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51.
Ohne Zusammenfassung 相似文献
52.
Wilckens Rudolf Leutelt L. Rüger W. Salomon C. W. Kockel Leuchs 《International Journal of Earth Sciences》1930,21(1):71-77
Ohne Zusammenfassung 相似文献
53.
54.
W. Salomon 《International Journal of Earth Sciences》1928,19(6):499
Ohne ZusammenfassungBd. XIX, S. 387. 相似文献
55.
W. Salomon Wilckens Steinmann Wilhelm Salomon Donath 《International Journal of Earth Sciences》1928,19(5):425-432
Ohne Zusammenfassung 相似文献
56.
Erzinger Jörg Hinz Karl Sibuet Jean-Claude Talwani Manik 《Marine Geophysical Researches》1998,20(4):251-252
Marine Geophysical Research - 相似文献
57.
Jean-Claude Vannay Zachary D. Sharp Bernhard Grasemann 《Contributions to Mineralogy and Petrology》1999,137(1-2):90-101
Inverted metamorphic field gradients are preserved in two amphibolite facies metapelitic sequences forming the crystalline
core zone of the Himalayan orogen in the Sutlej valley (NW India). In the High Himalayan Crystalline Sequence (HHCS), metamorphic
conditions increase upwards from the staurolite zone at the base, through the kyanite-in and sillimanite-in isograds, finally
to reach partial melting conditions at the top. The structurally lower Lesser Himalayan Crystalline Sequence (LHCS) shows
a gradual superposition of garnet-in, staurolite-in and kyanite + sillimanite-in isograds. Although phase equilibria constraints
imply inverted temperature field gradients in both units, garnet-biotite (GARB) rim thermometry indicates final equilibration
at a nearly uniform temperature around T ≈ 600 °C across these sequences. The P-T path and garnet zoning data show that this apparent lack of thermal field gradient is mainly the consequence of a resetting
of the GARB equilibria during cooling. In order to constrain peak temperature conditions, 20 samples along the studied section
have been analysed for oxygen isotope thermometry. The isotopic fractionations recorded by quartz-garnet and quartz-aluminosilicate
mineral pairs indicate temperatures consistent with phase equilibria and P-T path constraints for metamorphic peak conditions. Together with barometry results, based on net transfer continuous reactions,
the oxygen isotope thermometry indicates peak conditions characterized by: (1) a temperature increase from T ≈ 570 to 750 °C at a nearly constant pressure around P ≈ 800 MPa, from the base to the top of the HHCS unit; (2) a temperature increase from T ≈ 610 to 700 °C and a pressure decrease from P ≈ 900 to 700 MPa, from the base to the top of the LHCS metapelites. Oxygen isotope thermometry thus provides the first quantitative
data demonstrating that the Himalayan inverted metamorphism can be associated with a complete inversion of the thermal field
gradient across the crystalline core zone of this orogen.
Received: 1 April 1999 / Accepted: 12 July 1999 相似文献
58.
Using data from glacial geomorphology, tephra–soil stratigraphy and mineralogy, palynology, and radiocarbon dating, a sequence of glacial and bioclimatic stades and interstades has been identified for the last ca. 50000 yr in the Ruiz-Tolima massif, Cordillera Central, Colombia. Six Pleistocene cold stades separated by warmer interstades occurred: before 48000, between 48000 and 33000, between 28000 and 21000, from ≥16000 to ca. 14000, ca. 13000–12400, and ca. 11000–10000 yr BP. Although these radiocarbon ages are minimum-limiting ages obtained from tephra layers on top of tills, the tills are not significantly older because most are bracketed by dated tephra sets in measured stratigraphic sections. Two minor moraine stages likely reflect glacier standstill during cold intervals ca. 7400 yr BP and slightly earlier. Finally, glaciers readvanced between the seventeenth and nineteenth centuries. In contrast to the ice-clad volcanoes of the massif, ca. 34 km2 in area above an altitude of ca. 4800 m, the ice cover expanded to 1200 km2 during the Last Glacial Maximum (LGM) and was still 800 km2 during Late-glacial time (LGT). Glacier reconstructions based on the moraines suggest depression of the equilibrium line altitude (ELA) by ca. 1100 m during the LGM and 500–600 m during LGT relative to the modern ELA, which lies at ca. 5100 m in the Cordillera Central. Glaciers in this region apparently reached their greatest extent when the climate was cold and wet, e.g. during stades corresponding to Oxygen Isotope Stage 3; glaciers were still expanding during the LGM ca. 28000–21000 yr BP, but they shrank considerably after 21000 yr BP because of greatly reduced precipitation. © 1997 John Wiley & Sons, Ltd. 相似文献
59.
Jean-Claude Thouret Jean-François Oehler Avijit Gupta Akhmad Solikhin Jonathan N. Procter 《Bulletin of Volcanology》2014,76(10):1-26
Erosion processes on active volcanoes in humid climates result in some of the highest sediment yields on Earth. Episodic sediment yields after large eruptions have been evaluated, but not the long-term and continuous patterns on persistently active volcanoes. We have used high-spatial resolution satellite imagery and DEMs/DSMs along with field-based geologic mapping to assess accurately sediment budgets for the active Semeru Volcano in Java, Indonesia. Patterns of aggradation and degradation on Semeru differ from that of other active volcanoes because (1) both episodic pyroclastic density currents (PDC) and continuous supplies of tephra generate pulses of sediment, (2) sediment is transferred via cycles of aggradation and degradation that continue for >15 years in river channels after each PDC-producing eruption, and (3) rain-triggered lahars remove much greater material than fluvial transport during long, intense rainfall events. The geomorphic response of two of Semeru’s rivers to volcanic sediment migration indicates that (1) each river experiences alternating aggradation and degradation cycles following PDC-producing eruptions and (2) spatial patterns of sediment transfer are governed by geomorphic characteristics of the river reaches. Usually high degradation in the steep source reach is followed by a long bypassing middle reach. Aggradation predominates in the depositional reaches further down valley on the ring plain. Average sediment yields (103–105 t/km2/year) at persistently active volcanoes are two to three orders of magnitude lower than sediment yields after large and infrequent eruptions, but the continuous and steady sediment transfer in rivers removes more sediment on a mid-term (10 years) to long-term (30 years) basis. In contrast to the trend observed on composite cones after large and infrequent eruptions, decay of sediment yields is not exponential and river channels do not fully recover at steadily active volcanoes as episodic inputs from BAF eruptions, superimposed on the background remobilization of daily tephra, have a greater cumulative effect. 相似文献
60.
Giuliano Milana Paola Bordoni Fabrizio Cara Giuseppe Di Giulio Salomon Hailemikael Antonio Rovelli 《Bulletin of Earthquake Engineering》2014,12(5):2195-2209
Strong ground motions recorded on the sedimentary deposits of the Po River alluvial plain during the Emilia (Northern Italy) Mw 5.7 earthquake of May 29, 2012 are used to assess the vertical profile of shear-wave velocity above the limestone basement. Data were collected by a linear array installed for site effect studies after the Mw 5.9 mainshock of May 20, 2012. The array stations, equipped with both strong and weak motion sensors, are aligned in the South–North direction, at distances ranging from 1 to 26 km from the epicenter. The vertical components of ground motion show very distinctive, large-amplitude, low-frequency dispersive wave trains. Wavelet analysis yields group-velocity dispersion curve in the 0.2–0.7 Hz frequency band. The availability of a long ambient noise record allows estimates of the site resonance frequency along with its stability among stations. The joint inversion of dispersion of surface waves and ellipticity curves derived from ambient noise H/V allows extending investigations down to the sediment-limestone interface, at a depth of about 5,000 m. Our results add new information about the velocity structure at a scale that is intermediate between the local scale already investigated by other authors with small-aperture arrays using ambient noise and the regional scale inferred from modeling of seismogram waveforms recorded at hundreds of kilometers from the source. 相似文献