Estuaries and Coasts - Total biomass of the fiddler crabsUca pugnax andU. minax in fourSpartina marshes in the lower Cape Fear River estuary, North Carolina, declined by 65 to 70% between the... 相似文献
Taking into account the entire spectrum of potential harmonics, equations are developed for the secular motions of the node and pericenter referred to the invariant plane in a two-body problem when one is a sphere and the other a spinning asymmetrical rigid body (e. g., Sun-planet system, or point satellite-planet system). Oblateness precession of satellite orbits and equinoctial precession of planets are shown to be merely opposite extreme cases of the single phenomenon of precession in spin-orbit coupling, in which the determining parameter is the ratio of orbital to spin angular momentum (h0/hs). The critical inclination for apsidal motion also depends on this ratio, varying from 63.43° in the one extreme when (h0/hs)1, to 90° in the opposite extreme when (h0/hs)1. Application is made to the Earth-Sun-Moon system. 相似文献
Tertiary and/or Quaternary tectonic faulting is documented in three areas of southernmost Illinois: the Fluorspar Area Fault Complex (FAFC) in Pope and Massac Counties, the Ste. Genevieve Fault Zone (SGFZ) in Alexander and Union Counties, and the Commerce Fault Zone (CFZ) in Alexander County.
In the FAFC, faults that strike NE and NNE displace Mounds Gravel (late Miocene to early Pleistocene) and, locally, the Metropolis terrace gravel (Pleistocene; pre-Woodfordian). No Woodfordian or younger deposits are deformed. Faults typically outline narrow, linear grabens that formed under tension with a component of strike slip.
North-south to NW-trending vertical faults near the southeast end of the SGFZ displace Eocene sediments. Again, faults outline narrow grabens and show indications of strike slip. Deformed Quaternary sediments have not been observed.
The CFZ, which trends northeast, displaces Mounds Gravel in Illinois and units as young as Peoria Silt (Woodfordian) in Missouri. Quaternary movement has been interpreted as right-lateral strike-slip. The CFZ coincides with a subtle gravity and magnetic lineament and seems to reflect a major feature in the basement. Surface expression in Illinois is subtle, but mafic and ultramafic intrusions, hydrothermal alteration and small faults align with the Commerce geophysical lineament. Earthquake foci in Missouri and Illinois lie on or close to the CFZ; some focal mechanisms fit the fault trend.
Among these structures, only the CFZ exhibits slip that conforms to the current stress field (principal compressive stress axis E-W to ENE-WSW). Possibly, the stress field changed during Neogene time. Alternatively, high fluid pressures or local stress concentrations may have induced slip on less favorably oriented fractures. Tighter constraints are needed on timing, magnitude, and direction of Neogene displacement. 相似文献
More than 99% of mineral inclusions in diamonds from the River Ranch pipe in the Late Archean Limpopo Mobile Belt (Zimbabwe),
are phases of harzburgitic paragenesis, namely olivine (Fo92–93), orthopyroxene (Mg# = 93), G10 garnets and chromites. The diamond inclusion (DI) chemistry demonstrates a limited overlap
with River Ranch kimberlite macrocrysts: the DI garnets are more Ca-undersaturated, and DI spinel and garnet are more Mg-rich.
Most River Ranch diamond inclusions were equilibrated at T = 1080–1320 °C, P = 47–61 kbar, and fO2 between IW and WM buffers. The P/T profile beneath the Limpopo Mobile Belt (LMB) is consistent with a paleo-heat flow of 41–42 mW/m2, similar to calculations for Roberts Victor, but hotter than for the Finsch, Kimberley, Koffiefontein and Premier Mines.
This is ascribed to the younger tectonothermal age of the LMB and its proximity to Late Archean oceans. Like diamond inclusions
from all other kimberlites studied, the River Ranch DI have a lithospheric affinity and therefore indicate that an ancient,
chemically depleted, thick (at least 200 km) mantle root existed beneath the Limpopo Mobile Belt 530–540 Ma ago. The mantle
root might have developed beneath the continental Central Zone of the LMB as early as the Archean, and could be alien to the
overthrust allochthonous sheet of the Limpopo Belt. Oxygen fugacity estimates for diamond inclusions at River Ranch are similar
to other diamondiferous harzburgites beneath the Kaapvaal craton, indicating that the Kaapvaal mantle as a whole was well
buffered and homogeneous with respect to fO2 at the time of peridotitic diamond crystallization.
Received: 11 January 1995 / Accepted: 10 June 1997 相似文献
The terranes which outcrop to the north and south of the westward extension of the Jebha Fault show considerable differences in their nature and structural organisation. The pre-Oligocene basement is composed of synorogenic synclines filled with detrital deposits. In the North, the synclinal troughs are oriented North-South and filled with siliciclastic material. The synclinal structures on top of the western extension of the Jebha Fault are orientated N 140° and are also filled with the same material. South of this westward extension of the Jebha Fault, the orientation of the synclinal structures is north-south; they are filled with bioclastic calcareous material.The synorogenic synclines, situated on top of the Jebha-Arbaoua limit show characteristics of the detached sedimentary cover by their position and orientation. This cover formed the Arbaoua-Jebha lateral ramp during its movement towards the west. Developement of this ramp is explained by the crustal discontinuity inherited from the period of rifting.The resulting palaeomorphological relief allows the difference between the zones situated at each part of the limit to be understood, in particular, it permits the understanding of the differences in the detrital material, in its role as a barrier opposing the arrival of bioclastic calcareous material from the African margin (situated southwards of the limit).The Arbaoua-Jebha lateral ramp appears as a major and original feature of the Rift chain. 相似文献
We have measured the lifetimes of all compact emission features visible on three sets of high time resolution soft X-ray images. The spectrum of lifetimes is found to be heavily weighted toward short lifetimes. The number of features present on the disk which live 2–48 hours is at least ten times as great as the number living more than 48 hours. The distribution of lifetimes can be fit in all three cases by a four-parameter function N(t) = Ns exp(-t/s) + NL exp(-t/L), with
s = 8.7±0.2,
L = 35±4 and Ns 10NL. Features living two days or less have a very broad latitude distribution (Golub et al., 1974, 1975) whereas nearly all longer-lived features are found within 30° of the equator. The growth rates of long-lived vs short-lived points are the same to within 20%, the major difference being that long-lived points continue to grow and generally reach larger sizes.Harvard College Observatory/Smithsonian Astrophysical Observatory. 相似文献
Summary The trends appearing in the annual and seasonal rainfall of Athens were investigated by running 30-year averages. The period used began in 1860 and the data until December 1956 were used. The figures 1–5 show the 30-year running averages curves for each of the four seasons and for the year as a whole. 相似文献
H observations of two-ribbon flares often show secondary brightenings which are not directly spatially connected with the main center of activity but which are correlated in time with the primary impulsive flare. We present here a mechanism which explains these secondary brightenings via the reconnection of magnetic loops which are tied to only one of the two ribbons, in contrast with the loops responsible for the main flare which are tied to both ribbons. The distant footpoint is then interpreted as the site of the secondary brightening. We apply our model to the two-ribbon flare of 17:52 UT, 23 June, 1988, which started during the rocket flight of the Normal Incidence X-ray Telescope.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. Partial support for the National Solar Observatory is provided by the USAF under a Memorandum of Understanding with the NSF. 相似文献