. The present shape of the arc has largely resulted from Plio-Quaternary vertical tectonic movements, superimposed on compressive structures caused by previous phases of tectonic deformation. The effect can be visualized as an outward-moving topographic wave producing inversion of tilting movements. This kinematic process (termed ‘krikogenesis’) is postulated as being related to midplate domal upwarp, dilatation and cauldron-like collapse of the Marsili block in the core of the arcuate system. Volcanicity appears to be associated with various stages of this geological history. Rather than originating by collision of two rigid plates, present-day morphological, volcanic and seismic configurations seem to be due to interaction of intra-plate ‘arches’, activated by local mantle movements.
Deformation of the Makran accretionary sediment prism in the Gulf of Oman (north-west Indian Ocean)
Authors: White Robert S. 
Published: May 2008

Summary
The offshore Makran of Pakistan and Iran in the Gulf of Oman forms the seaward margin of a folded and faulted accretionary sediment wedge which extends several hundred kilometres inland across the onshore Makran. Sediment is being scraped off the oceanic Arabian plate as it subducts shallowly northward beneath the Eurasian plate. The submerged front of the accretionary prism has been traced along the entire width of the Makran continental margin, from the Strait of Hormuz in the west to the boundary with the Indian plate in the east. The structure of a 70 by 90 km portion of the deformed sediment belt was mapped in detail by a grid of continuous seismic reflection profiles. This survey demonstrates that the folds are laterally continuous and are well lineated, that the deformed belt appears to be migrating southward at a rate of about 10 km every million years and that folding of the initially undisturbed abyssal plain sediments occurs in the southernmost, or ‘frontal’ fold. Mapping of the three-dimensional structure of the frontal fold shows that it systematically increases then decreases in height along strike over a distance of about 80 km. Folding is initially restricted to the uppermost 2½ km of the sediment pile, and there is local evidence of small-scale shale diapirism. The frontal fold is then incorporated into the accretionary prism by uplift along a thrust fault which flattens out within the sedimentary section, possibly in overpressured shales. There is little subsequent deformation of the uplifted material or of the sediment which infills the basins between the fold ridges until some 70 km north of the frontal fold when further rapid uplift occurs, eventually elevating the sediment above sea-level. I attribute this second phase of uplift to major imbricate thrust faulting extending down to the oceanic basement; most of the shortening and thickening of the sediment wedge occurs in this region. The relatively simple pattern of uplifted folds and intervening basins in the frontal 70 km of the accretionary wedge results from a balance of compressive and normal stresses on the thick sediment section. This simple deformational style of the seaward part of the accretionary prism can be traced eastwards until it becomes chaotically disrupted by the consumption of a basement ridge which protrudes to just beneath the seafloor.
The Franciscan Complex of northernmost California: sedimentation and tectonics
Authors: Aalto K. R. 
Published: May 2008

Summary

The Franciscan Complex consists, from east to west, of a belt of foliated (textural zone 2 and 3) rocks deformed beneath the Coast Range thrust (CRT), a belt of broken formation (BF) and a belt of sheared olistostromes (SO) consisting of conglomerate, greywacke, limestone, chert, greenstone, plutonic and glaucophane schist blocks in chiefly argillaceous matrix. South of the Klamath River, zone 2 and 3 rocks are of an outer fan or basin-plain facies and have overthrust midfan unfoliated (textural zone 1) BF in which suprafan lobes are preserved as megaboudins. To the north, foliated rocks are in gradational contact with similar BF and two episodes of thrusting were confined to the CRT. Blocks of chert, gabbro and metavolcanic rock were tectonically transported along thrust faults. Greywacke and conglomerate of the SO belt are inner fan deposits. The BF-SO contact is gradational, delineated by the westward appearance of greenstone, chert and plutonic blocks increasing progressively in size and/or abundance. Olistostrome units are intercalated with isoclinally folded, recycled sediments. BF and SO greywackes are commonly feldspathic litharenites with mean parameters (Dickinson 1970):
Q
= 54.6,
C/Q
= 0.28,
F
= 21.6,
P/F
= 0.97,
L
= 23.8 and
V/L
= 0.82. Sediments were deposited in a trench slope basin and intercalated with olistostromes derived from elevating portions of the accretionary basement. Progressing upwards in the local sequence north of the Klamath River, the gradational SO-BF transition, decrease in overtuned beds and a retrograding fan sequence reflect basin filling, diminished faulting and lessened relief concomitant to basin elevation.
Sedimentation, metamorphism and tectonic accretion of the Franciscan assemblage of northern California
Authors: Blake M. C. , Jayko A. S. , Howell D. G. 
Published: May 2008

Summary
The Yolla Bolly terrane of the Franciscan assemblage in northern California is seemingly a typical subduction complex, having undergone penetrative deformation and metamorphism to the high pressure-low temperature blueschist facies. Detailed mapping combined with sedimentological analysis has enabled us to: (1) reconstruct a probable palaeosedimentary environment, (2) analyse the interaction during and after subduction between deformation and metamorphism, and (3) speculate on subsequent deformational history including tectonic accretion of the terrane to North America.
Rocks of the Yolla Bolly terrane consist of three thrust-fault-bounded lithological units: a lower unit of disrupted mudstone and thin-bedded sandstone (broken formation) containing scarce volcanic and radiolarian chert horizons, a middle unit predominantly of thick-bedded to massive sandstone (metagreywacke) that includes several horizons of radiolarian chert, and an upper unit of mudstone and thin-bedded sandstone (broken formation) with numerous intrusive and extrusive volcanic rocks plus rare radiolarian chert. Radiolarians from all three units are of the same age (Tithonian to Valanginian) and together with the sedimentological data, suggest that the rocks represent a continent-derived submarine fan, deposited in a complex transform graben possibly similar to the present-day Gulf of California or basins of the California Continental Borderland, rather than a trench setting.
Metagreywacke containing lawsonite and aragonite yields radiometric ages of approximately 110 Myr and indicate that these rocks were subducted to depths of 20–30 km about 30 or 40 Myr after they were deposited. Shortly after subduction, the rocks were probably involved in a collision that imbricated and tectonically returned the subduction complex to the surface.
Deformation of partly dewatered and consolidated Franciscan sediments near Piedras Blancas Point, California
Authors: Cowan Darrel S. 
Published: May 2008

Summary
Bedded sequences of turbidite sandstone and mudstone and associated chaotic, polymict pebbly mudstone record a post-depositional, pre-metamorphic deformation. Sandstone layers were extended and locally disrupted and fragmented and most clasts in pebbly mudstone were deformed into oblate ellipsoids. On the scale of outcrops and hand-specimens, extension in sandstone was accomplished by: (1) mesoscopically ductile pinch-and-swell behaviour and boudinage; (2) extreme necking, which locally resulted in extension fractures or brecciation; and (3) sets of parallel shear fractures inclined to bedding. On smaller scales, ductile changes in shape were accommodated by both intergranular flow of sand-rich sediment and slip along zones typically 0.1 mm or less in thickness. Microfracturing, granulation, and cataclasis of clastic grains are less commonly observed, even adjacent to microfaults. Mudstone was also mesoscopically ductile but generally it flowed by displacements on penetrative, anastomosing surfaces of slip and was transformed locally into ‘scaly clay’. These Franciscan sediments probably contained appreciable pore fluids when they were deformed, since the deformation of unconsolidated sands by homogeneous, intergranular flow rather than widespread cataclasis is fostered by high interstitial fluid pressures. More localized discontinuities, such as extension fractures, shear fractures, and microfaults, formed where sand had more completely dewatered and consolidated. Thus, material response may partly reflect water content and consolidation history. The axially symmetric extension recorded by small-scale structures suggests that sediments were deformed in a shallow-level, laterally unconfined environment on the trench slope, perhaps in response to vertical shortening and horizontal elongation that accompanied gravitational collapse and spreading.
Initiation and evolution of the Great Valley forearc basin of northern and central California, U.S.A.
Authors: Ingersoll Raymond V. 
Published: May 2008

Summary
The late Mesozoic Great Valley forearc basin of northern and central California evolved from a residual forearc basin formed on top of young oceanic crust to a composite forearc basin resting on both oceanic and continental crust. Depositional environments preserved in outcrop along the west side of the Sacramento Valley evolved from deep oceanic floor and slope in the Late Jurassic to basin plain in the Early Cretaceous to submarine fan complexes in the Late Cretaceous to slope and shelf in the Palaeogene. The forearc basin widened and enlarged, and was supplied with voluminous sediment primarily derived from the coeval magmatic arc to the east. However, significant quantities of ophiolitic detritus (chert, and sedimentary, mafic volcanic and mafic metavolcanic lithic fragments) occur in the lower Great Valley strata, thus indicating erosion of ‘tectonic highlands’ formed during arc-arc collision immediately preceeding initiation of the late Mesozoic subduction regime.
The Great Valley forearc owes its geometry and history to the peculiarities of subduction initiation and to the shapes of the continental margin and magmatic arcs extant before initiation of the Great Valley subduction phase. The residual forearc developed on oceanic crust that had formed previously by spreading behind an east-facing intraoceanic arc. After this east-facing arc collided with the west-facing continental-margin arc, a new trench formed west of the suture belt. The shape of the new continental margin was irregular, so that a wide residual forearc basin formed in the Great Valley area, whereas no residual forearc basin formed to the north (Klamath area) or possibly, to the south (southern California borderland area that has been dislocated by Neogene strike-slip motions). The northern coastal promontory (Klamath area) provided much of the ophiolitic detritus within the lower part of the Great Valley strata. Sediment derived from the Klamaths was transported southward directly into the forearc basin, as well as westwards and then southwards into the trench west of the forearc basin. The Great Valley forearc basin is preserved and displayed so well today due to its mode of initiation (residual forearc formed in a previously backarc area) and its mode of termination (northward migration of a triple junction that converted a convergent margin into a transform margin).
Cretaceous-Palaeogene Flysch Zone of the East Alps and Carpathians: identification and plate-tectonic significance of ‘dormant’ and ‘active’ deep-sea trenches in the Alpine-Carpathian Arc
Authors: Hesse Reinhard 
Published: May 2008

Summary
The Flysch Zone of the East Alps is interpreted as a Cretaceous-Palaeogene deep-sea trench fill that accumulated over a period of about 70 Ma when the subduction zone associated with the trench was dormant. In Aptian-Albian time the trench had an elongate, at least 100 km (possibly 200 or 300 km) long basin plain located below the calcite compensation level; sediment input was from two lateral sources (small acute-angled fan or broad feeder channel exposed in the Falknis- and Tasna Nappe; submarine canyon facies in the area north of Salzburg). The existence of a basin plain has also been proved for the Campanian by the recognition of sheet-like turbidites that are continuous for 50 km. The small number of lateral sediment sources is attributed to the existence of slope basins that intercepted the downslope movement of turbidity currents. The lack of syndepositional deformation and of volcanism and volcaniclastic detritus show that sediment accumulation in the trench was not accompanied by active subduction.
This 500 km long and 10 (in the east perhaps 80 or 100) km wide trench of the East Alps was connected with the 1000 km long Carpathian trench whose western segment was also not associated with subduction until Oligocene time. The East Carpathian flysch, however, experienced continuing deformation and (relative) eastward migration of the depositional trough from Albian to Oligocene time. Huge Neogene volcanic centres of the Inner Carpathians are associated with the final diastrophic phases both in the West and East Carpathians, whereas in the East Alps there is no volcanism because subduction does not seem to have reached a great enough depth. The East Alpine-West Carpathian segment of this trench system may represent a major Cretaceous-Palaeogene transform fault zone separating Europe and its bordering seas in the north from the Cretaceous Penninic-Pannonian plate in the south. The latter has been eliminated almost entirely from the surface due to Late Cretaceous-Palaeogene subduction at its southern boundary nearly juxtaposing the European plate (Helvetic and Ultrahelvetic domains) with the Austro-Alpine/South Alpine (plus Adriatic?) plate. Postulated strike-slip motion in the west-east trending segment of the trench was followed by convergent motion, when southward subduction (of the European plate) resumed in late Eocene-Oligocene time.
Combination of an eastward facing trench with active subduction and a dormant trench along a transform fault zone suggests an analogy between the Alpine-Carpathian Arc and the modern West Atlantic loop arcs in the Caribbean and South Scotia Seas. The geodynamic link between these loop-arc structures could be the westward drift of major lithospheric plates between which smaller plates remain relatively stationary because they are ‘sheltered’ behind westward-dipping subduction zones that are more or less anchored in the asthenosphere.
The anatomy of a Lower Palaeozoic accretionary forearc: the Southern Uplands of Scotland
Authors: Leggett J. K. , McKerrow W. S. , Casey D. M. 
Published: May 2008

Summary
The Southern Uplands of Scotland consists of an accretionary prism which had a prolonged (over 45 Ma) development off the SE coast of ancient North America (Laurentia) during the late Ordovician and Silurian. To the north, a forearc basin occupied the Midland Valley. An arc massif of older metamorphic rocks in the Grampian Highlands, and capping calc-alkaline volcanics, supplied much of the sediment to the trench. In its early development (late Ordovician) the accretionary complex incorporated slivers of ocean-floor material as well as thick turbidites into a steep lower trench slope. Later, in the Silurian, a trench slope break emerged shedding sediment north into the Midland Valley forearc basin. By that time only turbidites and black shales were being accreted. The Southern Uplands is dominated by coherent strata, and, despite intense imbrication, is devoid of mélange. We conclude that the accretionary prism was the result of high sediment input to the trench and very slow, oblique, subduction of the Iapetus Ocean eastwards below Scotland. Décollement surfaces developed during accretion preferentially utilised a highly incompetent black shale layer near the base of the subducting sequence. Prior to the inception of accretion (in the Caradoc), we postulate sediment subduction, and possibly subduction erosion, during the Cambrian and early Ordovician.
Sedimentology, volcanism, structure and metamorphism of the northern margin of a Lower Palaeozoic accretionary complex; Bail Hill-Abington area of the Southern Uplands of Scotland
Authors: Hepworth Barry C. , Oliver Grahame J. H. , McMurtry Michael J. 
Published: May 2008

Summary
NE-SW faults in the Bail Hill-Abington area of the Northern Belt of the Southern Uplands define blocks up to 3.2 km wide. The strata, folded and locally overturned, young predominantly to the NW but successive blocks to the SW contain progressively younger sequences. Analogous configurations occur in modern accretionary margins. The oldest rocks are Arenig basalts, dolerites, cherts and brown mudstones underlying red shales, possibly Llanvirn, and black fossiliferous shales and cherts of Llandeilo and Caradoc age.
Trench sediments overlying pelagic sequences represent a range of depositional mechanisms. Rudites and associated fine-grained lithologies of lateral origin relate to a lower trench slope canyon system, whilst axially transported sands, originating on the lower trench slope, were deposited by turbidity currents and related flows.
The Bail Hill Volcanic Group (Upper Llandeilo) represents a mildly alkaline seamount in the Iapetus Ocean, with volcanic activity spanning the transition from pelagic plate to trench sedimentation before accretion.
Faults, initially low-angle thrusts, and bedding were rotated through the vertical within the accretionary complex, pre-dating or accompanying slaty cleavage development. Soft sediment deformation, two fold phases and a kink-band set are recognized. Imbricate fault zones located in incompetent pelagic sequences are tentatively equated with tectonic mélanges of other accretionary complexes.
Index minerals, illite crystallinity and ‘vitrinite’ reflectance establish metamorphic grade as a zeolite to prehnite-pumpellyite facies.
Sedimentary facies associations within subduction complexes
Authors: Underwood Michael B. , Bachman Steven B. 
Published: May 2008

Summary
Sedimentation patterns within modern subduction zones are complex and variable, and do not necessarily follow models of submarine fan sedimentation. Environmental reconstructions within ancient subduction complexes should follow modern analogues as closely as possible and consider several criteria, including turbidite facies associations, vertical depositional cycles, regional palaeocurrent patterns, and in many cases, structural style and sandstone petrology.
Important variables in trench sedimentation include the volume and texture of sediment entering the trench and the distribution of major sediment sources, especially large submarine canyons. Sediment transport in the trench is commonly longitudinal, although locally, such as at the mouth of a submarine canyon, flow may be at a high angle to the continental margin.
Patterns of trench-slope sedimentation depend largely upon the topography of the slope. In general, coarse sediment is either trapped behind tectonic ridges (within slope basins) or bypasses the slope via submarine canyons. Background sedimentation is dominated by hemipelagic settling. Current directions are commonly at a high angle to the margin, but longitudinal flow may occur within large elongate slope basins. Major facies associations include submarine-canyon, slope, mature-slope-basin, and immature-slope-basin.
Evolution of the slope landward of the Middle America Trench, Nicoya Peninsula, Costa Rica
Authors: Lundberg Neil 
Published: May 2008

Summary
The Nicoya Peninsula of Costa Rica represents an uplifted portion of the trench slope break landward of the Middle America Trench, and is composed of the Nicoya Complex and its sedimentary cover. The Nicoya Complex is upper Mesozoic oceanic crust, showing the effects of continued igneous activity and deformation probably due to the Late Cretaceous initiation of subduction in an oceanic region. The sedimentary cover reflects uplift and progressive deformation throughout the evolution of this intra-oceanic arc-trench system.
Sediments of the Nicoya Complex are open-ocean deposits, comprising locally derived sedimentary breccias made up of recycled Nicoya Complex material as well as more typically pelagic radiolarian cherts, black shales and deep-water limestones. The basal unit of the sedimentary cover is the mainly hemipelagic Campanian Sabana Grande Formation, which was probably deposited on the juvenile trench slope. In the Sabana Grande Formation, basal siliceous mudstones give way up-section to the foraminifer-rich calcareous mudstones, representing the passage of the sediment surface up relative to the CCD. Interbedded conglomerates and sedimentary breccias reflect recycling of Nicoya Complex material, apparently by uplift and erosion of the forearc basement. The Sabana Grande Formation is overlain by the ?Campanian to Palaeocene Rivas and Las Palmas Formations which consist of thick, mainly volcanogenic, thin- to thick-bedded turbidites and massive and/or pebbly sandstones characteristic of mid-fan facies associations. These rocks were probably deposited in a forearc basin situated landward of a structural high. In contrast, Palaeocene turbidites which crop out to the SW and seaward of the proposed high are thin-bedded, associated with redeposited hemipelagic mudstones, and interpreted as trench slope deposits. This thin-bedded turbidite/hemipelagic mudstone unit is in turn overlain by Palaeocene or Eocene calcareous mudstones and Eocene siliceous mudstones, both of which are interpreted to represent continued deposition on the trench slope, respectively above and below the CCD. These ?Palaeocene and Eocene mudstones are overlain unconformably by Eocene to ?Quaternary shallow-water clastic and carbonate deposits, reflecting rapid Eocene tectonic uplift. The general trend of shallowing in depositional environments through time is paralleled by an overall decrease in intensity of structural deformation up-section, indicating progressive deformation in this forearc terrane.
Lichen weathering of minerals: implications for pedogenesis
Authors: Wilson M. J. , Jones D. 
Published: May 2008

Summary
The weathering of primary rock-forming minerals beneath crustose lichens is due principally to the activity of the fungal component in excreting extracellular organic acids, particularly oxalic acid. This results in extensive surface etching of the minerals, the conversion of some minerals to siliceous relics, the formation of poorly ordered weathering products and the crystallization of oxalates at the rock/lichen interface and within the lichen thallus. Interpretation of these features is facilitated by the fact that they can be simulated experimentally. The relevance of lichen weathering to the pedogenic weathering predominant in soils under a cool temperature climate is discussed.