ALBERT

Description: Major- and trace-element as well as Pb-isotope data are presented for greenschist- to amphibolite-facies greenstones from two locations: (1) metabasalt-breccias from the Galfipagos Rift at 100°W; and (2) metabasalt-breccias and unbrecciated greenstones from the Chile Ridge at 38°S. Greenstone-breccias from both locations display stockwork-like sulfide mineralizations related to the upflow portion of a hydrothermal convection system. Whereas Galfipagos Rift stockwork sulfides belong to the "normal" type containing Cu-Fe-sulfides, Chile Ridge stockwork sulfides are galena-rich Pb-Zn _ Cu-sulfides and represent a previously unknown type of sulfide mineralisation in a MORB environment. Geochemically, the greenstones can be divided into two types: (1) The unbrecciated galena-free greenstones from both Chile Ridge and Galfipagos Rift show at least a 10-20-fold Pb enrichment compared to fresh MORB. With respect to similar Pb enrichment measured in greenstones from two other locations, i.e. DSDP Hole 504B and Galfipagos Rift near 86°W, we suggest that this may be a general feature of all stockwork-mineralised oceanic greenstones. (2) The galena- and quartz-rich metabasalt-breccias from the Chile Ridge are up to 3000-fold enriched in Pb (up to 1000 Ixg/g Pb in the whole-rock analyses) compared to MORB and indicate Pb mineralisation two orders of magnitude higher than that of the "normal" greenstone-type. A mass-balance calculation carried out using crustal column thickness of 3000 m with a 200-m-thick greenstone layer and 0.15 m of galena-beating breccias shows that at the Chile Ridge ~ 42% of the entire Pb is concentrated in the greenstones. This suggests that the rest of the crustal column is depleted in 58% of its primary Pb content. This degree of depletion matches well with previous calculations that a 56% depletion of Pb in oceanic crust subjected to mantle-recycling via subduction would be necessary to yield a HIMU mantle source within 2 Ga. Despite the need for future investigations into the extent and volume of the Pb enrichment in Chile Ridge greenstones, we believe that this process of major Pb redistribution is capable of creating huge volumes of oceanic crust that on average are extremely Pb-depleted and which when recycled would produce the HIMU source. Keywords: Chile Ridge; Galfipagos Ridge; Hydrothermal alteration; Greenstones; Geochemistry; Mineralogy

Description: The coagulation of hydrosols was investigated theoretically and experimentally. A reduced form of the particle size distribution function, designated “self-preserving,” was found to satisfy Smoluchowski's equations of coagulation by Brownian motion and shear flow. Brownian motion coagulation experiments with two heterogeneous hydrosols showed that the distributions were self-preserving. The rate of coagulation for heterogeneous systems was found to be second order in total particle concentration, consistent with the self-preserving form of the distribution function. Coagulation experiments were carried out in a simple laminar shear field using a homogeneous Dow polystyrene latex dispersion. Smoluchowski's shear flow theory was confirmed for shear rates ranging from 1 to 80 sec.−1 The shear coagulation of a heterogeneous emulsion was studied at several shear rates, and the size distributions were self-preserving.

Description: Two case studies of the application of geoscientific maps for planning in semi-arid regions are presented, one for the Mediterranean province of Valencia and another for the island of Gran Canaria (Canaries). Both regions are very dynamic from the point of view of population growth and urban-touristic-industrial development, and they suffer from a serious degree of environmental degradation. The provincial/ island governments have undertaken programmes of geoscientific mapping and assessment to serve as a basis for the establishment of guidelines for future planning. Two map sets have been made (1:200,000 in Valencia and 1:50,000 in Gran Canaria), based on initial maps of homogeneous integrated units. These represent a series of hierarchical land subdivisions, progressively smaller and more detailed (morphodynamic environments, systems, units, elements), defined on the basis of morphostructure, climate, lithology, surficial deposits, landforms, topography, active processes, soils, vegetation and human influence. Each individual map unit is described by means of a form which includes 114 items, summarising its environmental features. Morphodynamic units have been evaluated in terms of qualities significant for planning, and a series of derivative maps has been developed (geologic hazards, soil capability, present degree of erosion, potential erodibility, quality for conservation). A final map shows the most advisable types of uses and the main limitations for human activities, mainly due to engineering geological factors. This is a synthesis document which can be used directly by planners.

Description: Middle Pleistocene strata of the Kidnappers Group consist of a conformable sequence of alternating fluvio-lacustrine and shallow marine sediments exposed along coastal cliffs near Cape Kidnappers, southern Hawkes Bay, New Zealand. Three major paleomagnetic polarity intervals are recognised and interpreted as Jaramillo Normal Subchron, upper Matuyama Reversed Chron and Brunhes Normal Chron. This and biostratigraphy indicates an age range of 0.97 to 0.54 Ma for the group, compared to 0.85 to 〈 0.33 Ma previously suggested by fission track ages of tuffs. The new age control and facies interpretations suggest that the upper part of the group represents oxygen isotope stages 22 to 15. The duration and magnitude of isotope stages is reflected in the relative thicknesses of lithological units. Glacial periods are recorded as alluvial aggradation in the form of braidplain conglomerates, while estuarine and subaerial sands and muds with temperate climate pollens represent interglacial periods. This contrasts with many coastal and shelf sequences where glacial periods are represented by unconformities. Chemical and paleomagnetic characterisation of silicic tuffs in the Kidnappers Group establishes correlation to other sections and cores in New Zealand, the Tasman Sea and the western Pacific Ocean, thus providing temporal correlation for a range of sedimentary environments.

Description: Fecal excretion of calcium of endogenous origin has been measured in 52 studies in 33 adult human subjects, under full metabolic balance conditions. Endogenous fecal calcium averaged .130 ± .047 Gm. per day, was positively correlated with both fecal calcium and dietary calcium and was inversely correlated with fractional calcium absorption. The regression line relating endogenous fecal calcium with fractional absorption allowed estimates for total intestinal calcium secretion at both zero and 100 per cent absorption; from these estimates it was calculated that approximately 15 per cent of the total intestinal calcium secretion was nonabsorbable even under conditions when dietary calcium was completely absorbed (presumably because it enters the gut caudad of the absorption sites). Total intestinal calcium secretion, calculated so as to allow for this nonabsorbable fraction, averaged .194 ± .073 Gm. per day, and could not be correlated with age, sex, dietary calcium intake, caloric intake, urine calcium, or plasma calcium. A weak correlation with body size (weight, surface area) was observed. The conditions studied were principally disorders of bone, calcium, and parathyroid metabolism, and in most of them total intestinal calcium secretion appeared identical. The sole exception was seen in two studies on a patient with acromegaly, in which total intestinal calcium secretion was over twice the mean value for the remainder of the group.

Description: A standard, universally useful classification scheme for deepwater habitats needs to be established so that descriptions of these habitats can be accurately and efficiently applied among scientific disciplines. In recent years many marine benthic habitats in deep water have been described using geophysical and biological data. These descriptions can vary from one investigator to another, which makes it difficult to compare habitats and associated biological assemblages among geographic regions. Using geophysical data collected with a variety of remote sensor systems and in situ biological and geologic observations, we have constructed a classification scheme that can be used in describing marine benthic habitats in deep water.

Description: A structural model encompassing the southern North Sea basin west of the Central Graben has been developed. This model consists of a rift system affecting the post-salt section around the basin margin and a large area of detached compressional buckle folds within the basin. This pattern is initially a response to gravity sliding of the post-salt section on the salt within the basin during the late Triassic to late Jurassic. A close relationship between the location and trend of the peripheral graben system and basement structures in the pre-salt is noted. Pre-Jurassic extension across the peripheral graben systems was balanced by the sum of fault heaves at the pre-salt (Rotliegend) level and shortening across salt-cored buckle folds in the post-salt section. Salt pillows and swells passively infilled the cores of these gravity-induced buckle folds. Cretaceous and Tertiary inversion involved basin tilt and renewed movement on basin-bounding basement faults; notably, reverse movements did not propagate from basement structures up into the peripheral graben systems. The post-salt sedimentary section experienced gravity spreading in response to inversion-related uplift, resulting in syn-inversion extensional faulting in the Sole Pit High, where the Mesozoic section was thickest. This extension, combined with a loss of fault heave in the pre-salt section, was balanced by amplification of salt-cored buckle folds in the centre of the basin. In the context of the model described here, salt pillows represent passive infill of thin-skinned, compressional buckle folds which later amplified during thick-skinned basement shortening. Crestal collapse of such folds occurs via normal faulting, accompanied by reactive diapirism. Such reactive diapirs establish conduits through which salt may leak, leading to pillow deflation and ultimately conduit preservation as a salt wall (flanked by rim synclines in areas where the buckle folds were emergent). The salt structures described here are related to cover folds and faults, which in turn reflect episodes of basin extension, tilting and inversion. Hence individual salt structures can be said to be only remotely connected with regional, intraplate stresses.