Heat source for Tongonan Geothermal Field

Abstract The primary mineral and whole-rock chemistry of 46 core samples from the host rocks of the Tongonan Geothermal Field (the Philippines) have been used to infer the likely composition of the heat source for the system. The host rocks consist of andesite lavas (with intercalated fossiliferous early to mid–Miocene shales and limestone), and a plutonic rock basement ranging in composition from gabbro to granite. The whole rock TiO₂, Fe₂O₃ (total iron), MgO, P₂O₅ and V data for volcanic and plutonic rocks are colinear on conventional Harker diagrams. This, along with similar hornblende chemistry, age and close spatial relationship suggests that the basement and cover rocks are cogenetic and evolved by low-pressure crystal fractionation. Crystal fractionation models indicate that separation of 60% plagioclase and 30% hornblende from original magma controlled the chemistry of the host rocks. The original Miocene magma chambers beneath the Tongonan field crystallized inwards from the walls at approximately 750°C and 1 kb pressure (3–4 km depth) thus forming a series of plutons or a batholith at drilled depths. A supercritical hydrothermal fluid trapped in the crystallizing, hornblende-granite-pegmatite core of a crystallized Miocene diorite batholith was gradually being released to shallower levels through antithetic cross fractures during creep and uplift along the main branches of the Philippine Fault from the Pliocene. This ascending fluid is now thought to be responsible for the present thermal activity of the field.     

The effects of spiral arms on the multi-phase ISM

Statistical parameters of the ISM driven by thermal energy injectionsfrom supernova explosions have been obtained from 3D, nonlinear,magnetohydrodynamic, shearing-box simulations for spiral arm andinterarm regions. The density scale height obtained for the interarm regionsis 50% larger than within the spiral arms because of thehigher gas temperature. The filling factorof the hot gas is also significantly larger between the armsand depends sensitively on magnetic field strength.     

Multiproxy Devensian Late‐glacial and Holocene environmental records at an Atlantic coastal site in Shetland

Marine erosion at Clettnadal, West Burra island off the west coast of Shetland, caused the drainage of a small water body at Clettnadal, exposing deposits of Late Devensian and Holocene age. Pollen, diatom and invertebrate analyses have provided variable records of environmental change during stratigraphical event GI‐1. Event GS‐1 is revealed by the non‐pollen evidence, especially by Coleoptera, by sediment stratigraphy, and by radiocarbon dating. In contrast, the pollen evidence indicates that an arctic tundra flora, in which dwarf shrubs were prominent, persisted throughout the Late‐glacial. The Holocene brought colonisation by tree birch, but by ca. 9000 ¹⁴C yr BP the taxon had almost disappeared. This contrasts strongly with other Holocene pollen records for Shetland where both Betula and Corylus avellana‐type survived longer—at some sites, for example, until ca. 2900 yr BP. The extreme westerly and exposed coastal situation of Clettnadal appears to be responsible both for a muted Late‐glacial response in the pollen record of terrestrial vegetation and for the early replacement of woodland by a maritime grassland. The results provoke questions concerning biological stability at times of marked climatic change. Copyright © 2003 John Wiley & Sons, Ltd.     

Temperature effects on the embryo development and hatching of the spiny lobster Sagmariasus verreauxi

Factors affecting the development of the embryos and production of larvae of the spiny lobster Sagmariasus verreauxi were investigated. Mature lobsters were collected from the fishery in New Zealand and held in captivity until they moulted, mated, and extruded eggs. For females, moulting took place in winter (July/August) and mating occurred 58–88 days later in early spring. The ovigerous females were then held at three temperatures and embryo development monitored at approximately weekly intervals. Mean times to hatch were 55, 75, and 130 days at 20°C, 17°C, and 13°C respectively. The total number of larvae that hatched from each female ranged from 0.97 to 1.4 million. The theoretical temperature at which embryo development ceases (a biological zero) for S. verreauxi, of 9.4°C, was calculated from data on the appearance of the median eye, the eyes and the chromatophores, and the time to hatch. An eye index formula was also derived to allow prediction of time to hatch at a range of temperatures using the cumulative difference between the rearing temperature and the biological zero. First instar phyllosomas from embryos reared at 20°C were significantly smaller than those from 17°C and 13°C but there was no significant difference in fitness. This study shows that hatching can be spread over a number of months, without significantly affecting larval quality, simply by manipulating holding temperature.     

Comparison of the ectosymbionts and parasites of an introduced crab,Charybdis japonica,with sympatric and allopatric populations of a native New Zealand crab,Ovalipes catharus (Brachyura: Portunidae)

The success of biological invaders is often attributed to escape from specialist enemies in their natural range, such as predators and parasites. For enemy escape to have direct consequences in competitive interactions, invaders need to be less vulnerable to enemies than native competitors in the region they invade, but first the presence of these enemies must be established. We investigated the macroparasite and ectosymbiont fauna of the recently introduced portunid crab Charybdis japonica, and compared it with sympatric and allopatric populations of the native New Zealand portunid, Ovalipes catharus. A total of 468 crabs (350 O. catharus and 118 C. japonica) were collected from six harbours throughout New Zealand (Whangarei, Waitemata, Nelson, Lyttelton, Dunedin, and Bluff) and the identity, incidence and prevalence of ectosymbionts and parasites were compared among the different populations. Charybdis japonica and O. catharus harboured different ectosymbionts. Serpulid polychaete tubes occurred on the exoskeleton of 85.4% of C. japonica examined, but were absent from O. catharus. The bryozoan, Triticella capsularis occurred on 97.4% of O. catharus but was not found on C. japonica. Few endoparasites were present in either species. An unidentified juvenile ascaridoid nematode occurred in the hindgut of 5.9% of C. japonica, but was not found in sympatric populations of O. catharus. A second, unidentified species of ascaridoid nematode occurred in 7.1% of O. catharus from Nelson, but was not present in specimens from the five other harbours sampled. Melanised lesions were observed in the muscle tissue of almost half (46.6%) of the C. japonica examined. Histological examination showed these to be of two types: (1) spherical bodies resembling melanised trematode metacercariae; and (2) lesions consistent with wound repair. Lesions were not observed in O. catharus. Although the identity of parasites and epibionts carried by each species differed, both C. japonica and O. catharus had relatively low parasite species richness. We could not test whether the introduced portunid, C. japonica, is any less vulnerable to parasite enemies than the New Zealand portunid, O. catharus.     

Middle to late Holocene chironomid-inferred July temperatures for the central Northwest Territories,Canada

We analyzed subfossil chironomids, sediment organic matter and sediment particle size data from a 1.11-m-long freeze core collected from Carleton Lake (unofficial name), located approximately 120 km north of the modern treeline. This well-dated core spans the last ca. 6,500 years. Two chironomid transfer functions were applied to infer mean July air temperatures. Our results indicated that the chironomid-inferred temperatures from this lake sediment record did not pass a significance test, suggesting that other factors in addition to temperature may have been important in structuring the chironomid community through time. Although not statistically significant, the chironomid-inferred temperatures from this site do follow a familiar pattern, with highest inferred temperatures occurring during the Holocene Thermal Maximum (~6–4 cal kyr BP), followed by a long-term cooling trend, which is reversed during the last 600 years. The largest change in the chironomid assemblage, which occurred between ca. 4,600 and 3,900 cal yr BP is possibly related to the well-documented northward advance and subsequent retreat of treeline in this region.     

Preserved landscapes underneath the Antarctic Ice Sheet reveal the geomorphological history of Jutulstraumen Basin

The landscape of Antarctica, hidden beneath kilometre-thick ice in most places, has been shaped by the interactions between tectonic and erosional processes. The flow dynamics of the thick ice cover deepened pre-formed topographic depressions by glacial erosion, but also preserved the subglacial landscapes in regions with moderate to slow ice flow. Mapping the spatial variability of these structures provides the basis for reconstruction of the evolution of subglacial morphology. This study focuses on the Jutulstraumen Glacier drainage system in Dronning Maud Land, East Antarctica. The Jutulstraumen Glacier reaches the ocean via the Jutulstraumen Graben, which is the only significant passage for draining the East Antarctic Ice Sheet through the western part of the Dronning Maud Land mountain chain. We acquired new bed topography data during an airborne radar campaign in the region upstream of the Jutulstraumen Graben to characterise the source area of the glacier. The new data show a deep relief to be generally under-represented in available bed topography compilations. Our analysis of the bed topography, valley characteristics and bed roughness leads to the conclusion that much more of the alpine landscape that would have formed prior to the Antarctic Ice Sheet is preserved than previously anticipated. We identify an active and deeply eroded U-shaped valley network next to largely preserved passive fluvial and glacial modified landscapes. Based on the landscape classification, we reconstruct the temporal sequence by which ice flow modified the topography since the beginning of the glaciation of Antarctica.     

Measuring the Performance of Mineral-Potential Maps

D. P. Harris and others have proposed a new method for comparative analysis of favorability mappings. In their approach, Weights-of-Evidence (WofE) consistently shows poorer results than other more flexible methods. Information loss because of discretization would be a second drawback of WofE. In this paper, we discuss that the random cell selection method proposed by Harris and others necessarily results in higher success ratios for more flexible methods but this does not necessarily indicate that these methods provide better mineral-potential maps. For example, a good point density contouring method that does not use any geoscience background information also would score high in the random cell selection approach. Additionally, we show that discretization usually is advantageous because it prevents occurrences of overly high posterior probabilities. For more detailed comparison, we have conducted a number of experiments on 90 gold deposits in the Gowganda Area of the Canadian Shield comparing WofE with the more flexible weighted logistic regression method. Mineral occurrences should be modeled as discoveries at points instead of randomly sampling them together with their surrounding environments in small cells.     

Analysing Product-Specific Behaviour to Support Process Dependent Updates in a Dynamic Spatial Updating Model

A scale‐independent database that allows derived maps to be dynamically updated from a centrally maintained data source is an appealing alternative to traditional map revision techniques, which by today's standards are costly and inefficient. This paper presents a dynamic spatial updating model that supports automated updating of non‐standard maps in a scale‐independent database‐centric map production environment. Maps derived from the database are not separate data sets, but rather active views of the database. Each derived map is displayed in a unique way by implementing cartographic operations at the map level. While the operations applied require user involvement for strategic cartographic decisions, and algorithmic initiation and control, the technique allows geographic data to be processed cartographically without affecting the geometric integrity of the database. Each time a derived map is opened it retrieves the spatial data (and updates) from the database and applies the unique cartographic representation methods that persist on the individual derived maps. Database updates are automatically triggered to cartographic products, as process dependent updates, according to their individual product‐specific behaviour. This paper investigates product‐specific behaviour (product multiplicities) and the cartographic processing requirements to support dynamic spatial updating techniques in an object‐oriented map publishing environment. These techniques are implemented in an off‐the‐shelf software environment using ArcGIS.     

Kinematics of the Danakil microplate

A refinement and extrapolation of recent motion estimates for the Danakil microplate, based on ancient kinematic indicators in the Afar region, describes the evolution of a microplate in the continental realm. The Danakil horst is an elevated part of this microplate, exposing a Precambrian basement within the Afar depression, the site of the Nubia-Somalia-Arabia triple junction. We compare evidence for strike- or oblique-slip faults in data from the Afar depression and southern Red Sea to small circles about published poles of rotation for the Danakil microplate with respect to Nubia. A reconstruction about the preferred pole reunites lengths of a Precambrian shear zone on the Nubia and Danakil sides and preserves a uniform basement fabric strike through Nubia, Danakil and Yemen. Since at least magnetic chron C5 (∼11 Ma) Danakil rotated about a different pole with respect to Nubia than either Somalia or Arabia, but between chrons C5 and C2A Nubia-Danakil motion was a close approximation to Nubia-Somalia motion. Since C2A relative motions of the Danakil microplate have been independent of movements on any of the neighbouring plate boundaries. We relate this to the onset of oceanic-type accretion within Afar. The resulting eastwards acceleration of Danakil was accommodated by westwards propagation of the Gulf of Aden rift that became the new, discrete, plate boundary between the Danakil microplate and the Somalia plate. Present-day activity suggests that the Red Sea and Aden rifts will link through Afar, thereby isolating the Danakil horst as a microcontinent on the Arabian margin.