bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fluid-flow processes and diagenesis in sedimentary basins
Authors: Bjørlykke Knut 
Published: April 2008

Abstract
Flow of fluids in sedimentary basins causes transport of heat and dissolved mass and is therefore potentially important in relation to diagenetic reactions. Rather large fluid fluxes are required, however, for this type of transport to be significant in terms of dissolution and precipitation of minerals. Before diagenetic processes are attributed to pore water flow, semi-quantitative calculation of flow rates and duration of flow should be attempted.

Heat flow in sedimentary basins is normally dominated by conduction, except on a local scale. The upwards pore water flux due to compaction is on average smaller than the subsidence rate, and the thermal anomalies caused by compaction are moderate in modern basins. Dissolution and precipitation of minerals which are in equilibrium with the pore water occur when the flow is oblique relative to the isotherms. Due to the low solubility/temperature gradient of the common silicate and carbonate minerals, very large fluxes of pore water are required to transport significant volumes of mass in solution. The greatest potential for transporting solids and creating secondary porosity is during meteoric water flow, because the flow rate then may be several orders of magnitude higher than what is typical for compaction-driven flow. Quartz overgrowth corresponding to 3% of the rock volume requires a total flow of 10
8
cm
3
cm
−2
if the silica is introduced by vertical compaction-driven flow from a source outside the sandstone. Pore water flow precipitating quartz due to cooling will dissolve carbonate cement at a much higher rate. An external import of silica through the flow of water would be expected to cement up the most permeable pathways, such as fractures and well-sorted permeable sand beds. In the case of carbonate cement the solubility gradient is negative and upwards flowing and cooling pore water would cause dissolution rather than precipitation. Also in the case of carbonate rocks, large-scale mass transfer such as dolomitization is easier to explain as occurring at relatively shallow depths rather than during deeper burial.

Ore minerals like galena have a steep solubility/temperature gradient, but concentrated precipitation requires rapid cooling of hot water. Such conditions are most likely to be met when hot fluids are cooled near the surface.
Hydrocarbons and other fluids: paragenesis, interactions and exploration potential inferred from petrographic studies
Authors: Parnell John 
Published: April 2008

Abstract

Residues of hydrocarbons (bitumens
sensu lato
) are found in a wide range of settings in addition to reservoir porosity, including microfractures, megafractures, and several types of vein porosity. Paragenetic relationships between hydrocarbons and inorganic minerals provide information on the relative timing of hydrocarbon migration and the migration of other fluids. Hydrocarbons in reservoir rocks and mineralized fractures are paragenetically late as they are in pre-existing fluid pathways. Some other types of hydrocarbon occurrence are paragenetically earlier, especially proximal to the source rock. Different types of ore mineralization (notably base metal and uranium) in which hydrocarbons occur exhibit varying parageneses which represent distinct burial/thermal histories responsible for the ore types. Co-migration of hydrocarbons and silicon-bearing fluids is evinced by the occurrence of large quantities of authigenic silicate minerals within hydrocarbon residues.

Interactions between metals and hydrocarbons may be exploited in the exploration for both metals and hydrocarbons. Metal-rich fossil fuels can preserve a signature of anomalous metal concentrations in the vicinity of ore deposits. Hydrocarbons precipitated by irradiation-solidification processes about radioelement-bearing phases help to identify hydrocarbon migration pathways and in some circumstances allow isotopic dating of migration.
Fluid-rock interactions during continental red bed diagenesis: implications for theoretical models of mineralization in sedimentary basins
Authors: Metcalfe R. , Rochelle C.A. , Savage D. , Higgo J.W. 
Published: April 2008

Abstract
Continental red beds are first-cycle, immature sediments which are deposited in oxidizing conditions and owe their red colouration to the early diagenetic development of hematite. Previously published work on the fluid/rock interactions which occur during the diagenesis of such sediments highlights that pH and redox are critical fluid parameters which control diagenesis and ore formation. However, except in modern surface water and shallow groundwater systems, these parameters cannot be measured directly, and must be estimated from theoretical considerations. These suggest that mixing between fluids of different redox states is likely to be a critical control on heavy metal mobility. Many diagenetic features can be explained largely by the chemical heterogeneity of red beds, and by the diagenetic ranges of redox conditions and pH which are among the greatest for any type of sediment. Such features include: the formation of red bed-hosted ore deposits; the extensive development of hematite; and the development of early diagenetic non-ferroan carbonate and late diagenetic ferroan carbonate cements. In order to develop theoretical models of fluid/rock interactions during such diagenesis, it is important to consider the interrelationships between fluid flow, mineral dissolution and precipitation, and sorption. At the present time such models are at an early stage of development.
Recognition of the thermal effects of fluid flow in sedimentary basins
Authors: Duddy I.R. , Green P.F. , Bray R.J. , Hegarty K.A. 
Published: April 2008

Abstract
Moving fluids are capable of transporting a large amount of heat over long distances in sedimentary basins, but the effects are often ignored when modelling the thermal evolution of sedimentary basins. If significant, the passage of these heated fluids through the sediment pile will leave a thermal signature which can be measured at the present-day using palaeotemperature determinants such as vitrinite reflectance and apatite fission track analysis (AFTA™). The interpretation of palaeotemperature-depth profiles, particularly the slope of a palaeotemperature-depth profile, i.e. the palaeogeothermal gradient, allows fluid-induced temperature profiles to be distinguished from those due to simple conduction of basal heat flow.
Steady-state systems, typified by large-scale lateral fluid flow in foreland basins or where low-temperature hydrothermal circulation systems occur associated with intrusions and thick volcanic piles, are characterized by dog-length geothermal gradients, with high-interval gradients near the surface, above the shallowest aquifer, and lower interval gradients beneath an aquifer. It is argued that the classic occurrence of near vertical vitrinite reflectance-depth profiles observed in many ancient foreland basins can result from this mechanism.
Thermal effects of transient fluid flow are most easily observed at the present-day, where they are characterized by low or negative geothermal gradients beneath aquifers in active geothermal systems, and the same criterion enables their recognition in ancient situations. Similarly, shallow-level igneous intrusion into porous and permeable sediments can produce observable thermal signatures further from the intrusion than will result from simple conduction, but which can be readily explained by movement of fluids heated by the intrusion. Complex steady-state profiles that may be difficult to distinguish from transient profiles without additional geological data may arise where multiple aquifers are separated by aquitards.
The thermal consequences of fluid flow in two of these situations, a foreland basin and igneous intrusion into porous sediments, are illustrated by examples of thermal history reconstruction from the Pliocene Papua New Guinea Fold Belt and the Canning Basin of Australia, respectively.
Geostatistical estimation of manganese oxide resources at the Nsuta Mine
Authors: Al-Hassan S. , Annels A. E. 
Published: April 2008

Abstract
The Nsuta manganese deposit is located about 6.5 km south of Tarkwa in the southwestern region of Ghana. It is associated with a carbonate horizon within a thick series of interbedded grey tuffs and thin argillaceous horizons of Precambrian, Upper Birimian age. The manganese oxide mineralization, produced by supergene enrichment of the stratiform carbonate horizon, occurs as massive, patchy or bedded accumulations of psilomelane, with numerous veinlets and cavity fillings of pyrolusite. Due to the impact of folding and faulting and past mining activity (open-pit), the remaining resources have a complex spatial distribution. The study described is based on a portion of this deposit referred to as Hill D (South Crest). Initial statistical studies revealed the existence of two assay populations which appear to correspond to two geologically identifiable ore types that cannot be differentiated at the present scale of mining. Two geostatistical methods (ordinary kriging and indicator kriging) were used to evaluate the resource and the estimates so produced were then compared. A wireframe model was used to constrain the three dimensional geostatistical block model.
Subduction systems and magmatism
Authors: Hamilton Warren B. 
Published: April 2008

Abstract

Most published subduction modelling and much palaeotectonic speculation incorporate the false assumption that subducting oceanic plates slide down fixed slots. In fact, hinges roll back into oceanic plates and slabs sink more steeply than the inclinations of the Benioff zones which define transient positions of the slabs. The lower parts of overlying mantle wedges sink with the slabs, pulling away from partial-melt zones higher in the wedges. The complex behaviour of arc systems can be comprehended in terms of this mechanism of subduction. The common regime in overriding plates is extensional, and leading edges are crumpled only in collisions. Shear coupling between subducting slabs and overriding plates is limited to shallow depths and varies widely, with corresponding variations in tectonic erosion, accretion, and regurgitation of high-
P
subducted materials. Arcs can advance, lengthen, change curvature, festoon around obstacles, rotate while deforming, and fold and pinch shut. Two arcs can collide as an intervening oceanic plate is subducted simultaneously beneath both, or they can migrate apart as new lithosphere is formed between them. Subduction cannot occur simultaneously beneath opposite sides of a rigid plate because impossible retrograde subduction would be required beneath one of them. Histories, including inception ages, collisions, polarity reversals and stage of petrological evolution, vary greatly along continuous arc systems. Long-continuing steady-state systems are uncommon.

Magmatic arcs are properly viewed as features migrating with sinking lower plates, not as fixed features of upper plates. Hot inclined zones within mantle wedges, midway between sinking slabs and overriding crust, are avenues for replenishment of mantle pulled away with subducting plates and also are sites of generation of arc protomelts as volatiles rise into them from dehydrating slabs. Back-arc basins form by spreading behind migrating arcs; strips of arcs may be abandoned in the spreading systems. An arc can migrate so rapidly that it plates out oceanic lithosphere rather than producing a welt.
Exposed sections of the upper mantle and basal crust of arcs show that the Mohorovičić discontinuity is a self-perpetuating density filter and that the already-evolved basaltic and melabasaltic melt that leaves the mantle forms great basal-crust sheets of norite, gabbro and granulite. All more-evolved rock types in these sections are generated in the crust by fractionation, secondary melting and contamination (and this falsifies much petrological modelling).
Cretaceous to Cenozoic volcanism in South Korea and in the Sea of Japan: magmatic constraints on the opening of the back-arc basin
Authors: Pouclet André , Lee Jin-Soo , Vidal Philippe , Cousens Brian , Bellon Hervé 
Published: April 2008

Abstract
The major element, trace element, and radiogenic isotope compositions of volcanic rocks in the back-arc area of the eastern Eurasian continental margin provide insight into the nature of the mantle wedge and constrain the magmatic evolution of the Japan Sea back-arc basin linked to its tectonic history. Different phases of post-Early Cretaceous volcanic activity are identified along the Korean margin and in the Japan Sea. Volcanic rocks from Korea include (1) Cretaceous and early Cenozoic calc-alkaline lavas of a volcanic arc at an active margin, and (2) Pliocene and Quaternary intraplate flood basalts and volcanic islands of alkaline composition. Japan Sea volcanic rocks consist of (1) early Cenozoic andesite flows of a remnant arc in the Yamato Bank, (2) early Miocene basalts of the Japan Sea basin basement, which share compositional characteristics of island arc tholeiites, continental rift tholeiites and back-arc basin basalts, (3) late Miocene seamounts of tholeiitic and mildly alkaline compositions, and (4) Pliocene and Quaternary alkaline volcanic islands.
Geochemically, these rocks belong to three broad magmatic groups: (1) an arc-related, calc-alkaline group of a continental, Andean margin type, which prevailed prior to the opening of the Japan Sea between the Cretaceous and early Miocene, (2) continental rift tholeiites and back-arc basin basalts, formed during the rifting stage in the early Miocene, and (3) an intraplate alkaline group similar to OIB, erupted later during spreading, between late Miocene and Holocene times.
Trace element and Sr, Nd and Pb isotopic compositions of selected samples show that the sources of magma Group 1 calc-alkaline lavas and magma Group 2 tholeiitic lavas included varying contributions of two main mantle components: an Indian Ocean MORB-like depleted mantle source (DMM) and an enriched mantle component similar to EM II. The latter component could represent DMM contaminated by subducted oceanic sediments incorporated into the lower lithosphere during the long-lived subduction of west Pacific crust. During the opening of the Japan Sea back-arc basin, the relative proportion of the DMM component dramatically increased between the rifting and spreading stages. It is also necessary to postulate a third component present in the sources of the Group 3, post-opening alkaline lavas, perhaps enriched mantle of EM I composition, which may also have resided in the subcontinental lithospheric mantle.
Arc and back-arc geochemistry in the southern Kermadec arc-Ngatoro Basin and offshore Taupo Volcanic Zone, SW Pacific
Authors: Gamble J. A. , Wright I. C. , Woodhead J. D. , McCulloch M. T. 
Published: April 2008

Abstract
Back-arc basin basalts from the Ngatoro Basin (the southern end of the Havre Trough) are similar geochemically to, yet subtly distinct from, basalts of the Havre Trough to the north. Whole rock and glass chemistry are consistent with derivation from a fertile mantle source with subsequent evolution by fractionation of olivine (+ Cr-spinel) + plagioclase, and then clinopyroxene. Basalts from the vicinity of Rumble IV seamount at the southern end of the Kermadec island arc, and the eastern Ngatoro rift escarpment, are strongly porphyritic relative to the back-arc basin basalts and show trace element (high LIL abundances and highly depleted HFS abundances) and isotopic signatures of subduction zone basalts.
At its southern end, the Ngatoro Basin penetrates the continental crust of New Zealand creating a major, 3000 m deep bathymetric re-entrant in the slope-break; the slope-break marks the transition from oceanic to continental crust. Basalts from the floor of the Ngatoro Basin re-entrant are isotopically distinct from the basalts of the oceanic sector in that they have higher Sr and correspondingly lower Nd isotope ratios and are comparable to basalts of the Taupo Volcanic Zone (TVZ) to the south.
In contrast to the basalt-dominated oceanic sector, basalts from the offshore TVZ, a 100 km long area extending roughly NNE from White Island to the submarine Whakatane arc volcano at the edge of the continental slope-break, occur in association with andesites, dacites and rhyolites. These basalts are generally strongly porphyritic (olivine + plagioclase + clinopyroxene) and show trace element abundances typical of suprasubduction zone rocks. However, offshore TVZ basalts show subtle distinctions from onshore TVZ basalts to the south; the former have more radiogenic Sr isotopes. Furthermore, their high field strength element and transition element systematics appear to overlap with those of basalts from the Kermadec arc to the north.
The authors attribute these lateral (along arc) and transverse (across arc) variations to source heterogeneity and variable fertility in the sources of the arc and back-arc basin magmas. Sources of the arc-front magmas are more refractory and also more susceptible to contamination by slab-derived fluids than sources for back-arc basin magmatism, reflecting the dynamic nature of flow from the back-arc into the mantle wedge beneath the volcanic front.
Cretaceous-Tertiary volcanism and syn-subduction crustal extension in northern central Peru
Authors: Petford Nicholas , Atherton Michael P. 
Published: April 2008

Abstract
Although subduction of the Nazca plate beneath the Peruvian continental margin has been in progress for nearly 200 Ma, the Andean cycle in western Peru is dominated by periods of contemporaneous rifting and large scale crustal extension. It began with the formation of the west Peruvian trough (WPT), a major depositional structure and one of a series of ‘marginal’ basins that developed along the entire Pacific coast of South America during the Cretaceous. The western element of the WPT north of Lima is the Albian Casma basin, composed of nearly 9000 m of mostly basaltic to intermediate volcanic rocks and minor intrusives. Facies analysis of the basinal fill is consistent with a spreading system in a relatively isolated, deep-sea environment.

The Tertiary is marked by two major episodes of extensional, subaerial volcanism: the
c.
53-15 Ma Calipuy Group, followed in the Late Miocene-Pliocene (
c.
7.6–4.65 Ma) by the more easterly Yungay volcanic rocks. Although both were extruded during periods of crustal extension, the prevailing tectonic regimes differ in detail. Thus the acid-intermediate Calipuy Group was extruded from fissure-type volcanoes over a long period with only minor plutonic activity, whereas the more easterly Yungay volcanic rocks, located furthest from the present trench, are closely associated with major batholith intrusion within a strike-slip transtensional system.

Although the volcanic rocks of the Casma-Calipuy-Yungay groups are dominantly ‘calc-alkaline’ in the classic sense, the role of extension has clearly been fundamental in their genesis. In contrast, their relation to contemporaneous subduction is less clear.
Developments in the structural geology of rifts over the last decade and their impact on hydrocarbon exploration
Authors: Morley C. K. 
Published: April 2008

Abstract
Three different aspects of rift geometry and their impact on hydrocarbon exploration are examined: rift architecture, fault angle and basin inversion. Rift architecture is controlled by fault geometry, which itself is heavily influenced by pre-existing fabrics. At the largest scale, rifts are divided into segments tens to hundreds of kilometres long. They can be joined along offset segments, separated by rift jumps and gaps, or terminated in splays. Rift jumps and gaps provide the entry points for large rivers to enter rifts and create along-axis drainage systems, while rift offsets are areas where anomalous structural patterns develop in response to oblique extension. Within rift segments transfer zones between boundary faults mark important changes in rift geometry and are the preferred sites of coarse clastic sedimentation. In the Gulf of Suez, for example, the structures and the syn-rift reservoir units within two major transfer zones are associated with over four billion barrels of reserves out of a total of six billion barrels. The way individual tilted fault blocks terminate include strike ramps, forced folds, rhomb-blocks, transfer faults, and major and minor cross-strike faults. In areas of relatively poor seismic data quality the choice of fault block termination interpreted on geophysical maps can make a considerable difference to structural interpretation. There has been considerable debate as to whether rifts are composed of high-angle (45–75°) faults or a mixture of high- and low-angle faults. Low-angle faults occur in the sedimentary sequence of rifts, where they occur in a variety of structural settings. Such faults can have a significant economic impact in field development. The presence of low-angled basement faults is more problematic. They do apparently occur in rifts, both due to reactivation of older faults and as completely new faults. Rifts can evolve through a variety of low- and high-angle fault structures with time, which impacts trap creation and destruction. Rifts commonly undergo changes in their stress regime which may lead to basin inversion features. This affects trap development and destruction and can lead to a variable subsidence history for basins, as the basin bounding faults change their senses of motion. The recognition of inversion features in many rifts indicates that this is a very important aspect of rift history.
Strike variation in deformation and diagenesis along segmented normal faults: an example from the eastern Gulf of Corinth, Greece
Authors: Roberts Gerald P. , Gawthorpe Robert L. 
Published: April 2008

Abstract
Structural and diagenetic studies at several localities along the strike of a single fault segment within the eastern Gulf of Corinth show that deformation and diagenetic textures vary along-strike. Uplifted phreatic carbonate cements fill fractures within footwall localities in the centre of the fault segment, whereas, at the termination of the fault segment within the Psatha interbasin transfer zone, fractures filled with vadose calcite cements are associated with an extensive karst system. A small-scale offset between two fault strands along the centre of the fault segment within the Asprokambos intrabasin transfer zone is also dominated by fracture-filling phreatic cements. Fractures filled with phreatic cements exhibit crack-seal textures and low porosities, and formed in fluid-saturated conditions below the water table. In contrast, fractures filled with vadose cements have asymmetric cement textures associated with connected karstic porosity, and formed above the water table. The variations in deformation and diagenesis result from decreasing displacement and footwall uplift towards the ends of the fault segment giving differential uplift across the water table/sea level. Variation in fracture styles and diagenetic textures have been correlated with the position of sample sites along the fault segment. It is therefore possible to use outcrop studies of deformation and diagenetic textures from different portions of fault segments to produce simple predictive models to aid hydrocarbon exploration and production strategies.