共查询到20条相似文献，搜索用时 31 毫秒
1.
2.
3.
4.
S. I. Sherman 《Geotectonics》2009,43(2):100-114
The further development of Peyve’s concept of deep faults in the Earth’s crust and brittle part of the lithosphere is discussed. Three aspects are accentuated in this paper: (1) the modern definition of the term deep fault; (2) the parameters of deep faults as ruptures of the geological medium and three-dimensional, often boundary, geological bodies; and (3) reactivation of deep faults, including the development of this process in real time. Peyve’s idea of deep faults readily fitted into the concept of new global tectonics (plate tectonics). This was facilitated, first of all, by the extensive efforts made to elaborate Peyve’s ideas by a large group of researchers at the Geological Institute of the Russian Academy of Sciences (GIN RAS) and other scientists. At present, the term deep fault has been extended and transformed to cover three-dimensional geological bodies; the geological and geophysical properties and parameters of these bodies, as well as their reactivation (recurrent activation) in real time, have been studied. 相似文献
5.
R. L. Stanton 《Australian Journal of Earth Sciences》2013,60(5):625-641
Some 65 years ago, C. E. Tilley, in his 1950 Presidential Address to the Geological Society of London, brought into sharp focus the then perhaps-not-fully-recognised problem of the origin of what he termed the ‘orogenic andesites’—and, in particular, their commonly constituent calc-alkaline lineage of lavas and pyroclastic materials. In spite of much investigation and progress since, the problem remains not fully resolved. The two most conspicuous features of such orogenic—i.e. island arc—volcanism are its copious, explosive, degassing and, as Tilley noted, its copious development of andesites and their more felsic associates. If these rock types were derived from basalt, the principal relevant changes in major element composition are reductions in Fe, Ca and Mg, and increases in Si, Al and (Na + K). Four principal mechanisms for inducing these changes have been proposed: (1) magmatic differentiation induced by fractional crystallisation, (2) magma mixing, (3) partial melting of an ultramafic-derived basaltic parent, and (4) crustal contamination. A fifth postulate—long recognised but only occasionally seriously considered—is that loss in the volatile phase during eruption and later degassing may make a significant contribution to the overall process. On the basis that Tilley's (and others’) orogenic basalt–andesite–dacite–rhyolite series constitutes a linear arrangement on the conventional FeOt–MgO–(Na2O + K2O) diagram it is shown on numerical grounds that fractional crystallisation alone cannot account for the observed compositional trend—that, while accumulates are neither uncommon nor insubstantial in amount in modern arcs, they are olivine-rich, not magnetite-rich, and that numerical, petrological and field evidence indicates that the high oxidation/magnetite subtraction hypothesis of orogenic andesite genesis can no longer be seriously entertained. The partial melting hypothesis encounters contrary numerical evidence, closely analogous with that adduced for fractional crystallisation. Magma mixing eventually encounters the difficulty of the nature of the felsic material required for rhyolite formation, and assimilation of the preservation of primitive isotope ratios as lava evolution progresses. A fifth mechanism—volatile loss—may make a significant contribution to the relevant compositional change, perhaps in combination with one or more of the other proposed processes. Geochemical, petrological and field evidence pertaining to this is reviewed and examined, and it is postulated that indeed a combination of fractional crystallisation as the principal mechanism, volatile loss as a contributing factor, provides a plausible process. A case is made for an exploratory experimental investigation of the possibility of significant loss in a gas/vapour phase. 相似文献
6.
7.
The age of formation of the Lapstone Monocline has been long considered to be late Pliocene/early Pleistocene (the Kosciusko Uplift) but it is now generally thought to be much older. Palaeomagnetic data from haematite‐rich beds within the Hawkesbury Sandstone on and about the monocline indicate that it formed before the oldest haematite was introduced to these beds. The age of this oldest haematite is 15 ± 7 Ma. On the basis of these data, the age of the monocline is unlikely to be less than 8 Ma, probably exceeds 15 Ma, and could be older than 22 Ma. 相似文献
8.
9.
10.
P. Yu. Petrov 《Lithology and Mineral Resources》2018,53(5):417-429
Analysis of modern paleontological, isotope-geochemical, and paleotectonic data on Vendian rocks in the Patom Basin (Siberia) is presented. The paper discusses depositional settings and features of the specifics of sedimentogenesis of the Barakun carbonate–terrigenous formation, which matches the lower strata of postglacial deposits of the Dal’nyaya Taiga Group. It is shown that formation of the transgressive Barakun Formation was governed by relatively deep-water (below the storm wave base) distal settings of a low-angle (about 1°) homoclinal ramp. Its formation was related to a more intense sagging of the northeastern part of the Ura Uplift. The formation of breccias and intrusions was fostered by high seismic activity of the paleobasin recorded in plastic deformations along with liquefaction and fluidization of sedimentary beds. The constant seismic destabilization of bottom beds provoked small but frequent landslides without the formation of turbidite flows. The continuous dislocation of sediments toward the depocenter actively governed specifics of the ramp architecture. The unusual behavior of sediments during their long-term thixotropic residence could be related to a high content of organic matter, processes of methanogenesis and, probably, dissemination of gas hydrate compounds. 相似文献
11.
《Applied Geochemistry》1997,12(1):97-103
Analyses for δ34S of 13 bedded, marine anhydrite samples from the “C” anhydrite member of the Red River Formation (Upper Ordovician) in the North Dakota portion of the Williston basin represent an addition of δ34S data to a portion of the S isotope age curve with few data. Previously published estimates of δ34S for Upper Ordovician marine sulfates apparently are limited to 4 samples from the Saskatchewan portion of the same basin. An adjusted mean value of +25.5‰ was calculated for all known Upper Ordovician δ34S determinations. This value is approximately 2 to 3‰ lighter than the previous estimate, which suggests that δ34S of the world ocean during the Upper Ordovician may have been lighter than previously thought. However, because all δ34S data are from one sedimentary basin, additional S isotopic data from several globally-distributed evaporite basins are needed to evaluate this hypothesis and further constrain δ34S for the Upper Ordovician. Similar re-examination of other portions of the S isotope age curve with limited amounts of data may increase our understanding of the secular variation in δ34S. 相似文献
12.
Two New“Notostracans”,Chenops gen.nov.and Jeholops gen.nov. (Crustacea:Branchiopoda:?Notostraca) from the Yixian Formation,Northeastern China 总被引：1，自引：1，他引：0
<正>The Early Cretaceous Jehol biota of northeastern China contains a diverse group of notostracans, including two genera,Chenops and Jeholops,described here.Chenops is characterized by a combination of an ovate carapace,narrow anal plate,equant distal endites and endopod on the anterior thoracic limbs.In addition to the new species,Chenops yixianensis,the genus also provisionally includes Prolepidurus oblongus Oleynikov, 1968.Jeholops,however,is monotypic,represented by the new species Jeholops hongi.It is characterized by a combination of kazacharthran and notostracan features unique to this taxon.Both new genera are provisionally placed in the taxon Notostraca.More detailed work exploring the morphology of exceptionally-preserved branchiopod crustaceans is needed.The difficulties in placing fossil notostracans into a phylogenetic framework are discussed. 相似文献
13.
14.
15.
16.
The premise of the Wilson et al. comment is that the Ti-in-quartz solubility calibration (Thomas et al. in Contrib Mineral
Petrol 160:743–759, 2010) is fundamentally flawed. They reach this conclusion because P–T estimates using the Ti-in-quartz calibration differ from their previous interpretations for crystallization conditions of
the Bishop and Oruanui rhyolites. If correct, this assertion has far-reaching implications, so a careful assessment of the
Wilson et al. reasoning is warranted. Application of the Ti-in-quartz calibration as a thermobarometer in rutile-free rocks
requires an estimation of TiO2 activity in the liquid ( (liquid–rutile); referenced to rutile saturation) and an independent constraint on either P or T to obtain the crystallization temperature or pressure, respectively. The foundation of Wilson et al.’s argument is that temperature
estimates obtained from Fe–Ti oxide thermometry accurately reflect crystallization conditions of quartz in the two rhyolites
discussed. We maintain that our experimental approach is sound, the thermodynamic basis of the Ti-in-quartz calibration is
fundamentally correct, and our experimental results are robust and reproducible. We suggest that the reason Wilson et al.
obtain implausible pressure estimates is because estimates for T and they used as input values for the Ti-in-quartz calibration are demonstrably too high. Numerous studies show that Fe–Ti oxide
temperature estimates of some rhyolites are substantially higher than those predicted by well-constrained phase equilibria.
In this reply, we show that when reasonable input values for T and (liquid–rutile) are used, pressure estimates obtained from the Ti-in-quartz calibration are well aligned with phase equilibria
and essentially identical to melt inclusion volatile saturation pressures. 相似文献
17.
18.
19.
This paper studies the basis and nature of the long-term factors that may have influenced the electoral behavior of St. Petersburgers between 1989 and 1995 from the perspective of geography. Our analysis shows two distinct periods in St. Petersburgs recent electoral history marked by differing behavioral motivations of voters in the city. The first period was marked by only one ideological cleavage between marketers and hard-liners. In 1993 protest motivation managed to erode the predominance of ideology as the determining variable in voting behavior, and began to act as a new independent variable. This marked the beginning of the second period. Four major groupings of St. Petersburg electorate are described in terms of the basic ideological cleavages, party affiliations and geographical gravity centers. 相似文献
20.
Geographies of identity theft in the U.S.: understanding spatial and demographic patterns, 2002–2006
Identity theft is among the fastest growing white-collar crimes in the United States, although official recognition of it
as a criminal act is a relatively recent development. Utilizing theoretical framework established in crime geography, GIS
mapping and spatial statistics are employed to conduct a spatial analysis of identity theft in the U.S. from 2002 to 2006.
Distinct regional variations, such as high rates in the western and southwestern states, and low rates in New England and
the central plains states, are identified for identity theft. Significant spatial patterns of identity theft victims alongside
social demographic variables are also revealed in order to better understand the regional patterns that may suggest underlying
social causes contributing to identity theft. Potential social variables, such as race/ethnicity and urban–rural populations,
are shown to have similar patterns that may be directly associated with U.S. identity theft victims. 相似文献