bluuebunny/crossref_metadata_2025_split huggingface dataset:
An oxygen and carbon isotopic study of multiple episodes of fluid flow in the Dalradian and Highland Border Complex, Stonehaven, Scotland
Authors: MASTERS R. L. , AGUE J. J. , RYE D. M. 
Published: June 2010

The carbon and oxygen systematics of rocks north of Stonehaven, Scotland were studied to provide new constraints on the nature and timing of metamorphic and post‐metamorphic fluid infiltration. Carbon and oxygen isotopic data were collected from carbonated spilites and carbonate‐bearing veins in the Highland Boundary Fault, from Dalradian metacarbonate layers and pervasively carbonated schists, and from three generations of carbonate‐bearing veins, and a quartz porphyry dyke within the Dalradian. Isotopic evidence for syn‐metamorphic fluid infiltration in the Dalradian is preserved in quartz–calcite veins in the upper chlorite zone and in staurolite zone metacarbonates. δ
18
O values for coexisting quartz (δ
18
O
quartz
= 13.6‰) and calcite (δ
18
O
calcite
= 11.6‰) in a vein from the upper chlorite zone are consistent with precipitation of both minerals from a single fluid at
c.
375°C. Oxygen isotopic data from staurolite zone metacarbonate layers (δ
18
O
calcite
= 10.4 to 12.9‰) suggest major isotopic exchange with an external fluid equilibrated with a quartzo‐feldspathic reservoir, such as the Dalradian metasediments, at metamorphic temperatures. Low, negative carbon isotope data from these metacarbonate layers (δ
13
C
calcite
= −12.4 to −17.7‰) may indicate a component of oxidized organic material in the infiltrating fluid. Post‐metamorphic fluids derived from or equilibrated with a high‐temperature silicate reservoir such as felsic igneous rocks were responsible for precipitation of post‐metamorphic vein carbonate, carbonation of pelitic schists, and alteration of metamorphic feldspar porphyroblasts from Barrow’s famous spotted chloritoid schists in an area geographically associated with several carbonated quartz porphyry dykes. Some veins in the biotite and garnet zones have been conduits for multiple generations of fluid flow. Quartz from this generation of veins preserves a metamorphic isotopic signature (δ
18
O
quartz
= 11.2 to 13.2‰) whereas dolomite and calcite are considered to be post‐metamorphic based on textural evidence and isotopic data indicating extreme oxygen isotopic disequilibrium between vein quartz and carbonate minerals (δ
18
O
dolomite
= 23.7 to 24.2‰, δ
18
O
calcite
= 25.3‰, δ
18
O
quartz
= 11.2 to 13.2‰). Variably depleted carbon isotopes from carbonate minerals in these veins (δ
13
C
dolomite
= −8.1 to −13.4‰, δ
13
C
calcite
= −12.2‰) may reflect input of oxidized organic material in the mineralizing fluid. Isotopic data from carbonate veins and variably carbonated spilites from the Highland Boundary Fault are consistent with hydrothermal alteration of basalts by seawater, which had its carbon isotope systematics modified by addition of magmatic CO
2
and/or oxidation of organic carbon. Such alteration may have occurred on the seafloor or during emplacement in the Highland Boundary Fault.
Death of a sand sea: an active aeolian erg systematically buried by the Etendeka flood basalts of NW Namibia
Authors: JERRAM D. A. , MOUNTNEY N. P. , HOWELL J. A. , LONG D. , STOLLHOFEN H. 
Published: June 2010

Here we report on a ‘fossilized’ sand sea that was progressively engulfed by the basal Etendeka flood basalts in NW Namibia. Preserved relict aeolian landforms include transverse barchanoid dunes and isolated barchan dunes. Present‐day preferential erosion of the lava flows exhumes relict aeolian bedforms preserved in the position in which they were migrating at the time of burial (
c.
133 Ma). A passive eruption style of inflated pahoehoe flows has preserved the bedforms without significant deformation. The sediment interlayers record a decrease in sand supply and a change in palaeowind direction, which may have been driven by the ongoing break‐up of west Gondwana, or may be a direct result of the widespread volcanism itself.
Late Quaternary evolution of a hyperactive rhyolite magmatic system: Taupo volcanic centre, New Zealand
Authors: SUTTON ANDREW N. , BLAKE STEPHEN , WILSON COLIN J.N. , CHARLIER BRUCE L. A. 
Published: June 2010

Taupo volcanic centre has been active for
c.
300 000 years. Since the
c.
26.5 ka caldera‐forming Oruanui eruption 28 eruptions have occurred from Taupo, varying between 0.1 and >45 km
3
in minimum bulk volume, and with repose periods ranging from
c.
20 to 6000 years. All magma erupted post‐26.5 ka is compositionally and mineralogically distinct from pre‐Oruanui and Oruanui eruptives, and is inferred to have formed at or after 26.5 ka. Four post‐Oruanui magma types are identified on the basis of whole rock and mineral compositions: one dacitic, forming three eruptions between 20.5 ka and 17 ka, and three subtly distinct rhyolite compositions erupted in discrete periods from 11.8 to 9.95, 7.05 to 2.75 and 2.15 to 1.74 ka. Stepwise compositional variations between, and limited variation within, rhyolite groups suggest emplacement of three petrogenetically separate batches of magma within only 10 000 years. The 15–35 km
3
of magma erupted at 1.77 ka evidently appeared in <10
3
years; this short residence time may have contributed to the lack of zonation within this magma chamber. Taupo is unusual amongst large rhyolite volcanoes in terms of the high frequency of activity since 26.5 ka, rapid stepwise changes in rhyolite compositions, and insignificant differentiation within individual subgroups. These traits are attributed to the combined effects of the extensional arc setting, thermal energy from mafic magma, and the shallow slope of the plagioclase‐saturated rhyolite liquidus.
Pre-emplacement structural history recorded by mantle peridotites: an example from the Lizard Complex, SW England
Authors: COOK C. A. , HOLDSWORTH R. E. , STYLES M. T. , PEARCE J. A. 
Published: June 2010

The Lizard Complex of SW England includes thrusted units of peridotites that were initially exhumed from upper mantle (
c.
52 km) to lower crustal (
c.
24 km) depths during a period of Early Devonian rifting and break-up. This basin closed during the Late Devonian, when the Lizard Complex was thrust towards the NNW along a major low-angle detachment and became incorporated within a series of Variscan thrust nappes. In the peridotites, a primary high-
T
and high-
P
spinel lherzolite mineral assemblage (
c
. 1119°C and
c.
15.7 kbar) was progressively exhumed and re-equilibrated to conditions of lower
T
and
P
(
c
. 991–1010°C and
c
. 7.5 kbar) during the development of kilometre-scale mylonitic plagioclase- and amphibole-bearing mantle shear zones. These fabrics demonstrably pre-date emplacement related structures. The new structural and geochemical evidence from the peridotites also strongly suggests that the Lizard Complex formed in a rifted, non-volcanic continental margin setting, possibly in a pull-apart basin, rather than at a mid-ocean ridge. The
P–T
and textural evolution of the Lizard peridotites supports growing evidence that shear zones in the lithospheric upper mantle may to some extent accommodate large-scale displacements associated with crustal extension and continental breakup.
Contrasting tectonic history of the arc–continent suture in the Southern and Middle Urals: implications for the evolution of the orogen
Authors: AYARZA P. , BROWN D. , ALVAREZ-MARRÓN J. , JUHLIN C. 
Published: June 2010

The Main Uralian Fault has been considered the original arc–continent suture for 2000 km along the Uralide orogen. The symmetry of the tectonic units across it suggested a consistent east-dipping polarity for the palaeosubduction zone, which, together with its topographic and aeromagnetic signature, supported the idea of a single suture. However, several characteristics vary at different latitudes. In the Middle Urals, it is a strike-slip fault zone with moderately deformed and metamorphosed volcanic arc fragments in its hanging wall, and low-grade metamorphic rocks of the East European Craton in its footwall. Here, it has a prominent NNW-trending magnetic signature which cross-cuts north-trending anomalies in its hanging wall, and a pronounced reflection seismic signature that can be traced to the top of the middle crust at
c.
5 s. TWT. In the Southern Urals, it is a serpentinite mélange zone of ambiguous kinematics, with a weakly deformed and metamorphosed volcanic arc in its hanging wall, and moderately metamorphosed to high pressure rocks of the East European Craton in its footwall. In this part of the orogen, it has a weak reflection seismic character, and a magnetic signature that parallels that of its hanging wall. On the basis of an integrated analysis of these different data sets, we suggest that the Main Uralian Fault, as it is currently defined, is not a single entity, but rather the original arc–continent suture in the south, and the western strand of a strike-slip fault system that reworked the original suture in the Middle Urals.
Evidence of the proto-Iceland plume in northwestern Ireland at 42 Ma from helium isotopes
Authors: KIRSTEIN LINDA A. , TIMMERMAN MARTIN J. 
Published: June 2010

Combined K–Ar and Ar–Ar dating of a xenolith-bearing alkaline dyke, previously considered to be of late Palaeozoic age, suggest a mid-Eocene age of
c.
43 Ma, indicating that it is part of extensive rift-related Tertiary intrusive activity. High
3
He/
4
He ratios of 11–16
R
a
, potentially up to 23
R
a
(
R
a
=atmospheric ratio of 1.39×10
−6
) have been measured from mantle xenoliths in the dyke and are consistent with previous determinations of the helium isotope composition of Tertiary lavas in Greenland and Scotland linking the magmatism with the proto-Iceland mantle plume.
Volatile phase fluxed anatexis of metasediments during late Caledonian ophiolite obduction: evidence from the Sogneskollen Granitic Complex, west Norway
Authors: SKJERLIE KJELL P. , PEDERSEN ROLF B. , WENNBERG OLE P. , DE LA ROSA JESÚS 
Published: June 2010

In the west Norwegian Caledonides minor granitic sheets were intruded during obduction of the
c.
443 Ma Solund–Stavfjord Ophiolite Complex. The Sogneskollen Granitic Complex is the largest intrusive complex and consists of several minor lenses and one larger lens of granodiorite. The Sogneskollen Granitic Complex samples generally have high Ba, Sr and Na
2
O, very low Y values (<7 ppm), negative ϵ

Nd
420 Ma

values (
c.
−7 to −10.1) and
87
Sr/
86
Sr
420 Ma
ratios of 0.70437–0.70705. The REE patterns are strongly HREE depleted and La/Yb
n
varies from 0.3 to 36. Most samples display small positive Eu anomalies, but those that are most fractionated have small negative anomalies. The main part of the Sogneskollen Granitic Complex is a white composite granodiorite which is intruded by a suite of grey biotite-granite dykes. It is suggested that this, and other similar granitic sheets in the area, most probably formed by melting of sediments in the presence of a H
2
O-bearing volatile phase during obduction of the ophiolite. The quartzofeldspathic source sediments most probably contained detritus from long-term Rb-depleted lower continental crust and from an island arc. The sediments were deposited in large amounts in the marginal basin now represented by the Solund–Stavfjord Ophiolite Complex. During obduction the sediments were buried beneath the hot overriding Ophiolite Complex and the associated island-arc, and yielded granitic magmas during partial melting.
Fluid-enhanced melting during prograde metamorphism
Authors: PRINCE C. , HARRIS N. , VANCE D. 
Published: June 2010

Anatexis is a commonly recognized feature of high-grade metamorphism, but segregated melts are generally ascribed to anatexis during peak metamorphic conditions and little is known about melting along the prograde path. A suite of small-volume, deformed, two-mica leucogranites has been recognized within the High Himalayan Crystalline Series of the Garhwal Himalaya. These granites are consistently more siliceous than minimum-melt granite compositions and are characterized by low Rb/Sr ratios, high Ba, low abundances of HFS elements and positive Eu anomalies. Such trace-element characteristics contrast strongly with the geochemistry of the well-studied Early Miocene leucogranites of the High Himalaya, derived from fluid-absent melting. Sm–Nd garnet dating of one deformed granite indicates a crystallization age of 39±3 Ma,
c.
15 Ma before the emplacement of the more voluminous High Himalayan leucogranites. Whilst some entrainment of restitic phases cannot be excluded, trace element signatures suggest a low temperature (<650°C) crustal melt formed under conditions of high H
2
O activity. Positive Eu anomalies and unusually low Rb/Sr ratios are indicative of rapid, disequilibrium melting.

Fluid-enhanced melting may be a common feature of prograde upper amphibolite-facies metamorphism of orogenic belts, predating peak metamorphism by at least 15 Ma. These melts will only crystallize within this period if they segregate from their protoliths. Subsequent dating of long-lived melts would indicate erroneously young ages for the prograde melting events. However, melts formed in this way may be recognized by their distinctive trace-element chemistry. The persistence of early formed melts within an orogen provides insights into the prograde heating path, and may be critical in controlling the rheology of the middle crust, and hence its deformational history.
U–Pb geochronological constraints on the timing of plutonism, volcanism, and sedimentation, Jersey, Channel Islands, UK
Authors: MILLER BRENT V. , SAMSON SCOTT D. , D’LEMOS RICHARD S. 
Published: June 2010

Uranium–lead dates for single and small multiple grain zircon separates are presented for the main geological units from Jersey, British Channel Islands. A turbiditic sandstone from the Jersey Shale Formation (Brioverian Supergroup) contains detrital zircons of a variety of ages, ranging from
c.
2.6 to 0.6 Ga. The youngest zircons yielded nearly concordant U–Pb dates of 586.7±3.0 Ma and 587.1±2.7 Ma providing a maximum depositional age for the unit. Zircons from overlying volcanic rocks (Anne Port Rhyolite) give an upper intercept date of 582.8
+3
−2.7
Ma, considered to be the age of eruption. The undeformed SW Jersey granite, which intrudes and locally thermally metamorphoses the folded Jersey Shale Formation, is dated at 580
+2.3
−1.6
Ma. These dates constrain tightly the timing of deposition of the Jersey Shale Formation and the age of deformation on Jersey, and indicate a dynamic arc environment during the late Neoproterozoic. Zircons from the NW Jersey granite define an upper intercept date of 482.7±1.6 Ma, similar to the previously reported
40
Ar/
39
Ar hornblende date of
c.
473 Ma, confirming a renewed pulse of magmatism during the Ordovician in this sector of Cadomia.
New evidence for a large Palaeoproterozoic impact: spherules in a dolomite layer in the Ketilidian orogen, South Greenland
Authors: CHADWICK BRIAN , CLAEYS PHILIPPE , SIMONSON BRUCE 
Published: June 2010

An unconformable sedimentary succession deposited between
c.
2130–1848 Ma on Archaean gneisses of the foreland of the Palaeoproterozoic Ketilidian orogen includes a layer with coarse sand-sized silicate spherules. The layer is
c.
1 m thick and consists mainly of coarse diagenetic dolomite. In addition to
c.
18% spherules, the layer also contains 3% well-sorted, very fine quartzose sand and 6% larger intraclasts of chert and carbonate. The spherules were previously interpreted as microfossils (
Vallenia
sp.) because of their spheroidal shapes and inclusions of carbonaceous matter. The spherules are reinterpreted as replaced impact ejecta because they have shapes typical of splash-form microtektites, some contain possible examples of replaced skeletal spinel crystals, perlitic cracks and devitrification spherulites, and non-spherical particles with shapes and textures of typical glassy and scoriaceous volcanic ash are absent. The carbonaceous matter is attributed to hydrocarbons that migrated into the spherule layer from elsewhere in the sedimentary succession. The spherules were reworked after deposition, probably as a result of turbidity currents or storm- or impact-induced waves. Analysis of one spherule-bearing sample revealed only 0.02 ppb iridium, a value comparable with low iridium abundances in distal layers of other terrestrial impact ejecta. The spherules in South Greenland are the first distal impact ejecta recognized in mid-Precambrian strata. They represent a major impact because their aggregate thickness exceeds the thickest spherule accumulations reported from the Cretaceous-Tertiary boundary layer. Given their loosely constrained age and the implied scale of the impact, the Ketilidian spherules could be distal ejecta from either the Vredefort, South Africa, (
c.
2025 Ma) or Sudbury, Canada, (
c.
1850 Ma) impacts.
Kinematic linkage between internal zone extension and shortening in more external units in the NW Alps
Authors: WHEELER J. , REDDY S. M. , CLIFF R. A. 
Published: June 2010

In the Alps a major extensional shear zone unroofed eclogites in its footwall from 30 kbar to
c.
10 kbar, implying of the order of 60 km of relative vertical movement in the period 45–36 Ma. The horizontal component of divergence was of the order of 100 km. We use the foreland basin sedimentary record to prove that the extension was contemporaneous with thrusting in units structurally beneath the eclogites (the Briançonnais and/or External Zones). This thrust-related convergence during that time period was of the order of 44–56 km and therefore of the same order of magnitude as internal zone divergence. Extension may have been driven by internal density contrasts. Buoyant continental crust underneath the mafic eclogites, or dense subducted slab offset from the orogen, can induce extension. Any dynamic model must account for the comparable magnitudes of extension and shortening in adjacent parts of the orogen: relative plate motions in the period 45–36 Ma played a subsidiary role.
Geochronological constraints on tectonic models for Australian Palaeoproterozoic high-K granites
Authors: PAGE R. W. , GRIFFIN T. J. , TYLER I. M. , SHEPPARD S. 
Published: June 2010

High-K granites extensively intruded all the Palaeoproterozoic terrains of northern Australia, and have been interpreted as the culmination of widespread intracratonic orogeny. One of these terrains, the Lamboo Complex, developed between the Kimberley and North Australian Cratons. The complex is divided into three terranes, referred to as the Western, Central, and Eastern zones, and was intruded by a variety of I-type granites and gabbros. High-K granites of the 1865–1850 Ma Paperbark supersuite are restricted to the Western zone. Tonalite sheets of the Dougalls suite, and unassigned leucogranite sheets, intruded the Central zone at
c.
1850 Ma. The 1835–1805 Ma Sally Downs supersuite is composed of tonalite and high-K granite that mainly intruded the Central zone. However, high-K granites of the Sally Downs supersuite intruded all three zones from
c.
1820 Ma onwards, and mark the amalgamation of the terranes. The youngest granites in the complex are high-K granites of the 1805–1790 Ma San Sou suite, which intrude the Eastern and Central zones. The temporal and spatial distribution of the granites is not easily reconciled with previous intracratonic models, but is consistent with tectonic processes similar to those operating at present.
Relocating and orientating cores by the integration of electrical and optical images: a case study from Ocean Drilling Program Hole 735B
Authors: HAGGAS S. L. , BREWER T. S. , HARVEY P. K. , ITURRINO G. I. 
Published: June 2010

While the dip of structural features on recovered rotary-drilled core can be accurately measured, the azimuth of such features in a geographical reference frame is not known. Scribing techniques and analysis of magnetic signatures have been used in attempts to solve this problem, but scribing has so far failed in deep-sea drilling operations and magnetic signatures cannot always be easily resolved. Here, we demonstrate a method for core reorientation and accurate location within a borehole using a comparison between borehole electrical images and whole-core digital images.
ODP Hole 735B penetrates a 1500 m section of lower oceanic crustal (gabbroic) rocks with an average core recovery of 86.6%. The absence of orientated core pieces severely restricts the interpretation of these data. In this study, the entire outer surface of individual core pieces was scanned using the DMT Digital Colour CoreScan™ system. Structural features on these unrolled digital images are correlated with images of the same features on Formation Microscanner logs obtained during the wireline-logging programme. Using this approach it is possible to reorientate and accurately locate core pieces within the drilled section.
Rotation of ductile fabrics across the Alpine Fault and Cenozoic bending of the New Zealand orocline
Authors: LITTLE TIMOTHY A. , MORTIMER NICK 
Published: June 2010

This study examines the role and kinematic mechanism of vertical‐axis rotations and folding during early development phases of a transform plate boundary in continental crust. Near the Alpine Fault in New Zealand, this involved an initial period of widely distributed shear (including wrench folding), together with vertical‐axis rotations and orocline development, followed by a focusing of slip onto a single fault. In the South Island, the Haast Schist has been displaced horizontally in the Neogene by
c.
480 km of dextral‐slip on the Alpine Fault. LS tectonites on either side of the fault lie on different limbs of a profound Z‐shaped orocline. Rotation of these limbs took place about a vertical axis, resulting in 25–30° of clockwise rotation of fabrics to the NW of the Alpine Fault relative to those to the south. Foliation anisotropy caused bending to take place locally by folding about an inclined hinge in the limbs of a pre‐existing synform, which tightened during the deformation. On both sides of the fault, involvement of post‐Oligocene age structures in wrench‐folding and bending suggests that the bending took place entirely in the Cenozoic, before or during Miocene development of the Alpine Fault as a through‐going structure. During this early phase of plate boundary deformation, shear was distributed across a zone >100 km wide. Vertical‐axis rotation affected, fault‐bounded basement slivers that shortened perpendicular to their strike, a style of deformation like that in the Transverse Ranges in California today.
Synoptic-Eddy Feedbacks and Circulation Regime Analysis
Authors: Straus David M. 
Published: June 2010

Abstract
A method to incorporate synoptic eddies into the diagnosis of circulation regimes using cluster analysis is illustrated using boreal winter reanalyses of the National Centers of Environmental Prediction (hereafter observations) over the Pacific–North American region. The motivation is to include the configuration of the high-frequency (periods less than 10 days) transients as well as the low-frequency (periods greater than 10 days) flow explicitly into the definition of the regimes.
Principle component analysis is applied to the low-frequency 200-hPa height field, and also to the low-frequency “envelope” modulations of the rms of high-frequency meridional velocity at 200 hPa. A maximum covariance analysis of the height and envelope fields, carried out using the appropriate principal components, defines three modes as explaining most of the covariance. This defines the minimum dimensionality of the space in which to apply k-means cluster analysis to the covariance coefficients. Clusters found using this method agree with results of the previous work.
Significance is assessed by comparing cluster analyses with results from synthetic datasets that have the same spectral amplitudes (but random phases) of seasonal means and, separately, intraseasonal fluctuations as do the original observed time series. This procedure ensures that the synthetic series have similar autocovariance structures to the observations. Building on earlier work, the clusters obtained are newly tested to be highly significant without the need for quasi-stationary prefiltering.