bluuebunny/crossref_metadata_2025 huggingface dataset:
Petrology, magnetic fabric and emplacement in a strike-slip regime of a zoned peraluminous granite: the Campanario-La Haba pluton, Spain
Authors: Alonso Olazabal A. , Carracedo M. , Aranguren A.
Published: April 2008

This paper reports field, petrological and structural data of the peraluminous cordierite-andalusite-bearing Campanario-La Haba granite. Crystallization age is constrained by Rb-Sr whole-rock dating at 309 ± 6 Ma (with (
87
Sr/
86
Sr)
i
= 0.70739 ± 0.00038) and took place during late Hercynian tectonic events. The pluton shows a petrographic zonation, although there are no marked differences in chemical compositions between the margin and the centre of the intrusion. Petrography, mineralogical data and geochemical modelling indicate melt generation by partial melting of a metasedimentary protolith, probably with some mantelic contribution as shown by its low Sr
i
value, followed by emplacement at
P
< 3 kbar. The internal structure of the pluton resulted from the lateral spreading in the stretching direction given by an N120–130E dextral strike-slip zone and the external geometry seems to be strongly conditioned by faults (Riedel R type fractures) formed in the host rocks. This emplacement model agrees with that defined for the adjacent Extremadura granitic plutons and for the Los Pedroches batholith suggesting the existence of a dextral regional shear-zone in the South branch of the Central Iberian Zone.
Evidence of magmatic hybridization related with feeding zones: the synkinematic Guitiriz granitoid, NW Iberian Massif
Authors: Menéndez M. , Ortega L. A.
Published: April 2008

The hybridization zone of Guitiriz (NW Iberian Massif) displays numerous features resulted from the interaction of two contemporaneously emplaced felsic and intermediate magmas. A combined study, including field geology, petrography, chemistry and Sr isotopic data, reveals a simple two-component mixing between a mantle-derived magma with an initial
87
Sr/
86
Sr isotopic ratio <0.7042 and a crustal-derived component with an initial Sr isotopic ratio > 0.7104. Both magmas rose through a common feeding zone developed in an extensional regime in which favourable conditions for magma mixing occurred. Calculated emplacement temperature and pressure for the Guitiriz hybridization zone are 700 °C and 2.5 kbar, respectively, and are comparable with those estimated from regional metamorphism. Magmatic epidote occurrence, exhibiting textural and compositional characteristics suggestive of magmatic origin, does not require high-pressure granite solidification. Its presence may be related to a rapid magma transport through the feeding zone that favoured the preservation of epidote.
Analysis and interpretation of Holocene sedimentary sequences in the Humber Estuary
Authors: Ridgway J. , Andrews J. E. , Ellis S. , Horton B. P. , Innes J. B. , Knox R. W. O’B. , McArthur J. J. , Maher B. A. , Metcalfe S. E. , Mitlehner A. , Parkes A. , Rees J. G. , Samways G. M. , Shennan I.
Published: April 2008

The interpretation of the Holocene evolution of the Humber Estuary has been made possible only through integrated multidisciplinary studies involving
inter alia
: drilling, to obtain sedimentary records of the Holocene Estuary fill; multi-element, carbon-nitrogen-sulphur and stable carbon isotope geochemistry; heavy and clay mineralogy; palaeomagnetism; radio-carbon dating; and pollen, diatom and foraminiferal studies. Eight chemostratigraphic suites and 14 palaeo-environments have been recognized. Sediment types, environments of deposition and provenance change in response to rising sea-level, showing a range from freshwater fluvial deposition of locally derived terrestrial sediment to intertidal and subtidal deposition of sediments from marine sources. The methods used are illustrated with reference to sediment cores from inner and outer estuary locations. The results show that Holocene environmental characterization is most secure when a number of different, but complementary, techniques are used. The integration of radiocarbon dates with palaeomagnetic and geochemical data improves the understanding of the presence and significance of time breaks, which is crucial to constraining sedimentation rates and material budgets.
Implications of a microfossil-based transfer function in Holocene sea-level studies
Authors: Horton B. P. , Edwards R. J. , Lloyd J. M.
Published: April 2008

Fifty-two sea-level index points are described from samples collected within the Land-Ocean Interaction Study area. The vertical relationship between relative sea-level and a reference water level for each index point was estimated using two contrasting methods: a lithological-based approach, which is routinely employed in sea-level studies, and a foraminiferal-based transfer function. Comparison of the two methods reveals that the range of the former is 0.14 ± 0.09 m smaller than the latter because the foraminiferal-based transfer function takes into account differences in tidal ranges between study sites. Furthermore, the reference water-level estimates of transgressive index points using the foraminiferal-based transfer function are on average 0.19 ± 0.12 m higher than those of the lithological-based approach. This may be due to the rapid response time of foraminiferal assemblages relative to lithological indicators or the uneven spatial sampling within the contemporary foraminiferal data set. Whilst these inter-method differences are small in magnitude, they are comparable in size to the scale of changes under investigation by recent high-resolution sea-level studies. In contrast, the reference water levels of both methods are comparable for regressive and basis index points. Index points from clastic sediments were also produced using the foraminiferal-based transfer function. Calcareous foraminifera from intertidal environments can be used to produce indicative meanings and supply material for accelerator mass spectrometry radiocarbon dating. This method expands the range of stratigraphic sequences that can be employed in sea-level reconstruction by redressing the over-reliance on transgressive and regressive contacts.
Luminescence dating of fine-grain Holocene sediments from a coastal setting
Authors: Bailiff I. K. , Tooley M. J.
Published: April 2008

A detailed study of a core of Holocene age from a site (Adventurers’ Land, F21) in the Fenlands, UK, based on the measurement of infra-red-stimulated luminescence (IRSL) with silt-sized fractions of water-laid deposits has yielded a sequence of 24 luminescence ages. An additive dose procedure was applied to evaluate the palaeodose, and the annual dose was assessed on the basis of radioactivity and elemental analyses of samples taken from the core. The proportions by weight of the mineral fraction of water and organic material within the sediments ranged fromc.20 to 170% for the former and betweenc.10 and 25% for the latter. Overall, the sequence of IRSL age evaluations is consistent with the calibrated radiocarbon ages obtained for three intercalated organic horizons within the core. Although the luminescence ages for F21A do not possess a resolution that would enable rates of sedimentation between the organic sediments to be determined with confidence, the general trend of the luminescence ages with depth suggests a chronological resolution of the order of 1 ka or better.
The development of a methodology for luminescence dating of Holocene sediments at the land-ocean interface
Authors: Clarke M. L. , Rendell H. M.
Published: April 2008

The main challenge in luminescence dating is to provide accurate ages for sediments derived from hillslope, fluvial and marine environments where grains have been transported and deposited by water. A new methodology has been devised for dating Holocene age sediments from the land-ocean interface. Alkali feldspars are recommended as the ideal dosimeter in these environments as they are: rapidly zeroed, have high sensitivity to dose, have an internal dose rate from the decay of
40
K, have signal intensities that are much higher than for quartz, and the equivalent doses (EDs) determined are not affected by chemical weathering. Studies of the fundamental characteristics of feldspars have been used to optimize the luminescence signal for use in dating applications. A quality assurance technique for discriminating between those samples that will give accurate dates and those that will yield inaccurate dates has been developed and is tested here on coastal-zone sediments from Lincolnshire. Sampling from sediment exposures rather than cores minimizes the uncertainties related to past water content fluctuations.
The Holocene evolution of the Humber Estuary: reconstructing change in a dynamic environment
Authors: Metcalfe S. E. , Ellis S. , Horton B. P. , Innes J. B. , McArthur J. , Mitlehner A. , Parkes A. , Pethick J. S. , Rees J. , Ridgway J. , Rutherford M. M. , Shennan I. , Tooley M. J.
Published: April 2008

The Holocene sequence of the Humber Estuary displays a wide range of sediment types within which the preservation of microfossils is highly variable. Its evolution has been reconstructed using a range of environmental proxies with chronological control provided by more than 90 radiocarbon dates. Results are presented of diatom analyses from three cores typical of the inner, middle and outer estuary (HMB20, HMB7 and HMB12) and of three cores that illustrate the role of organic deposits (peats) and their associated pollen (HMB13, HMB12 and the Ancholme Valley) in the definition of sea-level index points. The reconstruction of relative sea-level change shows a rapid rise in the early Holocene, followed by a reduced rate of rise in the mid-late Holocene. This reconstruction, together with information on the pre-Holocene surface and the different palaeoenvironments from the cores have been integrated within a geographical information system and then interpreted to yield a series of palaeogeographical maps of the Humber at 1000-year time slices between 8 and 3 cal. ka
bp
. The marine transgression progressed up the estuary after 8 cal. ka
bp
, reaching the inner estuary by 6 cal. ka
bp
. The expansion of intertidal environments probably reached its maximum around 3 cal. ka
bp
. Changes since 3 cal. ka
bp
are described using archaeological and historical records. Tidal asymmetry is a major controlling factor on the balance of sediment accretion and erosion in the estuary. Sedimentary and bathymetric evidence suggests a damped oscillation between flood and ebb asymmetry in the Humber over the Holocene period. Such a conclusion would be of great importance to estuarine managers and users since it could be used to predict the future development of the estuary.
Holocene isostasy and relative sea-level changes on the east coast of England
Authors: Shennan I. , Lambeck K. , Horton B. , Innes J. , Lloyd J. , McArthur J. , Rutherford M.
Published: April 2008

Analysis of sea-level data from the east coast of England identifies local-scale and regional scale factors to explain spatial and temporal variations in the altitude of Holocene sea-level index points. The isostatic effect of the glacial rebound process, including both the ice (glacio-isostatic) and water (hydro-isostatic) load contributions, explains regionalscale differences between eight areas:
c.
20 m range at 8 cal. ka
bp
and by 4 cal. ka
bp
relative sea-level in Northumberland was above present, whereas in areas to the south relative sea level has been below present throughout the Holocene. Estimates for pre-industrial relative sea-level change range from 1.04 ± 0.12 mm a
−1
in the Fenland to −1.30 ± 0.68 mm a
−1
(i.e. sea-level fall) in north Northumberland, although this may overestimate the current rate of sea-level fall. Isostatic effects will produce similar relative differences in rates of sea-level change through the twenty-first century. The data agree closely with the patterns predicted by glacio- and hydro-isostatic models, but small systematic differences along the east coast await testing against new ice models. Local scale processes identified include differential isostatic effects within the Humber Estuary and the Fenland, tide range changes during the Holocene, and the effects of sediment consolidation. These processes help explain the variation in altitude between sea-level reconstructions derived from index points taken from basal peats and those from peats intercalated within thick sequences of Holocene sediments.
Crustal structure in the northern North Sea: an integrated geophysical study
Authors: Christiansson P. , Faleide J. I. , Berge A. M.
Published: April 2008

This study focuses on the deep structure of the Viking Graben and adjacent areas of the northern North Sea (60–62°N), and its implications for the amount, timing and nature of lithospheric extension. Two regional transects have been constructed based on an integrated analysis of deep seismic reflection and refraction data, gravity and magnetic data, and correlations between offshore and onshore geology. The shallow interpretation is based on high-quality conventional seismic reflection data calibrated against a large number of exploration wells. The new and partly reprocessed seismic data, combined with the other geophysical data, make possible a better documentation of the crustal configuration, such as the pre-Jurassic sediment distribution, basement and Moho relief, and deep fault geometries. A lower-crustal body characterized by an 8+ km s
−1
velocity and an average bulk density of 2.95 g cm
−3
is present beneath the Horda Platform. This body probably represents a deep crustal root of partially eclogitized rocks that formed during the Caledonian orogeny. Heterogeneities within this body give rise to the non-typical velocity-density relation. The crust-mantle boundary is located at the base of this body at a depth of 30–35 km and does not coincide with the seismically defined Moho. The geometry of crustal thinning reflects the cumulative effect of several post-Caledonian rift phases. Results show that Permian rifting affected a wide area, from the Øygarden Fault Complex to the Hutton Fault.
Repeated lithosphere extension in the northern Viking Graben: a coupled or a decoupled rheology?
Authors: Ter Voorde M. , Færseth R. B. , Gabrielsen R. H. , Cloetingh S. A. P. L.
Published: April 2008

The Late Permian-Early Triassic and Jurassic-Cretaceous rift events that influenced the structure of the northern Viking Graben are examined. Here, a 2D forward numerical model including faults is applied on seismic line NVGT88-04, which crosses the basin in the E-W direction. We concentrate on (1) the amount of Jurassic basin subsidence that can be explained by thermal contracting resulting from the Permo-Triassic event, (2) the spatial connection between the two rift events and (3) the apparent mode of flexure (coupled v. decoupled) of the lithosphere. Modelling results indicate that post-rift subsidence as a result of Permo-Triassic rifting has practically ceased at the onset of Jurassic rifting. The position of the rift axis is shown to migrate with time, from the Horda Platform in Permo-Triassic time to the present Viking Graben centre in Jurassic-Cretaceous time. The major difference between the consequences of a coupled versus a decoupled mode of flexure is that the latter causes a larger amount of fault-block rotation. On this basis, we suggest a decoupled mode of flexure for the Permo-Triassic rift phase, a coupled mode of flexure for the Early Jurassic rift phase, and a decoupled mode of flexure again for the Late Jurassic period.
Cenozoic evolution of the central and northern North Sea with focus on differential vertical movements of the basin floor and surrounding clastic source areas
Authors: Jordt Henrik , Thyberg Brit I. , Nøttvedt Arvid
Published: April 2008

Changes in outbuilding directions and shifts in sediment provenance are key factors for understanding the development of the Cenozoic succession in the central and northern North Sea. By establishing a seismic stratigraphic framework for the Cenozoic succession, and through utilization of velocity data and analyses of sediment compositions, these factors are investigated. Sequence geometries and reflection terminations are identified and related to basin-floor geometry and variations in erosional base level. Mineralogical and geochemical analyses of sediment samples from selected wells are compared with their seismic sequences. Paleogene clastic wedges rich in smectite were built from the East Shetland Platform and probably drained a source area west and northwest of the present North Sea. Outbuilding from southern Norway took place during Late Paleocene-Early Eocene and in Oligocene to mid-Miocene time. In mid-Miocene time outbuilding from the west stopped and subsequently sediments with a high content of feldspar, detrital chlorite and carbonate were deposited from easterly directions in the central and northern North Sea. The seismic velocity of the Cenozoic sediments increases down to a mid-Miocene unconformity, but the velocities of Oligocene and Eocene sediments below are lower and nearly unaffected by burial depth, resulting in a marked velocity inversion. Two tectonic subsidence events, late Eocene-early Oligocene and late Miocene-early Pliocene, have been identified subsequent to general eustatic sea-level lows. These subsidence events cannot be explained by thermal subsidence, and they may have crucial implications for the understanding of hydrocarbon generation, migration and trapping in the Tertiary and deeper stratigraphic levels.
Relationships between sequence stratigraphy, mineralogy and geochemistry in Cenozoic sediments of the northern North Sea
Authors: Thyberg B. I. , Jordt H. , Bjørlykke K. , Faleide J. I.
Published: April 2008

Cuttings of Cenozoic sediments from selected wells in the northern North Sea have been analysed both mineralogically and geochemically, and compared with seismic sequence stratigraphic units. Variations in the composition with respect to clay minerals, feldspars, major elements and selected trace elements have been used to establish changes in the provenance of the Cenozoic sequences. The Eocene sequence consists of a thickness of several hundreds of metres of almost exclusively smectitic clays with high Ni and Zn contents and little or no quartz. This represents a strong input from subaerial volcanism related to the rifting and initial spreading of the Norwegian-Greenland Sea. The Eocene-Oligocene smectitic mudstones have high porosity and low seismic velocity (<2km s
−1
) compared with the underlying Paleocene sediments and overlying Miocene-Pliocene sequences. The Plio cene and Pleistocene mudstones are coarse-grained clays with an immature mineralogy, which compact much more rapidly than the underlying smectitic sediments. The seismic velocity may then reach 2.5–3.0 km s
−1
and thus cause a strong velocity inversion. This sequence is partly glacial and mineralogically immature, but may contain some kaolinite and smectite, which indicate reworking of lower Tertiary and Mesozoic sediments. Our obser vations indicate that sequence boundaries are closely related to tectonic movements and to changes in the sediment supply from adjacent areas. Both mineralogical and geochemical data can be used as additional tools for correlation in Cenozoic sediments in the northern North Sea. The mineralogy of these sediments also determines the rate of compaction and other factors relevant for basin modelling.
Cenozoic tectonic subsidence from 2D depositional simulations of a regional transect in the northern North Sea basin
Authors: Kyrkjebø Rune , Hamborg Martin , Faleide Jan Inge , Jordt Henrik , Christiansson Peter
Published: April 2008

The Cenozoic depositional history along a regional E–W profile across the northern North Sea has been simulated using a forward process-based simulation program of dynamic-slope type. It involves a depth-dependent, dual-lithology diffusion equation that handles transport, erosion and deposition of sediments. The data used in the simulation were derived from a seismic line calibrated against wells, and from the regional literature concerning the northern North Sea. The most important of the factors used are: the initial basin form (Paleocene bathymetry), tectonic subsidence, isostatic variables, sediment supply (sand-shale), sediment compaction (porosity-depth relationships for sand-shale) and eustatic sea-level changes. The interaction between the data values extracted from the literature could not reproduce a cross-section similar to the observed cross-section from seismic data. Therefore, the subsidence pattern and the initial basin form were reconsidered. The resulting model gave an anomalous Cenozoic subsidence pattern, different from the expected post-rift thermal subsidence, with deviations corresponding to Paleocene and Late Miocene-Pliocene times. The model-derived Paleocene subsidence might have been overestimated by using an over-shallow palaeobathymetric value, although a deepening of the basin is also indicated by biostratigraphic data. The pronounced Neogene subsidence created accommodation space for a thick Pliocene sequence, derived from the uplifted eastern source area.
NE Atlantic continental rifting and volcanic margin formation
Authors: Skogseid Jakob , Planke Sverre , Faleide Jan Inge , Pedersen Tom , Eldholm Olav , Neverdal Flemming
Published: April 2008

Deep seismic data from the Hatton-Rockall region, the mid-Norway margin and the SW Barents Sea provide images of the crustal structure that make it possible to estimate the relative amounts of crustal thinning for the Late Jurassic-Cretaceous and Maastrichtian-Paleocene NE Atlantic rift episodes. In addition, plate reconstructions illustrate the relative movements between Eurasia and Greenland back to Mid-Jurassic time. The NE Atlantic rift system developed as a result of a series of rift episodes from the Caledonian orogeny to early Tertiary time. The Late Palaeozoic rifting is poorly constrained, particularly with respect to timing. However, rifted basin geometries, inferred to be of this age, are observed at depth in seismic data on the flanks of the younger rift structures. Intra-continental rifting in Late Jurassic-Cretaceous times causedc.50–70 km of crustal extension and subsequent Cretaceous basin subsidence from the Rockall Trough-North Sea areas in the south, to the SW Barents Sea in the north. In late Early to early Late Cretaceous times, new rifting occurred in the Rockall Trough and Labrador Sea associated with the northward propagation of North Atlantic sea-floor spreading. When sea-floor spreading was approached in the Labrador Sea the Rockall rift apparently became extinct. The final NE Atlantic rift episode was initiated near the Campanian-Maastrichtian boundary, lasted until continental separation near the Paleocene-Eocene transition, and causedc.140 km extension. The late syn-rift and the earliest sea-floor spreading periods were affected by widespread igneous activity across ac.300 km wide zone along the rifted plate boundary. The deep seismic data provide lower-crustal structural geometries that represent boundary conditions for a better mapping and understanding of the extensional thinning of the crust. The crustal geometries question extension estimates previously made from basin subsidence analysis, and aid in the definition of bodies of magmatic underplating beneath the outer volcanic margins.
The tectonic evolution of the Norwegian Sea Continental Margin with emphasis on the Vøring and Møre Basins
Authors: Brekke Harald
Published: April 2008

The Norwegian Sea continental margin is dominated by two major basins with a very thick Cretaceous basin fill: the Vøring and Møre Basins. The basins are flanked by the uplifted mainland and the Cretaceous Trøndelag Platform to the east and by the Møre and Vøring Marginal Highs capped by Eocene lavas to the west. The tectonic development of the area is controlled by two structural trends: NE-SW and NW-SE. The area has been tectonically active from Carboniferous to Late Pliocene time with the main tectonic phases in Late Palaeozoic, late Mid-Jurassic-Early Cretaceous and Late Cretaceous-Early Tertiary time. The general tectonic development comprised a long period of extension and rifting that ended in Early Eocene time by continental separation, major volcanism and subsequent sea-floor spreading in the Norwegian-Greenland Sea. In Carboniferous to Early Cretaceous time the extensional tectonics were related to within-plate continental rifting. The tectonics of the Late Cretaceous and the Tertiary periods were controlled by the relative movements along plate boundaries. The overall NE-SW structural grain is constituted by faults and basin axes that probably originated in Late Palaeozoic time and were active during all subsequent tectonic phases. The transverse NW-SE trend is expressed as major lineaments that probably reflect the old, Precambrian grain of the basement. These lineaments, two of which are the continuation into the continental crust of major oceanic fracture zones, controlled the tectonic activity throughout Cretaceous and Tertiary time and constitute the boundaries between the major structural provinces of the area. The differentiation into the Cretaceous basins and the bounding platforms and marginal highs started by the late Mid-Jurassic-Early Cretaceous extensional phase. The subsequent Cretaceous subsidence history, where the basin flanks formed by flexuring rather than faulting, resulted in an exceptionally thick basin fill. In the Vøring Basin the Cretaceous development comprised an early thermal subsidence phase and a post-Cenomanian phase of tectonically driven subsidence involving intermittent phases of normal faulting and compression and folding. The Vøring Basin was tectonically active also during Tertiary time with the main phases of strike-slip-compression coinciding with the Alpine orogenies in Late Eocene and Mid-Miocene time. Within the Vøring Basin there is evidence of the formation of a fossil opal A-opal-CT transition and extensive regional marine erosion in Mid-Miocene and Late Pliocene times. In contrast, the Møre Basin was generally tectonically quiet throughout the Cretaceous and Tertiary periods, experiencing mainly continuous subsidence.
Atlantic volcanic margins: a comparative study
Authors: Eldholm O. , Gladczenko T. P. , Skogseid J. , Planke S.
Published: April 2008

Volcanic margins in the Atlantic Ocean reveal a series of common crustal units and structural features developed during continental extension and break-up. We suggest that four main crustal zones can be recognized on volcanic margins. This tectono-magmatic zonation implies a history of development where tectonic and magmatic styles and dimensions depend on the interaction of lithospheric and asthenospheric properties and dynamics. The amount of excess igneous activity depends on the temperature and fluid content of the asthenosphere along the incipient plate boundary and the dynamic history of the lithosphere during the rift phase. An adequate understanding of the margin history requires studies of the entire rift, i.e. the conjugate margins. We also note that the spectacular wedges of seaward-dipping reflectors observed along many rifted margins are only one of many igneous features originating during the process of break-up and initial seafloor spreading. Probably, most passive rifted margins represent intermediate cases relative to the volcanic and non-volcanic end-members. A mantle plume impinging on lithosphere already under extension emplacing Large Igneous Province-type initial oceanic crust, including an extensive extrusive cover, is considered the most likely explanation for volcanic margins. Hydrocarbon resource evaluations of volcanic margins have to include their characteristic tectono-magmatic features and their consequences for vertical motion, erosion, sedimentation, thermal and burial histories, and maturation.
Interlayer slip and joint localization in the East Kaibab Monocline, Utah: field evidence and results from numerical modelling
Authors: Cooke M. L. , Mollema P. N. , Pollard D. D. , Aydin A.
Published: April 2008

The mechanics of deformation in multilayer flexures is analysed by comparing field observations of joint clusters from the East Kaibab Monocline, Utah with fracture patterns produced in analytical and numerical experiments. Dune boundaries (bedding planes) were mapped through the thickness of the aeolian Navajo Formation, and the occurrence of joints related to dune boundary slip and fold curvature was documented. Slip along dune boundaries, as evidenced by joint clusters oblique to bedding, occurs along the steep limb of the fold and in the middle of the Navajo. Joints perpendicular to bedding and parallel to the fold axis occur near the synclinal hinge. Numerical experiments examine a layer flexed to match the Navajo at Hackberry Canyon with both uniform and observed distribution of dune boundaries. Within the numerical experiments, horizontal frictional interfaces slip within the centre of the layers where dips are steepest, and opening-mode fractures related to curvature form within the anticlinal and synclinal hinges of the fold. Thus, the first-order numerical results match field observations. This study illustrates the important roles of mechanical stratigraphy and interlayer slip in multilayered folding and the contribution of bedding-plane faults and fold curvature in the production of joint clusters.
Regional tectonics and fracture patterns in the Fall River Formation (Lower Cretaceous) around the Black Hills foreland uplift, western South Dakota and northeastern Wyoming
Authors: Wicks John L. , Dean Stuart L. , Kulander Byron R.
Published: April 2008

The Fall River Formation around the Black Hills uplift is pervasively fractured by layer-perpendicular joints. Systematic joints in the formation maintain consistent orientations over large areas and are commonly abutted by later-formed fractures, resulting in an orthogonal pattern. There are two major systematic sets, trending northeast and northwest, and one minor set trending north-south. The first two sets define two major fracture domains in the study area. The northwest joint set occupies a southern domain where it is the sole systematic fracture set. The northeast joint set is pervasively established throughout the northern domain, where northwest and north-south fracture sets are also developed in well-defined sectors. There is no genetic or spatial relationship between joint sets and local Laramide monoclines or folds of the region. Instead, the stratigraphic record indicates that joint development originated early in the lithification history of Fall River sandstones. Jointing occurred in response to local and regional extensional stresses that pervaded the northern and southern domains as a result of recurrent movement on basement faults that parallel the regional lineament system and surface structural zones throughout the region. Major uplift of the Black Hills and local fold development during Laramide time merely resulted in passive rotation of the early formed systematic and non-systematic joints.
The evolution of the Main Mantle Thrust in the Western Syntaxis, Northern Pakistan
Authors: Argles T. W.
Published: April 2008

Neogene events in the Nanga Parbat-Haramosh massif have obscured much of its earlier evolution. However, structural mapping of the eastern margin reveals a ductile contact zone preserving many features of the original Main Mantle Thrust that emplaced the Ladakh island arc over the Indian margin in the late Cretaceous. The sequence of ductile deformation was controlled both by the contrasting rheologies of the Ladakh island arc and the Main Mantle Thrust footwall, and the changing thermal regime during subduction, collision and burial. Preliminary
P-T
estimates indicate conditions during southward thrusting on the Main Mantle Thrust of
c.
650 °C and 9.5 kbar, with later deformation (post-dating garnet growth) in some units at
c.
500 °C and 7.4 kbar. The concordant fabrics and lithological boundaries on either side of the contact are only disrupted by a NW-vergent, brittle thrust south of the village of Subsar (Indus gorge) which cross-cuts the steepened Main Mantle Thrust Zone. This thrust is related to the neotectonic Liachar Thrust on the western margin of the massif, and is an expression of the regional tectonics at the western termination of the Himalayan arc. This late thrusting followed formation of the syntaxial antiform in Neogene times.
Unroofing of the Nanga Parbat Himalaya
Authors: Shroder J. F. , Bishop M. P.
Published: April 2008

The rapid erosional unroofing of the Nanga Parbat Himalaya in late Cenozoic time is thought to have been initiated when the Indus River, initially flowing somewhat north and well to the west of its present location, was captured and diverted south close to the massif of today by extensional structures and downfaulted topography across the Kohistan-Ladakh island arc terrane. It is hypothesized that the Nanga Parbat pop-up structure was initiated at
c.
12-10 Ma, as a tectonic aneurysm caused by rapid incision by the Indus River and other surface processes. Because of this subsequent rapid unroofing of the region, however, the oldest sediments to record erosion in the immediate region of Nanga Parbat are < 200 ka old: most sediments and our cosmogenic and ISRL exposure dates are more than five times younger. Diverse field measurements of rates of local incision and areal denudation for mass movement, glacial, river and catastrophic floods for the past
c.
55 ka are highly differential but internally replicative and externally consistent with research indicating long-term, severe denudation. Averaged rates of maximum incision at more than 15 points around the massif are 22 mm ± 11 mm a
−1
. Late Pleistocene surface processes at Nanga Parbat were capable of erosional unroofing of the massif sufficiently vigorous to produce the pronounced relief of today.
Remote sensing and geomorphometric assessment of topographic complexity and erosion dynamics in the Nanga Parbat massif
Authors: Bishop M. P. , Shroder J. F.
Published: April 2008

The dynamic mountains of the western Himalaya are the result of complex interactions involving tectonic, structural, lithological, climatic and surface processes. The multi-scale dynamics of surface processes in this region are largely unknown. This paper assesses the spatial complexities of the topography at Nanga Parbat, as we seek to understand erosion dynamics, differential denudation and the geodynamics of uplift and denudation. Spatial analysis of a high resolution digital elevation model and three-dimensional terrain simulations using satellite imagery indicate that the topographic complexity of Nanga Parbat is highly scale-dependent and exhibits a hierarchical order that is reflective of erosion dynamics. Observations and analyses reinforce prior understandings of rapid rates of uplift and high rates of surficial denudation. Results indicate that climate controls the topographic complexity of the massif, although a tectonic influence is present and is largely masked by the overprinting of surface processes with time. Consequently, Nanga Parbat is seen to owe its origin to erosionally induced tectonic uplift and rapid surficial denudation. Rapid uplift altered erosion dynamics and further accelerated erosion resulting in extreme relief. Nonetheless, the differential denudation resulting from erosion dynamics does not appear to be in spatial balance with the regional scale tectonic mass flux. Systematic integration of dynamic models that account for the scale-dependencies of subsurface and surface processes are required to study the nature of this complex system and explain topographic evolution.
Tracing the origins of the western Himalaya: an isotopic comparison of the Nanga Parbat massif and Zanskar Himalaya
Authors: Whittington A. , Harris N. B. W. , Ayres M. W. , Foster G.
Published: April 2008

New Sr and Nd isotope data for basement gneisses and leucogranites are presented from two contrasting areas of the western Himalaya; the Nanga Parbat-Haramosh massif (NPHM) and Zanskar. Sr-isotope systematics of metapelites and anatectic migmatites from the Zanskar Himalaya are characterized by εSrof 515–930, typical of the High Himalayan Crystalline unit as exposed for more than 2000 km along strike. Moreover, Zanskar leucogranites are typical of the belt of Early Miocene granites intruding the High Himalayan Crystallines across the orogen (mean εSr= 834). In contrast, the NPHM leucogranites show an elevated average εSrof 2400, and basement samples show a wide range in εSrfrom 1850 to 8150. Errorchrons for the metasedimentary gneisses indicate isotopic homogenization of the basement atc.500 Ma for the Zanskar samples compared withc.1800 Ma from the NPHM, confirming that the two terrains have experienced contrasting pre-Himalayan histories.

Nd isotopic data from the NPHM indicate model ages from 2300 to 2800 Ma, indicating the mean crustal formation ages of the protoliths from which the sediments were derived. A compilation of published Nd data from the Himalaya indicates average protolith formation ages of 2640 ± 220 Ma for the Lesser Himalaya lithologies, compared with 1940 ± 270 Ma for the High Himalaya unit.

Gneissic lithologies from Zanskar and the NPHM have previously been correlated with the High Himalayan Crystalline Series, since both display high-grade Himalayan metamorphism and are intruded by syn- to post-tectonic tourmaline-bearing leucogranites. Isotopic systematics in the Zanskar region confirm this correlation. In contrast, the NPHM basement rocks are better correlated with Lesser Himalayan lithologies, exposed south of the Main Central Thrust. We conclude that the NPHM represents either a lower structural level of the Lesser Himalaya Series, or its protolith.
From buckling to asymmetric folding of the continental lithosphere: numerical modelling and application to the Himalayan syntaxes
Authors: Burg J.-P. , Podladchikov Y.
Published: April 2008

The eastern and western Himalayan syntaxes are large-scale, coeval antiforms developed late in the history of India-Asia collision. We use two-dimensional finite element models of lithospheric folding to develop a mechanically plausible structural interpretation. The models mimic the coeval development of adjacent synformal basins, analogous to the Peshawar and Kashmir basins on either side of and adjacent to the western syntaxis. Pure-shear thickening and symmetric buckling accommodate shortening until, at a certain strain, an asymmetric thrust-like flow pattern occurs on a crustal to lithospheric scale. Similarities between geological data and calculated models suggest that lithospheric buckling is a basic response to large-scale continental shortening. To generalize these results, we suggest that a typical shortening history would include: (1) locking of an early thrust system in hinterland regions, followed by (2) pure shear shortening and symmetric buckling of the shortened lithosphere, and (3) loss of symmetry leading to the formation of an asymmetric fold in which a new thrust system will nucleate.
Geological evolution of the Hindu Kush, NW Frontier Pakistan: active margin to continent-continent collision zone
Authors: Hildebrand P. R. , Searle M. P. , Shakirullah  , Khan Zafarali , Van Heijst H. J.
Published: April 2008

A geological map of the eastern Hindu Kush, northwest of Chitral, Northern Pakistan, is presented. The lithologies are placed into two main categories, divided by the Tirich Mir Fault Zone. To the northwest, the units of the eastern Hindu Kush are dominated by monotonous sequences of graphite-rich pelitic rocks. Southeast of the fault, the phyllites and diamictites are thought to be lateral equivalents of the Northern Sedimentary Belt of the Karakoram. A structural analysis of the area studied identifies a major, early deformation phase which is usually characterized by tight to isoclinal folding with a well developed axialplanar schistosity. This deformation is thought to have been related to the northward-directed subduction and accretion beneath the southern margin of Asia during the Mesozoic, and may have taken place over a considerable period of time. A major phase of crustal melting at
c.
24 Ma generated migmatites and biotite + muscovite ± garnet ± tourmaline leucogranites (including dykes and the Gharam Chasma pluton). This age is comparable to that of the Baltoro pluton in the Karakoram to the east, confirming the regional importance of crustal melting along the southern margin of the Asian plate during the earliest Miocene. The crustal melting was associated with thrusting and folding of the earlier schistosity. Subhorizontal stretching lineations indicate a phase of strike-slip deformation that is thought to have been associated with anticlockwise rotation of the regional foliation strike from E to NE and N after the emplacement of the Gharam Chasma pluton at
c.
24 Ma. This deformation and rotation was probably a direct result of the northward-moving Indian plate forcing Kohistan to indent into Asia, resulting in a left-lateral transpressional tectonic environment which remains today. The anomalous height of the Tirich Mir massif, relative to other peaks in the Hindu Kush and the nearby Hindu Raj, may be accounted for by the onset of this transpression.

Intensely active seismicity to depths of 300 km beneath the Hindu Kush is associated with seismic shear wave velocities that are significantly faster than those beneath Tibet, where earthquake occurrence is restricted to the upper crust, and previous geophysical studies indicate elevated thermal conditions and possible crustal melts. U-Pb ages suggest that post-India-Asia collision crustal melting beneath the Hindu Kush is restricted to
c.
24 Ma, whereas in the Karakoram, the record is both more voluminous and more continuous from
c.
37 to
c.
9 Ma. These observations reflect major differences in the thermal histories of these regions, where the relatively cooler conditions beneath the Hindu Kush are associated with continental subduction-related seismicity.
Timing of magmatic and metamorphic events in the Jijal complex of the Kohistan arc deduced from Sm-Nd dating of mafic granulites
Authors: Yamamoto H. , Nakamura E.
Published: April 2008

Mafic to ultramafic granulites in the northeastern part of the Jijal complex include two-pyroxene granulite, garnet-clinopyroxene granulite and garnet hornblendite. Field and textural relations indicate that two-pyroxene granulite is a relict left after formation of the garnet-clinopyroxene granulite and garnet hornblendite was an originally intrusive rock which dissected the protoliths of mafic granulites. Sm-Nd mineral isochron ages of 118 ± 12 Ma, 94.0 ± 4.7 Ma and 83 ± 10 Ma were determined for two-pyroxene granulite, garnet-clinopyroxene granulite and garnet hornblendite respectively. These ages, together with previously reported chronological data, led to the following tectonic implications: (1) crystallization of the granulite protoliths predates, or is coeval with, the tectonic accretion of the Kohistan arc to the Asian continent; (2) crustal thickening related to the accretion was probably responsible for the high-pressure granulite-facies metamorphism in the Jijal complex; (3) formation of the garnet hornblendite assemblage was probably after crystallization of garnet-clinopyroxene granulite.
Exotic conglomerates of the Neogene Siwalik succession and their implications for the tectonic and topographic evolution of the Western Himalaya
Authors: Abbasi I. A. , Friend P. F.
Published: April 2008

Published information on the Siwalik Group (Neogene) conglomerates in the Sub-Himalayan belt of Himachal Pradesh, India, and the Potwar Plateau, Pakistan, is used as the basis of a model that recognizes two types of conglomerates with different relationships to the linear Himalayan mountain front. The two types are: (1) foothills-fed conglomerates, widespread along the mountain front, that mark the appearance in the basinal succession of sediments derived from within the Sub-Himalayan fold-and-thrust belt or the neighbouring Lower Himalaya; these Upper Siwalik conglomerates provide information about relatively young frontal fault activity and the growth of local river systems that transferred the sediment generated; and (2) high-mountain-fed conglomerates, with restricted lateral extent along the front, that mark the presence of large trunk rivers, draining the Lower and Higher zones of the Himalaya; these Middle and Upper Siwalik conglomerates provide information about the extent of older incision in the high mountains, and the position in the basin of the major drainage paths.

Our work on the Janak (formerly Indus) Conglomerate Formation, outcropping near the present Indus River, shows that it is a high-mountain-fed conglomerate, and was deposited by a large braided system (channels up to 15 m deep) that drained southwards from the High Himalaya of northernmost Pakistan. The conglomerate was deposited between 9 and 1 Ma, and is preserved as a formation 1.5 km thick and 25 km wide, perpendicular to flow. This conglomerate marks the position of the Palaeo-Indus in this part of the foreland basin. The syntaxial position of the present Indus in the mountain front, and the remarkable route of the upper Indus, have resulted from drainage evolution during the later stages of transpressive indentation of the western margin of the Indian block. Our interpretation of the Janak Conglomerate implies that this special role of the Indus must have already started by 9 Ma.
The advent of archaeoseismology in the Mediterranean
Authors: Jones R. E. , Stiros S. C.
Published: April 2008

This paper presents a brief historical overview of the development of archaeoseismology from the observations of Lanciani at ancient sites in Rome, of Kritikos in Athens, Evans at Knossos and Blegen at Troy, to the emergence in the last years of the twentieth century of archaeoseismology as a distinct sub-discipline of palaeoseismology. Some current issues are explored, beginning with major seismic events such as that in
AD
365 in the Eastern Mediterranean whose effects were geographically widespread but uneven in their destructive severity; generalizations are hard to come by, and each case has to be examined on its own merits. The need to examine the suitability of building methods and materials in areas of seismic risk is emphasized. Finally, the contribution of seismic events to destruction horizons in two contrasting cases in the prehistoric Aegean is considered: at Mycenaean centres in the Argolid in the 13th–12th centuries
BC
, and in the Peloponnese at the end of Early Bronze II.
The eruption of the Santorini volcano and its effects on Minoan Crete
Authors: Driessen Jan , MacDonald Colin F.
Published: April 2008

Sometime in the course of the second millennium
BC
, an earthquake appears to have triggered a massive eruption of the Santorini volcano. The immediate consequences of the earthquake closely followed by the eruption for Cretan society during the Late Minoan I period are rather difficult to characterize, although physical evidence in the form of Theran ash has shown up at an increasing number of sites. Certain features of the archaeological record, taken in isolation, have hardly been noticed in the past. The long-term effects of the eruption, however, have recently become more comprehensible thanks to a reconsideration of old and new archaeological evidence. The combined picture gives the impression of a period of societal stress following these events. Changes in architecture, storage and food production, artisan output, the distribution of prestige items, administrative patterns and ritual manifestations can be pinpointed archaeologically. These may and should be interpreted as disturbances in the political, economic, cult and security-related domains. It is argued that the inability of the Minoan palatial centres to adapt to changing circumstances caused by a double disaster, an earthquake followed by the eruption of Santorini, led to an increase in crisis-related situations, culminating in the widespread fire destructions which brought this palatial phase of Minoan civilization to an end and opened the way for mainland Mycenaean domination of the Aegean.