Cenozoic Magmatism of the North-Eastern Eurasian Margin: The Role of Lithosphere Versus Asthenosphere   总被引：6，自引：1，他引：6  

OKAMURA  SATOSHI; ARCULUS  RICHARD J.; MARTYNOV  YURI A. 《Journal of Petrology》2005,46(2):221-253

Sikhote-Alin and Sakhalin are located in the Russian Far Eastflank of the northernmost part of the Sea of Japan. Magmatismin this region preceded, was concurrent with, and continuedafter the extension and sea-floor spreading (25–18 Ma)that formed the Sea of Japan. Among the Sikhote-Alin and Sakhalinvolcanic suites, Eocene–Oligocene (55–24 Ma) lavasare characterized by greater large ion lithophile element andrare earth element enrichments compared with Early–Mid-Miocene(23–15 Ma) tholeiites, and also show a depletion in highfield strength elements (HFSE). The geochemical characteristicsof the Eocene–Oligocene and Early–Mid-Miocene basaltsare consistent with migration of the locus of magma generationbeneath the Sikhote-Alin and Sakhalin areas from subduction-modifiedlithospheric mantle into mid-ocean ridge basalt (MORB)-sourceasthenosphere as spreading in the Sea of Japan progressed. Mid-Miocene–Pliocene(14–5 Ma) lavas, erupted following the opening of theSea of Japan, include alkaline and sub-alkaline basalts withwide ranges in trace-element abundances, varying between twodistinct end-members: (1) volumetrically minor alkaline basaltswith Zr–Nb and Sr–Nb–Pb isotope compositionssimilar to asthenosphere-derived, intra-plate–hotspotbasalts from eastern China; (2) more abundant, lithosphere-derived,low-alkali tholeiites depleted in HFSE. The similarity of isotopicsignatures coupled with systematically different rare earthelement (REE) abundances in the Mid-Miocene–Pliocene andChinese basalts are best modeled by similar extents of meltingof spinel lherzolite and garnet lherzolite, respectively. TheMid-Miocene–Pliocene alkali basalts were generated bysmall degrees of partial melting of hot asthenosphere beneatha thin lithospheric lid; the thin lithospheric mantle beneaththe Sikhote-Alin and Sakhalin region resulted from heating andextension associated with the opening of the Sea of Japan. KEY WORDS: north-eastern Eurasian margin; Sikhote-Alin–Sakhalin; Japan Sea opening; subcontinental lithosphere; asthenosphere  相似文献   

CEMPS: A prototype spatial decision support system to aid in planning emergency evacuations     

MICHAEL PIDD  RICHARD EGLESE  F NISHAKUMARI DE  SILVA 《Transactions in GIS》1996,1(4):321-334

CEMPS is a prototype spatial decision support system which links the topographical support and analysis provided by a geographic information system, ARC/INFO, with the ability to simulate the dynamics of an evacuation process. CEMPS has been designed to enable emergency planners to experiment with different emergency evacuation plans in order to devise a plan which meets their requirements. ARC/INFO is used to parameterize a dynamic simulation with topographical information and to display its results. The prototype runs on a Sun SPARCStation cluster but could be modified to run on other hardware and software.  相似文献   

Raft-like Metabasaltic Inclusions in the Fongen-Hyllingen Layered Intrusive Complex, Norway, and their Implications for Magma Chamber Evolution     

HABEKOST  ELLEN M.; WILSON  J. RICHARD 《Journal of Petrology》1989,30(6):1415-1441

The Hyllingen Series comprises the southern part of the Caledoniansynorogenic Fongen- Hyllingen layered mafic intrusion, whichoccupies an area of 160 km², southeast of Trondheim, Norway.Large, raft-like inclusions form an important part of the HyllingenScries. Most of these are of fine-grained, equigranular rocksof basaltic composition with lithologies matching those of theadjacent country rocks. The rafts, which compose up to 22% ofthe lower part of the Hyllingen Series, are broadly concordantwith modal layering in the host gabbroic rocks. Individual bodiescan be up to 1500 m long and over 100 m thick. Some of the raftsare branching, and appear locally to form a threedimensionalnetwork. Impact structures are associated with small metabasicinclusions but not with the large rafts. The Hyllingen magma chamber is believed to have developed asa southerly expanding, thin wedge, forming the upper part ofthe Fongen chamber. The magma was compositionally zoned andcrystallized along the inclined floor of the wedge-shaped chamber.The wedge expanded as a result of the influx of dense, primitivemagma in the northern part of the chamber. The highly evolvedmagma at the top of the chamber penetrated along fractures inthe roof and spread laterally to form sill-like bodies. Theroof zone consisted of a network of veins and sills penetratingan interconnected framework of metabasic hornfels. Continuedcrystallization at the floor, while the magma chamber expanded,finally resulted in the interconnected rafts being engulfedby the crystallization front. Fragments detached from the roofsank to the floor to cause the observed impact structures. Thelarge, raft-like, fine-grained, granular, gabbroic bodies areconsidered to be in situ country rock inclusions. Reprints available from J. R. Wilson  相似文献   

AUTOMATIC EDITING OF NOISY SEISMIC DATA1     

RICHARD G. ANDERSON  GEORGE A. McMECHAN 《Geophysical Prospecting》1989,37(8):875-892

Seismic data often contain traces that are dominated by noise; these traces should be removed (edited) before multichannel filtering or stacking. Noise bursts and spikes should be edited before single channel filtering. Spikes can be edited using a running median filter with a threshold; noise bursts can be edited by comparing the amplitudes of each trace to those of traces that are nearby in offset-common midpoint space. Relative amplitude decay rates of traces are diagnostic of their signal-to-noise (S/N) ratios and can be used to define trace editing criteria. The relative amplitude decay rate is calculated by comparing the time-gated trace amplitudes to a control function that is the median trace amplitude as a function of time, offset, and common midpoint. The editing threshold is set using a data-adaptive procedure that analyses a histogram of the amplitude decay rates. A performance evaluation shows that the algorithm makes slightly fewer incorrect trace editing decisions than human editors. The procedure for threshold setting achieves a good balance between preserving the fold of the data and removing the noisiest traces. Tests using a synthetic seismic line show that the relative amplitude decay rates are diagnostic of the traces’S/N ratios. However, the S/N ratios cannot be accurately usefully estimated at the start of processing, where noisy-trace editing is most needed; this is the fundamental limit to the accuracy of noisy trace editing. When trace equalization is omitted from the processing flow (as in amplitude-versus-offset analysis), precise noisy-trace editing is critical. The S/N ratio of the stack is more sensitive to type 2 errors (failing to reject noisy traces) than it is to type 1 errors (rejecting good traces). However, as the fold of the data decreases, the S/N ratio of the stack becomes increasingly sensitive to type 1 errors.  相似文献   

Contact aureoles as constraints on regional P-T trajectories: an example from the Northern Alabama Piedmont, USA   总被引：1，自引：0，他引：1  

RICHARD G. GIBSON  J. A. SPEER 《Journal of Metamorphic Geology》1986,4(3):285-308

Abstract Contact aureoles of plutons emplaced into regionally metamorphosed terranes can provide indicators of physical conditions along a portion of regional metamorphic P-T trajectories, thereby allowing reconstruction of more complete P-T loops than would be otherwise possible. In the Northern Alabama Piedmont of the southern Appalachians, Wedowee Group metapelites preserve evidence for two regional metamorphic phases overprinted by contact metamorphism adjacent to the Blakes Ferry Trondhjemite. Textural evidence indicates that an early bt+st+grt assemblage was replaced by bt+chl+grt during the latter stages of regional metamorphism. Changes in AKFM topology, complex Fe-Mg-Ca garnet zoning, and the latestage appearance of epidote indicate that a sequence of continuous reactions (bt+st = grt+ ms followed by chl+ms+Ca-grt+Ca-pl=bt+ (Fe+Mg)-grt+ep) occurred in response to increasing pressure and resulted in the observed changes in mineral assemblage. Pl-ms-bt-grt thermobarometry indicates conditions of 580° 65°C, 8.5±0.8 kbar for equilibration of grt+ bt+chl. Pluton emplacement, subsequent to penetrative deformation, caused textural annealing and mineral re-equilibration by the continuous reaction bt+(Fe+Mg)-grt+ep = chl+ms+Ca-grt+Ca-pl within 50 m of the pluton. Conditions of 510±65°C, 5-7 kbar are inferred. A reconstructed P-T trajectory for this area is characterized by (1) early moderate- T , moderate- P metamorphism; (2) an increase in P to approximately 8.5 kbar; and (3) decompression and slight cooling prior to pluton emplacement. The compressional phase of this path is interpreted to result from underthrusting of the Wedowee metasediments to mid-crustal levels during Palaeozoic crustal thickening. Late-stage decompression prior to intrusion records uplift of these rocks in response to movement on structurally lower thrusts.  相似文献   

The effect of ductile deformation on the kinetics and mechanisms of the aragonite-calcite transformation   总被引：2，自引：0，他引：2  

ELEANOUR SNOW  RICHARD A. YUND 《Journal of Metamorphic Geology》1987,5(2):141-153

Abstract The effect of ductile deformation (dislocation creep) on the kinetics of the aragonite-calcite transformation has been studied at 1 atm (330° C and 360° C) and 900-1500 MPa (500° C) using undeformed and either previously or simultaneously deformed samples (500° C and a strain rate of 10^-6 s). Deformation enhances the rate of the transformation of calcite to aragonite, but decreases the rate of transformation of aragonite to calcite. The difference results from a dependence of transformation rate on grain size, coupled with a difference in the accommodation mechanisms, climb versus recry-stallization, of these minerals during dislocation creep. Dislocation climb is relatively easy in calcite and thus plastic strain results in high dislocation densities without significant grain size reduction. The rate of transformation to aragonite is enhanced primarily because of the increase in nucleation sites at dislocations and subgrain boundaries. In aragonite, on the other hand, dislocation climb is difficult and thus plastic strain produces extensive dynamic recry-stallization resulting in a substantial grain size reduction. The transformation of aragonite is inhibited because the increase in calcite nucleation sites at dislocations and/or new grain boundaries is more than offset by the inability of calcite to grow across high angle grain boundaries. Thus the net effect of ductile deformation by dislocation creep on the kinetics of polymorphic phase transformations depends on the details of the accommodation mechanism.  相似文献   

Contained (reflected) turbidity currents from the Middle Ordovician Cloridorme Formation, Quebec, Canada: an alternative to the antidune hypothesis   总被引：2，自引：0，他引：2  

KEVIN T. PICKERING  RICHARD N. HISCOTT† 《Sedimentology》1985,32(3):373-394

The parautochthonous Cloridorme Formation is a syn-orogenic flysch succession that was deposited in an elongate foredeep basin as mainly lower middle-fan, outer-fan, and basin-floor deposits. The basin-floor deposits (about 1.5 km thick) are confined to members β1, β2 and γ1, and are characterized by graded, thick (1–10 m) mud-rich calcareous greywacke beds previously interpreted as deposits of concentrated, muddy, unidirectional turbidity currents that locally generated backset (antidune) lamination in internally stratified flows. The dominant flow directions were from east to west, but west to east transport also occurred, as seen in the orientation of ripples, climbing ripples, flutes, consistently overturned flames, and grain imbrication. We believe that the flows that deposited these thick calcareous greywacke beds reversed by roughly 180° one or more times during deposition of the lower sandy part of the beds. Flow reversals are consistent with the sharp grain-size breaks and mud partings within sandy divisions. Measurement of grain fabric relative to stratification in the most celebrated ‘antidune’ bedforms indicates flow from west to east; thus, the bedforms were produced by west-to-east migration of megaripples, not by the upcurrent migration of antidunes. The thick muddy beds were deposited by large-volume, muddy flows that were deflected and reflected from the side slopes and internal topographic highs of a confined basin floor, much like the ‘Contessa’ and similar beds of the Italian Apennines. Large quantities of suspended mud were ponded above the irregular basin floor and settled to produce the thick silty mudstone caps seen on each bed. Because of their mode of emplacement, we propose that these beds be called contained turbidites.  相似文献   

Long-Term Evolution of Fluid-Rock Interactions in Magmatic Arcs: Evidence from the Ritter Range Pendant, Sierra Nevada, California, and Numerical Modeling     

HANSON  R. BROOKS; SORENSEN  SORENA S.; BARTON  MARK D.; FISKE  RICHARD S. 《Journal of Petrology》1993,34(1):23-62

A record of > 100 million years of fluid flow, alteration,and metamorphism in the evolving Sierra Nevada magmatic areis preserved in metavolcanic rocks of the Ritter Range pendantand surrounding granitoids. The metavolcanic rocks consist of:(1) a lower section of mostly marine volcaniclastic rocks, lavas,and intercalated carbonate rocks that is Triassic to Jurassicin age, and (2) an upper section comprising a subaerial caldera-fillcomplex of mid-Cretaceous age. Late Cretaceous high-temperaturecontact metamorphism (2 kbar, >450–500C) occurredafter renewed normal faulting along the caldera-bounding faultsystem juxtaposed the two sections. The style and degree of alteration and ¹⁸O values differ amongthe rocks of the upper and lower sections and the granitoids.Rocks of the lower section show pervasive lithologically controlledalkali alteration, local Mn and Mg enrichment, and oxidation.Some ash flow tuffs now contain up to 10% K²O by weight. Therocks of the upper section show lesser extents of alkali alteration.Granitoids that cut both sections are generally unaltered. Mostmetavolcanic rocks of the lower section have high ¹⁸O values(+ 11 to + 16%; whole rock and quartz phenocrysts); however,lower-section rocks within the caldera-bounding fault systemhave low ¹⁸O values of + 4 to +7. The metavolcanic rocks ofthe upper section also have low ¹⁸O values of + 2 to + 7. Granitoidshave ¹⁸O values of + 7 to + 10, typical of unaltered Sierrangranitoids. The lower section contains discontinuous veins ofhigh-temperature (450–500C) calc-silicate minerals. Theseveins are typically <5 m long, do not cross intrusive contacts,and postdate the pervasive alkali alteration. Late veins aretypically > 10 m long, formed at temperatures of less than450–500C, and cross intrusive contacts. Veins have similar¹⁸O values to those of the local host rocks. The nature of the alteration and the high oxygen isotopic valuesof the rocks of the lower section indicate that these rocksinteracted extensively with seawater at temperatures <300C,probably in superposed marine hydrothermal systems associatedwith coeval volcanic centers. Metavolcanic rocks of the uppersection evidently interacted with meteorie waters, probablyin a hydrothermal system associated with the Cretaceous caldera;rocks of the lower section that were adjacent to the calderawere also affected by this alteration. The preservation of thesignatures of these earlier events, the nature of the earlyveins, and results from numerical models of hydrothermal flowthat include fluid production indicate that during progradecontact metamorphism, the rocks of the pendant primarily interactedwith locally derived fluids. Fluid flow was predominantly upwardand away from intrusive contacts and down-temperature. Permeabilitiesare estimated to have been between 0•1 and 1µD, whichis that necessary for maintenance of lithostatic fluid pressures.In hydrothermal models with such permeabilities, large-scalecirculation of meteoric fluids develops after prograde metamorphismceases. The nature of the late veins in the Ritter Range pendantsuggests that such a flow pattern evolved only after the pendantand granitoids had cooled below 450–500C. The long-termhistory of alteration documented in the Ritter Range pendantis probably typical of wall rocks in most batholiths *Present address: Department of Geosciences, University of Arizona, Tucson, Arizona 85721  相似文献   

Testing the case for a Middle Pleistocene Scandinavian glaciation in Eastern England: evidence for a Scottish ice source for tills within the Corton Formation of East Anglia, UK   总被引：1，自引：0，他引：1  

JONATHAN R. LEE  JAMES ROSE  JAMES B. RIDING  BRIAN S. P. MOORLOCK  RICHARD J. O. HAMBLIN 《Boreas: An International Journal of Quaternary Research》2002,31(4):345-355

The provenance of the Happisburgh Till and Corton Till of the Corton Formation is investigated using erratic clast lithologies and allochthonous palynomorphs to test whether the long held assumption that they were deposited by ice that originated in Scandinavia is valid. The results show a wide range of lithologies including Carboniferous Limestone and Coal Measures, and Permian Magnesian Limestone that are not found in Scandinavia, and an absence of distinctive Scandinavian material such as rhomb porphyry and larvikite. Lithologies found indicate deposition by an ice sheet which flowed southwards into north-east East Anglia from central and southern Scotland eroding and transporting materials derived from outcrops in these areas and from eastern England and the western margins of the southern North Sea Basin. It is concluded that the long held assumption that the Happisburgh Till and Corton Till of the Corton Formation were deposited by a Scandinavian ice sheet is erroneous and that they were instead deposited by Scottish ice.  相似文献   

JURA SEPARATISM IN SWITZERLAND. By John R.G. Jenkins     

RICHARD V. WELCH 《New Zealand geographer》1989,45(2):94-95

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