PENDING FEDERAL GROUND-WATER LEGISLATION TWO STEPS FORWARD OR ONE STEP BACK: YOU DECIDE     

Jay H. Lehr  Chris Reimer 《Ground water》1988,26(3):274-278

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The extent of Greater India,II. Palaeomagnetic data from the Ladakh Intrusives at Kargil,northwestern Himalayas     

Chris Klootwijk  Madan Lal Sharma  Jozef Gergan  Biras Tirkey  S.K. Shah  Vinod Agarwal 《Earth and Planetary Science Letters》1979,44(1):47-64

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Continent — Island arc collision in the Banda Arc     

Chris C. Von Der Borch   《Tectonophysics》1979,54(3-4)

Acoustical structure of seismic profiles, and morphology of the Timor—Tanimbar—Ceram troughs and adjacent slopes of the outer Banda Arc, show remarkable similarities to equivalent parameters of many arcs subducting oceanic lithosphere and sediments, despite the fact that the outer Banda Arc is underlain by continental crust continuous with that of the colliding Australian craton. Such similarities include diffractions and anticlinal folds at the toe of the inner slope of the Timor—Tanimbar—Ceram troughs, which could be interpreted as thrust slices and thrust folds. Slope basins comprising sediments obviously dammed behind acoustic basement highs are also common on the trough inner slope, with some basins containing strata adjacent to the highs dipping away from the trough. Ridges and basins occur on the trough inner slope oriented parallel to the trough trend, and a slab continuous with down-bowed continental margin can often be detected a considerable distance in from the trough below the inner slope. On face value these observations are compatible with a mechanism of underthrusting by Australian and New Guinea crust with consequent imbrication and accretion of packages of off-scraped sediments. However, they may also be explained as possible outward-directed gravity slides of nappes displaced from uplifted inner portions of the arc, similar to the published structural interpretation of at least the eastern portion of the neighbouring, closely related New Guinea Fold Belt. It is shown that the weight of marine geological and geophysical evidence, including the alignment with the oceanic Indonesian Arc, the gravity anomalies, and the persistence of the various morphological and structural entities around the arc, favours subduction in the Timor—Tanimbar—Ceram troughs rather than massive gravity sliding towards the troughs. By this working model the outer Banda Arc would be the accretionary prism of a subduction zone which was formerly in an ocean-crust setting but since Pliocene has been interacting with continental lithosphere. If its structural evolution is analogous to that of the New Guinea orogenic belt, then the Banda Arc has not yet reached the stage of major, foreland-directed gravity slides. The proposed structural model for the Banda Arc is at variance with some but not all structural interpretations of the island of Timor, which is an emergent portion of the outer arc. Further critical studies are obviously required, both in marine and terrestrial areas, to resolve this impasse.  相似文献   

Deprivation,resources and planning: Some implications for applied rural geography     

Paul J. Cloke  Chris C. Park 《Geoforum》1980,11(1):57-61

Recent concern over social deprivation in rural areas of the U.K. has provided a new focus for applied rural geographers. However, the concept of deprivation may be broadened to include many other aspects of the rural environment, and therefore it offers a framework for more integrated approaches to planning in the countryside. A more dynamic strategy of rural research, involving greater cooperation between academic geographers and practising planners, and focussing upon problems of rural deprivation, is advocated in this paper.  相似文献   

Crustal accretion in the Pan African: Nd and Sr isotope evidence from the Arabian Shield     

Henk J. Duyverman  Nigel B.W. Harris  Chris J. Hawkesworth 《Earth and Planetary Science Letters》1982,59(2):315-326

Nd and Sr isotope determinations on late Precambrian to early Palaeozoic igneous and sedimentary rocks from the Arabian Shield are used to investigate the proportion of reworked “older” crust, and the rate at which new crust was generated during the Pan African event. Eight Rb/Sr whole rock isochrons on igneous suites yield ages in the range 770?590 Ma and initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7038?0.7023. These data confirm that magmatism in this area was largely restricted to the period 850-550 Ma, and the initial ratios are sufficiently low to preclude significant contributions from a long-lived upper crustal source. The initial ¹⁴³Nd/¹⁴⁴Nd ratios of a variety of lithologies, including several samples of possible “basement”, are all higher than the contemporaneous values for CHUR (ε_Nd = +1.6 to +6.9), suggesting that many were derived directly from the upper mantle, and that any inferred crustal source regions for the remainder could not have separated from likely LREE-depleted mantle reservoirs before 1200 Ma. The Arabian Shield therefore provides an example of rapid crustal growth during the Late Proterozoic, and contrasts with the Damara intracratonic belt of Namibia where Nd and Sr isotopes provide strong evidence for extensive reworking of older continental crust during the same period.  相似文献   

Concordant late Paleozoic paleomagnetizations from the Atacama Desert: implications for tectonic models of the Chilean Andes     

Chris Jesinkey  Randall D. Forsythe  Constantino Mpodozis  John Davidson 《Earth and Planetary Science Letters》1987,85(4)

Paleomagnetic results are reported from three formations of late Paleozoic age from the northern Chilean Andes of the Atacama Desert. For the first time primary NRM components are resolved for Paleozoic units along the western flank of the central Andes. Pole positions are calculated for the formations, and compared with APW data for cratonic South America. These comparisons reveal that the collecting sites in the northern Domeyko and Almeida Ranges of the central Andes have undergone no paleomagnetically defined rotations or translation with respect to cratonic South America since the time of NRM acquisition, which is likely to have been in the lower parts of the Kiaman Reverse Interval. If growth of the South American lithosphere has involved accretion of exotic microplates they are either likely to be substantially older than units sampled here, or be restricted to more coastal terranes. The results, taken together with other paleomagnetic data from northern Chile and southern Peru which have showed a wide range of discordance in their declinations when compared to each other or APW data, lead to the conclusion that this region of the Andes during the Mesozoic or Cenozoic has not been affected by simple processes of clockwise oroclinal bending from Peru to Chile, nor regionally consistent patterns of block rotations.  相似文献   

A review of Indian Phanerozoic palaeomagnetism: Implications for the India-Asia collision     

Chris T. Klootwijk   《Tectonophysics》1984,105(1-4)

An overview is presented of the Indian apparent polar wander path (APWP) for the Phanerozoic and in particular for post-Late Palaeozoic times. This APWP is compiled on basis of data available at October 1981 from peninsular and extrapeninsular Indo-Pakistan and from DSDP cores from the Indian plate. One of the more important and newly recognized features of this APWP is a large-scale Triassic-Jurassic loop. This loop indicates a changeover from a Late Palaeozoic-Early Mesozoic northwards and counter-clockwise rotational movement, with Greater India reaching moderately low southern latitudes, into a southwards and clockwise rotational movement during the Early to Middle Jurassic. Recognizable likewise in APWP's from other Gondwana continents, this loop reflects the opening of the Neotethys.Studies of extrapeninsular regions up to and north of the Indus-Tsangpo suture zone have shown wide-spread presence of magnetic overprints, which delineate two regionally confined age groups. Younger overprints (20–40 m.y.) predominate in the more external thrust zones. Older overprints (50–60 m.y.), in contrast, are found in the more internal zones both north and south of the Indus-Tsangpo suture zone. The latter are interpreted to reflect a late phase of relaxation in the Early Tertiary collision of Greater India with south-central Asia or off-shore island arcs, which occurred at equatorial to low northern palaeolatitudes (0°–10°N). Subsequent northwards movement over 2500–3000 km or more and impingement of Greater India into southern Asia resulted into large-scale underthrusting of Greater India along the Main Central Thrust beneath southern Tibet, and to clockwise rotation of thrust units in the Western Himalaya. A discrepancy between Indian palaeomagnetic data and results available todate from southern Tibet is discussed.  相似文献   

13C Record of benthic foraminifera in the last interglacial ocean: Implications for the carbon cycle and the global deep water circulation     

Jean-Claude Duplessy  Nicholas J. Shackleton  Robley K. Matthews  Warren Prell  William F. Ruddiman  Michèle Caralp  Chris H. Hendy 《Quaternary Research》1984,21(2):225-243

The ¹³C/¹²C ratios of Upper Holocene benthic foraminiferal tests (genera Cibicides and Uvigerina) of deep sea cores from the various world ocean basins have been compared with those of the modern total carbon dioxide (TCO₂) measured during the GEOSECS program. The δ¹³C difference between benthic foraminifera and TCO₂ is 0.07 ± 0.04‰ for Cibicides and ?0.83 ± 0.07‰ for Uvigerina at the 95% confidence level. δ¹³C analyses of the benthic foraminifera that lived during the last interglaciation (isotopic substage 5e, about 120,000 yr ago) show that the bulk of the TCO₂ in the world ocean had a δ¹³C value 0.15 ± 0.12‰ lower than the modern one at the 95% confidence level, reflecting a depletion, compared to the present value, of the global organic carbon reservoir. Regional differences in δ¹³C between the various oceanic basins are explained by a pattern of deep water circulation different from the modern one: the Antarctic Bottom Water production was higher than today during the last interglaciation, but the eastward transport in the Circumpolar Deep Water was lower.  相似文献   

Structural deformation and sedimentation in an active Caldera, Rabaul, Papua New Guinea     

H.Gary Greene  Donald L. Tiffin  Chris O. McKee 《Journal of Volcanology and Geothermal Research》1986,30(3-4)

Recent seismic and tectonic activity in Rabaul Caldera, Papua New Guinea, suggests that magma is accumulating at a shallow depth beneath this partially submerged structure and that a new volcano may be developing. Changes in onshore elevation since 1971 (as much as 2 m on south Matupit Island) indicate that rapid and large-scale uplifts have occurred on the seafloor near the center of the caldera. The frequency of seismic events within the caldera has also increased during this period. Earthquake locations define an elliptical ring surrounding the center of this uplift within the caldera.A marine geophysical survey in 1982 by the U.S. Geological Survey's R/V “S.P. Lee” in Rabaul Caldera shows the development of a bulge in the seafloor near the center of the caldera. High-resolution seismic reflection profiles show that this bulge consists of two domal uplifts bounded and separated by two major north-south-trending fault zones. Deformed sediments overlie these zones; a prominent slump flanks the area of the bulge.Five major acoustic units were identified in the seismic reflection profiles: an acoustic basement and four sedimentary units consisting of irregularly layered, cross-layered, contorted, and well-layered sequences. The acoustic basement is probably composed of crystalline volcanic rocks, and the layered acoustic units are probably sediments, primarily ash deposited in different environments. The cross-layered, irregularly layered, and contorted units appear to have been deposited in a dynamic environment subjected to strong currents, seismicity, and/or mass wasting, while the well-layered units were deposited in a low-energy environment. Locally, well-layered sequences interfinger with the other sedimentary units, indicating a transitional environment that alternated between high-energy and low-energy depositional processes.A submarine channel cuts most of the acoustic units and appears to be the conduit for sediment transport out of the caldera; it occupies an older buried channel north of the caldera that is presently being exhumed. In the south, active erosion of well-layered sediments is taking place. What are believed to be several young volcanic cones also disrupt the depositional layers.We conclude that the bulge in the seafloor and the associated fault zones are a result of emplacement of magma at a shallow depth. Contorted sediment and slumps adjacent to the bulge are probably the result of uplift and seismic activity. The pattern of seismicity appears to reflect increased magma pressure at depth beneath the caldera floor. This activity may eventually lead to an eruption.  相似文献   

Aldicarb Studies in Ground Waters from Florida Citrus Groves and Their Relation to Ground—Water Protection     

Forrest E. Dierberg  Chris J. Given 《Ground water》1986,24(1):16-22

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