Eastern Peninsula Research Articles

Ophiolites of the Eastern Peninsulas zone (Eastern Kamchatka): Age, composition, and geodynamic diversity

Abstract The geological, geochemical and mineralogical data of dismembered ophiolites of various ages and genesis occurring in accretionary piles of the Eastern Peninsulas of Kamchatka enables us to discriminate three ophiolite complexes: (i) Aptian–Cenomanian complex: a fragment of ancient oceanic crust, composed of tholeiite basalts, pelagic sediments, and gabbroic rocks, presently occurring in a single tectonic slices (Afrika complex) and in olistoplaques in Pikezh complex of the Kamchatsky Mys Peninsula and probably in the mélange of the Kronotsky Peninsula; (ii) Upper Cretaceous complex, composed of highly depleted peridotite, gabbro and plagiogranite, associated with island arc tholeiite, boninite, and high‐alumina tholeiitic basalt of supra‐subduction origin; and (iii) Paleocene–Early Eocene complex of intra‐island arc or back‐arc origin, composed of gabbros, dolerites (sheeted dykes) and basalts produced from oceanic tholeiite melts, and back‐arc basin‐like dolerites. Formation of the various ophiolite complexes is related to the Kronotskaya intra‐oceanic volcanic arc evolution. The first ophiolite complex is a fragment of ancient Aptian–Cenomanian oceanic crust on which the Kronotskaya arc originated. Ophiolites of the supra‐subduction zone affinity were formed as a result of repeated partial melting of peridotites in the mantle wedge up to the subduction zone. This is accompanied by production of tholeiite basalts and boninites in the Kamchatsky Mys segment and plagioclase‐bearing tholeiites in the Kronotsky segment of the Kronotskaya paleoarc. The ophiolite complex with intra‐arc and mid‐oceanic ridge basalt geochemical characteristics was formed in an extension regime during the last stage of Kronotskaya volcanic arc evolution.

Collision of the Kronotskiy arc at the NE Eurasia margin and structural evolution of the Kamchatka–Aleutian junction

Structural evolution of the Kamchatka–Aleutian junction area in late Mesozoic and Tertiary was generally controlled by (1) the processes of subduction in Kronotskiy and Proto-Kamchatka subduction zones and (2) collision of the Kronotskiy arc against NE Eurasia margin. Two structural zones of the pre-Pliocene age and six structural assemblages are recognized in studied region. 1: Eastern ranges zone comprises SE-vergent thrust folded belt, which evolved in accretionary and collisional setting. Two structural assemblages (ER1 and ER2), developed there, document shortening in the NW–SE direction and in the N–S direction, respectively. 2: Eastern Peninsulas zone generally corresponds to Kronotskiy arc terrane. Four structural assemblages are recognized in this zone. They characterize (1) precollisional deformations in the accretionary wedge (EP1) and in the fore-arc basin and volcanic belt (EP2), and (2) syn-collisional deformation of the entire Kronotskiy terrane in plunging folds (EP3) and deformations in the foreland basin (EP4). Analysis of paleomagnetic declinations versus present day structural strike in the Kronotskiy arc terrane shows that originally the arc was trending from west to east. Relative position of the accretionary wedge, fore-arc basin and volcanic belt, as well as northward dipping thrusts in accretionary wedge indicate, that a northward dipping subduction zone was located south of the arc. The accretionary wedge developed from the Late Cretaceous through the Eocene, and it implies that the subduction zone maintained its direction and position during this time. It implies that Kronotskiy arc was neither a part of the Pacific nor Kula plates and was located on an individual smaller plate, which included the arc and Vetlovka back-arc basin. Motion of the Kronotskiy arc towards Eurasia was connected only with NW-directed subduction at Kamchatka margin since Middle Eocene (42–44 Ma). Emplacement of the Kronotskiy arc at the Kamchatka margin occurred between Late Eocene and Early Miocene. This is based on the age of syn-collisional plunging folds in Kronotskiy terrane, and provenance data for the Upper Eocene to Middle Miocene Tyushevka basin, which indicate in situ evolution of the basin with respect to Kamchatka. Collision was controlled by the common motion of the Kronotskiy arc with Pacific plate towards the northwest, and by the motion of the Eurasian margin towards the south. The latter motion was responsible for the southward deflection of the western part of the Kronotskiy arc (EP3 structures), and for oblique transpressional structures in the collisional belt (ER2 structures).

Stable Isotope Evidence for Large-Scale Infiltration of Metamorphic Fluids Generated during Shallow Subduction into the Eastern Peninsular Ranges Mylonite Zone (EPRMZ), Southern California

New δ18O and δD data confirm and amplify the conclusion by Holk et al. (1991) that, during the late Cretaceous or earliest Tertiary, there was large-scale infiltration of metamorphic water at depths of at least 15 km into the lower plate of the EPRMZ, a major crustal shear zone that transects a 15 x 15 km tonalite pluton west of Borrego Springs, California. Whole-rock δ18O values in undeformed tonalite are +11.2 ± 0.4 (n = 9) and in mylonitized tonalite are +12.3 ± 0.3 (n = 21), indicating a 1 per mil increase in 18O during open-system water-rock exchange. Quartz, feldspar, and biotite δ18O values in undeformed tonalite are +12.9 ± 0.4 (n = 8), +11.0 ± 0.6 (n = 8), and +7.7 ± 0.7 (n = 8), compared with +13.5 ± 0.2 (n = 8), +11.8 ± 0.3 (n = 9), and +9.2 ± 0.3 (n = 10) in mylonitized tonalite. The extremely uniform quartz-feldspar and quartz-biotite 18O fractionations in the mylonitized tonalite indicate equilibration at 500-600°C. Biotite and hornblende δD values from undeformed tonalite are -73 ± 3 (n = 12), compared with -52 to -68 (n = 21) in mylonitic tonalite, even though the biotite and hornblende have the same Fe/Mg (≈1.25; Anderson, 1983) in both kinds of tonalite. This implies that the EPRMZ was infiltrated by large amounts of high-D water (δD ≈ -10 to -30) at 500-600°C, probably derived at depth by dehydration of subducted oceanic crust or underplated volcanogenic sediments. Syndeformational tonalitic pegmatites have quartz and feldspar δ18O values of +13.5 ± 0.3 (n = 4) and +12.2 ± 0.3 (n = 6), and biotite and muscovite δD values of -64 ± 1 (n = 2) and -42 (n = 1), suggesting a genetic relationship between the pegmatites and these deep-seated fluids. Higher whole-rock δ18O values (+13.2 to +16.1, n = 3) and much lower δD values (-72 to -114, n = 3) occur where the EPRMZ cuts upper-plate amphibolite-facies metasediments. The shift to lower δD values in these finer grained rocks probably occurred during interactions with heated meteoric groundwaters during Pliocene detachment faulting associated with the opening of the Gulf of California.

Early Holocene delevelling and deglaciation of the Cumberland Sound region, Baffin Island, Arctic Canada

Radiocarbon, cosmogenic surface exposure, and relative sea-level data are used to examine deglaciation and glacioisostatic adjustment of Cumberland Sound and Cumberland Peninsula, and southeastern Baffin Island, in the context of a new model for the glacial history of the eastern Canadian Arctic. Over the last decade, a multidisciplinary effort on easternmost Baffin Island has documented far greater ice expansion during the last glacial maximum than previously believed, including low gradient glaciation in marine embayments coexisting with ice free or thin cold-based ice on adjacent upland crystalline terrain. This study documents that the Cumberland Sound region underwent about twice as much glacioisostatic movement during the last glacial maximum as shown in previous reconstructions. However, the loading impact of the Laurentide Ice Sheet and local glaciation on adjacent Cumberland Peninsula was limited; the mapped zero isoline on emergence shows that postglacial eustatic rise exceeded glacial isostatic uplift for much of the eastern peninsula, a finding that is consistent with that of prior studies. The center of loading and the major source of glacial ice for the entire Cumberland Sound region were Foxe Basin and western Baffin Island. Strandlines dated 10,500 and 8500 1 4 C yr B.P. show that slow deglaciation of Cumberland Sound was punctuated by at least two periods of faster grounding line retreat. Coastal southeastern Cumberland Peninsula was deglaciated before 9400 1 4 C yr B.P., and other areas surrounding Cumberland Sound were deglaciated after ca. 9000 1 4 C yr B.P.; these land areas experienced relatively slow glacial retreat and restrained rebound. Cosmogenic surface exposure ages on glacially-scoured bedrock support the 1 4 C-based inferred timing for deglaciation of the sound, although inheritance of nuclides from prior exposure is evident in samples, indicating limited bedrock erosion in many areas. For central Cumberland Sound, a rapid rise of relative sea-level of ∼4-5 m/100 1 4 C yr (4-6 m/100 yr) and a half life for crustal response of <720 1 4 C yr (<1400 yr) are consistent with those values obtained in other studies of isostatic adjustment around the edges of the former Northern Hemisphere ice sheets where lithospheric influences were relatively dominant.

Forearc ophiolites: a view from the western Pacific

Abstract Many of the world’s largest ophiolite masses are now being interpreted as remnants of oceanic forearcs stranded on continental margins in the course of arc-continent collision. This interpretation implies a former association between the ophiolite and a volcanic arc at a distance of 100–200 km. The New Caledonia region of the SW Pacific is one of the few areas where there is good evidence for the presence of such an arc. On New Caledonia itself, the Grand Massif du Sud ophiolite has been thrust over the Norfolk Ridge continental fragment, while the coral islands of the Loyalty Group, c. 100 km to the NE, cap large sub-sea edifices with volcanic morphology. New Caledonia can be correlated geologically with New Guinea, despite the considerable width of open ocean that now separates the two. In central New Guinea, where ophiolites emplaced along the northern flank of the main mountain spine lie some 100 km south of exposures of arc-volcanic basement in the north coast ranges, the similarities include the relationship between New Caledonia and the Loyalty Islands. There is, however, no obvious comparable relationship in the case of the largest of the New Guinea ophiolites, the Papuan Ultramafic Belt of the eastern peninsula, which is backed to the north and east by the oceanic Solomon Sea. An associated volcanic arc can be recognized in this area only by assuming a complicated history of collision, post-collision arc-forearc separation and sea-floor spreading, followed by renewed contraction and a very recent and continuing second collision. The case for such a sequence of events can be made on a number of grounds. If the processes responsible are general in their nature, they could explain the apparent absence of arc-volcanic belts in association with many other supposedly forearc ophiolites.

Information and Communications Technology in Asia Pacific Countries: implications for small and medium enterprises in Malaysia

Information communications and technology (ICT) is transforming the environment in which SMEs operate and changing the paradigms of value creation, customer satisfaction and business effectiveness. This paper attempts to explore global and Asia Pacific ICT usage and the major factors influencing SMEs. It focuses particularly on Malaysia where the development of ICT usage amongst SMEs is one of the main policy items in the agenda of the Malaysian government. It describes a survey of SMEs in north and eastern peninsula Malaysia 1999-2000.

Potential for long-range regional precipitation prediction over India

The potential for long-range precipitation prediction over the Indian monsoon region is generally good where climate noise (i.e., variability due to daily weather fluctuations) is small as compared to the climate signal (i.e., variability due to year to year fluctuations in monthly/seasonal means) being in the tropical belt. In order to understand the potential on smaller spatial scales, the ratios of inter-annual variability to that associated with climate noise have been computed for precipitation of four seasons as well as SW monsoon sub-seasons/months over 1656 stations in the Indian subcontinent.&#x0D; &#x0D; Precipitation in SW monsoon has been found potentially predictable on seasonal as well as intra-seasonal scale. The west coast and contiguous northwest India, part of the 'northeast India are more predictable. Potential for long-range prediction over northwest India is highest during the active monsoon period from July to September. Over eastern peninsula potential for prediction is generally found low whereas over north-central India it is always moderate. Over northern latitudes precipitation due to western disturbances during January to May is potentially predictable. Precipitation over southeast India and Sri Lanka during October to February due to northeast (NE) monsoon shows good potential for long-range prediction. It is manifested that long-range precipitation forecasting schemes for SW monsoon season, sub-seasons and months and for the other seasons over India on point to regional scale have good scope by taking into account the potential predictability at the individual stations as well as at contiguous resemblance areas over the country.

Pseudotachylites in the Eastern Peninsular Ranges of California

A continuous zone containing pseudotachylites in the Eastern Peninsular Ranges of California extends over more than 15 km from Deep Canyon in the north to at least Toro Canyon in the south. Pseudotachylites are found in rocks of tonalitic to dioritic composition. While the overall compositions of host rock and pseudotachylite veins are similar, veins are characteristically enriched in Fe and Ti and depleted in Si. Many veins are cataclastic, and all contain fragments, but a large number have a groundmass with skeletal and spherulitic microlites of calcic plagioclase (An 40–50), biotite and ilmenite, indicative of partial melting. The pseudotachylites formed mainly during a late brittle event (56–62 Ma) and postdate the high-strain, ductile mylonitic deformation in the Santa Rosa mylonite zone (65–87 Ma) as ascertained by 40Ar/ 39Ar ages. The size of veins ranges from less than 1 mm to more than 10 cm in thickness and aspect ratios display a broad log-normal distribution. Three-quarters of the veins are more or less parallel to the foliation. The orientation of the veins is consistent with a top to the west displacement, similar to that for the ductile mylonites. From the sizes, energies required for melting are estimated to range between 10 5 J for smaller veins and 10 10 J for larger veins. Interestingly, the energy distribution and geometry of these pseudotachylites correspond closely with energy distributions of current microseismic events along the San Andreas fault at Parkfield, suggesting that basic mechanisms may be similar and due to intrinsic mechanical properties of rocks. In particular these indicate that local stress concentrations, rather than average crustal stresses, are relevant for earthquakes.

Past distribution and ecology of the cork oak (Quercus suber) in the Iberian Peninsula: a pollen‐analytical approach

Abstract. This study presents pollen‐analytical data from continental and offshore Iberian Peninsula sites that include pollen curves of Quercus suber, to provide information on the past distribution and ecology of the cork oak (Q. suber). Results centre on a new pollen record of Navarrés (Valencia, eastern Spain), which shows that the cork oak survived regionally during the Upper Pleistocene and was important during a mid‐Holocene replacement of a local pine forest by Quercus‐dominated communities. This phenomenon appears linked to the recurrence of fire and reinforces the value of the cork oak for reforestation programmes in fire‐prone areas. In addition to Navarrés, other Late Quaternary pollen sequences (Sobrestany, Casablanca‐Almenara, Padul, SU 8103, SU8113, 8057B) suggest last glacial survival of the cork oak in southern and coastal areas of the Peninsula and North Africa. Important developments also occur from the Late Glacial to the middle Holocene, not only in the west but also in the eastern Peninsula. It is suggested that, in the absence of human influence, Q. suber would develop in non‐monospecific forests, sharing the arboreal stratum both with other sclerophyllous and deciduous Quercus and Pinus species.

Discovery of a New Species ofLuperosaurus(Squamata; Gekkonidae) from Sulawesi, with a Phylogenetic Analysis of the Genus, and Comments on the Status ofLuperosaurus serraticaudus

We describe a new species of Luperosaurus from first growth, low-elevation, closed canopy rain forest on Mt. Tompotika at the tip of the eastern peninsula of the island of Sulawesi (Celebes), Indonesia. The new species is the first record of the genus Luperosaurus from this island and differs from all known species of Luperosaurus by numerous morphological characters and a unique color pattern. The new species also shares some presumably derived character states with members of the genus Ptychozoon. A phylogenetic analysis of 24 morphological characters is consistent with the previously hypothesized presence of two species groups (putative lineages) within the genus Luperosaurus. The analysis suggests that the new species from Sulawesi may either belong to a clade also including L. brooksi and L. browni or may fall basal to the remaining Luperosaurus. The monophyly of the species currently referred to Luperosaurus is questionable. We consider Luperosaurus serraticaudus a junior synonym of L. browni.

Th Rise of Malaysia's Tourism Industry

Malaysia's government is focusing more than ever on its tourism industry, which could soon become the nation's number-one source of foreign exchange. In particular, Malaysia hopes to develop its hitherto overlooked eastern peninsula, as well as several of its island destinations. Already tourists come to Malaysia to tour Penang's classic Chinatown area and its rubber plantations. Because of its location, Malaysia poses a challenge to neighboring Singapore's current hegemony as a destination and as a transfer site for tourists visiting Southeast Asia. Singapore is not blind to the challenge, but faces physical limitations as it seeks to reinvent itself. Moreover, Singapore's efforts to increase supply are at the moment not supported by increases in demand. Faced with a potential image as a relatively high-price destination due to a strong currency, Singapore needs to control costs and boost its value perception, as well as reinvigorate its current tourist attractions. Ironically, strategic alliances with Malaysian tourism operations may also strengthen Singapore's hand.

Archaeobotanical remains of hulled and naked cereals in the Iberian Peninsula

Archaeobotanical finds in Spain show differences in the representation of the different wheats and barleys. From the beginning of agriculture (around 5000 B.C.) onwards, all wheats and barleys can be found at the sites of the eastern Peninsula. But in later periods of the early Neolithic, free-threshing wheat becomes more important in the northeast and the southeast, compared to the hulled wheats (emmer and einkorn). Nevertheless, both naked and hulled barleys can be found in similar frequencies in this period. Seed analyses in the southeast and the east of Spain show the importance of naked barley compared with hulled barley in the third millenium uncal B.C. This is not the case in the northeast, where hulled barley has a similar frequency in this period until the Iron Age, when both hulled barley and free-threshing wheat are the most important taxa. The substitution of naked barley for hulled barley in the south-east Iberian Peninsula is very significant in the period of greatest growth of the Argar culture. Free-threshing wheat can be found at a similar frequency throughout the study area, and was an important human food source together with the barleys. Hulled wheats seem to have played a secondary role as food in all periods, although they are constantly present in our samples. Nevertheless spelt wheat does not appear until the Roman period, when it is only found on the Cantabrian north coast, where it is important.

Habitat, isolation and the evolution of Madeiran Iandsnails

The Madeiran archipelago consists of Madeira itself, Porto Santo and the Deserta islands. On Madeira, the forest arid the coastal floral associations are so different that their faunas are effectively isolated and have undergone largely independent development. There are different faunal associations on the eastern peninsula and in the SE coastal region, which may have been separated from each other in the past. On Porto Santo, western and eastern hills have different faunas. Most observations on the fauna are compatible with evolution by allopatric speciation, consequent upon isolation on different islands or mountains, as opposed to parapatric or sympatric processes following disruptive selection. Some cases where the taxonomy is difficult to unravel may, however, indicate parapatric speciation; examples belong to the genera Discula and Heterostoma (Helicidae) and Amphorella (Ferussaciidae). Most evidence relating to species composition in communities is compatible with a balance of random immigration and extinction, rather than selective interaction, allowing clusters of similar sympatric species to accumulate. However, this impression may indicate that test procedures are insufficiently sensitive to detect interactions, and detailed ecological studies are required. Questions about speciation and distribution would be clarified if dates of divergence were established.

Response to Dynamic Flood Hazard Factors in Peninsular Malaysia

Rapidly-industrializing, developing countries face increasing environmental disaster potential. Rising disaster losses are an indicator of non-sustainable development. Analysis of flood hazard in peninsular Malaysia exemplifies these problems. Malaysia has a rapidly-growing economy and evidence suggests that the flood hazard is worsening largely because of rapid urbanization and development. This is revealed by analysing trends in five 'flood hazard factors': variables which explain flood disaster potential. Flood risk, exposure and damage potential are all increasing. High levels of poverty in flood plains suggest that peoples' vulnerability to floods is not being reduced. A large proportion of interviewed flood-prone households have low incomes, especially in eastern peninsula locations, and reported flood damages are high. Indigenous household flood adjustments, including 'stilt houses', limit flood vulnerability especially in the rural east. Unfortunately, modernization threatens traditional life-styles and erodes indigenous hazard-adaptations. State response is heavily engineering-oriented and is failing to address development-induced flood hazard potential. Policies are required which marry hazard reduction to poverty reduction and sustainable development.

The Southeast Asian tin belt

The Southeast Asian Tin Belt is a north-south elongate zone 2800 km long and 400 km wide, extending from Burma (Myanmar) and Thailand to Peninsular Malaysia and the Indonesian Tin Islands. Altogether 9.6 million tonnes of tin, equivalent to 54% of the world's tin production is derived from this region. Most of the granitoids in the region can be grouped geographically into elongate provinces or belts, based on petrographic and geochronological features. - The Main Range Granitoid Province in western Peninsular Malaysia, southern Peninsular Thailand and central Thailand is almost entirely made up of biotite granite (184–230 Ma). Tin deposits associated with these granites contributed 55% of the historic tin production of Southeast Asia. - The Northern Granitoid Province in northern Thailand (0.1% of tin production) also has dominant biotite granite (200–269 Ma) but it is distinguished by abundant post-intrusion deformation. - The Eastern Granitoid Province extends from eastern Peninsular Malaysia to eastern Thailand. The Malaysian part is subdivided into the East Coast Belt (220–263 Ma), Boundary Range Belt (197–257 Ma) and Central Belt (79–219 Ma). The granitoids cover a wide compositional range from biotite granite to hornblende-biotite granite/granodiorite and diorite-gabbro. Tin deposits are associated with biotite granite in the East Coast Belt (3% of tin production). The granitoids in the other areas of the Eastern Granitoid Province are barren. - The Western Granitoid Province (22–149 Ma) in northern Peninsular Thailand, western Thailand and Burma has biotite granite and hornblende-biotite granite/granodiorite. Tin deposits are associated with biotite granite, which probably is the dominant phase (14% of tin production). The granitoids of the Indonesian Tin Islands (193–251 Ma) do not permit grouping into geographically distinct units. Main Range-type and Eastern Province-type plutons occur next to each other. Most of the tin deposits are associated with Main Range-type plutons (28% of tin production). Tin-mineralized plutons are characterized by high concentrations of SiO 2, K 2O, Rb, Sn, Th and U, whereas the concentrations of Fe 2O 3, MgO, CaO, Na 2O, Ba and Sr as well as the Fe 2 O 3 FeO ratios are low. Tin-mineralized plutons are also distinguished by high initial 87 Sr 86 Sr ratios low magnetic susceptibilities.

Genetic variation and population structure in Korean endemic species: III.Hosta minor (Liliaceae)

Hosta minor, an insect-pollinated and rhizomatous herbaceous perennial, occurs in eastern and southern Korean Peninsula. AlthoughH. minor is a Korean endemic species and most populations of the species are scattered, the species maintains considerably high levels of genetic variation within the species, with a moderate level of variation (14%) found among populations. Nineteen of the 29 putative loci resolved (66%) were polymorphic within the species, the mean number of alleles per locus was 2.10 across all populations and averaged 1.68 within populations. In addition, genetic diversity was a considerably higher (for species and population level, mean estimates of genetic diversity were 0.275 and 0.230, respectively) than the average for other long-lived herbaceous perennials. Indirect estimate of the number of migrants per generation (Nm=1.03, calculated from mean GST) was moderate. Factors contributing to the high levels of genetic diversity found within populations ofH. minor include population maintenance via sexual and asexual modes of reproduction, primarily outcrossing breeding system, long generation time, probable ancient polyploid origin of the species, and moderate levels of seed dispersal by wind. Human disturbance in South Korea such as road and apartment constructions appears to be the major threat to this genetically diverse species.

Entwicklung der immergruenen Oekosysteme nach Waldbrand in Athos

Development of the evergreen broadleaved ecosystems after a forest fire in Athos. - The peninsula of Athos is the third eastern peninsula of Chalkidiki in Central Macedonia (N. Greece) and it constitutes a self-governed region in the Hellenic State. Its organized monastic history begins in the 10th century and continues uninterruptedly until today. The monastery of Simonopetra, one of the 20 monasteries of Athos, represents a continuous historic life of seven centruries from its establishment, during the 13th century and constitutes the most during edifice on Mount Athos, a miracle of the byzantine and post-byzantine architecture. The territory of Simonopetra on Mount Athos, occupies an area of 1265 ha. The destructive forest fire on Mount Athos which started on August 14, 1990, was extinguished 14 days later. During this period, it caused heavy damage to the forests on the peninsula and destroyed a number of historical buildings. Most of the damage occured in the area of the Sacred Monastery Simonopetra, where 855 ha of the total of 1265 ha were burned. The greatest part of the burned forest area, about 665 ha, they were evergreen broadleaved forests. The ecosystems of the evergreen broadleaved forests are perscribed as well as their development after the forest fire. After the fire, all species which appear in this zone, begun to coppice sprout in a few weeks and after two years, the coppicing sprouts exceeded in height 0,5 - 2 metres depended on the species and site quality. Two years after the fire the vegetation was restored and covered 30 - 76% of the area. The only measure taken in certain positions was the removal of the standing dead material.

Collision tectonics in the late Precambrian Eastern Ghats Mobile Belt: mesoscopic to satellite‐scale structural observations

ABSTRACTRegional mapping of a section across the Eastern Ghats Mobile Belt (EGMB) north of the Godavari graben in Eastern Peninsular India by using Landsat Thematic Mapper data enables recognition of a number of shear zones, lineaments, and structural domes and basins. A conspicuous megashear occurs at the western boundary of the granulite facies rocks of the EGMB adjacent to the Archean granite‐greenstone craton. The confinement of a suite of alkaline igneous rocks to this shear zone is a notable feature. The strike extensions of this shear belt extend through to the Elchuru alkaline complex, Prakasam District, Andhra Pradesh, and the syenite plutons of Koraput district, Orissa. The contrasting lithologies, metamorphism and structural history on either side of the shear zone suggests that it might be a Precambrian suture zone.The mesoscopic structural features in the EGMB include prominent foliation with moderate to steep dips, folds, faults/shears, S‐C fabrics, pinch and swell structures and other linear fabric elements. These observations favour the consideration of drastic crustal shortening and thickening and a complex deformational sequence. The major rock units in this part of EGMB comprise garnetiferous sillimanite gneisses, quartzites and calc‐granulites forming the khondalitic suite of rocks and a wide variety of charnockitic rocks. The contact of the two rock units is generally sheared and often migmatised.The structural fabric suggests two major tectonic events: an essentially horizontal tectonic regime resulting in thrust systems and associated structures, subsequently followed by strike‐slip tectonics characterized by high shear strains. Features such as westward‐verging thrusts, large‐scale recumbent folds, major shear zones, structural domes and basins, indications of tectonic crustal shortening, extensive calc‐alkali magmatism and widespread migmatization in the region are attributed to collisional processes during Proterozoic times. The spatial disposition of the EGMB and its linkage with the distribution of similar rock units during the late Precambrian time in a global tectonic scenario are discussed.

Land snails of eastern Madeira : speciation, persistence and colonization

The Madeiran archipelago has an exceptionally rich land snail fauna (over 250 taxa), consisting mostly of endemic species with affinities with pre-Pleistocene Europe. Two surveys have been done to examine the distribution of species on the main island of the group, Madeira. The first shows that there is a faunal discontinuity between the eastern peninsula and the rest of the island. The second analyses the relation of the peninsula to the rest of Madeira. The peninsula has several distinctive species of its own. It also includes species usually from damp woodland, which appear to have a relict distribution there, and taxa nearly confined to it on Madeira but abundant on the Deserta islands and Porto Santo. Exam­ination of a fossil sequence shows that damper conditions have occurred on the peninsula in the past. Variation in Discula polymorpha Heterostoma , Steenbergia spp. and Amphorella spp. may be interpreted as showing local adaptations that perhaps indicate parapatric evolution. The general pattern of distribu­tion and the geological history of the islands suggests, however, that the present distributions result mostly from allopatric speciation in a geo­logically unstable region. As a whole, the archipelago is very species rich, but individual samples show low diversity. The possible contribution of interspecies competition to this pattern is considered.

Crustal structure in the Kamchatkan segment of the pacific transition zone

Based on deep seismic sounding data, a velocity model of the Earth's crust has been developed for the Kamchatkan segment of the Pacific transition zone. The velocity difference in the structure of the continental and oceanic blocks of the Earth's crust is shown. It has been revealed that these crustal blocks join each other along the deeply inclined fault zone. This zone is located 120 km northwest of the axis of the deep-sea trench. It separates the high-velocity block of eastern peninsulas and bays of Kamchatka from the low-velocity block of the Shatsky Ridge. The latter may be considered to be a contact zone between the continental and oceanic crust. The crust of the regions of Recent volcanic activity in Kamchatka has a number of specific features, such as: a complex heterogeneous structure of the basement; relatively high velocity values in the crust and low values in the upper mantle; anomalous behaviour and velocity inversions related to the complex alternation of sedimentary-volcanogenous and intrusive rocks and zones of hydrothermal alterations; and the possible presence of magma chambers of different types within the crust and the crust-mantle transition zone.