bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Laurentian? Grenville-age oceanic arc/back-arc terrane in the Sierra de Pie de Palo, Western Sierras Pampeanas, Argentina
Authors: Vujovich Graciela I. , Kay Suzanne Mahlburg 
Published: April 2008

Abstract
Whole-rock trace element, field, and petrographical studies indicate that the protoliths of highly deformed metamorphic rocks of the Pie de Palo Complex, Argentina, formed in an oceanic setting like that of SW Pacific supra-subduction complexes (e.g., Lau Basin). Age constraints suggest that this Mesoproterozoic complex, which includes some of the most primitive Grenville-age magmas known on Earth, formed in < 60 million years. Amphibolites (Las Pirquitas/Quemado region) with N-MORB like light-depleted REE patterns and Hf/Ta/Th relations, associated with Fe-rich schists interpreted as hydrothermally altered lavas and gabbros, formed in a back-arc spreading centre. Other ultramafic/mafic units (Quebrada del Gato, Cerros Valdivia/Barboza) formed as arc cumulates, and (central region) as ridge or arc/back-arc lavas (including shoshonite). Intermediate and silicic schists/gneisses are interpreted as arc region greywackes and silicic lavas, and marbles as reef deposits. Quebrada del Gato gneisses with trace elements indicating high pressure residual mineral assemblages are interpreted as younger subduction-related magmas emplaced in a thickened crust. The Pie de Palo Complex probably formed offshore of eastern Laurentia, and subsequently collided with Laurentia east of the Llano uplift, Texas, in Grenvillian times. This block, along with the Precordillera, was rifted from Laurentia in the latest Precambrian, arriving in Gondwana by Ordovician time.
The Pampean Orogeny of the southern proto-Andes: Cambrian continental collision in the Sierras de Córdoba
Authors: Rapela C. W. , Pankhurst R. J. , Casquet C. , Baldo E. , Saavedra J. , Galindo C. , Fanning C. M. 
Published: April 2008

Abstract

A detailed study of the pre-Silurian geology of the Sierras de Córdoba, Eastern Sierras Pampeanas, is used to define the sequence of magmatic and metamorphic events during the Pampean orogeny. This primarily involved Early to Mid-Cambrian subduction and terrane collision at the western margin of Gondwana during the amalgamation of the super-continent. Evidence for this is based principally on new information concerning (a) regional mapping and field relations, (b) analysis of the structures, deformational history and meta-morphic evolution and (c) geochronology and geochemistry of the igneous and metamorphic rocks. The main events recognized are (1) Late Proterozoic break-up of Rodinia (Nd model ages of 1500 ± 200 Ma, inherited zircons 800–1400 Ma), (2) development of an Early Cam-brian passive margin sequence (Puncoviscana Formation and equivalents), (3) emplacement of metaluminous calc-alkaline granitoids (G1a, dated at 530 ± 3 Ma) as a result of NE-directed subduction, (4) crustal thickening, ophiolite obduction, compression and high-grade metamorphism (M2: 8.6±0.8 kbar, 810 ± 50°C,
c.
525 Ma) related to collision, and culmina-ting in (5) isothermal uplift and widespread low-
P
anatexis (M3, 4.0±0.5 kbar, 715 ± 15°C,
c.
520 Ma). The last event is responsible for the linked generation of highly peraluminous granites (G1b) and cordieritites. Subsequent emplacement into the accreted terrane of Ordovician trondhjemite-tonalites (500-470 Ma) and dextral wrench shear are interpreted as inner cordilleran counterparts of the Famatinian arc, which developed to the west along the newly-formed proto-Andean margin.
U-Pb, Th-Pb and Ar-Ar geochronology from the southern Sierras Pampeanas, Argentina: implications for the Palaeozoic tectonic evolution of the western Gondwana margin
Authors: Sims J. P. , Ireland T. R. , Camacho A. , Lyons P. , Pieters P. E. , Skirrow R. G. , Stuart-Smith P. G. , Miró R. 
Published: April 2008

Abstract

New SHRIMP zircon and monazite
206
Pb/
238
U and
208
Pb/
232
Th ages on structurally controlled units and
40
Ar-
39
Ar step-heating ages from shear fabrics, define three distinct regional tectonic events in the southern Sierras Pampeanas. The first, the Pampean orogeny, involved closure of a late Neoproterozoic basin on the western margin of Gondwana. New rims on detrital zircons and concurrent monazite growth suggest that the metamorphic peak was attained by
c.
530 Ma. The second event, the Famatinian orogeny, marks the initiation of eastward-dipping subduction on the western Gondwana margin, and may represent a continuation of the earlier Pampean event. Metasedimentary rocks from the Sierras de San Luis have zircons with a predominantly Early Cambrian detrital age, indicating a Pampean source. The metamorphic peak in these rocks was contemporaneous with the emplacement of felsic, mafic and ultramafic rocks at
c.
480 Ma in a collisional setting. Monazite ages and limited new zircon growth in the metasedimentary rocks suggest that the Famatinian orogeny had ceased by about 450 Ma. This correlates well with a 450–460 Ma Ar-Ar age for late shearing in the southern sierras of La Rioja province. The third tectonic event, the Achalian orogeny, involved W-directed compression and emplacement of multiple, voluminous, granite intrusions. Deformation during this event was partitioned between discrete shear-zones and regions of open to tight folding. The shear zones alternate between W-directed thrusts and NNW-trending, sinistral shear-zones. Ar-Ar data from the low-grade shear fabrics indicate that transpressional deformation continued through most of the Devonian.
The Early Palaeozoic magmatic record of the Famatina System: a review
Authors: Saavedra J. , Toselli A. , Rossi J. , Pellitero E. , Durand F. 
Published: April 2008

Abstract
The Famatina System is an elongated geomorphological zone between the Eastern and Western Sierras Pampeanas, characterized by important Ordovician volcanism. The basement consists mainly of a sedimentary protolith, metamorphosed to low grade during the Pampean orogeny (Early-Mid-Cambrian), together with sparse outcrops of high-grade metamorphic rocks. Overlying this basement, the Volcancito Formation consists of thin sediments of uppermost Cambrian and Tremadocian age, deposited in restricted basins. A much more voluminous series of volcanic and sedimentary deposits, initiated in the Arenig and culminating in Early-Mid-Llanvirn times, indicates a significant increase in the rate of tectonic subsidence. The form of these deposits shows that they were laid down in an ensialic marginal basin that developed contemporaneously with active volcanic activity. The products of the latter were predominantly acidic, generated by crustal anatexis, with much rarer occurrence of basaltic and trachyandesitic compositions. The volcanic rocks are cut by granitoids of unknown absolute age, although the few radiometric ages obtained on them do not exceed 460 Ma. The volcano-sedimentary basin is interpreted as related to subduction, and the granitic and volcanic rocks together represent a continental magmatic arc developed regionally during the Early Ordovician.
Timing of fluid flow in a sandstone reservoir of the north German Rotliegend (Permian) by K-Ar dating of related hydrothermal illite
Authors: Zwingmann Horst , Clauer Norbert , Gaupp Reinhard 
Published: April 2008

Abstract
Authigenic illite is the most abundant clay mineral in Carboniferous and Rotliegend rocks of northern Germany. In spite of extreme present-day burial depths of 4580 to 5280 m, the Rotliegend sandstones are characterized by moderate permeabilities which are controlled, together with their reservoir qualities, by omnipresent illite. It is admitted that deep-crustal hydrothermal fluids, migrating along major fault systems, interacted with the Carboniferous Coal Measures and generated acidic fluids inducing primary leaching processes, mass transfers and concomitant pervasive clay authigenesis.
The investigated samples belong to wells located in a horst-graben structure covering an area of 20 by 20 km. This restricted area allowed investigation of a three-dimensional distribution of fluid flows and related illitization in distinct sandstone reservoirs. The K-Ar ages of the < 2 μm fractions decrease from 210-180 Ma (11 analyses with a mean at 198 Ma) for illite in the horst position to 190-155 Ma (24 analyses with a mean at 177 Ma) for illite in the graben area up to about 4 km away from faults, suggesting a relationship between timing of illite formation and structural position of the host rocks. The decrease in the illite K-Ar ages from the horst into the graben allowed calculation of a migration rate of 0.2 μm per year for the illitization front in the Rotliegend sandstones towards the centre of the graben, which might be of use for prediction of the illite distribution in these rocks.
Authigenic potassium feldspar: a tracer for the timing of palaeofluid flow in carbonate rocks, Northern Calcareous Alps, Austria
Authors: Spötl Christoph , Kunk Michael J. , Ramseyer Karl , Longstaffe Fred J. 
Published: April 2008

Abstract

Feldspar is a common authigenic constituent in Permian carbonate rocks which occur as tectonically isolated blocks within the evaporitic Haselgebirge mélange in the Northern Calcareous Alps (NCA). Coexisting with pyrite, anhydrite, (saddle) dolomite, magnesite, fluorite and calcite, K-feldspar and minor albite record an event of regionally extensive interaction of hot brines with carbonate rocks. Detailed petrographic, crystallographic and geochemical studies reveal a variability in crystal size and shape, Al-Si ordering, elemental and stable isotopic compositions of the K-feldspar, which is only partially consistent with the traditional view of authigenic feldspar as a well-ordered, compositionally pure mineral.
40
Ar-
39
Ar step-heating measurements of authigenic potassium feldspar from several localities yield two age populations, an older one of 145–154 Ma, and a younger one of
c.
90–97 Ma. Most age spectra reflect cooling through the argon retention temperature interval, which was rapid in some localities (as indicated by plateau ages) and slower in others. Rb-Sr isotope data are more difficult to interpret, because in many K-feldspar samples they are controlled largely by Sr-bearing inclusions. The Jurassic
40
Ar-
39
Ar dates are interpreted as minimum ages of feldspar growth and hence imply that fluid-rock interaction is likely to be simultaneous with or to slightly predate mélange formation. Deformation associated with the closure and subduction of the Meliata-Hallstatt ocean south of the NCA during the Upper Jurassic is regarded as the principal geodynamic driving force for both enhanced fluid circulation and mélange formation. Some localities were reheated beyond the argon retention temperature for microcline during mid-Cretaceous nappe stacking of the NCA, thus obliterating the older signal.
Dating fluid flow in shear zones: Rb-Sr and U-Pb studies of syntectonic veins in the Néouvielle Massif, Pyrenees
Authors: Wayne D. M. , McCaig A. M. 
Published: April 2008

Abstract
Rb-Sr and Pb-Pb data are reported from separated minerals (amphibole, albite, calcite, epidote), altered wall rocks, and fluid inclusions trapped in quartz, from veins associated with retrogressive shear zones cutting the Néouvielle granodiorite massif in the central French Pyrenees. Alteration in the shear zones was caused by movement of hypersaline brines during deformation. Shear zones with similar kinematics occur in granodiorites and high grade gneisses throughout the northern Axial Zone of the Pyrenees, and have been attributed variously to both the Variscan and Alpine orogenies. Rb-Sr data on a syntectonic, polymineralic vein and its altered wall rock support an Alpine age for deformation and fluid flow, giving an isochron of 47 ± 8 Ma, or 48 ± 2 Ma if albite is excluded. Another vein gives a similar age for altered wall rock and albite, but chlorite and quartz-hosted fluid inclusions are out of equilibrium. Pb data plot as quasi-linear arrays on ratio plots, with no age significance. The usefulness of this latter technique is restricted by the slow rate of uranium decay in these young rocks, but in any case Pb isotopic ratios do not appear to have homogenized during vein formation.
Thermal history and timing of fluid flow at the Ardèche palaeomargin, France
Authors: Pagel Maurice , Clauer Norbert , Disnar Jean-Robert , Mossmann Jean-Rémi , Sureau Jean-François , Steinberg Michel , Vinchon Charlotte 
Published: April 2008

Abstract
The fluid evolution, the timing of fluid flow and the thermal history of the faulted Ardèche passive palaeomargin, France, were reconstructed using detailed mineralogical, petrological, geochemical and geophysical studies applied on core material from Triassic sandstone and Liassic carbonate units of the BA1 and MM1 boreholes. It could be shown that an early cementation significantly reduced the porosity of the rocks. Application of various geothermometers and chronothermometers showed that the outcropping Jurassic units underwent a degree of diagenetic evolution corresponding to the onset of the oil window. In the Triassic sandstone, temperatures reached 130–145°C as recorded by the dolomitic cements. Fluids in thermal disequilibrium with their host rock were found, implying supply of fluids from deeper levels. The decrease of temperature below 120 ± 10°C during the Eocene is explained by the erosion of 1900 m of mainly Cretaceous sediments. A fault system was active at different periods, especially at 190 Ma and during the post-Cretaceous uplift.
Unravelling complex filling histories by constraining the timing of events which modify oil fields after initial charge
Authors: Lisk M. , Eadington P. J. , O’Brien G. W. 
Published: April 2008

Abstract
Complex and multiphase charge histories are a feature of many hydrocarbon discoveries. Previous descriptions of charge history that have relied on the chemical properties of hydrocarbons do not define the geometry of hydrocarbon accumulations prior to the attainment of their present state. In this paper, examples of oil charge studies conducted on hydrocarbon discoveries from the Australian North West Shelf are presented to demonstrate the application of a new technique for the mapping of hydrocarbon charge called GOI™ (Grains containing Oil-bearing fluid Inclusions). In Australian oil fields GOI values in oil leg samples are an order of magnitude higher than in underlying water zones and record the maximum oil saturation experienced through time. An empirical threshold for oil saturation consistent with accumulation (GOI > 5%) rather than migration (GOI < 1%) of oil has been established from a database of 20 Australian oil fields. Oil inclusions are retained if oil is lost from the pore spaces of the rock, which allows GOI to be used to identify relict oil columns and locate the original oil-water contact. GOI measurements allow the original size and disposition of palaeo-oil columns to be determined and the physical events controlling the composition and size of hydrocarbon accumulations to be deduced in space and time. These data allow issues which cause changes to the original fluid contacts, such as trap integrity, tilting and gas displacement, to be confidently identified and characterized. When combined with conventional approaches to prospect evaluation, these new data allow a more sophisticated description of the filling history of hydrocarbon discoveries. They also allow the oil charge risk associated with new plays to be appropriately constrained before new drilling is commissioned.
Predicting the distribution of small faults in a hydrocarbon reservoir by combining outcrop, seismic and well data
Authors: Steen Ø. , Sverdrup E. , Hanssen T. H. 
Published: April 2008

Abstract
This paper investigates the possibility of identifying small faults in a hydrocarbon reservoir from spatial derivatives of seismic horizons (dip, azimuth, rate of change of dip), combined with well log structural data and analogue models. The analogue models include examples from the literature and a faulted surface constructed from Kilve beach, Bristol Channel, which represent typical surface attributes associated with small faults and artefacts produced by modelling. Well log structural data of good quality were integrated with the seismic data to study the 1D spatial distribution of subseismic faults and their expression on seismic horizons. The results suggest that dip and azimuth modelling can be useful, but the methods need to be combined to achieve reliable interpretations of the individual features. The rate of dip change has less potential to trace individual structures, unless the signal/noise ratio is very high. The ductile strain observed on seismic sections is, to a large degree, assumed to be produced by subseismic faults. The amount of ductile strain may be quantified by calculating the rate of dip change across curved seismic horizons. Exact predictions of fault densities are difficult because of the inaccuracies related to the modelling technique and the variability in fault and fold styles that occurs on a subseismic scale. Detailed dipmeter and core interpretation can be used to calibrate structural dip and spatial frequency of faults.
Fault sealing processes in siliciclastic sediments
Authors: Fisher Q. J. , Knipe R. J. 
Published: April 2008

Abstract
The microstructure and petrophysical properties of fault rocks from siliciclastic hydrocarbon reservoirs of the North Sea are closely related to the effective stress, temperature and sediment composition at the time of deformation, as well as their post-deformation stress and temperature history. Low permeability fault rocks may develop due to a combination of processes including: the deformation induced mixing of heterogeneously distributed fine-grained material (principally clays) with framework grains, pressure solution, cataclasis, clay smear, and cementation. Fault rocks can be classified into various types (disaggregation zones, phyllosilicate-framework fault rocks, cataclasites, clay smears, and cemented faults/fractures) based upon their clay and cement content as well as the amount of cataclasis experienced. In the absence of extensive cementation, the distribution of fault rock types along a fault plane can often be predicted from a detailed knowledge of the reservoir sedimentology. The permeability of fault rocks can vary by over six orders of magnitude, depending on the extent to which the porosity reduction processes have operated. Utilizing the strong link between the petrophysical properties of fault rocks and their geohistory allows the risks associated with fault seal evaluation to be reduced.
Thermal effects of fluid flow in steep fault zones
Authors: Fleming C. G. , Couples G. D. , Haszeldine R. S. 
Published: April 2008

Abstract

Two-dimensional, porous-medium, steady-state, coupled fluid- and heat-transport models are used to investigate some of the hydrogeological and thermal consequences of steeply dipping fault damage zones in a normally pressured basin setting. Simple geometries and conservative petrophysical properties can produce large-scale buoyancy-driven circulation, both outside and within the fault zone. An average (homogeneous) basin permeability of only 7 mD
k
h
(horizontal permeability) and 0.07 mD
k
v
(vertical permeability) results in a free convection cell of this type, with the upflow being localized by a 300 m wide fault zone (50 mD
k
h
, 0.5 mD
k
v
). Steady-state temperature anomalies as large as 15°C at the top of the fault zone can be produced by this arrangement. Smaller values of basin permeability still result in a similar circulation pattern, but at flow rates which produce temperature anomalies that are below detection levels. When the basin fill is more heterogeneous (layered), higher permeabilities can exist in some layers without large-scale convection occurring, because of the dampening effect of other, lower permeability units. In realistic geometrical configurations that are similar to the North Sea Central Graben, the fluid flow system is dominated by within-fault-zone convective circulation that produces local (<10 km half-wavelength), high amplitude (50°C) temperature anomalies which are comparable to the largest of those actually observed in the subsurface.
The impact of faults on fluid flow in the Heidrun Field
Authors: Knai T. A. , Knipe R. J. 
Published: April 2008

Abstract

A quantitative analysis of fault seal properties has been used in reservoir simulation modelling in the Heidrun Field. The inclusion of microstructural and petrophysical data from core analysis has resulted in a better prediction of reservoir communication and drainage patterns during production. Three main fault rock types were observed in the Heidrun cores, namely;
cataclasites
developed from clean sandstones,
phyllosilicate framework fault rocks
, created from impure sandstones and
clay smears
. The clay content of the host sediment is the controlling factor in determining which fault rock type dominates in the fault zones. Fault plane geometries were assessed from seismic-based juxtaposition analysis for input into the reservoir simulation model. The fault planes were divided into areas following the reservoir zonation, and transmissibility multipliers were assigned to each subarea of the fault planes in the model. The transmissibility multipliers are a function of fault rock permeability and fault rock width, as well as the matrix (host rock) permeability and the dimensions of the grid blocks used in the simulation model. Introducing a quantitative description of the faults has had a significant effect on the results of the reservoir simulation runs and has played an important role in the successful modelling and prediction of the observed gas breakthrough and pressure evolution. After actively using the transmissibilities during history matching of the simulation model, a remarkably good match to the observed well rates and pressures (flowing and shut-in) for the Jurassic Fangst and Upper Tilje reservoir units was achieved.
Facies and curvature controlled 3D fracture models in a Cretaceous carbonate reservoir, Arabian Gulf
Authors: Ericsson J. B. , McKean H. C. , Hooper R. J. 
Published: April 2008

Abstract
The Late Cretaceous Ilam Formation of the Arabian Gulf’s Fateh Field is a very heterogeneous, fractured carbonate reservoir. Porosity, matrix permeability and facies trends do not appear to be related, but fracture density exhibits a strong relationship to both facies distribution and structural curvature. Three-dimensional (3D) models of dip change, position with respect to the crest of the field, facies and porosity variation are combined to produce a qualitative 3D model of fracture density which matches empirical fracture density data from more than 16 750m of interpreted image log. The fracture model aids in transmissibility prediction for reservoir simulation, producing a better history match and decreasing uncertainty for future drilling programmes.