Tourist Carrying Capacity Measures: Crowding Syndrome in the Caribbean

International tourism is increasing at an unprecedented rate. Understanding the variety of national and local impacts of this increase is of importance to a growing number of governments. Butler's resort cycle model (1974, 1980, 1991) provides for several long‐term possibilities as to the relationship between crowding and growth. McElroy, de Albuquerque, and Dioguardi (1993) focus on one of those possibilities. Specifically, using their penetration ratio, they predict that as tourist crowding continues for a group of Caribbean islands, the appeal of these islands decreases in the eyes of potential tourists and that, as time increases, the growth rate of the affected islands, actually decreases. Our article indicates that such a simple, straight‐line relationship between increased crowding and a decrease in the rate of change may not be inevitable; indeed, diseconomies of scale may be avoided. The use of a curvilinear regression function reveals how both positive and negative scale economies existed in the Caribbean during the years 1992 through 1996.     

Commingling and mixing of S-type peraluminous, ultrapotassic and basaltic magmas in the Cayconi volcanic field, Cordillera de Carabaya, SE Peru

The Cayconi district of the Cordillera de Carabaya, SE Peru, exposes a remnant of an upper Oligocene–Lower Miocene (22.2–24.4 Ma) volcanic field, comprising a diverse assemblage of S-type silicic and calc-alkaline basaltic to andesitic flows, members of the Picotani Group of the Central Andean Inner Arc. Basaltic flows containing olivine, plagioclase, clinopyroxene, ilmenite and glass, and glassy rhyolitic agglutinates with phenocrystic quartz, cordierite, plagioclase, sanidine, ilmenite and apatite, respectively exhibit mineralogical and geochemical features characteristic of medium-K mafic and Lachlan S-type silicic lavas. Cordierite-bearing dacitic agglomerates and lavas, however, are characterized by dispersed, melanocratic micro-enclaves and phenocrysts set in a fine-grained quartzo-feldspathic matrix. They contain a bimodal mica population, comprising phlogopite and biotite, as well as complexly zoned, sieve-textured plagioclase grains, sector-zoned cordierite, sanidine, quartz, irregular patches of replaced olivine, clinopyroxene and orthopyroxene and accessory phases including zircon, monazite, ilmenite and chromite. The coexistence of minerals not in mutual equilibrium and the growth/dissolution textures exhibited by plagioclase are features indicative of magmatic commingling and mixing. Trachytic-textured andesite flows interlayered with olivine+plagioclase–glomerophyric, calc-alkaline basalts have a phenocrystic assemblage of resorbed orthopyroxene and plagioclase and exhibit melanocratic groundmass patches of microphenocrystic phlogopite, Ca-rich sanidine, ilmenite and aluminous spinel. The mineralogical and mineral chemical relationships in both the dacites and the trachytic-textured andesites imply subvolcanic mixing between distinct ultrapotassic mafic melts, not represented by exposed rock types, and both the S-type silicic and calc-alkaline mafic magmas. Such mixing relationships are commonly observed in the Oligo-Miocene rocks of the Cordillera de Carabaya, suggesting that the S-type rocks in this area and, by extension, elsewhere derive their unusually high K₂O, Ba, Sr, Cr and Ni concentrations from commingling and mixing with diverse, mantle-derived potassic mafic magmas.     

Area selection for diamond exploration using deep-probing electromagnetic surveying

Previously proposed methods of area selection for diamond-prospective regions have predominantly relied on till geochemistry, airborne geophysics, and/or an appraisal of tectonic setting. Herein we suggest that a novel, deep-probing geophysical technique—electromagnetic studies using the natural-source magnetotelluric (MT) method—can contribute to such an activity. Essentially, diamondiferous regions must have (1) old lithosphere, (2) thick lithosphere, and (3) lithosphere that contains high concentrations of carbon. Deep-probing MT studies are able to address all three of these. The second and the third of these can be accomplished independently using MT, but for the first the geometries produced from modelling the MT observations must be interpreted with appropriate interaction with geologists, geochemists and other geophysicists. Examples are given from the Slave and Superior cratons in North America, with a brief mention of an area of the Rae craton, and general speculations about possible diamondiferous regions.     

An intercomparison between finite difference and finite element (TELEMAC) approaches to modelling west coast of Britain tides

A finite element model (namely TELEMAC) with a range of mesh refinements and assumptions of coastal water depths is used to determine an optimal mesh for computing the M ₂ tide in a region of significant geographical extent. The region adopted is the west coast of Britain covering the Irish and Celtic Seas. The nature of the spatially varying topography and tidal distribution, together with a comprehensive set of measurements and existing accurate finite difference model makes it ideal for such a study. Calculations show that a water-depth dependent criterion for determining element size gives an optimal distribution over the majority of the region. However, local refinements in narrow channels such as the North Channel and Bristol Channel are required. Although the specification of a zero coastal water depth, leads to a fine near coastal grid, this does not yield the most accurate solution. In addition the computational cost is high. In practice in a large area model the use of a non-zero coastal water depth yields optimum accuracy at minimal computational cost. However, calculations show that accuracy is critically dependent upon nearshore water depths. Comparison with the finite difference model shows that the bias in elevation amplitude in the finite difference solution is removed in the finite element calculation.     

Comparison of finite difference and element models of internal tides on the Malin–Hebrides shelf

A three-dimensional baroclinic finite element model with a coarse and fine (i.e. local refinement along the shelf edge) grid is used to examine the influence of shelf edge grid refinement upon the internal tide generation and propagation off the west coast of Scotland. Comparisons are made with observations in the region and with a published solution using a finite difference model. The calculations show that provided that the finite element grid is refined in the internal tide generation area and the adjacent region through which the internal tide propagates, then a numerically accurate solution is obtained. In the regions of strong internal tide generation with a local grid refinement, internal wave energy can accumulate at small scales and must be removed by a scale-selective filter.     

Iron isotope fractionation during planetary differentiation

The Fe isotope composition of samples from the Moon, Mars (SNC meteorites), HED parent body (eucrites), pallasites (metal and silicate) and the Earth's mantle were measured using high mass resolution MC-ICP-MS. These high precision measurements (δ⁵⁶Fe ≈ ± 0.04‰, 2 S.D.) place tight constraints on Fe isotope fractionation during planetary differentiation.Fractionation during planetary core formation is confined to < 0.1‰ for δ⁵⁶Fe by the indistinguishable Fe isotope composition of pallasite bulk metal (including sulfides and phosphides) and olivine separates. However, large isotopic variations (≈ 0.5‰) were observed among pallasite metal separates, varying systematically with the amounts of troilite, schreibersite, kamacite and taenite. Troilite generally has the lightest (δ⁵⁶Fe ≈ − 0.25‰) and schreibersite the heaviest (δ⁵⁶Fe ≈ + 0.2‰) Fe isotope composition. Taenite is heavier then kamacite. Therefore, these variations probably reflect Fe isotope fractionation during the late stage evolution and differentiation of the S- and P-rich metal melts, and during low-temperature kamacite exsolution, rather than fractionation during silicate-metal separation.Differentiation of the silicate portion of planets also seems to fractionate Fe isotopes. Notably, magmatic rocks (partial melts) are systematically isotopically heavier than their mantle protoliths. This is indicated by the mean of 11 terrestrial peridotite samples from different tectonic settings (δ⁵⁶Fe = + 0.015 ± 0.018‰), which is significantly lighter than the mean of terrestrial basalts (δ⁵⁶Fe = + 0.076 ± 0.029‰). We consider the peridotite mean to be the best estimate for the Fe isotope composition of the bulk silicate Earth, and probably also of bulk Earth. The terrestrial basaltic mean is in good agreement with the mean of the lunar samples (δ⁵⁶Fe = + 0.073 ± 0.019‰), excluding the high-Ti basalts. The high-Ti basalts display the heaviest Fe isotope composition of all rocks measured here (δ⁵⁶Fe ≈ + 0.2‰). This is interpreted as a fingerprint of the lunar magma ocean, which produced a very heterogeneous mantle, including the ilmenite-rich source regions of these basalts.Within uncertainties, samples from Mars (SNC meteorites), HED (eucrites) and the pallasites (average olivine + metal) have the same Fe isotope compositions as the Earth's mantle. This indicates that the solar system is very homogeneous in Fe isotopes. Its average δ⁵⁶Fe is very close to that of the IRMM-014 standard.     

Discordant bodies from olivine-bearing zones III and IV of the Stillwater Complex, Montana – evidence for postcumulus fluid migration and reaction in layered intrusions

Mineralogically zoned and unzoned discordant bodies composed predominately of plagioclase with up to 35% olivine, occur at three different levels in Olivine-Bearing zones III and IV of the Middle Banded series of the Stillwater complex. The discordant bodies are elongate perpendicular to the layering of the host cumulates with slender concordant apophyses. Although the host olivine-gabbros are foliated with tabular plagioclase, the discordant bodies lack a discernible fabric and have blocky plagioclase. Average olivine in the host rocks is slightly more magnesian than that of the discordant bodies (Mg#_{75.8 ± 0.7} versus Mg#_{74.6 ± 0.3} respectively) but plagioclase compositions are indistinguishable (An_{77.6 ± 2.0} versus An_{76.6 ± 4.3}– average host and discordant bodies respectively). Whole-rock major- and trace-element compositions of the discordant bodies are generally indistinguishable from cumulates with similar modal abundance. However, bulk compositions of anorthositic cores from the discordant bodies are enriched in K, Na, Ba, Sr and P. We conclude that the discordant bodies formed when cooler volatile fluids or fluid-rich silicate liquids moved upward and encountered a hotter undersaturated solid-plus-liquid assemblage. Continued liquid/fluid fluxing increased the permeability along the flow path and focused the flow, allowing the original bulk compositions to be modified and leaving plagioclase-rich troctolites and anorthosites. The shapes of the discordant bodies suggest that the cumulus pile had anisotropic permeability during late-stage liquid/fluid flow. Chemical and mineralogical evidence from other parts of Olivine-Bearing zones III and IV suggests that the processes that formed the discordant bodies may have influenced other cumulates. In fact, it appears that the same processes that formed the discordant bodies operated within an anorthositic layer, strongly modifying the chemistry of the rock but leaving no mineralogical or textural evidence. Received: 10 December 1996 / Accepted: 12 August 1997