Granite Domes Research Articles

Estimation of episodic exfoliation rates of rock sheets on a granite dome in Korea from cosmogenic nuclide analysis

AbstractWe have measured concentrations of cosmogenic 10Be and 26Al produced in situ at bare bedrock surfaces of successive sheets developing on a granite dome in Korea and calculated the exfoliation rate of sheeting joints. The exfoliation rate was obtained using a simple model in which the sheeting joints experience intermittent denudation, i.e. peeling off along the bedrock face. We find that the average exfoliation (erosion) rate of the episodic peeling‐off process is 5·6 cm/ka−1. The analysis is useful for understanding the evolution of granite sheeting structures on this dome in Korea. Copyright © 2006 John Wiley & Sons, Ltd.

Penecontemporary tectonic forms in basement areas: evidence derived from quarry exposures on northwestern Eyre Peninsula, South Australia

Monitoring of quarry exposures on northwestern Eyre Peninsula, South Australia has shown that the granite domes of that region are structurally complex features, commonly with several structural domes within each topographic form. The rock masses are in horizontal compression so that few steeply inclined fractures have been penetrated by water and hence are not weathered, though sheet fractures, which are tectonic features, are arched, dilated, and thus readily infiltrated by water. Neotectonic forms, such as fault scarps, A-tents, or pop-ups, and disturbed blocks are still developing. These observations provide further evidence of neotectonism, even in cratonic lands.

Park Offers Forests, Lakes, And Some History, Too

Back to table of contents Previous article Next article Information on Host City and Meeting HighlightsFull AccessPark Offers Forests, Lakes, And Some History, TooJoan Arehart-TreichelJoan Arehart-TreichelSearch for more papers by this authorPublished Online:18 Feb 2005https://doi.org/10.1176/pn.40.4.00400040Georgia can be a wonderful place to visit in the spring, and you can experience some of its magic if you can find a few free hours to visit Stone Mountain Park. The park is the state's most visited attraction, drawing nearly 4 million visitors a year.In May, this 3,300-acre park near Atlanta boasts not only stunning emerald forests and a cobalt-blue lake, but enticing parkland flowers and floral scents. Jack-in-the-pulpits, magnolias, mountain laurels, and Oconee azaleas will be in bloom. If you walk around the park, you can wet your feet in a gurgling brook, stroll across a covered bridge, or pause to listen to a goldfinch or indigo bunting serenading its mate. And in May, the park's temperature is caressingly warm, but not yet hot.Pre-Civil War homes and buildings transplanted into the park provide a sense of what at least one slice of life in the Old South might have been like.The park likewise offers numerous family attractions such as the“ Tall Tales of the South” show, which activates your senses via a three-dimensional film with fourth-dimension special effects like a sprinkle of rain or whiffs of hot chocolate; a ride in an authentic paddlewheel riverboat on Stone Mountain Lake; or a ride in open-air cars pulled by a 1940s locomotive.In a replica of an 1870s town, you can watch glassblowing, candymaking, and blacksmithing. Storytellers spin their tales from porches as you walk by. If you stroll by a barrel, someone hiding inside may try to spit tobacco juice at you. If you visit one restaurant in the town, rolls may be tossed to you to catch. And if you put some change in a certain machine, it will massage your feet.The park attraction that youngsters often like best is the new Treehouse Challenge, Christine Parker, public relations manager for the park, told Psychiatric News. The attraction consists of a large tree house for boys and another for girls. The younsters use their wits and hands to master games and rack up points. One of the challenges consists of finding secret passages into the opponents' tree house.The centerpiece of the park, however, is Stone Mountain—purportedly the largest mass of exposed granite in the world. You can ride a cable car up to the top of the mountain and see a splendid view of Atlanta and the surrounding terrain, including the Appalachian Mountains. If you think that the top of the mountain looks something like the surface of the moon, you're not alone. Parts of the Hollywood movie “Apollo 13” were shot here.Stone Mountain originated some 300 million years ago. Intense heat and pressure forced molten material upward; gradual cooling resulted in compact, uniform granite crystals. Today Stone Mountain consists of an 825-foot-high granite dome, covering 583 acres. Granite quarried from the mountain has been used to construct the U.S. Capitol, Panama Canal, and other structures throughout the world.At night the north side of Stone Mountain becomes a natural screen for the park's popular Lasershow Spectacular. During APA's annual meeting, shows will be held on May 20 and 21 at 9:30 p.m.The best way to get to Stone Mountain Park from downtown Atlanta is to rent a car.Stone Mountain Park is at 5525 Bermuda Road, Stone Mountain, Ga. Additional information is available by phone at (800) 317-2006 or online at<www.stonemountainpark.com>.▪ ISSUES NewArchived

Major and trace elements in river-borne materials from the Cuyuni basin (southern Venezuela): evidence for organo-colloidal control on the dissolved load and element redistribution between the suspended and dissolved load

The Cuyuni basin is a metallogenic-rich area located in southern Venezuela in the Precambrian Guyana shield. It comprises two geologically distinct zones, one with granite domes and intercalated greenstone belts in the northern and western part of the basin and the other with stratified arenaceous deposits in the south. The suspended, dissolved and total load of the rivers draining these contrasting zones show similar characteristics to those observed in other major tropical rivers such as the Congo and Amazon, and vary in composition between the different source areas. Although the river-borne material in this basin varies in composition from one river to another and contains highly variable proportions of dissolved constituents, the ratio between the suspended and the dissolved load ( M susp/ M diss) appears related to the ratio of suspended to dissolved organic carbon contents (SS/DOC), according to the relationship: M susp / M diss = K i * SS / DOC The coefficient of proportionality K i in this equation varies from one element to another. This relationship leads us to recognize (a) the important role of organo-colloidal phases in controlling the elements in solution (b) the occurrence of a re-distribution of elements between the suspended and dissolved load in the river environment. According to this analysis, coefficients K i appear to represent partition coefficients between two phases, the suspended load and the organic-rich colloidal fraction of the dissolved load. These coefficients, estimated from analysis of the total/dissolved load versus SS/DOC diagrams, yield values which classify in an order similar to that classically proposed for the relative capacity of the elements to form organic ligands or their adsorption capacity. The coefficients actually vary as a function of the hydrolysis constants of the respective elements. Theoretical considerations show that equilibrium processes between the surfaces of suspended material and those of colloidal-type species in solution are able to explain the observed relationship. We show that such surface equilibria can be extended to the whole products in conditions which may prevail in tropical river waters, that is suspended matter primarily consisting of phases for which surface complexation is important, as is the case of clays or iron-manganese oxides produced by the present-day weathering of tropical soils. Finally, we analyse the specific behaviour of the REE in rivers of the Cuyuni basin.

Exposure ages deduced from cosmogenic 10Be and 26Al produced in situ: application to granite domes and tors in Korea

The cosmogenic radionuclides 10Be and 26Al produced in situ were analyzed to determine the exposure age and to estimate the landform evolution of a granite dome and tor in Korea. Since the tor of Mt Sapae has no joints, and the 26Al/10Be ratio has a singular point near the steady state island, the sample is supposed to have undergone steady-state erosion over a long period. In the dome on Mt Bukhan, many sheeting joints having thickness 20–70 cm develop on the slope surface, to make step-like sheet structures by exfoliation. Since the 26Al/10Be ratio of samples from Mt Bukhan is plotted into the lower area apart from the steady erosion curve, we work with a two-stage exposure model. Results show that (1) the minimum surface exposure ages of the two landforms based on the 10Be model are about 8 and 71 kyr respectively, (2) the sample from Mt Sapae was taken to have undergone steady-state erosion at rate of 7.0×10−4 cm/yr, and (3) a two-stage exposure model on Mt Bukhan suggests that the samples were irradiated by cosmic radiation in the past several thousand years, after having being shielded at the depth of 300–400 cm.

Earth Surface Processes and Landforms, Volume 28, Issue 10 ‘Testing etching hypothesis for the shaping of granite dome structures beneath lateritic weathering landsurfaces using ERT method’ by Anicet Beauvais, Michel Ritz, Jean‐Claude Parisot and Christian Bantsimba, pages 1071–1080, 2003.

AbstractThe original article to which this Erratum refers was published in Earth Surface Processes and Landforms 28(10) 2003, 1071–1080.

Contribution of mantle plumes, crustal thickening and greenstone blanketing to the 2.75–2.65Ga global crisis

Abstract Assuming that the period 2.75–2.65 Ga corresponds to a single, but global, geodynamic event, we investigate—through numerical experiments—the mechanisms that could have led to the profound continental reworking that occurred at that time. Although the extent of the crisis at the Earth’s surface pledges in favour of the involvement of mantle plumes, our numerical experiments suggest that the thermal impact of mantle plumes is unlikely to explain both the amplitude and timing of the thermal anomaly, as observed in the Superior Province (Canada) and the Yilgarn Craton (Australia). Similarly, moderate crustal thickening can not lead to significant reworking of the continental crust within the observed time constraint. Crustal thickening with a factor ≥1.5 is also unlikely because it is not consistent with the moderate metamorphic grade observed at the surface of many Archaean cratons. Burial of a radiogenic crust under a 10 km thick greenstone cover also falls short of explaining, not so much the amplitude and the extent, but the timing of the thermal anomaly. In contrast, the combination of the thermal anomaly related to the greenstone blanketing effect with the heat transfer from a plume head spreading at the top of the thermal boundary layer can adequately explain the amplitude, the timing, and the extent of the 2.75–2.65 Ga crisis. Our favoured model involves a global rearrangement of convection cells in the deep mantle and formation of multiple mantle plumes. The greenstones emplaced at the surface and the plumes that spread in the thermal boundary layer contributed to heat the crust from both above and below. This produced massive crustal partial melting that reached its climax ca. 40 Myr after the emplacement of the plumes and associated greenstone cover rocks. This led to gravitational instabilities in the crust, as dense greenstone cover rocks began to sink into the thermally softened crust and granite domes rose in response. The extraction of heat-producing elements toward the upper part of the crust has contributed to the cooling and stabilisation of the cratons. This succession of events, which is not incompatible with plate-tectonic processes, may have profoundly changed the nature of the crust exposed at the surface and could explain the contrasting geochemical signatures of Archaean and post-Archaean shales.

Testing etching hypothesis for the shaping of granite dome structures beneath lateritic weathering landsurfaces using ERT method

Abstract An Erratum has been published for this article in Earth Surface Processes and Landforms 28(13) 2003, 1491. Granite domes, boulders and knobs buried within saprolite have been detected beneath lateritic weathering landsurfaces using 2D electrical resistivity tomography (ERT). This technique provides a valuable means of mapping the bedrock topography and the regolith structures underneath landsurfaces, as it is intrinsically very sensitive to the electrical properties of superimposed pedological, hydrological and geological layers, allowing the determination of their relative geometry and spatial relationships. For instance, 2D inverse electrical resistivity models including topographic data permit the definition of lithostratigraphic cross‐sections. It shows that resistive layers, such as the more or less hardened ferruginous horizons and/or the bedrock, are generally well differentiated from poorly resistive layers, such as saprolite, including water‐saturated lenses, as has been corroborated by past and actual borehole observations. The analysis of the 2D geometrical relations between the weathering front, i.e. the bedrock topography, and the erosion surface, i.e. the landsurface topography, documents the weathering and erosion processes governing the development of the landforms and the underlying structures, thus allowing the etching hypothesis to be tested. The infiltration waters are diverted by bedrock protrusions, which behave as structural thresholds compartmentalizing the saprolite domain, and also the regolith water table, into distinct perched saturated subdomains. The diverted waters are thus accumulated in bedrock troughs, which behave like underground channels where the saprolite production rate may be enhanced, provided that the water drainage is efficient. If the landsurface topography controls the runoff dynamics, the actual bedrock topography as depicted by ERT imaging influences the hydrodynamics beneath the landsurface. In some way, this may control the actual weathering rate and the shaping of bedrock protrusions as granite domes and knobs within thick saprolite, before their eventual future exposure. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Plant communities of a Central Namib inselberg landscape

Abstract. Three granite inselbergs and six dolerite dykes and their surroundings were investigated in the Central Namib, at the interface between the Namib Desert and Nama Karoo biomes. The main objectives of this study included a phytoso‐ciological interpretation of the described plant communities, explanation of the correlation of the communities with environmental variables and quantification of the relative contribution of different types of variables to structuring plant communities. Nine grassland and shrubland plant communities were recognized, largely organized according to general habitat, elevation, size of inselberg and geology. Soil properties, often thought to play an important role in arid environments, showed no clear patterns in the level of analyses used in this study. Other environmental parameters of importance in arid mountain habitats, such as slope aspect and angle, also played a minor role. The main implications of the study are: 1. Central Namib inselbergs, particularly granite domes, harbour diverse plant communities, often with species from neighbouring higher rainfall areas, and are thus of high conservation value. 2. The poor contribution of environmental variables in this study, which are conventionally used in field studies of plant community – environment relationships, may demand a critical review of additional parameters to be included when analysing plant community – environment relations in arid environments. In particular between‐season variation, phytogeographic aspects and the heterogeneity of microhabitats, often contained within a plant community, need to be taken into account.

Plant communities of a Central Namib inselberg landscape

Three granite inselbergs and six dolerite dykes and their surroundings were investigated in the Central Namib, at the interface between the Namib Desert and Nama Karoo biomes. The main objectives of this study included a phytoso- ciological interpretation of the described plant communities, explanation of the correlation of the communities with envi- ronmental variables and quantification of the relative contri- bution of different types of variables to structuring plant communities. Nine grassland and shrubland plant communi- ties were recognized, largely organized according to general habitat, elevation, size of inselberg and geology. Soil proper- ties, often thought to play an important role in arid environ- ments, showed no clear patterns in the level of analyses used in this study. Other environmental parameters of importance in arid mountain habitats, such as slope aspect and angle, also played a minor role. The main implications of the study are: 1. Central Namib inselbergs, particularly granite domes, harbour diverse plant communities, often with species from neigh- bouring higher rainfall areas, and are thus of high conservation value. 2. The poor contribution of environmental variables in this study, which are conventionally used in field studies of plant community - environment relationships, may demand a critical review of additional parameters to be included when analysing plant community - environment relations in arid environments. In particular between-season variation, phyto- geographic aspects and the heterogeneity of microhabitats, often contained within a plant community, need to be taken into account.

Upper crust of the Pilbara Craton, Australia; 3D geometry of a granite/greenstone terrain

The Pilbara Craton in Northwest Australia is a 600×550 km region of early-mid Archaean granite/greenstone terrain, dominated by granite domes, and in part covered by younger rocks. Gravity and magnetic anomalies are used to map the granite/greenstone surface under cover, and infer the depth extent of the granite/greenstone structures. A published seismic refraction interpretation gives a two layer crust for the Pilbara Craton, with the layers separated by a velocity gradient at about 14 km. Some magnetic anomalies have a 1000–3600 nT amplitude, a width at one-half amplitude of 9 km, and a strike length of >100 km. Their causative bodies have a top at 1–2 km, an average apparent susceptibility of 0.1–0.2 (SI), and importantly a base about 14 km. The magnetic material is thought to be a small proportion of banded iron formation within the greenstone belts. Gravity anomalies are interpreted to indicate that granite margins are generally steep, and many granites have a base at a similar level to one another. The shape of the gravity anomalies over the granite/greenstone boundaries, and the amplitude of the anomalies (up to 650 μm s −2) together with the inferred granite/greenstone density contrast, are consistent with both the granites and greenstones extending to a depth of 14 km. The domes are therefore vertical cylinders extending to mid-crustal depths. The great depth of the greenstone belts is consistent with the domal structure being due to convective crustal overturn. The Pilbara Craton may be unusual, because greenstone belts elsewhere in the world have smaller amplitude gravity anomalies (commonly 200–400 μm s −2), a shallower inferred base to the greenstone belt (generally <8 km), and the base of the greenstone belt is thought to be truncated.

Rock bursts and associated neotectonic forms at Minnipa Hill, northwestern Eyre Peninsula, South Australia

Abstract Disturbance of the surface of Minnipa Hill Southeast, a low granite dome located on the northwestern Eyre Peninsula, on 19 January 1999, coincided with a shallow earth tremor, and it is suggested that the two events are causally related. The disturbance, which affected an area 170X100 m, took the form of rock bursts, reverse fault scarps, low angle planes of dislocation and overriding sheets, A-tents, dislocated slabs and blocks and widespread surficial flaking. Evidence of two earlier disturbances was noted. The event directly confirms the association of A-tents and dislocated slabs with compressive stress and by implication links bornhardts and sheet fractures with similar strain environments.

Les syénites du castillet (massif de l'agly, pyrénées orientales, France): une roche exceptionnelle dans les pyrénées

Le Castillet syenites (Agly massif) are unusual rocks in the eastern Pyrenees made up of more than 95 % of potash feldspar and albite. These rocks are hosted in the Variscan Saint-Arnac granite and form small domes, the shape of which suggests an emplacement by magmatic stopping. Syenites and their closest host rocks suffered various hydrothermal alterations, the most obvious being transformation of biotite into muscovite + rutile. Discussion of the origin of these syenites is difficult because of those alterations: many magmatic features are well preserved but metasomatic transformation may have very much modified the primary rocks.

Fluid inclusions in the Harney Peak Granite, Black Hills, South Dakota, USA: Implications for solubility and evolution of magmatic volatiles and crystallization of leucogranite magmas

Experimental and theoretical studies have shown that magmatic fluids have strong influence on phase equilibria of granitic systems. A microthermometric study of fluid inclusions in the Proterozoic Harney Peak Granite, Black Hills, South Dakota, USA, was undertaken to obtain direct evidence for the composition and evolution of magmatic fluids in a leucogranitic system and to evaluate their effect on liquid-lines-of-descent of leucogranite magmas. A previous stable isotopic study has demonstrated that the granite has not interacted with nonmagmatic fluids since its crystallization. Therefore, fluids found in the inclusions are of magmatic origin and present an opportunity to directly sample magmatic fluids trapped during crystallization of a granitic magma and during subsolidus conditions. The Harney Peak Granite was emplaced as multiple sills, dikes, and small intrusions, many of which differentiated into coupled aplite-pegmatite layers. Three types of fluid inclusions are found in the granite. Type 1 consist of variable saline H 2OC0 2 mixtures with minor CH 4 or other gases. Inclusions of this type are found in tourmaline and quartz in aplite layers, are generally isolated, and have negative crystal shapes. They are interpreted to be primary. There is a general increase in salinity and decrease in isochore temperature with decreasing CO 2/H 2O ratio of the inclusions. The trend is ascribed to progressive change in fluid composition with crystallization due to the differential solubility of CO 2 and H 2O in the high-silica magma. Isochores, coupled with independently determined crystallization temperatures, suggest entrapment pressure ∼3.5 kbar, consistent with geobarometry in the wallrocks. Type 2 inclusions are carbonic fluids dominated by CO 2, whereas type 3 inclusions are saline aqueous fluids without a detected carbonic component. Both types are mostly found along healed fractures in quartz. They are interpreted to be secondary inclusions that formed as a result of unmixing of type 1 inclusions at subsolidus conditions during uplift and cooling of the Harney Peak Granite dome. Freezing-point depressions, birefringent daughter crystals, phase-equilibria considerations, and α-track mapping of B and Li distribution in thin sections, all indicate that both type 1 and type 3 inclusions contain solutes such as K, Li, and B in addition to NaCl. Using published solubility models for H 2O and CO 2 in granitic melts and the composition of the most CO 2-rich type 1 inclusions ( X CO 2 = 0.55), the initial H 2O and CO 2 concentrations in the Harney Peak Granite magma are deduced to have been ∼3.5 wt% and 1500 ppm, respectively. The relatively low water concentration is consistent with temperatures of dehydration-melting reactions that produced the magma. It is suggested that the aplite-pegmatite segregations found in parts of the Harney Peak Granite are the result of initial rapid near liquidus crystallization of minerals with high Na/K ratios, including plagioclase and tourmaline, along a wide range of increasing αH 2O. Aplite crystallization was followed by crystallization of relatively potassic residual liquid enriched in fluxing elements under conditions of high αH 2O.

Popups on Moon Rock, Augrabies Falls National Park

Naturally occuring popups (or A-tents) occur mainly on outcrops of horizontally compressed, sheeted granite. They consist of two slabs of surface rock pushed up to form a tent-like structure, or a surface sheet pushed up into an arc. Although popups have been studied in several countries, none have so far been described in South Africa. A survey of Moon Rock, a granite dome in the Augrabies Falls National Park, led to the discovery of 14 of these structures, including both angular and arched forms. The dimensions and orientations of the high, angular forms support the hypothesis that they constitute a stress release phenomenon, but the characteristics of the low, thin plated forms suggest that these are erosional features. The structures are eventually destroyed by the movements, as yet largely unexplained, of surrounding rock slabs, and by the gradual abrasion of the edges of the popped up slabs as a result of slight movements caused by daily heating and cooling of the surface sheet.

Tourmalinites and Sn-Li mineralization in the Valdeflores area (C�ceres, Spain)

Tourmalinites containing quartz, Li- and Cs-micas, and small amounts of arsenopyrite occur near Caceres, Spain. The tourmalinites are developed within Ordovician pelites near the eastern margin of the Cabeza de Araya batholith and close to several small bodies of tectonized granite. Field and textural relationships document an epigenetic character for the tourmalinites. The tourmaline is fine to very fine-grained and its composition is intermediate within the schorl-dravite solid-solution series. Hydrothermal veins containing quartz, muscovite, amblygonite-montebrasite, apatite, fluorite, and/or cassiterite appear spatially related to the tourmalinites. The mineralized area is located in a shear zone that was active during D3 Hercynian deformation and the emplacement of granitic bodies. Tourmalinites and veins derived from B- and Li-rich magmatic-hydrothermal fluids are believed to have been associated with the intrusion of a hidden granite dome, the tourmalinites being produced by extensive metasomatism of Ordovician metasedimentary rocks.

10Be and 26Al Evidence for Exceptionally Low Rates of Australian Bedrock Erosion and the Likely Existence of Pre-Pleistocene Landscapes

Analysis of in situ-produced 10Be and 26Al demonstrate that some Australian inselbergs (granitic domes) are among the most stable geomorphic surfaces in the world, eroding at rates as low as 0.6 m/myr. Twenty isotopic analyses of ten samples suggest that the bare bedrock tops of these isolated granitic domes have been exposed to cosmic radiation for at least 0.5 myr and are eroding at a mean model rate less than 0.7 ± 0.1 m/myr (n = 6). Isotopic analyses of samples collected from the top of Mt. Wudinna, Little Wudinna, and Yarwondutta Rock are most consistent with continuous exposure during erosion. On the other hand, samples collected from the flanks of some domes and the tops of other domes have isotopic abundances suggestive of complex exposure histories including burial and reexposure. These unique isotopic data provide the first quantitative information for evaluating longstanding, but previously untested, hypotheses regarding the antiquity and development of these enigmatic landforms and indicate that some Eyre Peninsula inselbergs are probably relict features of pre-Pleistocene landscapes.

SATELLITE IMAGE ANALYSIS OF CIRCULAR ANOMALIES AND FRACTURING NETWORKS IN THE ARMORICAN MASSIF, FRANCE

This paper describes results from a detailed study of circular anomalies—related to outcrops of granitic domes over the western part of the Armorican Massif—using SPOT, Landsat TM, Seasat, and composite imagery in conjunction with aerial photographs. Two types of features have been distinguished: (1) simple and circular, related to small granitic bodies or to hidden domes, which correspond with concentric networks of fractures formed during the cooling of the granite, and (2) complex and composite of the onion skin type, related to the larger plutonic domes. This type of feature could also be related to the concentric cooling networks but would more probably correspond to the magmatic foliation planes. Semi-circular features of the “half-moon” type, derived from these described structures, are located on the periphery of plutonic domes. These could correspond to preliminary intrusions cross cut by the major structures. From the lineament maps and based on the relationship between regional foliation fracturing networks and circular features, the following networks can be distinguished: (1) radial networks centered on plutonic diapirs, which seem to be contemporary with the granitic intrusions; (2) transverse networks that pass around or across circular features, creating fan-shaped forms and which are late with respect to the granitic intrusions; (3) post-tectonic fracturing networks that cross all previously described structures; and (4) a network, parallel to the regional foliation N070, which crosses or twists the circular features. This system documents the syntectonic pattern of the granites. Translated by Judit Ozoray, Chicoutimi, Quebec from: “Structures circulaires et réseaux de fractures en pays granitique. Analyse de données SPOT, Landsat TM et Seasat sur le Massif armoricain,” Bull. Soc. géol. France, 1993, Vol. 164, No. 2, pp. 199-214, with permission of the Société Gèologique de France (please cite original paper).

Basin structure and Tertiary magmatism on Skye, NW Scotland

The emplacement of igneous material into upper crustal rocks of sedimentary basins is likely to be strongly controlled by the geometry of the pre-existing basin structures. These controls are investigated using examples from the Tertiary igneous complexes of Skye, part of the Sea of Hebrides basin of NW Scotland. The basin consists of an array of half-graben related to SE-dipping normal faults. These pre-volcanic, Mesozoic structures are traced near the igneous complexes using geological relationships preserved unconformably beneath the widespread basaltic lava fields. The unconformity represents a period of Cretaceous uplift and denudation of the basin and its flanks, entirely pre-dating the Tertiary volcanism of NW Scotland. This unconformity seals stratigraphically the major basin faults, preserving field relationships that permit the tracing of these faults in the country rocks to the Tertiary intrusions. The major Camasunary fault is separated from the Raasay fault via a series of minor graben, linked by a series of steep, NW–SE-trending faults that transfered Mesozoic displacements between the principal fault strands. A broad range of igneous material of various compositions was intruded into part of the Mesozoic Sea of Hebrides basins and their flanks during Palaeocene times. Different emplacement styles and different structural controls are found. The major gabbroic centres do not appear to be controlled by upper crustal structures, having been emplaced into the footwalls of major faults. However, minor synmagmatic displacements on the basin faults may have been sufficient to generate dilatational sites in these footwall positions, thereby facilitating emplacement. In contrast, the granitic melts have been emplaced as sheets and domed into the sediments and overlying lava pile, reactivating segments of the basin fault network. Doming occurred from an array of sills, the stratigraphic levels of which can be reconstructed using structural relationships preserved in the roofs and walls of the intrusions. The sill levels and their transgressive forms are strongly related to inferred Mesozoic basin structures. The major fold structures of Tertiary age in southern Skye are interpreted as accommodating granitic emplacement rather than crustal shortening. The NW-SE Mesozoic transfer fault trend appears to have strongly influenced the segmentation of the granite domes. These interpretations are illustrated using field relationships mapped in the vicinity of the Coire Uaigneich granophyre. It is concluded that although the higher parts of the basin faults were reactivated to facilitate the doming of granitic intrusions, the deeper levels of the Mesozoic faults show no evidence of substantial reactivation.

Distribution of the native earthworm fauna of Australia - a continent-wide perspective

Based on nearly 2000 available records, the broadscale geographical distribution of the native earthworm fauna of Australia was mapped. Native earthworms were recorded from south-eastern, eastern and northern Australia within 400 km of the coast. Isolated faunas were present in Tasmania and south-west Western Australia, and apparently isolated faunas occurred in the Adelaide area/Fleurieu Peninsula of South Australia and the ranges of central Australia. All but 30 locality records occurred where annual rainfall averaged or exceeded 400 mm; 16 of these records were instances of moisture-gaining sites (moist caves, waterholes, banks of large rivers, edge of granite domes). A collecting strategy to both fill in gaps in the distribution map and discover additional anomalous occurrences (with respect to the 400 mm isohyet) is outlined.