bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geometric controls on the evolution of normal fault systems
Authors: Walsh J. J. , Childs C. , Meyer V. , Manzocchi T. , Imber J. , Nicol A. , Tuckwell G. , Bailey W. R. , Bonson C. G. , Watterson J. , Nell P. A. , Strand J. 
Published: April 2008

Abstract
The growth of normal fault arrays is examined in basins where sedimentation rates were higher than fault displacement rates and where fault growth histories are recorded by thickness and displacement variations within syn-faulting sequences. Progressive strain localization is the principal feature of the growth history of normal faults for study areas from the Inner Moray Firth, a sub-basin of the North Sea, and from the Timor Sea, offshore Australia. The kinematics of faulting are similar in both study areas. Fault displacement rates correlate with fault size, where size is measured in terms of either displacement or length. Small faults have higher mortality rates than larger faults throughout the growth of the fault system. Displacement and strain are progressively localized onto the larger faults at the expense of smaller faults at progressively larger scales. Strain localization and the preferential growth of larger faults are attributed to geometric factors, such as size and location, rather than to the mechanical properties of fault rock in individual faults. This conclusion is supported by numerical models that reproduce the main characteristics of fault system growth established from both study areas.
The nature and origin of asymmetric arrays of shear surfaces in fault zones
Authors: Wojtal Steven F. 
Published: April 2008

Abstract

Mid- to upper-crustal fault zones often possess arrays of shear surfaces whose traces on sections perpendicular to the fault surface and parallel to the
ac
-plane conform with one or more of the ‘Riedel shear’ orientations. These shear surfaces often are oblique to the transport plane, however, so arrays exhibit monoclinic rather than orthorhombic symmetry. In a mudstone-dominated mélange in Humber Arm Supergroup strata in the Bay of Islands, Newfoundland, and in serpentinites from the base of the Bay of Islands complex, shear surfaces have orientations inclined to major fault-zone boundaries and an inferred
ac
-plane for macroscopic fault-related deformation. Deformation in these zones exhibits an overall monoclinic symmetry. The 3D, asymmetric character of shear surface fabrics suggests that a factor other than stress or the symmetric strain rate tensor controlled their formation. The velocity gradient tensor in a steady, non-coaxial shearing flow possesses a symmetry consistent with monoclinic fabrics. Shear surfaces in asymmetric arrays may initiate with predictable orientations relative to the velocity gradient tensor and then rotate toward flow apophyses, which identify stable positions in steady, 3D flows.
A quantitative study of the influence of pre-existing compositional and fabric heterogeneities upon fracture-zone development during basement reactivation
Authors: Beacom L. E. , Holdsworth R. E. , McCaffrey K. J. W. , Anderson T. B. 
Published: April 2008

Abstract
In common with many other regions of exposed continental basement, the Late Archaean to Palaeoproterozoic Lewisian Complex, NW Scotland, preserves numerous examples of faults that appear to reactivate pre-existing compositional and structural heterogeneities in the host gneisses. A regionally recognized set of late Laxfordian sinistral strike-slip faults and fractures are spatially associated with pre-existing NW-SE-trending ductile shear zones of Inverian and Laxfordian age. Field observations suggest that most of the sinistral displacements have been accommodated along laterally persistent faults (here termed principal displacement zones (PDZ)) that lie sub-parallel to the pre-existing foliation in the shear zones. Geometric and orientation data collected during structural logging of the PDZ faults have been used to quantitatively test the influence of lithology and pre-existing structural geometry on the spatial patterns of fault development. Stereographic analysis shows a strong geometrical correspondence between the intensity and form of the pre-existing anisotropy and the alignment of the PDZ brittle faults. Spatial clustering of PDZ faults varies depending on lithology (amphibolite v. acid gneiss v. quartz-mica schist). A close correlation exists between the geometry and intensity of the pre-existing foliation and fault spatial clustering. The results demonstrate that reactivation of pre-existing anisotropies in typical continental basement gneisses exert a significant control on brittle fault development and growth in the upper crust.
Sequential ductile to brittle reactivation of major fault zones along the accretionary margin of Gondwana in Central Argentina
Authors: Simpson Carol , Whitmeyer Steven J. , De Paor Declan G. , Gromet L. Peter , Miro Roberto , Krol Michael A. , Short Heather 
Published: April 2008

Abstract
Metamorphic and plutonic basement rocks and cover sequences of the Eastern Sierras Pampeans, Argentina, have undergone multiple episodes of fault reactivation. Faults take advantage of mid- to late Cambrian, NW-SE-striking, steeply east-dipping foliations in Vendian-aged accretionary prism metasedimentary rocks. Foliations in peraluminous schists, paragneisses and migmatites are deflected into late Cambrian amphibolite-grade high-strain zones. Greenschist-grade mylonite zones and thick retrogressed ultramylonite zones with mainly NNW strikes, easterly dips, and east-over-west movement, affect the metasedimentary rocks and Ordovician-aged intrusive rocks and are presumably related to early Devonian accretion of terranes to the west of Gondwana. pseudotachylyte veins occur in nearly all mylonite zones. Brittle deformation during Carboniferous to Triassic time produced major pull-apart basins located above terrane boundaries. Outcrop patterns of Triassic to Cretaceous sedimentary rocks are consistent with transtensional pull-apart basins followed by Andean transpressional deformation. The theoretical basis for fault reactivation and production of ‘short cuts’ is examined in the context of Tertiary to Recent basin inversion faults. The inversion faults follow the Palaeozoic trends and produce the present-day NNW-oriented, deep sedimentary basins and intervening ranges of basement rocks.
Repeated reactivation in the Apennine-Maghrebide system, Italy: a possible example of fault-zone weakening?
Authors: Tavarnelli Enrico , Decandia Francesco Antonio , Renda Pietro , Tramutoli Mariano , Gueguen Erwan , Alberti Mauro 
Published: April 2008

Abstract
Italy owes its complex geological structure to a double switch in tectonic regime, which involved the opening of the Tethys Ocean during Early Mesozoic time, its closure leading to development of the Apennine-Maghrebide fold-and-thrust belt during the Eocene-Recent interval, and the post-orogenic opening of the Tyrrhenian Sea since Miocene time. This history of tectonic inversion is partly preserved within two major fault zones, the Valnerina Line, in the central Apennines, and the Gratteri-Mount Mufara Line, in central-northern Sicily, which were repeatedly reactivated with different kinematic characters. The relatively long life of these structures indicates that strain was localized along anisotropies inherited from early deformation episodes. However, the progressive widening of both fault zones through time may result from strain-hardening fault-rock behaviour during subsequent deformations, thus suggesting that fault reactivation does not imply fault-zone weakening as is often assumed.
Weak zones in Precambrian Sweden
Authors: Talbot C. J. 
Published: April 2008

Abstract
Examples of weak fault zones in and bordering Precambrian Sweden are reviewed and then analysed in terms of the factors that rendered them weak. The criterion taken here for weak zones is evidence of post-glacial uplift having reactivated old shear zones that are still active now. Strain analysis of the Singö shear zone demonstrates that it was already weak while it was deep and ductile between 1.86 and 1.6 Ga. Thus the orientations of strain ellipsoids indicate pure rather than simple shear across shear strands in which the dissolution of quartz and feldspar indicate high synshear fluid pressures. The characteristics of weak strands of the Baltic-Bothnian shear zones and the Senja-Bothnia shear zones are long histories of superimposed ductile, semi-ductile and brittle structures, indicating repeated reactivations with different kinematics. The shear zones that weakened are those that reactivated in several episodes during their history. Repeated reactivation renders major shear zones in the ‘brittle’ upper crust ‘ductile’ by rounding major angularities along subvertical and subhorizontal zones. This generates continuous seams of cataclasites in which pore fluids can pressurize so that internal strains can remain ductile and almost aseismic by frictional sliding or flow. This review ends by discussing how multiple reactivations weaken major faults and how reactivation remains focused on particular zones.
The role of syn-rift magmatism in the rift-to-drift evolution of the West Iberia continental margin: geophysical observations
Authors: Whitmarsh R.B. , Minshull T.A. , Russell S.M. , Dean S.M. , Louden K.E. , Chian D. 
Published: April 2008

Abstract
The presence of a well-defined ocean-continent transition (OCT) and the absence of large volumes of extrusive or intrusive rocks on the West Iberia margin make it a good place to investigate how the largely amagmatic rifting and break-up of continental lithosphere evolves into oceanic crust produced by magmatic sea-floor spreading. In the southern Iberia Abyssal Plain there is a broad OCT with a characteristic seismic and magnetic character, distinct from both thinned continental crust and normal oceanic crust, which supports the notion that it consists predominantly of exhumed and serpentinized mantle. Interpretations of magnetic and seismic data indicate that on average only small amounts of syn-rift melt exist within the OCT. Isolated, probably margin-parallel, intrusive melt bodies are scattered within the eastern part of the OCT well beneath the top of acoustic basement. Within the western part of the OCT, closer to unambiguous sea-floor spreading magnetic anomalies, such bodies were later(?) emplaced at higher levels and more closely together in the basement until eventually sea-floor spreading began. The evidence does not support the hypothesis that ultraslow sea-floor spreading can explain the magnetic anomalies observed within the wider parts of the West Iberia OCT, where the OCT evolution is best resolved.
Petrochemistry of serpentinized peridotite from the Iberia Abyssal Plain (ODP Leg 173): its character intermediate between suboceanic and sub-continental upper mantle
Authors: Abe Natsue 
Published: April 2008

Abstract

Highly serpentinized peridotites derived from the upper mantle beneath a non-volcanic continental margin were sampled from the southern Iberia Abyssal Plain (Ocean Drilling Program Leg 173), and the primary mantle minerals were analysed for major and trace elements to petrologically characterize the upper mantle. The
Cr
-number (= Cr/(Cr + Al) atomic ratio) of the peridotite spinels varies widely from 0.1 to 0.6. The Na
2
O content of clinopyroxene is rather constant, 0.5–0.8 wt %. The chondrite-normalized rare earth element (REE) patterns have light REE (LREE) depleted convex-upward shapes. The LREE/HREE (heavy REE) ratio in clinopyroxene is constant irrespective of the degree of melt extraction of the sample as measured by the
Cr
-number of spinel. The trend of the peridotites’ mineral chemistry is different from both the simple melt extraction and the general mantle metasomatic trends. The geochemical character of the Iberia Abyssal Plain peridotite is intermediate between those of abyssal peridotites and peridotite xenoliths from continental regions. These geochemical features, especially for the trace elements in clinopyroxene, are rather similar to those in peridotite xenoliths from arcs. This chemical trend is probably the result of ‘open-system melting’, which involves melting simultaneously with enrichment of trace elements by the influx agent.
The evolution of amphibolites from Site 1067, ODP Leg 173 (Iberia Abyssal Plain): Jurassic rifting to the Pyrenean compression
Authors: Gardien V. , Poupeau G. , Muceku B. , Hébert R. , Beaudoin G. , Labrin E. 
Published: April 2008

AbstractDuring ODP Leg 173 (April–May 1997) five new sites (1065, 1067–1070) were drilled at the ocean-continent transition (OCT) zone off the West Iberia margin in the Iberia Abyssal Plain. At Site 1067 the 92 m of cored amphibolites were subdivided into three units based on textural criteria. Unit 1 consists of highly foliated and folded amphibolites and acidic gneiss concordant to and folded along with the foliation of the amphibolite. Unit 2, in the middle part of the section, consists of brecciated amphibolites. Unit 3, at the bottom of the hole, is a weakly deformed zone where magmatic textures are observed in the amphibolites and in associated anorthosites. The amphibolites contain tschermakitic to magnesio-hornblende amphibole, plagioclase, zircon, apatite ± titanite ± Fe-oxide ± quartz. The acidic gneiss consists of garnet, plagioclase, alkali-feldspar, quartz, biotite and zircon. Chlorite, sericite and ilmenite occur as secondary phases. The metamorphic evolution of the amphibolite and acidic gneiss started under amphibolitefacies conditions (Stage I: 670 ± 40°C and 7 ± 1 kbar). Further exhumation took place through low-grade amphibolite-facies (Stage II: 550 ± 50°C and 5.5 ± 1 kbar) to green-schist-facies (Stage III: < 500°C and < 3 kbar) conditions contemporaneous with the development of ductile structures. The late metamorphic evolution of the amphibolite ended under ocean-floor conditions. Oxygen isotope ratios and studies of fluid inclusion indicate that a magmatic water-rich fluid in equilibrium with the igneous protolith predominated during Stage I. During Stages II and IIII low-temperature water-rich fluids of metamorphic origin predominated, with a probable contribution of sea water. Apatite fission-track dating indicates that the amphibolites record two thermal excursions below 120°C. The first took place atc.113–100 Ma and could be related to Cretaceous rifting. The second was brief, and so did not anneal older tracks; it occurred between 75 and 55 Ma and could be related to the Pyrenean orogeny.
The role of lower crust and continental upper mantle during formation of non-volcanic passive margins: evidence from the Alps
Authors: Müntener Othmar , Hermann Jörg 
Published: April 2008

Abstract

The remnants of a Mesozoic passive continental margin and of the Tethyan ocean floor are preserved in the Austroalpine and Upper Penninic nappes in eastern Switzerland and northern Italy. Reconstructions of the continent-ocean transition indicate that large areas of subcontinental mantle rocks, but only limited areas of lower-crustal rocks were exposed on the Tethyan sea floor. Microstructures, large shear zones, and the retrograde metamorphic evolution of peridotite and gabbro from Malenco (northern Italy) are investigated to evaluate the role of lower crust and upper mantle during formation of non-volcanic passive continental margins. The combination of petrological constraints and microstructures suggests two contrasting stages: (1) high-temperature (> 650 °C) shearing and annealing of microstructures are attributed to pre-rift tectonics; (2) localized mylonitic shear zones cut the high-temperature structures and developed during nearly isothermal decompression (
T
<600°C), followed by cooling and hydration of the rocks. These shear zones formed during exhumation of the lower crust and upper mantle and are related to early rifting of the Adriatic passive continental margin. The microstructures of the hydrous mylonites display drastic grain-size reduction, which results from a combination of dynamic recrystallization and metamorphic hydration reactions at temperatures <650°C. Strain softening facilitated the formation of crustal-scale shear zones along which the lower crust and upper mantle were exhumed to shallow crustal levels of
c.
10–15 km. Such large shear zones excised 10–20 km of mostly intermediate and lower crust, and are linked to and contemporaneous with the formation of rift-related basins in the upper crust. Boudinage of the lower crust during early rifting is proposed as a major process to explain the scarcity of exposed lower crust along non-volcanic passive margins. The compilation of pressure-temperature data and rift-related structures in the deep crust and upper continental mantle from the Alps suggests that most peridotites preserve a high-temperature evolution that is not related to Mesozoic rifting. Granulite-facies rocks occur in pre-rift lower and middle continental crust. Exhumed granulites along passive continental margins preserve much of a history that is not related to the exhumation itself, but to tectonic processes predating rifting.
A tale of two kinds of normal fault: the importance of strain weakening in fault development
Authors: Buck W. Roger , Lavier Luc L. 
Published: April 2008

Abstract

We search for a description of fault formation consistent with the main features of two very different types of extensional faults: (1) large-offset, low-angle normal faults; (2) small-offset, high-angle normal faults. We use an advanced numerical model to predict how the pattern of faulting varies as a function of the imposed magnitude and rate of weakening of an extending Mohr-Coulomb layer. We assume that fault weakeing is due to reduction of cohesion with fault offset. Faults initiate and slip at high dip angles. When the fault offset is large (i.e. comparable with layer thickness) then the inactive footwall fault surface can be rotated to a flat orientation. We find two requirements for development of a large-offset fault. The magnitude of cohesion loss must be greater than
c.
20% of the initial total extensional yield strength. Also, the rate of weakening with fault offset has to be moderate: the fault offset to lose cohesion has to be less than
c.
2 km and more than
c.
100 m, with the lower bound being harder to define. Using the same cohesion and rate of offset weakening, extension of a thick layer can lead to development of multiple, small-offset, high-angle faults rather than a single ‘low-angle’ fault. For cohesion reduction of 20 MPa a brittle lithosphere thicker than 20 km leads to multiple faults. Finally, we show that inclusion of thermal advection weakening can shift the transition to thinner layers for the same magnitude and rate of cohesion weakening.
Evidence for seismogenic normal faults at shallow dips in continental rifts
Authors: Abers Geoffrey A. 
Published: April 2008

Abstract

Several recent observations indicate that normal faulting earthquakes occasionally occur on faults dipping <35°, dips often considered shallow. Most of these occur in the Woodlark and Aegean rifts. These two rifts are found to generate significantly more earthquakes than others and are the most rapidly extending, and so display the widest variety of fault behaviour. Even within the Woodlark Rift system extension rates vary along strike, with the shallowest-dipping faults confined to the most rapidly rifting segment. Here, several events (M
w
6.0–6.8) feature nodal planes dipping 23–35°. These planes are subparallel to shear zones bounding nearby metamorphic core complexes, including one imaged to 8–9 km depth by seismic reflection profiling. In the western Gulf of Corinth at least one large event (M
w
6.4) occurred on a fault dipping
c.
33°. Similarly to the Woodlark example, this rift segment exhibits a high opening rate (10–20 mm a
−1
). Several other cases elsewhere, based on older historical data, microseismicity, or geological inference suggest seismic slip at similar or shallower dips. However, no documented large earthquake exhibits seismic slip on subhorizontal surfaces (dip <10–15°). Stress rotation may explain the 23–35° dips, but thus far no realistic mechanism has been found. More likely, these faults represent surfaces somewhat weaker than surrounding rock, through some combination of modest cohesion of the surrounding rock and slightly lower frictional coefficients on the fault. Such weakening may be a consequence of high slip rates, which rapidly generate large offsets, and of mature fault systems.
Evolution of the Miocene-Recent Woodlark Rift Basin, SW Pacific, inferred from sediments drilled during Ocean Drilling Program Leg 180
Authors: Robertson A.H.F. , Awadallah S.A.M. , Gerbaudo S. , Lackschewitz K.S. , Monteleone B.D. , Sharp T.R. ,   other members of The Shipboard Scientific Party
Published: April 2008

Abstract

The results of drilling during Ocean Drilling Program Leg 180 provide insights into fundamental processes of continental break-up, because rifting can be related to westward propagation of a spreading centre into continental crust. A generally north-south transect of holes was drilled across the Woodlark Rift on the uplifted northern rift margin on the Moresby Seamount (Sites 1114 and 1116), on the hanging wall of the low-angle (25–30°) extensional Moresby Detachment Fault (Sites 1108, 1110–1113 and 1117) and across the downflexed northern rift margin (Sites 1118, 1109 and 1115). The results, when placed in the regional tectonic context, document a history of Palaeogene ophiolite emplacement, followed by Miocene arc-related sedimentation. Regional uplift and emergence of the forearc area took place in Late Miocene time. Submergence to form the Woodlark Rift began in latest Miocene time, marked by widespread marine transgression and shallow-water deposition, accompanied by input of air-fall tephra and volcaniclastic sediments. During Pliocene time, deposition within the rift basin was dominated by deep-water turbidites, including high-density turbidites in the south. Strong extension along the north-dipping Moresby Detachment Fault was active during Pleistocene time, associated with uplift of the Moresby Seamount and shedding of fault-derived talus, mainly of meta-ophiolitic origin. During Pleistocene time, a carbonate platform was constructed to the NW, trapping clastic sediment and resulting in a switch to slower, more pelagic and hemipelagic deposition within the Woodlark Rift Basin. The marked change in rift basin configuration during Pleistocene time may relate to westward propagation of the Woodlark oceanic spreading centre at
c.
2 Ma.