bluuebunny/crossref_metadata_2025 huggingface dataset:
Fault rocks and fault mechanisms
Authors: SIBSON R. H.
Published: December 2007

Physical factors likely to affect the genesis of the various fault rocks—frictional properties, temperature, effective stress normal to the fault and differential stress—are examined in relation to the energy budget of fault zones, the main velocity modes of faulting and the type of faulting, whether thrust, wrench, or normal. In a conceptual model of a major fault zone cutting crystalline quartzo-feldspathic crust, a zone of elastico-frictional (EF) behaviour generating random-fabric fault rocks (gouge—breccia—cataclasite series—pseudotachylyte) overlies a region where quasi-plastic (QP) processes of rock deformation operate in ductile shear zones with the production of mylonite series rocks possessing strong tectonite fabrics. In some cases, fault rocks developed by transient seismic faulting can be distinguished from those generated by slow aseismic shear. Random-fabric fault rocks may form as a result of seismic faulting within the ductile shear zones from time to time, but tend to be obliterated by continued shearing. Resistance to shear within the fault zone reaches a peak value (greatest for thrusts and least for normal faults) around the EF/QP transition level, which for normal geothermal gradients and an adequate supply of water, occurs at depths of 10–15 km.
Structural control of batholithic emplacement in Peru: a review
Authors: PITCHER W. S. , BUSSELL M. A.
Published: December 2007

In the Andes, major lineaments controlled sedimentation, vulcanicity, batholithic intrusions and mineralisation throughout the Mesozoic and Cenozoic. These lineaments represent major fault lines in an ancient crystalline basement. The magmas of the Coastal Batholith were emplaced along one such lineament and the emplacement of the individual plutons was closely controlled by transcurrent faults and by smaller scale joint patterns. Such structures were continuously exploited throughout the long emplacement history of the batholith. Exceptionally, plutons were forcefully emplaced along early lineaments and lifted roof blocks along shear zones coincident with pre-existing faults. More generally subsidence of large fracture-bound crustal blocks provided the space for the emplacement of magma in bell-jar and cauldron-subsidence structures while stoping along the regular, closely spaced joints resulted in a rectilinear pattern of contacts at outcrop scale.
Metamorphic rocks in the SW Ox Mountains Inlier, Ireland; their structural compartmentation and place in the Caledonian orogen
Authors: LONG C. B. , MAX M. D.
Published: December 2007

Three tectono-sedimentary units having Caledonian tectono-thermal histories are recognized within the metamorphic rocks of the SW Ox Mountains Inlier. The different structural levels represented by each of these units were juxtaposed along tectonic contacts late in the individual tectono-thermal histories. The highest structural unit is the virtually unmetamorphosed, probably Southern Highland (Upper) Dalradian, Ardvarney Formation which can be related on a regional scale to the Donegal 'Tay Nappe' structure. The Raheen Barr succession probably ranges from the Islay to Easdale subgroups of the Middle Dalradian and can be correlated with the metamorphic rocks of the Nephin Beg succession in NW Co. Mayo. The Ox Mountains succession represents the deepest structural level seen and consists of basic volcanic rock, graphite schist, marble quartzite, psammite, and semi-pelite. It forms the envelope to the syn- to late kinematic 500 ± 18 Ma Ox Mountains Granodiorite and stratigraphically it can best be compared with the Appin and Argyll groups of the Dalradian of Connemara.

The differing tectono-thermal histories of the different structural levels in this part of the metamorphic Caledonides of western Ireland possibly reflect the diachronous nature of the deformation and metamorphism in the orogen. Interaction during juxtaposition must have involved movement related to more than one direction of tectonic transport.
Seismic refraction studies of geological structure in the inner part of the Bristol Channel
Authors: BROOKS M. , AL-SAADI R. H.
Published: December 2007

Nine E–W seismic refraction lines about 12 km long provide information on the thickness and structure of the Mesozoic succession in the inner Bristol Channel area. About 2000 m of mainly Jurassic strata occupy the Bristol Channel syncline north of Foreland Point but this structure attenuates eastwards and is replaced by the Glastonbury syncline which contains nearly 800 m of Mesozoic strata under Bridgwater Bay. The Central Bristol Channel fault zone has been traced eastwards towards Bridgwater Bay, and has a southerly downthrow of several hundred metres in mid-Channel north of Porlock. There is some evidence for an early phase of movement along the fault zone, bringing Lower Palaeozoic against Upper Palaeozoic rocks.
Stable isotopes and limestone lithification
Authors: HUDSON J. D.
Published: December 2007

Data on the carbon and oxygen isotopic composition of the carbonate sediments, limestones and calcite cements are compiled and reviewed, and an elementary exposition of the factors that control them is given. Typical compositions and diagenetic trends are displayed on δO
18
–δC
13
scatter diagrams, and an attempt is made at an isotopic categorization of environments of carbonate lithification. Many limestones pass through several diagenetic environments, which are recorded isotopically by cement generations of distinct isotopic composition. Most limestones contain essentially 'marine' carbon, but extreme compositions can result from organic reactions, especially those involving methane; some of these may be important in petroleum exploration, but their volumetric abundance is probably quite small.
Strontium isotope evidence for mantle events in the continental lithosphere
Authors: PANKHURST R. J.
Published: December 2007

Following current interpretation of isotope data from oceanic basalts, the case for inheritance of Rb/Sr and
87
Sr/
86
Sr ratios in continental igneous rocks from long-lived heterogeneities in the mantle is reviewed, both from the point of view of necessary conditions and the evidence of published 'mantle isochrons'. Such inheritance seems unlikely for magmas undergoing plagioclase fractionation and can hardly be claimed for rocks where crustal contamination (especially selective contamination with trace elements or
87
Sr alone) is a feasible alternative. Nevertheless, some unfractionated transitional or undersaturated basic volcanics do show remarkable co-variance of Rb/Sr and initial
87
Sr/
86
Sr ratios, indicating ages far in excess of extrusion. These and other arguments suggest that heterogeneous mantle, both enriched and depleted in lithophile trace elements, is incorporated into the continental lithosphere during major crust-mantle differentiation events. Re-distribution of isotopes and incompatible elements in fluid phases or small partial melts may be an important mechanism, although others have suggested addition of enriched material from below the asthenosphere.
The anatomy of a large submarine slump on a sheared continental margin (SE Africa)
Authors: DINGLE R. V.
Published: December 2007

The morphology and structure of a large submarine slump (Agulhas Slump) on the sheared continental margin off SE Africa are described from bathymetric and continuous seismic reflection records. It is a composite feature consisting of proximal and distal allochthonous sediment masses separated by a large glide plane scar. The locations of the various structural elements of the slump are related to underlying features: in the head region these are controlled by large-scale Cretaceous and Palaeogene depositional features, and in the toe region by older basement ridges. In the western part of the slump, the basement ridges have dammed the slump over continental crust, whereas in the east, allochthonous material has spread into the oceanic Transkei Basin. Characteristics related to a structural setting on a sheared continental margin are emphasized and discussed. The Agulhas Slump is probably the largest slumped mass so far recognized from modem oceans (750 km long, 106 km wide, with a volume of over 20,000 km
3
) and is post-Pliocene in age. A seismic triggering mechanism is tentatively proposed: the slump lies on two major fault zones whose extensions are known to be seismically active (the Cape Fold Belt and the Agulhas marginal fracture zone).
Authigenic K-feldspar in British Permo-Triassic sandstones
Authors: Waugh B.
Published: December 2007

Authigenic K-feldspar, occurring as overgrowths around detrital orthoclase and microcline, is a common minor diagenetic constituent in British Permo-Triassic sandstones. Overgrowths began as crystallographically oriented rhombs (∼10
μ
m) with an adularia habit. By merging, stacking and overlapping, these eventually produced complete overgrowths with crystalline perfection. The overgrowths possess extraordinary chemical purity, being stoichiometric KAlSi
3
O
g
. This together with − 2 V values of 20–25°, suggests that the authigenic phase is potassian intermediate sanidine. The source of the K
2
O, A1
2
O
3
and SiO
2
is ascribed to the
in situ
dissolution of detrital K-feldspar, plagioclase, biotite and other silicates. The intrastratal solutions thus produced also provided authigenic quartz, illite, haematite and calcite.
Diagenetic sequences in low-permeability argillaceous sandstones
Authors: Thomas J. B.
Published: December 2007

A regular sequence of mineral paragenesis is observed in low-permeability (‘tight’), very fine-grained sandstones of brackish marine to fresh water origin in portions of the Cretaceous of the Rocky Mountains, North America. From pore throat to pore centre in these rocks, the common authigenic sequence is illite (pore throat), kaolinite, silica (pore centre), and siderite (pore centre but after silica). Associated fine- to medium-grained sandstones exhibit a sequence of quartz followed by kaolinite plus traces of calcite from pore throat to centre.

Comparison of Gibbs' free energies of formation calculated by the method of Tardy & Garrels show values decreasing in the same order as paragenesis (illite, kaolinite, silica, siderite) observed in the low permeability very fine-grained sandstones. Diagenetic sequences in the coarser sandstones do not match the order of free energies of formation. This implies that early precipitation in very fine-grained sandstones probably occurs under nearly static conditions, whereas constant fluid throughput in coarser grained rocks leads to a markedly different diagenetic sequence. Thus, two potential sandstone reservoirs, one coarse and one very fine, commonly will have different authigenic mineral suites though their original pore waters were broadly identical.
Possible links between sandstone diagenesis and depth-related geochemical reactions occurring in enclosing mudstones
Authors: Curtis C. D.
Published: December 2007

Within compacting mudstone sequences several depth zones can be recognised in which distinctive diagenetic reactions take place. Most striking are those involving carbonate precipitation or replacement. The major carbon source is organic matter which is degraded by various microbiological and inorganic reactions to bicarbonate as one product. Other reactions involving silicates and sesquioxides introduce cations to the porewater system and carbonates are precipitated. Their chemical and isotopic composition can be linked with temperature and depth of formation.

Analysis of some of the literature of sandstone diagenesis suggests that carbonate cements in sandstones often originate in mudstones, and that precipitation may take place far from the site of solute generation. Vast volumes of porewater excluded from mudstones during compaction are channelled into and travel great distances within sand units. Early diagenetic reactions drastically modify the permeability of both potential source and reservoir rocks. The component of horizontal flow is greatly increased and this must affect later migration of liquid hydrocarbons.
The Andean geosyncline in Peru, and its distinction from Alpine geosynclines
Authors: Cobbing E. J.
Published: December 2007

The Andean geosyncline in Peru is divided into faulted strips of crust. This has resulted in the isolation of basins of deposition which have both subsided and deformed independently. Five basins were formed, two of which were filled with sediments and pertain to the miogeosyncline, two with volcanics form the eugoesyncline, and a fifth composed of both volcanics and sediments forms a miogeanticlinal horst between the two.

A volcano-plutonic chain was superimposed upon the fractured continental crust and the eugeosyncline was filled with material derived from the volcanoes and also from plutons of the rising batholith. The miogeosynclinal basins were filled with material derived from the continental hinterland.

The eugeosyncline was deformed during the Upper Albian and the Coastal Batholith was emplaced during the Upper Cretaceous while sedimentation continued in the miogeosyncline. Deformation of the miogeosyncline occurred during the Palaeocene.

Aubouin's distinction of Andean from Alpine chains is confirmed. Andean chains are characterised by andesite volcanics and tonalite batholiths, whereas Alpine chains contain ophiolite belts and sedimentary flysch. The differences may reflect their different tectonic setting, the Andes having developed under a convergent regime between a continent and a large ocean while the. Alpine chains may have evolved under a regime involving the opening and closing of small ocean basins between continents. It is suggested that andesite volcanics and tonalite batholiths are characteristic indicators of the subduction process at continental margins.
Conference Report
Mineralization associated with acid magmatism and other aspects of ore geology
Authors: Evans A. M.
Published: December 2007

The first part of the title of this conference is also the title of an international group co-ordinating research in this field. This meeting was held at the request of the Group's British representatives and produced varied group of papers covering mineralization in both the volcanic and plutonic associations.

It had been hoped that Dr M. Štemprok would give an opening address but, as he was unable to be present, Dr Alan Bromley kindly stepped into the breach. In a very comprehensive survey of the field he commenced with the problem of the generation of granitic magmas particularly those associated with subduction zones, because at this plate juncture we often see a zoning of metallic deposits which suggests derivation of the metals from the subduction zone, with perhaps the rising granite magmas acting only as carriers. The metals probably move as complex halide ions with, perhaps for tin, the possibility of fluoride, liberated from the breakdown of apatite, being the carrier ion. Bromley emphasized the importance of manganese nodules as carriers of many metals down the subduction zones but not of tin and tungsten. He noted that in Cornwall, joints in mineralized areas are coated with much manganese and posed the question, 'Does manganese give a broad halo useful in exploration in such areas?'

Manganese nodules and the sediments of layer 1 of the oceanic crust could supply the metals of deposits in the zones nearest to the trenches. However, the genesis of tin and tungsten ores seems
Namurian mesothems in South Wales and northern France
Authors: Ramsbottom W. H. C.
Published: December 2007

Mesothemic cycles, which are unconformity-bounded on shelf areas but defined by marker points at the bases of chronozones in continuous sections in basinal areas, are delineated in the Namurian (Carboniferous) of South Wales and northern France. The patterns of successive transgressions in these areas show many similarities to those in northern England. The suggested explanatory hypothesis of eustatic rises and falls of sea level in the Namurian is strengthened. There is evidence that the same mesothemic cycles are also present in western Germany.
Metallogenesis in the Japanese island arc system
Authors: Ishihara S.
Published: December 2007

Ore deposits in the Mesozoic and Cenozoic orogenic belts of the Japanese island arc system consist essentially of stratabound, vein and skarn types. The stratabound base-metal deposits, which are the main source of copper, are divided into the lead-free, chalcopyrite-pyrite, Besshi-type, which occur mainly in glaucophane schists (metamorphosed basaltic pyro-clastic rocks) of the Sanbagawa belt, and the lead-bearing, polymetallic, massive sulphide, Kuroko-type, associated with rhyolite extrusion. Both types are regarded as having been formed syngenetically in a submarine environment. Vein-type deposits are widely distributed and economically the most important for metals, containing more than 50 per cent of the available tin, tungsten, molybdenum, gold, silver and manganese. The ore deposits are genetically related to either 'geosynclinal basalt' or an andesite-dacite-rhyolite and plutonic association of island arc magmatism. Special attention is given to deposits of plutonic affinity.

Most Japanese plutons are granitoids. Ore deposits associated with Cretaceous-Palaeogene granitoids in southwest Japan constitute two metallogenic provinces, characterised by W-Sn-Cu and Mo-Pb-Zn veins and skarns. Northeast Japan shows a similar, but reversed, zoning, with no tin. Miocene granitoids in southwest Japan are accompanied by tin and some copper mineralization. The Japanese granitoids consist of approximately equal proportions of magnetite-series and ilmenite-series rocks. The magnetite-series is thought to be derived from a parental magma generated from mafic igneous rocks of the upper mantle—lower crust and related to major subduction. The ilmenite-series, with which tin deposits may be associated, is ascribed to magma originating in the lower crust from sedimentary, metamorphic and granitoid rocks. These magma types appear to be the most important factors in producing the various metallogenic provinces in Japan.
Glauconite dating of Palaeocene-Eocene rocks from East Kent and the time-scale of Palaeogene volcanism in the North Atlantic region
Authors: Fitch F. J. , Hooker P. J. , Miller J. A. , Brereton N. R.
Published: December 2007

Glauconite dates obtained by conventional K-Ar and
40
Ar/
39
Ar age spectrum techniques from Palaeocene horizons in Kent are examined against a Palaeogene K-Ar time-scale derived from the Tertiary igneous rocks of the North Atlantic region. Isotope ratio plots (correlation diagrams) are used to analyse and test the validity of the results. The boundary ages suggested by the dating of North Atlantic igneous rocks are: base Danian –66Ma, base Thanetian ~60Ma, base Lower Sparnacian ~56Ma, base Upper Sparnacian ~54 Ma, base Ypresian ~53 Ma and base Lutetian ~49 Ma (when calculated using Geological Society of London 1964 standard constants). A variety of natural deficiencies may impair the dating of authigenic glauconite grains, some specific to glauconite in addition to those generally applicable in K-Ar dating. These shortcomings prevent direct use of the majority of
unconfirmed
glauconite dates in the definition of the standard K-Ar time-scale. Nevertheless, accurate and precise glauconite dates can be obtained from
ideal
glauconite dating samples. It is suggested that ideal glauconite dating samples can be recognised and confirmed as such from the character of the
40
Ar/
39
Ar step heating correlation diagrams obtained from them and that careful experimental procedures are essential if argon loss error in the laboratory is to be avoided.
U–Pb zircon ages for late Precambrian igneous rocks in South Wales
Authors: Patchett P. J. , Jocelyn J.
Published: December 2007

U–Pb zircon data are presented for two Precambrian calc-alkaline intrusive bodies associated with large volumes of felsic volcanic rocks in SW Wales. The Johnston complex was probably emplaced 643
–28
+5
Ma ago, while the St. Davids granophyre was intruded between the limits 650 and 570 Ma ago, a later Pb loss rendering the precise magmatic age in this case uncertain. The St. Davids granophyre result indicates major Precambrian volcanic/intrusive activity in this area of southern Britain, and the emplacement of the Johnston complex may be part of these events.

Initial
87
Sr/
86
Sr ratios for the St. Davids granophyre fall between 0.7037 and 0.7053 and probably suggest an ultimate derivation of the magma from the mantle. The variation of initial ratios could be explained by factors operating during the genesis or ascent of the magma, or by contamination during late- to post-magmatic hydrothermal activity.
Ordovician intrusions in the English Lake District
Authors: Rundle C. C.
Published: December 2007

Rb–Sr whole rock isochron and K–Ar whole-rock and mineral ages suggest that there were four intrusive episodes in the Lake District in Ordovician times, in addition to the widely recognized end-Silurian event. The Carrock Fell Gabbro has given an age of 468 ± 9 Ma and is probably coeval with the Eycott Volcanic Group. A suite of dioritic lamprophyres, including the Great Cockup ‘Picrite’, has a preferred age of 458±9 Ma and may be related to the main Borrowdale Volcanic Group. The Eskdale Granite was emplaced around 429 Ma, probably during the Caradoc, and the Ennerdale Granophyre, Carrock Fell Granophyres, and the Harestones Felsite are coeval with the Stockdale Rhyolite (421Ma) and of Ashgillian age. Muscovites from various facies of the Eskdale Granite show a wide spread of K–Ar ages from 426 to 388 Ma. The implications of these results for the tectonic and mineralogenic history of the area are discussed and previous research is reviewed in their light.
Late Mesozoic sedimentary rocks of Fuerteventura, Canary Islands: Implications for West African continental margin evolution
Authors: Robertson A. H. F. , Stillman C. J.
Published: December 2007

The basal complex of Fuerteventura, inner Canary Islands, includes a thick sequence (c. 1.5 km) of early Cretaceous terrigenous and calcareous clastic sediments and black shales. Previously interpreted as shallow-water deposits, these rocks are reinterpreted as part of a deep-sea fan on the rifted West African continental margin. Sediments were derived from ancient crystalline massifs inland, and from a probable collapsed carbonate platform located offshore.

Stable passive margin conditions ended in the Albian with onset of calcareous pelagic sedimentation coupled with major localised uplift. After a hiatus, alkalic submarine volcanic rocks were extruded, followed by folding, then a substantial sheeted-dyke complex was intruded from late Eocene to mid-Miocene. After renewed uplift and peneplanation of the Basal Complex, Neogene plateau lavas were extruded.

Structural analysis of Fuerteventura rocks and regional comparisons, including IPOD data, show that from early Cretaceous to mid-Tertiary the island experienced successive phases of crustal uplift, compression and extension, possibly related to orogenic events in the High Atlas.
The Ningi-Burra complex, Nigeria: dissected calderas and migrating magmatic centres
Authors: Turner D. C. , Bowden P.
Published: December 2007

A series of overlapping ring structures each contain varied, pre-caldera volcanic sequences, overlain by massive intra-caldera rhyolitic ignimbrites and enclosed within ring dykes of fayalite-hedenbergite granite-porphyry. Early basalts are hypersthene-normative but may originally have been alkaline or transitional to nepheline-normative. They are linked, through a series of andesine basalts, mugearites and trachyandesites, to aphyric trachytes. Pre-caldera rhyolitic rocks, interbedded with and overlying the basic and intermediate volcanics, are mainly ignimbrites which were perhaps originally peralkaline or near peralkaline, but are often recrystallized to subalkaline compositions. They formed mainly through partial melting with zone refining of crustal rocks, the mantle-derived basic to intermediate magmas providing the heat source. In the early stages of each caldera-forming cycle the ignimbrite eruptions were of small volume and the rocks have varied crystal contents. Later, large high level magma chambers must have developed, from which crystal-rich ignimbrites with volumes in the order of 100 km
3
were erupted, with accompanying caldera collapse. The form of the complex as a whole shows that this cycle occurred repeatedly, but with the location of magma generation migrating progressively westwards, resulting in a chain of rhyolitic cauldrons, into which subvolcanic granites and syenites have been emplaced.
Rates of transgression and regression in the Carboniferous of NW Europe
Authors: Ramsbottom W. H. C.
Published: December 2007

The Carboniferous in NW Europe shows more than 30 large transgressions (with intervening regressions) up to the middle part of Westphalian C. Marginal areas of deposition show stratigraphical breaks between each transgressive cycle. Each large transgression was not continuous but appears to have been pulsed, with each small transgressive pulse reaching further than its predecessor. The rates of transgression are assessed at several different levels in the Carboniferous. Many of the features found in NW Europe appear to have been of general occurrence.
Rapid marine transgressions and regressions of the Upper Permian Zechstein Sea
Authors: Smith Denys B.
Published: December 2007

Evidence bearing on the rates of transgression and regression of the early Zechstein Sea in NE England is reviewed and the hypothesis that this sea was formed virtually instantaneously when the Boreal Ocean broke into and flooded a chain of sub-sea-level inland drainage basins is restated. Subsequent formation of a thick marginal carbonate wedge was apparently followed by an unusually rapid marine recession, the cause of which is postulated as evaporative drawdown after renewed isolation of the Zechstein Sea. The possibility of other rapid Zechstein transgressions and recessions is briefly discussed.
The great transgressions of the Late Cretaceous
Authors: Hancock J. M. , Kauffman E. G.
Published: December 2007

During the Late Cretaceous (94–64 Ma) sea level was up to 650 m higher than at the start of the Albian, when it was perhaps about the same as it is today. Facies analysis in both the Western Interior of the USA and in NW Europe reveals simultaneous major oscillations in sea level that controlled the principal transgressions and regressions except in regions of rapid contemporaneous tectonics. The peak transgressions of the Late Albian, Early Turonian, Early Coniacian, Middle Santonian and Late Campanian, probably recognisable world-wide, involved rises of sea level at rates of about 10–90 m per m.y. The peak regressions are more difficult to measure, but were usually faster and involved falls of sea level of about 95–170 m per m.y.
The North Anatolian transform fault: its age, offset and tectonic significance
Authors: Sengör A. M. C.
Published: December 2007

The North Anatolian transform fault is a morphologically distinct and seismically active strike-slip fault which extends for about 1200 km from Karliova to the Gulf of Saros along the Black Sea mountains of N. Anatolia. It takes up the relative motion between the Black Sea and the Anatolian plates, thereby connecting the E. Anatolian convergent zone with the Hellenic Trench through the complex plate boundary zone of the Aegean. For most of its length, the transform has a typical strike-slip fault zone morphology, characterized by narrow ‘rift zone,’ offset, captured and dammed streams, sag ponds and other deformed morphological features. The fault zone is a broad region of extensively crushed country rock cut by a number of parallel and/or anastomosing strike-slip faults. The transform has periods of seismic activity the last of which, from 1939 to the present, is characterized by frequent 6 ≤ M≤7earthquakes; these are separated by quiet periods of about 150 years. The crust along the fault zone is thinner than normal. The transform probably originated some time between the Burdigalian and the Pliocene and has an offset of about 85 km. Whether the offset of the fault changes systematically along its strike is not known. The North Anatolian transform fault seems to have originated as a consequence of the Arabia-Anatolia collision durmg the late (?middle) Miocene, when the Anatolian Plate originated and was wedged out into the oceanic tract of the E. Mediterranean from the converging jaws of Arabia and Eurasia to prevent excessive crustal thickening in E. Anatolia. The westerly motion of Anatolia with respect to Eurasia and Africa caused a great change in the tectonic evolution of the eastern Mediterranean, giving rise to the Aegean extensional regime and to internal deformation of Anatolia.
The San Andreas fault system through time
Authors: Crowell J. C.
Published: December 2007

The active San Andreas fault system today lies at the splintered boundary between the Pacific and North American lithospheric plates, a tectonic arrangement that originated in California in the Oligocene. By late Miocene time sedimentary breccias derived from San Andreas scarps were being shifted laterally from their source areas. During the Pliocene the system extended from the Mendocino triple-junction to the head of the Gulf of California. The Big Bend in the San Andreas developed and the Transverse Ranges rose, in association with the opening of the Gulf of California.

The boundary between the Pacific and North American plates is wide and fragmented and during the late Cenozoic, the crust has yielded laterally by simple shear and deformed through pull-apart stretching and fault-block squeezing and uplift and rotation. Splay faults, such as the San Jacinto, Calaveras, and Hayward, branch from the main fault near constraining bends. The strewn out arrangement of displaced slices may account for displacements of 600 km on the northern San Andreas and only 300 km on the southern across a wide mobile boundary zone that has a total displacement exceeding 1000 km. Strike slip may also have occurred along faults parallel to the system in Cretaceous-Palaeocene times when the Kula Plate was moving laterally northwestward with respect to the North American Plate.
Interfluvial drainage on Siluro-Devonian alluvial plains in Wales and the Welsh Borders
Authors: Allen J. R. L. , Williams B. P. J.
Published: December 2007

Type A intraformational conglomerates are associated with relatively thick quartzose channel sandstones and include a matrix of quartzose sandstone accompanied at some stratigraphical levels by exotic pebbles and cobbles. They are related to the major streams that entered from distant uplands and drained across the Lower Old Red Sandstone alluvial plains. Type
B
intraformational conglomerates, frequently interbedded with mudstones and pebbly mudstones, lack a matrix of quartzose sandstone and other exotic elements, and consist wholly of debris (calcrete and mudstone fragments) whose immediate origin was within the bounds of the Old Red Sandstone depositional basin. Erosively overlying calcretes, interpreted as formed on temporarily stabilized geomorphic surfaces, they represent minor systems of ephemeral drainage developed from time to time on broad and probably slightly elevated interfluves situated between the then envalleyed principal rivers.
Geochronology and geochemistry of granite magmatism in Thailand in relation to a plate tectonic model
Authors: Beckinsale R. D. , Suensilpong S. , Nakapadungrat S. , Walsh J. N.
Published: December 2007

3 Rb-Sr whole rock isochron ages for Thai granitoids are presented. These new results and a systematic survey of available Rb-Sr whole rock isochron data indicate that there is substantial evidence for granite magmatism in Thailand at
c.
240 Ma (Lower Triassic),
c.
210 Ma (Upper Triassic),
c.
130 Ma (Lower Cretaceous) and
c.
90 Ma (Middle Cretaceous). K-Ar ages for mica separates are commonly grossly discordant—up to about 150 Ma younger than the corresponding Rb-Sr whole rock isochron age. This resetting is attributed to water/rock interaction in hydrothermal circulation systems probably driven by deep burial in areas of high heat flow. Hot springs are common in Thailand, with estimated subsurface water temperatures up to 200°C. The chemistry of the Thai granites allows them to be grouped into I-types or S-types (magnetite-series or ilmenite-series). These 2 types of granite are related respectively to subduction of oceanic lithosphere and continent-continent or continent-magmatic arc collisions. The major tin deposits of Thailand are associated with collision related S-type granites of Triassic and Middle Cretaceous age.
Origin of the Uliasser Islands, eastern Indonesia
Authors: Milsom J. S.
Published: December 2007

The Seram segment of the Banda Arc appears to conform to the structure of a ‘typical’ arc, but the geology of the area reveals a number of deviations from the norm; these are briefly listed. The late Tertiary or Quaternary volcanoes forming the Uliasser Islands mark the southern margin of an extensional zone, and have been intruded along a localized transform fault. Intermediate magmas are not solely associated with active subduction, and the interpretation of the geology of the Seram area is greatly simplified if the Uliasser volcanics are not regarded as subduction-related.
P-T conditions in the Moines of the Central Highlands, Scotland
Authors: Wells P.R.A.
Published: December 2007

P-T conditions of regional Caledonian metamorphism recorded by calc-silicate assemblages in Moine rocks from the Central Highlands vary from 550°C, 7 ± 2 kbar, near Loch Laggan, to 670°C, 10 ± 2 kbar in the central Spey valley. The pressure conditions correspond to 30–35 km of tectonic cover in the Central Highlands during the metamorphic temperature maxima. These estimates place much of the Moines of the Central Highlands in the kyanite zone.

Spatial variations in estimated pressure conditions at comparable temperatures suggest differential initial tectonic cover thickness and/or differential erosion over the Caledonide orogen.

Numerical models of these alternative thermal regimes predict different P–T histories for the metamorphic rocks of the Central Highlands. Mineral assemblages exhumed by differential erosion, related to different cover thickness, record maximum temperature conditions at progressively earlier times with increasing recorded pressure. These time relations are reversed for differential erosion of initially uniform cover thickness. These results have general application to metamorphic rocks developed within zones of tectonic thickening.
The use of balanced cross-sections in the calculation of orogenic contraction: A review
Authors: Hossack John R.
Published: December 2007

Balanced section calculations assume that the section has been deformed by a plane strain. If the section is underlain by a décollement, it can be restored to its predeformational length by dividing the area of the section by its original stratigraphic thickness. The thickness can be measured in undisturbed foreland beds or reconstructed by unstraining deformed beds. The restoration of the balanced section does not depend on any particular mechanism of deformation or folding, but in the special case of flexural slip folding the section can be unstrained by straightening out the sinuous bed lengths of the folds. However, in nature the area of the section may have decreased by 15–45%, but the assumption of plane strain always leads to a minimum estimate of shortening. Balanced section calculations suggest that the margins of orogenic belts have contracted by 35–54%.
The geology and palynology of the Oligocene Lough Neagh Clays, Northern Ireland
Authors: Wilkinson G. C. , Bazley R. A. B. , Boulter M. C.
Published: December 2007

Results from research on the Tertiary deposits in the Lough Neagh region of Northern Ireland are presented. The fossil pollen and spores show that the Lough Neagh Clays are of Chattian (late Oligocene) age. The deposits were formed in shallow temporary lakes around river deltas. Comparisons are made with the Oligocene deposits in the western part of the British Isles.
The origin of granite magmas: a discussion
Authors: Leake B. E. , Brown G. C. , Halliday A. N.
Published: December 2007

A summary of the arguments both in favour of, and against, the mantle and crustal origin of granitic magmas is presented, with reference to the literature for detailed and fuller exposition of the relevant criteria.

B.E.L.:
I
find it difficult to understand why granitic bodies appear to be totally absent from the oceanic crust if granitic magma is commonly derived from the mantle. Not only are oceanic granites unknown, but geophysical evidence does not support the existence of buried batholiths in the oceanic crust that have not risen high enough to be exposed. Moreover, as it is generally agreed that the upper mantle is dominantly ultrabasic and rich in olivine, it seems that this is the least likely sort of composition to yield substantial quantities of quartz-rich granitic magma by partial melting. Indeed, Wyllie
et al.
1976 argued that any melt formed from a peridotite must be in equilibrium with the residual olivine, and such melts cannot also be silica-rich. I believe, therefore, that most granitic magma is dominantly derived by partially melting the lower continental crust, sometimes by uprise of basaltic or other mantle-derived magma, sometimes by deep faults that bring hot mantle against already nearly melting basal crust, and sometimes simply by deep faults uplifting segments of the base of the crust, resulting in isothermal melting under reduced pressure. The detailed exposition of this view is in
Leake (1978)
.

I know that the rather low initial 87Sr/86Sr ratios of many granites, such as the Caledonide suite of Britain,
Towards a classification of shales
Authors: Spears D. A.
Published: December 2007

The problems relating to the classification of mudrocks, and in particular the role of grain size, are discussed. Classification based on silt-clay proportions is more realistic than a silt-clay-sand system. The grain size, as measured in mudrocks, is an uncertain quantity and the use of the quartz content is advocated. The method is applicable in the field using standard rocks of known quartz content. Attention is drawn to the property of fissility, which may in certain cases be shown to be due to the presence of laminae. The formation and preservation of laminae provide important sedimentological information.
Cretaceous anoxic events: from continents to oceans
Authors: Jenkyns H. C.
Published: December 2007

Pelagic Cretaceous sediments, deposited in a range of palaeotectonic and palaeogeographic settings, from continents to oceans, are commonly black and bituminous. 3 particular time-envelopes define the major occurrences of such facies: late Barremian-Aptian-Albian, the Cenomanian-Turonian boundary and, to a lesser extent, the Coniacian-Santonian. These intervals define the duration of so-called Oceanic Anoxic Events during which global marine waters were relatively depleted in oxygen, and deposition of organic matter, derived from both terrestrial and planktonic sources, was widespread. Cretaceous OAEs correlate closely with transgressions, and such a correlation exists throughout the stratigraphical column. Flooding of land-masses is thought to have transported much terrestrial plant material seawards; the progressive increase in shelf-sea area is thought to have stimulated production of marine plankton. Bacterial consumption of this organic matter favoured the development of poorly oxygenated mid-to late Cretaceous waters in which many of the characteristic facies of the Period, including glauconitic sandstones and phosphatic chalks, were deposited.
The significance of basement gneiss domes in the tectonic evolution of the Salta Region, Norway
Authors: Cooper M. A. , Bradshaw R.
Published: December 2007

The Sørfold area, within the Salta region, Norway, provides a section through a major depression of Caledonian cover sequences bounded to E and W by Precambrian basement gneisses, which allows study of the basement/cover relationships on both sides of the depression. The cover sequences are disposed in major fold-nappes, most of which are represented in the Sørfold area. Geochemically, the basement gneisses exposed in the Salta domes are akin to the rapakivi granites of Finland. This geochemical affinity and the irregularity of dome distribution suggests that the Precambrian basement is heterogeneous in character due to the intrusion of numerous, light, Precambrian rapakivi granites. The Caledonian D1 emplacement of the large fold-nappes created a gravitationally metastable system of heavier cover rocks over locally lighter basement. The less dense areas of basement that consisted of rapakivi granite rose in response to these gravitational forces when activated by rising temperatures, producing the mantled gneiss domes and their associated deformation effects. Experimental and theoretical models of mantled gneiss dome development are relevant in interpreting these structures. The role of the basement was critical in the evolution of the Salta region, and geochemical and spatial evidence suggests that pre-Caledonian patterns influenced the distribution of the domes, the behaviour of the rest of the basement, and the intensity of Caledonian deformation in the cover fold-nappes.
Deformation studies in the Irish Caledonides
Authors: Sanderson D. J. , Andrews J. R. , Phillips W. E. A. , Hutton D. H. W.
Published: December 2007

An interpretation of the major structure of parts of the Irish Caledonides is made, based on the results of mapping of the main early penetrative fabrics. Interpretation of major changes in fabric are attributed to strain variation, and models are developed to explain these changes. The regional nappe structures in the Dalradian rocks have been modified by (1) D
2
slide zones, and (2) a D
4
sinistral shear zone adjacent to the Main Donegal Granite in NW Donegal. In N Mayo the major structure is interpreted in terms of a steep dextral E-W shear zone modifying the early formed nappe pile. The strain history adjacent to the Iapetus suture in central Ireland is described and a wide zone of non-axial planar cleavage discussed. In SE Ireland the regional strain pattern is modified in the tectonic aureole of the Leinster Granite.
Metamorphic and tectonic history of the Pennsylvania Piedmont
Authors: Crawford M. L. , Crawford W. A.
Published: December 2007

The Piedmont Province of SE Pennsylvania consists of gneisses overlain by, or in fault contact with, metasedimentary phyllites and schists. Correlation of these crystalline rocks with similar units in Maryland and isotopic ages of the metamorphic events suggest ages from pre-Grenville (1000 Ma) to Ordovician; Cambrian and Ordovician fossil-bearing units occupy a narrow band across the central part of the region. A 1000 Ma regional granulite facies episode is documented in the basement gneiss units. A second younger and lower pressure granulite facies metamorphism centres around an intrusive anorthosite-norite complex. A third metamorphism ranging from greenschist to upper amphibolite facies affects the entire terrain; this is probably close to 440 Ma old. Major folds and faults formed during or after the last metamorphic episode; earlier structural features are either obliterated or not exposed. The proposed tectonic model includes a rifting of continental basement forming a basin with a lower Palaeozoic carbonate bank on the NW margin and an island arc to the SE. Compression produced major nappes and possible thrusts during the last regional metamorphism. Vertical movements associated with major block faulting marked the end of the orogenic activity
Dental caries prevalence and trace elements in soil, with special reference to lead
Authors: Anderson R. J. , Davies B. E.
Published: December 2007

Epidemiological investigations in human populations in several parts of the world, including England, together with animal experiments have revealed associations between caries prevalence and trace elements in the environment or diet. These reports led to collaborative studies on caries prevalence in school children in England and Wales in areas where past base metal mining has left a legacy of extensive heavy metal contamination of garden and agricultural soils. In the Tamar Valley of Cornwall and Devon and in Ceredigion (Dyfed, Wales) a raised caries prevalence has been associated with high levels of plant-available Pb in soils, whereas in Somerset Cd pollution was not associated with any change in caries prevalence. If Pb is causal in these relationships then dietary Pb is probably more significant than Pb in air or water.
Regional geochemical mapping and health in the United Kingdom
Authors: Thornton I. , Plant J.
Published: December 2007

Geochemical atlases based on the analysis of sediments from surface tributary drainage have been published for Northern Ireland, and England & Wales; the data are smoothed by computer and show regional patterns for the distribution of 20 and 21 elements respectively. Atlases for parts of Scotland present point-source data for up to 25 elements in stream sediments; additional data have been obtained for pan concentrates and stream waters. Regional surveys to provide point-source information are continuing and it is intended that they will in due course cover the whole of the United Kingdom.

Research has been successfully undertaken into the applications of geochemical maps to problems of plant and animal health and production, and maps are currently used to delineate areas of potential trace element deficiency and heavy metal excess, particularly where problems may be of a sub-clinical nature. Applications to human health are illustrated with examples of metal anomalies in old mining areas in Derbyshire (Pb) and Somerset (Cd, Zn). Geochemical atlases continue to provide valuable sources of multi-element data for area selection in food, water and medical surveys, and comprise useful base-line information for epidemiological studies.
The analysis of flow profiles in a basaltic dyke using strained vesicles
Authors: Coward M. P.
Published: December 2007

Strains shown by vesicles in a basaltic dyke have been factorized into components of simple shear along the dyke and shear-parallel longitudinal strain. The dyke shows high shear strains at the margins, decreasing to the axial zone. Profiles of differential displacement are almost parabolic in form, suggesting Newtonian flow of the magma. The components of longitudinal strain indicate compressional flow in the axial zone of the dyke but extensional flow at the margins. Flow profiles and hence flow rates must have varied along the length of the dyke, possibly due to temperature changes.