The nature of urbanization in the gulf countries

This paper analyses the urban process in the oil producing countries of the Gulf. The mode of urbanization is identified as one characterized by an extreme case of primacy but with rates varying among the countries of the region. This pattern is related to the historical evolution of human settlements as affected by the local environmental qualities and the recent large scale development of urban infrastructures which favoured the already existing capital cities. The relative city growth rates are among the highest in the world but with a declining tendency which reflects expenditure patterns and the nature of the regional economies. The high growth rates are essentially due to massive foreign migration into the region and to extremely high natural increase rate — an abnormal condition in an urban process approaching saturation point. The role of these primate centres in the development of the region is undeniable and, furthermore, all indications suggest that this pattern of urban development will continue in the furture as it is, perhaps economically and politically less costly.     

Past and present geotectonic position of Sulawesi, Indonesia

Sulawesi with its peculiar K-shaped pattern is situated in an area where the Eurasian, Indian—Australian and Pacific plates interact and collide.Complex geological processess in this area resulted in the transformation of a normal island-arc structure into an inverted one, deformation of an already tectonized belt, sweeping of fragments against unrelated terrain, thrusting of oceanic and mantle material over the island arc, closing of deep-sea basins behind the arc, trapping of old oceanic crust caused by the rolling up of an island arc, formation of a marginal basin by the spreading of the sea floor behind the arc, development of small subduction zones with reverse polarities etc.Small deep-sea basins surrounding Sulawesi such as the Gulf of Bone and the Gulf of Gorontalo originally formed the arc—trench gap of the Sulawesi island arc.The Banda Sea is considered as an oceanic crust trapped by the bending of the east—west trending Banda arc due to the northward drift of Australia combined with the westward movement of the Pacific plate. Similarly the Sulawesi Sea consists of an old Pacific crust trapped by the westward bending of the Sulawesi island arc, caused by the spearheading westward thrust along the Sorong transform-fault system, in which later a minor spreading center became active in its central part. The Molucca Sea comprises tectonic mélange in which presumably a small spreading center developed between the two colliding arcs of northern Sulawesi and western Halmahera. While the Benioff zones dip under the northern Sulawesi and Halmahera arcs in normal fashion, the mélange thrusts over them. The Strait of Makassar is a marginal basin which was brought into existence by the spreading of the sea floor between Kalimantan and Sulawesi.The evolution of Sulawesi started in Miocene time or even earlier when 800 km east of Kalimantan a north—south trending east-facing island arc came into existence, originating from a spreading center located in the Pacific Ocean. Volcanism and plutonism accompanied this subduction process.Collision between Sulawesi and the Australian—New Guinea plate which occurred in early Pliocene time severely transformed Sulawesi into an island with its convex side turned towards the continent, at the same time causing obduction of ophiolite in the eastern arc of this island.The movement of the Pacific plate continued and gradually pushed Sulawesi towards the Asian continent, resulting in the closing of the sea between Kalimantan and Sulawesi islands separated by small straits and deep seas resembling the complicated pattern of the Philippine Archipelago, in which the original double island-arc structure can no longer be recognized.     

Geographic aspects of urbanization and its peculiarities in countries with different social systems

The complex process of urbanization is obtaining under the impress of scientific and technological revolution of global dimensions. But the process of urbanization depends very much on geographical differentiation of the factors and conditions on the Earth' surface. So it is deeply geographical in its essence. It is not only geographically conditioned but it also has deep spatial manifestations, which makes it one of the most important and universal fields of investigation for the whole system of geographic sciences. The common global features and general regularities of urbanization take peculiar forms in each of the three main groups of countries having different social systems: socialist, economically developed capitalist and developing, which leaves its deep imprints not only on the social contents of urbanization but also on the very process of forming of specific spatial-urbanistic structures, existing on the Earth. To this we should further add the results of working of individual traits of different countries and regions. So to get the real pattern of world urbanization it is necessary to study profoundly not only its global and typological features but also the specific local factors. To these ends geographers must elaborate a system of basic notions and characteristics of the urbanization process and stage. Some of them are treated in this paper.     

Mid-Holocene vertebrate bone Concentration-Lagerstätte on oceanic island Mauritius provides a window into the ecosystem of the dodo (Raphus cucullatus)

Although the recent history of human colonisation and impact on Mauritius is well documented, virtually no records of the pre-human native ecosystem exist, making it difficult to assess the magnitude of the changes brought about by human settlement. Here, we describe a 4000-year-old fossil bed at Mare aux Songes (MAS) in south-eastern Mauritius that contains both macrofossils (vertebrate fauna, gastropods, insects and flora) and microfossils (diatoms, pollen, spores and phytoliths). With >250 bone fragments/m² and comprising 50% of all known extinct and extant vertebrate species (n_s = 44) of Mauritius, MAS may constitute the first Holocene vertebrate bone Concentration-Lagerstätte identified on an oceanic volcanic island. Fossil remains are dominated by extinct giant tortoises Cylindraspis spp. (63%), passerines (～10%), small bats (7.8%) and dodo Raphus cucullatus (7.1%). Twelve radiocarbon ages [four of them duplicates] from bones and other material suggest that accumulation of fossils took place within several centuries. An exceptional combination of abiotic conditions led to preservation of bones, bone collagen, plant tissue and microfossils. Although bone collagen is well preserved, DNA from dodo and other Mauritian vertebrates has proved difficult. Our analysis suggests that from ca 4000 years ago (4 ka), rising sea levels created a freshwater lake at MAS, generating an oasis in an otherwise dry environment which attracted a diverse vertebrate fauna. Subsequent aridification in the south-west Indian Ocean region may have increased carcass accumulation during droughts, contributing to the exceptionally high fossil concentration. The abundance of floral and faunal remains in this Lagerstätte offers a unique opportunity to reconstruct a pre-human ecosystem on an oceanic island, providing a key foundation for assessing the vulnerability of island ecosystems to human impact.     

Chemistry versus time in the volcanic complex of Ischia (Gulf of Naples,Italy): evidence of successive magmatic cycles

An extensive petrochemical and geochronological study of the volcanic complex of the island of Ischia has been made in order to assess the variation of the magmatic characteristics through time. The major and trace element chemistry and the mineralogy of more than 40 samples, coupled with their K/Ar ages, reveal four phases of volcanic activity: (1) prior to 150000 years B.P. — alkali-trachyte pyroclastic products; (2) 150000–75000 years B.P. — alkali-trachytic to phonolitic lava domes and minor pyroclastics; (3) 55000–20000 years B.P. — great pyroclastic emissions of trachytic and alkali-trachytic composition; (4) 10000 years B.P.-1302 A.D. — mainly lava flows, ranging from alkali-trachytes to magmas between basalt and latite. In spite of a relatively monotonous major element chemistry, the trace element contents of the rocks show a large variation (up to a factor of 9). Comparison of glass compositions with the modal phases permits us to distinguish at least four clearly established supplies of new magma to a shallow chamber. After the first three events, the magmas possibly evolved in a closed system controlled by fractional crystallization with at least one single eutectic crystallization occurring afterwards (sodalite, nepheline and alkali feldspar+aegirine and salite). During the fourth event, increasing proportions of a less evolved liquid, suddenly charged with mafic xenocrysts, contaminated the residual liquid in the chamber and generated through time more and more basic products. Their high Th/Ta and Th/Hf ratios and Ta, Nb and Ti negative anomalies suggest an orogenic tendency of the recent volcanic activity on the island of Ischia.     

Independence,dependence and fragmentation in the South Pacific

Since the 1960s most island groups of the South Pacific have achieved independence and many new nations have been established; only the very smallest islands remain colonies. Most of the small nations are extremely small yet secession movements in many areas have resulted in fragmentation producing the break-up of the Gilbert and Ellice Islands and the disintegration of the Trust Territory of the Pacific Islands. This has emphasized the distinctive characteristics of the Pacific nations: their small size (in population and in area) and limited natural resources, their isolation from each other and from markets and fragmentation within multiple island countries. The extension of outside interests into the Pacific has brought rapid economic changes, the emergence of cash cropping and the decline of subsistence agriculture, increased dependence on imports (especially food, resulting in some nutritional problems) and rapid urbanization, producing growing dependence and inequality which regional ties between the Pacific nations have not been able to overcome. Outmigration from the smallest nations to USA and New Zealand is likely to be maintained and the unusual characteristics of these small island nations suggest that strategies of development that appear viable elsewhere have little chance of success in the Pacific.     

Crustal strain phenomena in the Solomon Islands, constraints from field evidence, and relationship to the India-Pacific plates' boundary

The Solomon Islands lie along the India-Pacific plates' margin and have recorded a history of deformation resulting from the interaction of these two plates. Various kinematic models have been proposed for the Solomons and these have involved a variety of plate tectonic processes. It is pointed out that almost without exception these models have been based on a provincial geological classification of the island group in which it is assumed that two of these provinces—Pacific and Central provinces—commenced their geological development in regions distant from one another. Invariably such models require that Santa Isabel represents part of a collision zone between these two provinces, though field evidence from Santa Isabel for such a collision has in the past been largely lacking.These various kinematic models are examined in the light of more recent field evidence, and a premise on which they have been based—initial separate development for two of the provinces—is questioned. Rather it is here suggested that the Central and Pacific provinces developed in roughly similar positions, one with the other as they occur today, and that they were at least in part separated from Oligocene time onward by a linear peridotite-gabbro ridge, Korighole-Florida high, which acted as a sediment barrier to much of the coarser clastic and volcanogenic sedimentation.The initial development of the Solomon Islands began in an oceanic environment with the extrusion of extensive submarine tholeiitic ‘flood basalts’ and intrusion of associated gabbroic and ultramafic rocks at depth, during the Late Mesozoic to Early Tertiary. This igneous phase occurred with the whole of the island group representing the western margin of the Ontong Java Plateau. Subsequent asymmetric development of the Solomons during the Eocene and Oligocene resulted in uplift, shearing, and the initiation of arc volcanism, plutonism, and arc-related sedimentation in the Central province to the west. In contrast, through much of the Tertiary the Pacific province to the east continued to receive dominantly pelagic sediments before undergoing uplift and renewed deformation in the Pliocene. The recognition that the ophiolite crust in the Solomon Islands represents an autochthonous entity, which has acted as basement to subsequent arc volcanism, has significant implications on geochemical studies of these islands now being undertaken.     

Design and implementation of a smart solid waste collection system

Solid waste collection systems are very important in today’s urban environment. The last three decades witnessed the development in urban areas over rural ones in a process called urbanization. Growth of urbanization is much more in developing countries than in the developed countries to the extent that it became a trend characterizing several developed and even least developed countries. Unfortunately, it has been observed that the systems currently used in modern cities do not provide a service of sufficient efficiency and quality, despite their high running costs. As an alternative, a smart solid waste collection system with all subcomponents was developed and applied in a small city in Turkey. In addition to the conventional waste collection systems, this system included smart features and optimization algorithms for route planning. The study presents the design philosophy, feasibility and pilot implementation of a smart solid waste collection system which can be operated with high efficiency at low cost.     

Conservation,integration and foreign dependency: Prelude to a new economic security strategy

With dramatic changes in the international environment, and the resulting substantial defense budget reductions, defense planners are being forced to grabble with old problems in new ways. The intractability of efforts to foster industrial conversion, and the cumulative record of acquisition reform, are leading toward a consensus about relying more heavily on the commercial sectors of the economy to meet defense requirements. Carrying through with a policy of civil-military integration (CMI) will require a concept of economic security that is more internationally oriented than is traditional for the Department of Defense (DOD) and, at the same time, accommodates very real concerns about foreign dependency. New analatical approaches will be required to help focus attention on high-risk foreign dependencies. One such approach —the Foreign Vulnerability Index (FVI) — is developed here. Its strengths and weaknesses are discussed.     

Natural hazard impacts in small island developing states: A review of current knowledge and future research needs

Small island developing states (or SIDS) are exposed to a large number of natural hazards and many characteristics of small island developing states make them particularly vulnerable to the impacts of natural hazards. In spite of this acknowledged vulnerability, there are relatively few studies which focus on the impacts of natural hazards in these countries. This paper presents a review of our current state of knowledge of impacts in small island developing states and highlights a number of research needs. Central to these is the need to integrate natural hazards research within a sustainable development context and the need to exploit existing procedures such as government coordinated disaster impact assessments to generate a detailed understanding of natural hazards impacts.     

贵阳市城镇化进程与土地利用转变关系

贵阳市岩溶地貌十分发育,可利用土地资源缺乏,城镇化发展与土地利用相互制约.基于贵阳市2001~2014年城镇化指标数据及1996、2001、2004、2009、2016年五期遥感影像数据,采用指标权重法和土地利用类型转移矩阵,分析了2001~2014年贵阳市城镇化发展趋势和1996~2016年土地利用的时空分布特征及演变规律.并运用相关性分析方法建立函数响应度模型,探讨了城镇化与土地利用之间的作用关系.结果表明:（1）2001~2014年间,贵阳市城镇化水平呈上升趋势,综合城镇化得分增长率为52.46%,其中人口（26.0%）、生态（20.4%）、空间（19.9%）和经济（18.3%）城镇化对综合城镇化贡献较大,社会（15.4%）城镇化相对较小;（2）贵阳市农用地、建设用地面积增加,净增长总量23.66%,未利用土地面积减少,净减少总量23.56%,土地利用类型总变化量为87.77%;（3）城镇化进程推动着土地利用的变迁,2001~2014年水田（13.767响应度）、裸地（4.476）、旱地（1.708）、灌木（1.319）土地利用类型对城镇化的综合响应度较高,乔木（0.897）、草地（0.878）、建设用地（0.693）、水域（0.180）相对较低.城镇用地面积的快速扩张是土地利用类型转变的直接因素.因此,建议在城镇化进程中,优化土地利用结构,以提高土地资源利用效率,保证城镇化进程可持续发展.      

Systematic Variation of Sr-, Nd- and Pb-Isotopes with Time in Lavas of Mauritius, Reunion Hotspot

We report Sr-, Nd- and Pb-isotopic compositions for the lavasof Mauritius, the second youngest volcanic island in the Réunionhotspot. The lavas of the Older Series (7·8–5·5Ma) have identical isotopic compositions (⁸⁷Sr/⁸⁶Sr = 0·70411to 0·70422,¹⁴³Nd/¹⁴⁴Nd = 0·512865 to 0·512854,and ²⁰⁶Pb/²⁰⁴Pb = 19·016 to 19·041) to those ofRéunion, where the center of volcanic activity is currentlylocated. The lavas of the Intermediate Series (3·5–1·9Ma) and Younger Series (0·70–0·17 Ma) areshifted to lower Sr-isotopic compositions (0·70364–0·70394,with ¹⁴³Nd/¹⁴⁴Nd = 0·512813 to 0·512948 and ²⁰⁶Pb/²⁰⁴Pb= 18·794 to 18·984). The Intermediate Series lavashave similar trace-element characteristics (e.g. Zr–Nb,Ba–Y) to those of Rodrigues, in both cases requiring theinvolvement of an enriched mantle-like component in the mantlesource. During the volcanic history of Mauritius, the magmaslost the principal isotopic characteristics of the Réunionhotspot with time, and became gradually imprinted with the isotopicsignature of a shallower mantle source that produced the CentralIndian Ridge basalts. KEY WORDS: hotspot; isotopes; Mauritius; Réunion; trace element     

Garnet-cordierite-biotite equilibria in the Steinach aureole,Bavaria

Three garnet-biotite pairs and eleven garnet-cordierite-biotite triplets from the Steinach aureole (Oberpfalz, North-East Bavaria) were analyzed using an electron probe microanalyzer.The regional metamorphic muscovite-biotite schists contain garnets strongly zoned with Mn-Ca-rich centers and Fe-rich edges, the average composition being almandine 67 — spessartine 4 — pyrope 4 — grossular (+andradite) 25.The first contact garnet that is formed in mica schists of the outermost part of the aureole is small, virtually unzoned, and has an average composition of almandine 52 — spessartine 37 — pyrope 8 — grossular (+andradite) 3. With increasing metamorphic grade, there is a consistent trend to form garnets richer in Fe ending up with a composition almandine 84.5 — spessartine 5.5 — pyrope 7.5 — grossular (+andradite) 2.5. This trend is accompanied by a general increase in grain size and modal amount of garnet. Associated cordierites and biotites also become richer in Fe with increasing grade. While the garnets in the highest grade sillimanite hornfelses are poorly zoned, the transitional andalusite-sillimanite hornfelses contain garnets with distinct but variable zonation profiles.These facts can possibly be explained by the time-temperature relationships in the thermal aureole. In a phase diagram such as the Al-Fe-Mg-Mn tetrahedron, the limiting mineral compositions of a four-phase volume or a three-phase triangle are fixed by T and P (the latter remaining effectively constant within a thermal aureole). Thus, in garnet-cordierite-biotite assemblages, garnet zonation should be controlled by temperature variation rather than by a non-equilibrium depletion process. Taking into account the experimental data of Dahl (1968), a zoned garnet from a transitional andalusite-sillimanite hornfels would reflect a temperature increase of about 40° C during its growth. A hypothetical P-X diagram is proposed to show semi-quantitatively the compositional variation of garnet-cordierite pairs with varying pressures (T constant).     

Structural characteristics and tectonisms around the microcontinent in the outer margin of the Paleozoic-Mesozoic geosyncline of Japan

Consideration of the paleogeography and large and small structures in the outer part (the Sakawa Fold Belt) of the Paleozoic—Mesozoic geosyncline of Japan suggests that the main part of the Japanese Islands has grown up not from an arc—trench system but from a marginal sea basin—microcontinent system: the Chichibu Geosyncline and the Kurosegawa — Ofunato Island Arc, Minor structures are superposed in a complicated way and they are analyzed in terms of the concepts of tectonic level and multiple deformation.Stratigraphic evidence shows that an early deformation was pre-middle Triassic in the Chichibu Terrain but northwards in the Sambagawa terrain it may have continued until early Cretaceous in relation to minor scale subduction within the marginal basin. A late Cretaceous phase of deformation produced the greatest crustal shortening in the microcontinent area of the Kurosegawa Tectonic Zone and was nearly contemporaneous with the intrusion of granitic rocks in the Ryoke Zone Younger secondary eugeosynclines were developed by progressive encroachment on the arc—trench gap south of the Kurosegawa zone from late Permian times onwards.     

Crustal deformation in the Central Ionian Islands (Greece): Results from DGPS and DInSAR analyses (1995–2006)

Ground deformation studies based on Differential GPS (DGPS) and Differential Interferometric SAR (DInSAR) analyses have been conducted in the seismically active area of the Central Ionian Islands. Local GPS networks were installed in Cephallonia (2001) and Zakynthos (2005). The Cephallonian network has been remeasured five times and Zakynthos' once as of July 2006. The studies have yielded detailed information regarding both local and regional deformations that are occurring in the area.For Lefkas Island, DInSAR analysis (March to September 2003) revealed 56 mm of uplift in the central and western parts and is attributed to the August 2003 earthquake (M_w = 6.3) that occurred offshore to the west. Synthetic DInSAR modelling of the magnitude and extent of deformation is consistent with the seismologically deduced parameters for the ruptured segment along the Lefkas Transform Fault. Subsidence (< 28 mm) along the northern part of the island is attributed to local conditions unrelated to the earthquake. For Zakynthos Island, large-magnitude earthquakes that occurred offshore to the south in October 2005 and April 2006 most likely contributed to the observed deformation as deduced from DGPS measurements for an encompassing period (August 2005 to July 2006). The largest amount of horizontal deformation occurred in the south, where its western part moved in a W–NW direction, while the eastern part moved towards the NE, with magnitudes ranging from 15 to 26 mm. The southern part of the island uplifted a maximum of 65 mm whereas the north subsided from 12 to 28 mm.For Cephallonia Island, DInSAR analysis (1995 to 1998) indicated ground deformation up to 28 mm located in small sections of the island. Further interferometric analysis for the period 2003 to 2004, encompassing the occurrence of the Lefkas earthquake in August 2003, indicated 28 mm of uplift in the northern part, while during the next two years (2004 to 2005), further uplift of at least 56 mm had taken place at the western and northern part of the island.DGPS measurements for the period 2001 to 2006 revealed a clockwise rotation of the island with respect to a centrally located station on Aenos Mt. The horizontal component of deformation generally ranged from 6 to 34 mm, with the largest values at the western and northern parts of the island. Considering the vertical deformation, two periods are distinguished. The first one (2001 to 2003) is consistent with anticipated motions associated with the main geological and tectonic features of the island. The second one (2003 to 2006) has been tentatively attributed to dilatancy in which relatively small uplift (20–40 mm) occurred along the southern and southeastern parts of the island, while larger magnitudes (> 50 mm) happened at the western part (Paliki Peninsula). These large magnitudes of uplift over an extended area (> 50 km), in conjunction with an accelerated Benioff strain determined from the analysis of the seismicity in the broader region, are consistent with dilatancy. This effect commenced some time after 2003 and is probably centered in the area between Zakynthos and Cephallonia. If this interpretation is correct, it may foreshadow the occurrence of a very strong earthquake(s) sometime during 2007 to 2008 in the above designated region.     

Effects of human population growth on the Fraser and Okanagan River systems,Canada: a comparative inquiry

Perhaps nowhere in Canada, if indeed in North America, could two adjacent watershed basins be selected which show such remarkable differences in their historical and recent response to human population growth effects. One — the Fraser — covers some 234,000 km² (about one quarter of the province of British Columbia) and houses nearly two-thirds of its total population. The other — the Okanagan — forms a small part (some 14,000 km²) of the upper Columbia River drainage in Canada. Native Indian populations at maximum before European contact in the late 1700s were about 50,000 in the Fraser basin and probably less than a fifth of that in the Okanagan. Present total resident populations of the Fraser and Okanagan basins, about 2 million and 1\4 million respectively, have greatly different distributions and thereby effects within the watersheds they occupy. In addition seasonal tourist populations have important and differential impacts within the two watersheds. Expression of these effects on water, fisheries and other aquatic resources of the two basins are explored along with possibilities and suggestions for their sustainable development. The latter, despite some glimmers of hope, will not be tenable without major changes in public attitude, in government policy at all levels, and in other measures which to many may seem impossible.     

Pollution of limestone aquifer due to urban waste disposal around Raipur,Madhya Pradesh,India

During the rainy season deterioration in the quality of water, supplied through dug wells and tube wells, near an abandoned limestone quarry was reported. The abandoned quarry is now being used as an urban waste disposal site. The problem was further complicated by hospitalization of several inhabitants who were using this water for domestic purposes. Looking into the consequences, chemical analysis of water from the quarry, dug wells and tube wells was carried out. The water was found to be contaminated. The transportation of pollutants from the quarry to the groundwater system was facilitated by karst features. Furthermore, four major sources—domestic waste disposal, water conservation structures, landfills, and water wells—contributing to pollution were identified. This case study is an attempt to provide an understanding of how the karst features facilitate groundwater contamination. It will help us answer a few questions such as why karst hydrogeology deserves special attention in urban expansion and what protective measures should be planned in view of rapid urbanization.     

Ophiolite belts and the collision of island arcs in the Arabian Shield

The Arabian Shield is divided into several segments by ophiolite zones. The segments display features of island arcs with respect to their magmatic evolution as well as their mineralization.The northern part of the “Hulayfah—Hamdah ophiolite belt” which cuts the Arabian Shield in a north—southerly direction, has been sampled and described. Serpentinized ultramafics, gabbros, doleritic dike rocks and basalts are the most important members. The ophiolite belt is marked by magnetic anomalies with amplitudes of 200–500 gammas.In conclusion, the Arabian Shield is considered to be built up of several generations of juxtaposed volcanic arcs of Late Proterozoic age. The arcs have been closely swept together squeezing out the trench-fill sediments in the case of the Hulayfah—Hamdah belt. Cratonization was completed by the end of the Precambrian.     

Diffuse magnetic anomalies in marginal basins: Their possible tectonic and petrologic significance

Marginal basins, areas of oceanic lithosphere peripheral to large ocean basins, may be formed by several processes, but the young active marginal basins have the geophysical and geochemical characteristics of young normal oceanic lithosphere. We recognize two distinct tectonic settings in which new oceanic lithosphere may be formed in areas which would be termed marginal basins:

1. (1) Upwelling of fractional melts of mantle material from the region above subducted lithospheric slabs leads to the generation of new oceanic lithosphere behind island arcs. The general case for this tectonic setting involves random location of magma leaks and does not produce correlatable magnetic anomalies. In special cases, an orthogonal ridge—transform system may duplicate the magnetic patterns found on ocean-basin crust.

2. (2) The second tectonic setting develops on very long “leaky” transform faults separating spreading ridges. In areas where the transform has dislocated a block of continental crust, or an island arc, the map view of the resulting marginal basin may resemble the setting of a basin behind an active island arc. However, the “leaky” transform setting is unrelated to active plate convergence or to Benioff zones.

At “normal” ridge-crests, and possibly in some marginal basins, basalt is erupted on long linear magma leaks and rapid cooling forms thick lithosphere with correlatable linear magnetic anomalies. Some marginal basins have high thermal flux, spread slowly and may have thick sediment cover. Slow cooling, numerous point-source magma leaks and extensive hydrothermal alteration diminish magnetic intensities and cause diffuse magnetic patterns. The correlation problems caused by diffuse magnetic anomalies make interpretations of spreading rates and directions in young marginal basins a difficult, if not futile, task.It is likely that fragments of marginal-basin lithosphere form some of the ophiolite complexes; their recognition is critical to paleo-tectonic interpretations. The geochemical characteristics of marginal-basin basalts do not appear to be useful criteria for distinguishing them from ocean-ridge basalts. However, the abundance of short ridges and seamounts in many young marginal basins suggests that an abundance of seamount material, as well as differentiated volcanic and plutonic rocks, in ophiolites may be an indication of derivation from marginal-basin lithosphere.     

Isotopic composition of strontium in three basalt-andesite centers along the Lesser Antilles arc

Si⁸⁷/Sr⁸⁶ ratios have been determined for lavas and py lastic rocks from three basalt-andesite centers along the Lesser Antilles arc—Mt. Misery on the island of St. Kitts, Soufriere on the island of St. Vincent, and Carriacou, an island of The Grenadines. The average Si⁸⁷/Sr⁸⁶ content of these rocks is 0.7038 for Mt. Misery, 0.7041 for Soufriere, and 0.7053 for Carriacou. All the Sr⁸⁷/Sr⁸⁶ values from each center are the same within analytical uncertainty (±0.0002). The constancy of strontium isotopic data within each center supports the hypothesis that basalts and andesites for each specific center investigated are generated from the same source — in agreement with petrographic and major- and minor-element data. Strontium isotopic compositions and elemental concentrations, particularly of strontium and nickel, indicate that this source was mantle peridotite and that the relationship between the respective basalts and andesites is probably fractional crystallization.Publication authorized by the Director, U.S. Geological Survey.