bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intraplate strike-slip tectonics as an alternative to mantle plume activity for the Cenozoic rift magmatism in the Ross Sea region, Antarctica
Authors: Rocchi S. , Storti F. , Di Vincenzo G. , Rossetti F. 
Published: April 2008

Abstract
The West Antarctic Rift System is one of the largest areas of crustal extension in the world. Current interpretations on its driving mechanisms mostly rely on the occurrence of one or more mantle plumes, active during the Cenozoic or the Mesozoic. Recent studies of structural-chronological relationships between emplacement of plutons, dyke swarms, and volcanic edifices since middle Eocene in northern Victoria Land imply that magma emplacement is guided by strike-slip fault systems that dissect the western rift shoulder in Victoria Land. These studies led to a critical re-examination of the arguments used to support plume models. In Victoria Land, the linear geometry of the uplift and the relative chronology of uplift and extension are inconsistent with the traditional concepts of lithospheric evolution above a mantle plume. The geochemical signature of the mafic rocks is equivocal, because both OIB and HIMU features cannot be exclusively interpreted in terms of plume activity. From a thermal point of view, magma production rates are low compared with the core part of plume-related provinces. Additionally, the hot mantle below the West Antarctic Rift System is not documented as deep as expected for mantle plumes and the shape of thermal anomaly is related to lithospheric geometry, being linear rather than having circular symmetry. The lack of any decisive evidence for plume activity is contrasted by evidence that large-scale tectonic features guide magma emplacement: the Cenozoic fault systems reactivated inherited Palaeozoic tectonic discontinuities and their activity is dynamically linked to the Southern Ocean Fracture Zones. As an alternative to both active, plume-driven rifting and passive rifting, we propose that lithospheric strike-slip deformation could have promoted transtension-related decompression melting of a subplate mantle already decompressed and veined during the late Cretaceous amagmatic extensional rift phase. Magma ascent and emplacement occurred along the main strike-slip fault systems and along the transtensional fault arrays departing from the master faults.
Phanerozoic strike-slip faulting in the continental interior platform of the United States: examples from the Laramide Orogen, Midcontinent, and Ancestral Rocky Mountains
Authors: Marshak S. , Nelson W. J. , McBride J. H. 
Published: April 2008

Abstract

The continental interior platform of the United States is that part of the North American craton where a thin veneer of Phanerozoic strata covers Precambrian crystalline basement. N- to NE-trending and W- to NW-trending fault zones, formed initially by Proterozoic/Cambrian rifting, break the crust of the platform into rectilinear blocks. These zones were reactivated during the Phanerozoic, most notably in the late Palaeozoic Ancestral Rockies event and the Mesozoic-Cenozoic Laramide orogeny — some remain active today. Dip-slip reactivation can be readily recognized in cross section by offset stratigraphic horizons and monoclinal fault-propagation folds. Strike-slip displacement is hard to document because of poor exposure. Though offset palaeochannels, horizontal slip lineations, and strain at fault bends locally demonstrate strike-slip offset, most reports of strike-slip movements for interior-platform faults are based on occurrence of map-view belts of en echelon faults and anticlines. Each belt overlies a basement-penetrating master fault, which typically splays upwards into a flower structure. In general, both strike-slip and dip-slip components of displacement occur in the same fault zone, so some belts of en echelon structures occur on the flanks of monoclinal folds. Thus, strike-slip displacement represents the lateral component of oblique fault reactivation; dip-slip and strike-slip components are the same order of magnitude (tens of metres to tens of kilometres). Effectively, faults with strike-slip components of displacement act as transfers accommodating jostling of rectilinear crustal blocks. In this context, the sense of slip on an individual strike-slip fault depends on block geometry, not necessarily on the trajectory of regional σ
1
. Strike-slip faulting in the North American interior differs markedly from that of southern and central Eurasia, possibly because of a contrast in lithosphere strength. Weak Eurasia strained significantly during the Alpine-Himalayan collision, forcing crustal blocks to undergo significant lateral escape. The strong North American craton strained relatively little during collisional-convergent orogeny, so crustal blocks underwent relatively small displacements.
Transform zones in the South Atlantic rifted continental margins
Authors: Mohriak W. U. , Rosendahl B. R. 
Published: April 2008

Abstract
Integration of seismic, potential field, and borehole data from conjugate basins along the South Atlantic continental margin, particularly the northeastern Brazilian and northwestern African segments, indicates that the rift architecture is controlled by fracture zones that extend from the oceanic crust and penetrate through the continental crust, locally corresponding to Precambrian structures in cratonic regions. The fracture zones may divide the continental margin into several compartments with independent sedimentary depocentres, separate crustal domains along oceanic transforms, and affect the rift architecture by shearing. Oceanic transform zones may leak igneous rocks originated from the mantle.
This work discusses conjugate sedimentary basins in the South Atlantic salt basins, particularly from Jacuípe to Sergipe-Alagoas on the Brazilian side, and from Gabon to Rio Muni on the African side. The following aspects are emphasized: (1) rift depocentres are controlled by border faults subparallel to the margin and by transverse faults that may continue as transform fractures in the oceanic crust; (2) the southernmost segment of the South Atlantic continental margins is characterized by Early Cretaceous volcanic rocks that underlie continental lacustrine Neocomian to Barremian syn-rift sediments; (3) the pre-rift sequences (Mesozoic and Palaeozoic sediments) that underlie the syn-rift depocentres in Gabon and Sergipe/Alagoas are mainly devoid of volcanics; (4) there is seismic evidence of magmatic underplating in the deeper portions of the continental crust, which are expressed by antiformal features locally aligned with transform fractures; (5) basement-involved extensional faults and volcanic activity along leaking transform faults are imaged along several conjugate segments of the margin, particularly along the equatorial margin (Romanche fracture zone); (6) in some segments of the divergent margin, the transition from outer rift blocks to oceanic crust is characterized by wedges of seaward-dipping reflectors with a possible origin associated with emplacement of oceanic ridges; (7) locally, the outermost rift blocks near the continental-oceanic crust boundary seem to be highly eroded by post-rift uplift caused by transform fault shearing or by magmatic underplating; (8) tectonomagmatic episodes climaxed in the Late Cretaceous/Early Tertiary in northeastern Brazil and extended to the Late Tertiary on the West African margin, forming large volcanic complexes along transverse lineaments that affect both oceanic and continental crust.
Tectonic stress in the Earth’s crust: advances in the World Stress Map project
Authors: Sperner B. , Müller B. , Heidbach O. , Delvaux D. , Reinecker J. , Fuchs K. 
Published: April 2008

Abstract
Tectonic stress is one of the fundamental data sets in Earth sciences comparable with topography, gravity, heat flow and others. The importance of stress observations for both academic research (e.g. geodynamics, plate tectonics) and applied sciences (e.g. hydrocarbon production, civil engineering) proves the necessity of a project like the World Stress Map for compiling and making available stress data on a global scale. The World Stress Map project offers not only free access to this global database via the Internet, but also continues in its effort to expand and improve the database, to develop new quality criteria, and to initiate topical research projects. In this paper we present (a) the new release of the World Stress Map, (b) expanded quality ranking schemes for borehole breakouts and geological indicators, (c) new stress indicators (drilling-induced fractures, borehole slotter data) and their quality ranking schemes, and (d) examples for the application of tectonic stress data.
3D analogue models of variable displacement extensional faults: applications to the Revfallet Fault system, offshore mid-Norway
Authors: Dooley T. , McClay K. R. , Pascoe R. 
Published: April 2008

Abstract
The Revfallet Fault system, Heidrun area, offshore mid-Norway, illustrates considerable variation in structural style along strike which is attributed to variation in coupling between basement and cover (separated by Triassic salt), due to the variable displacement along the fault system and to distinct phases of shallow level as well as basement-involved extension. Deformation in the southern part of the fault is partitioned over a number of cover-graben and associated with the development of a monoclinal flexure above the basement fault system. With an increase in displacement northwards, cover-graben become grounded on the pre-salt basement resulting in the rotation and breaching of the extensional drape fold and, eventually, partial and full coupling between basement and cover fault systems.
Analogue models were designed to simulate the 3D evolution of cover deformation above a variable displacement extensional fault separated from the cover by a ductile basal unit and to validate the structural interpretations and evolutionary models for the Revfallet Fault system. Analogue model results reveal the changing geometry along strike from a gentle extensional drape fold with minimal brittle deformation at low extension, to a breached drape fold system with significant rotation and collapse of the cover across the basement fault as displacement increases. Models conducted with a two-phase history — shallow extension (orthogonal and oblique) followed by basement-involved extension illustrate variable reactivation of cover-graben along strike during the basement-involved event, and collapse and rotation of the extensional footwall to the basement fault as displacement increases to a maximum. Coupling between cover faults and the basement fault only occurred where an oblique, precursor cover-graben cuts across the basement fault from hanging wall to footwall. Closer examination of the structural and stratigraphic relationships reveals major discrepancies between throw on cover and basement fault segments. The analogue model results compare favourably to seismic data from the Revfallet Fault system and validate the structural model for this fault system.
3D evolution of a pop-up structure above a double basement strike-slip fault: some insights from analogue modelling
Authors: Schellart W. P. , Nieuwland D. A. 
Published: April 2008

Abstract

In analogue modelling, pop-up structures have previously only been described in models of basement-involved strike-slip deformation with a stepover or restraining bend configuration. We describe the results of an analogue experiment with an alternative model configuration to investigate the structural development of pop-up structures. This model consists of a cover sequence of sand overlying two parallel running basement faults, which experience the same sense and the same amount of slip during deformation. The ratio of basement fault separation (1 cm) to overburden thickness (4 cm) is small. The experiment has been recorded in an X-ray tomograph, by which it was possible to investigate the 3D structural evolution of the model. During deformation, an elongated rhombic pop-up structure developed centrally above the basement faults. The faults bounding the pop-up structure displayed convex-upward as well as straight to concave-upward shapes. During deformation the topography above the basement faults increased to a maximum of
c.
4.8 mm, compared to a maximum subsidence of
c.
1.5 mm on both sides of the basement faults. During progressive deformation, local maximum horizontal principal stresses displayed a considerable rotation, from 45° in the initial stages, to (sub)parallel in a more advanced stage and finally back to
c.
45° to the strike of the basement faults.
Hanging wall accommodation styles in ramp-flat thrust models
Authors: Mulugeta G. , Sokoutis D. 
Published: April 2008

Abstract
In this paper we study the dynamic and rheologic control of hanging wall accommodation in ramp-flat thrust models. In particular we vary the dimensionless ratio of shear strength to gravity stress to model hanging wall accommodation styles in different materials. In all models we require that the flat-ramp-flat footwall provides a surface of low frictional resistance. In viscous materials hanging wall accommodation progresses by wedge flow. In Bingham materials, wedge flow is also the preferred mode in cases where the gravity stress exceeds the yield limit of materials. Such models simulate the flow of salt or snow glaciers above ramp obstructions. At high ratios of shear strength to gravity stress the hanging wall blocks translate forward without bending and unbending to the form of the rigid footwall. In elastic-plastic strain-hardening materials ramp-flat accommodation progresses by fault-bend folding in case there is a near balance between the yield stress and gravity stress. In frictional materials hanging wall accommodation progresses by shear or kink-band nucleation above fault-bends. The shear or kink-bands which initially nucleate at the lower fault-bend change shape and reactivate by normal faulting or tensile failure at the upper fault-bend, depending on the ratio of shear strength to gravity stress. In nature, hanging wall accommodation by thrust nucleation above ramps and their subsequent reactivation may be anticipated in frictional sediments at upper crustal levels, where temperatures and pressures are low.
3D discrete kinematic modelling applied to extensional and compressional tectonics
Authors: Cornu T. , Schneider F. , Gratier J. -P. 
Published: April 2008

Abstract
The 3D simulation of coupled backward and forward deformation of geological layers is a new step in basin modelling. Although this problem could be addressed with either mechanical or kinematic approaches, the mechanical approach remains too complex to be addressed properly. The kinematic model described here allows a geologically valid path, which takes into account an incremental evolution in time. To obtain a better description of 3D geometries, the model uses a full hexaedric discretization and the discrete neutral surface of each layer is used when performing the flexural slip deformation. An application to a synthetic geological case is then proposed, to study the behaviour of the structure in compressional and extensional contexts.
Experimental constraints on volatile abundances in arc magmas and their implications for degassing processes
Authors: Scaillet B. , Pichavant M. 
Published: April 2008

Abstract

Recent phase equilibrium studies, combined with analytical and petrological data, provide rigorous constraints on the pre-eruptive
P-T-f
H
2
O-
f
O
2
-
f
S
2
-
f
CO
2
conditions of silicic to mafic arc magmas. Pre-eruptive melts show a broad negative correlation between temperature and melt H
2
O contents. Pre-eruptive melt S contents cluster around 100 ppm in residual rhyolitic liquids of silicic to andesitic magmas, and range up to 5000 ppm in more mafic ones. For the entire compositional spectrum, melt sulphur contents are almost independent of prevailing
f
O
2
. In contrast, they are positively correlated to
f
S
2
, in agreement with experimental observations. Using these intensive constraints, the composition of coexisting fluid phases has been modelled through a MRK equation of state. Pre-eruptive fluids in silicic to andesitic magmas have
X
H
2
O (mole fraction of H
2
O) in the range 0.65–0.95.
X
H
2
O decreases as pressure increases, whereas
X
CO
2
increases up to 0.2–0.3. Pre-eruptive fluids in hydrous mafic arc magmas, such as high-alumina basalts, generally have similar mole fractions of H
2
O and CO
2
at mid-crustal levels, with
X
H
2
O increasing only for magmas stored at shallow levels in the crust (<1 kbar). The sulphur content of the fluid phase ranges from 0.12 up to 6.4 wt% in both mafic and silicic magmas. For silicic magmas coexisting with 1–5 wt% fluid, this implies that more than 90% of the melt+fluid mass of sulphur is stored in the fluid. Calculated partition coefficients of S between fluid and melt range from 17 up to 467 in silicic to andesitic magmas, tending to be lower at low
f
O
2
, although exceptions to this trend exist. For mafic compositions, the sulphur partition coefficient is constant at around 20. The composition of both melt and coexisting fluid phases under pre-eruptive conditions shows marked differences. For all compositions, pre-eruptive fluids have higher C/S and lower H/C atomic ratios than coexisting melts. Comparison between volcanic gas and pre-eruptive fluid compositions shows good agreement in the high temperature range. However, to reproduce faithfully the compositional field delineated by volcanic gases, silicic to andesitic arc magmas must be fluid-saturated under pre-eruptive conditions, with fluid amounts of at least 1 wt%, whereas mafic compositions require lower amounts of fluid, in the range 0.1–1 wt%. Nevertheless, volcanic gases colder than 700 °C are generally too H
2
O-rich and S-poor to have been in equilibrium with silicic to andesitic magmas under pre-eruptive conditions, which suggests that such gases probably contain a substantial contribution from meteoric or hydrothermal water.
Sulphur release from flood lava eruptions in the Veidivötn, Grímsvötn and Katla volcanic systems, Iceland
Authors: Thordarson T. , Self S. , Miller D. J. , Larsen G. , Vilmundardóttir E. G. 
Published: April 2008

Abstract

Emissions of SO
2
by volcanic eruptions have been shown to be important for short-term environmental and climate changes. Stratospheric sulphur mass-loading by explosive silicic eruption is commonly considered to be the principal forcing factor for these changes. The SO
2
emissions from basaltic flood lava eruptions have not featured strongly in the discussions on volcano-climate interactions, notwithstanding the fact that basaltic magma is typically richer in sulphur (by a factor of two to four), than silicic magmas, as well as the evidence of widespread atmospheric impact associated with historical flood lava eruption.

Fourteen Holocene flood lava eruptions are known from the Veidivötn, Grímsvötn, and Katla volcanic systems of the Eastern Volcanic Zone in South Iceland, which include the three largest of its kind in Iceland; the 1783–1784 Laki, 934–40 Eldgjá, and
c.
8600 years
BP
Thjórsá events. We present new data on the sulphur content in melt inclusions from the Veidivötn system and use this information, along with existing inclusion data from the Grímsvötn and Katla volcanic systems, to establish an empirical method for estimating the sulphur mass release from these basaltic flood lava eruptions. The results show that these eruptions released a total of
c.
700 Mt SO
2
into the atmosphere in four 600- to 850-year-long eruption periods. During each period, between 98 and 328 Mt SO
2
were emitted into the atmosphere, and the mass loadings from individual eruptions ranged from 5 to 210 Mt SO
2
. These flood lava eruptions are likely to have resulted in widespread atmospheric perturbations and, by analogy with the 1783–1784 Laki eruption, the effects of the largest eruptions may have been felt on a hemispheric scale.
Optical sensing of volcanic gas and aerosol emissions
Authors: McGonigle A. J. S. , Oppenheimer C. 
Published: April 2008

Abstract
Volcanic gas and aerosol surveillance yield important insights into magmatic, hydrothermal, and atmospheric processes. A range of optical sensing and sampling techniques has been applied to measurements of the composition and fluxes of volcanic emissions. In particular, the 30-year worldwide volcanological service record of the Correlation Spectrometer (COSPEC) illustrates the point that robust, reliable, straightforward optical techniques are of tremendous interest to the volcano observatory and research community. This chapter reviews the field, in particular the newer and more versatile instruments capable of augmenting or superseding COSPEC, with the aim of stimulating their rapid adoption by the volcanological community. It focuses on sensors that can be operated from the ground, since they generally offer the most flexibility and sensitivity. The success of COSPEC underlines the point, however, that such devices should be comparatively cheap, and easy to use and maintain, if they are to be widely used.
Fumarole migration and fluid geochemistry at Poás Volcano (Costa Rica) from 1998 to 2001
Authors: Vaselli O. , Tassi F. , Minissale A. , Montegrossi G. , Duarte E. , Fernández E. , Bergamaschi F. 
Published: April 2008

Abstract

We report the results of a geochemical survey of fumaroles, thermal springs, and gas discharges from areas in and around the active crater lake of Poás volcano (Costa Rica) from February 1998 to February 2001. The springs are highly acidic-sulphate waters with temperatures approaching boiling point, whereas gas chemistry is characterized by typical magmatic species, such as SO
2
, HF, HCl, H
2
, and CO. From February 1998 new fumarolic fields formed inside the southern part of the crater. They moved anticlockwise from the S to the NE inner walls of the crater, while those located in the southern part of the crater and close to the pyroclastic cone south of the crater lake diminished or disappeared altogether, during 1999 and 2000. This shift was also characterized by chemical variation of the magmatic gas species. In spite of the chemical changes of fumaroles, the composition of the lake changed little during this time. This fact, together with the chemical profile with depth of the lake, suggests that the lake is a very efficient condenser of magmatic fluids. An apparent chemical stratification of the lake suggests that dilution with meteoric water is not complete, due to the presence of liquid sulphur at the lake bottom and/or due to the continuous influx of new magmatic components.
Degassing processes of Popocatépetl and Volcán de Colima, Mexico
Authors: Varley N. R. , Taran Y. 
Published: April 2008

Abstract
To understand the behaviour of a volcano and try to predict future eruptive activity, it is imperative to investigate its degassing processes. Areas of study include direct degassing of the magma through the conduit, the interaction between the hydrothermal system and volcanic gases and fluids, and diffuse degassing through the volcanic edifice. Various aspects of the degassing processes of Popocatépetl and Volcán de Colima in Mexico have been studied. The results are summarized in this chapter, and new data on diffuse degassing at both volcanoes and analyses of fumarolic gases from Volcán de Colima are presented.

Variations in the flux of SO
2
at both volcanoes have led to models of the degassing processes. At Colima, isotopic analyses of condensates suggest a shallow degassing magma body. Volcán de Colima showed geochemical precursors prior to its 1998/9 eruption and variations in certain parameters continue to relate to the behavior of the volcano during its on-going eruption. Both volcanoes yield interesting data on their diffuse degassing of CO
2
and radon: at Popocatépetl, the large plume degassing contrasts with a small diffuse contribution. Volcán de Colima has anomalous concentrations of diffuse CO
2
associated with faults. The challenge is how to interpret the geochemical data to provide a fresh insight into the mechanics of the volcanic system.