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Determination of the age of rocks by whole rock Sm-Nd isochron method has several limitations imposed by petrogenetic processes.
If the age of the rocks can be determined by other independent methods, the Sm-Nd system provides a wealth of information
to understand crustal genesis. Sm-Nd isotopic studies of metabasaltic rocks of the Archaean Kolar and Ramagiri Schist belts
in the eastern Dharwar Craton indicate that the system was disturbed by postmagmatic fluid alteration processes associated
with terrane accretion. 相似文献
2.
Assessment of Planetary Boundary-Layer Schemes in the Weather Research and Forecasting Mesoscale Model Using MATERHORN Field Data 总被引：1，自引：0，他引：1
3.
Controls on early post-rift physiography and stratigraphy, lower to mid-Cretaceous, North Viking Graben, Norwegian North Sea 总被引：1，自引：0，他引：1
The transition from syn- to post-rift is often poorly constrained and in contrast to syn-rift systems, the controls on the development of post-rift systems are poorly understood. This paper documents the timing of the post-rift onset and discusses the controls that affected the subsequent development of the post-rift infill of the North Viking Graben using an integration of seismic and well data. The study enhances our understanding of post-rift system development in general and provides an analogue for other post-rift systems. Within the early post-rift infill of the North Viking Graben five key seismic surfaces were mapped [Base Cretaceous Unconformity (BCU), Intra-Aptian, Top Albian, Top Cenomanian and Top Turonian], which divide the post-rift interval into four key seismic stratigraphic units (K1–K4). The BCU has an intra-Volgian age on the basin slopes and shelfal and terrace areas and is interpreted to mark the end of rifting in the study area. On the footwall crests adjacent to the graben the BCU represents a complex unconformity from the syn- and post-rift combined, and in the graben it forms a conformable contact. Therefore, the BCU could not be used to date the onset of the post-rift in these locations. The thickness variations and age relationships between the syn-rift stratigraphy and the K-units reveal that the early post-rift infill of the North Viking Graben was dominantly controlled by the significant local syn-rift topography, especially in the K1 and K2 stages. The Cretaceous post-rift stratigraphy was also influenced by relative base level, which controlled the sediment source areas, the development of the basin geometry itself and subsequently the style of sediment deposition in the study area. Regional variations are also recognised in the post-rift stratigraphy although these variances are strongly influenced by the local basin physiography. 相似文献
4.
Ocean Dynamics - Westward propagation and the dynamics of intensification of Lakshadweep low (LL) have been investigated in detail. In this study, it is observed that LL is not propagated westwards... 相似文献
5.
A marble band in the ≈ 2.75 Gyr old Ramagiri schist belt in the Dharwar craton of south India gave a Pb–Pb age of 3.075 ± 0.095 Gyr. The geochemical data, including high Sr and low Ba and Mn indicate seawater origin for the parent rock, and that there was insignificant geochemical exchange between the marble and the surrounding rocks. The calculated initial Nd isotopic composition and μ1 indicate an older continental crustal source for the Nd and Pb. The initial 87 Sr/86 Sr of the marble is 0.70128, which is higher than the calculated mantle value at ≈ 3 Ga. Although pre-3 Gyr old marine carbonate rocks are thought to be buffered by mantle Sr, the Ramagiri marble contains evolved, crustal Sr. Despite this, the marble has the lowest measured 87 Sr/86 Sr among carbonates and represents one of the least radiogenic periods in seawater Sr isotope composition. 相似文献
6.
Daniel D.P. McCarthy Graham S. Whitelaw Scott Anderson Donald Cowan Fred McGarry Anthony Robins Holly L. Gardner Christine D. Barbeau Nadia A. Charania Zachariah General Jeff Liedtke Celine Sutherland Paulo Alencar Leonard J.S. Tsuji 《Geoforum》2012,43(2):305-314
The remote First Nation (FN) communities of the Mushkegowuk Territory on the west coast of James Bay, Ontario, Canada are currently facing increased development pressures and the imposition of a government land use planning process. The land use planning process is mandated in the Far North Act (received Royal Assent on September 23, 2010). There is a need for capacity enhancement for community-based natural resource planning and management in the Territory. A number of frameworks are emerging for addressing change brought on by resource development and building resilience to such change at the community level. Among these include the concept of adaptive capacity. In collaboration with FN community leaders, we explored the use of “collaborative geomatics” tools to foster adaptive capacity. Our action research suggests that collaborative geomatics technologies should enhance the Mushkegowuk First Nations’ adaptive capacity to address environmental and policy change by allowing them to collect and manage data collaboratively (e.g., traditional environmental knowledge, western science) to create opportunities for innovative community development, including natural resource development and management. 相似文献
7.
John K. Zachariah V. Rajamani Gilbert N. Hanson 《Contributions to Mineralogy and Petrology》1997,129(1):87-104
The N–S trending, 2–4 km wide Ramagiri schist belt is made up of three blocks dominated by metavolcanic rocks, separated
and surrounded by granitic rocks of distinct characteristics. The metavolcanic rocks are tholeiitic in composition and are
very similar in their major element composition as well as in their abundances of some trace elements. However, the rare earth
elements (REE) require distinct sources. The rocks of the amphibolite facies eastern block have LREE depleted REE patterns
([Ce/Yb] = 0.7–0.9), requiring derivation from depleted mantle-like sources. The greenschist facies metatholeiitic rocks of
the central block have LREE enriched REE patterns ([Ce/Yb] = 3–6), reflecting the nature of their source(s). The Nd isotopic
data require that the LREE enriched nature could not have been attained significantly prior to its melting. The fine-grained,
upper greenschist facies metatholeiites of the western block have flat to slightly LREE depleted patterns ([Ce/Yb] = 0.8–0.95).
Minor fractional crystallization of rock forming minerals may relate a few samples to each other among samples from each of
the three blocks. Different extents of partial melting of distinct mantle sources have played a dominant role in the generation
of the parent magmas to the central versus eastern and western block metatholeiites.
The geochemical data suggest that the mantle sources were non-lherzolitic, and that these sources may have seen previous episodes
of melt addition and extraction prior to melting that gave rise to the parent melts to the rocks ∼2750 Ma ago. The REE data
indicate that while the sources of the eastern and western block rocks were similar to depleted mantle (ɛNd(
i
) about +2), the source of the central block rocks (ɛNd(
i
) about +3.5) were enriched in large ion lithophile element (LILE)-rich fluids/melts probably derived from subducting oceanic
crust. This and other trace element signatures point to magma extraction in tectonic settings similar to modern island arcs.
Subsequent to magma emplacement and crystallization, all the three suites of rocks were affected by interaction with low-temperature,
crustal derived fluids (ɛNd 2750Ma of about −8 to −12), probably during the accretion of the three blocks of the belt in the present form. The inferred source
characteristics, tectonic setting of magma generation and the crustal fluid processes seem to suggest that Phanerozoic-style
tectonic processes may have been important in the generation of Archean crust in the Dharwar craton.
Received: 31 July 1995 / Accepted: 12 May 1997 相似文献
8.
Babatunde J. Abiodun Zachariah D. Adeyewa Philip G. Oguntunde Ayobami T. Salami Vincent O. Ajayi 《Theoretical and Applied Climatology》2012,110(1-2):77-96
This study investigates the potential impacts of reforestation in West Africa on the projected regional climate in the near two decades (2031–2050) under the SRES A1B scenario. A regional climate model (RegCM3) forced with a global circulation model (ECHAM5) simulations was used for the study. The study evaluates the capability of the regional model in simulating the present-day climate over West Africa, projects the future climate over the region and investigates impacts of seven hypothetical reforestation options on the projected future climate. Three of these reforestation options assume zonal reforestation over West Africa (i.e., over the Sahel, Savanna and Guinea), while the other four assume random reforestation over Nigeria. With the elevated GHGs (A1B scenario), a warmer and drier climate is projected over West Africa in 2031–2050. The maximum warming (+2.5°C) and drying (?2?mm?day?1) occur in the western part of the Sahel because the West Africa Monsoon (WAM) flow is stronger and deflects the cool moist air more eastward, thereby lowering the warming and drying in the eastern part. In the simulations, reforestation reduces the projected warming and drying over the reforested zones but increases them outside the zones because it influences the northward progression of WAM in summer. It reduces the speed of the flow by weakening the temperature gradient that drives the flow and by increasing the surface drag on the flow over the reforested zone. Hence, in summer, the reforestation delays the onset of monsoon flow in transporting cool moist air over the area located downwind of the reforested zone, consequently enhancing the projected warming and drying over the area. The impact of reforesting Nigeria is not limited to the country; while it lowers the warming over part of the country (and over Togo), it increases the warming over Chad and Cameroon. This study, therefore, suggests that using reforestation to mitigate the projected future climate change in West Africa could have both positive and negative impacts on the regional climate, reducing temperature in some places and increasing it in others. Hence, reforestation in West Africa requires a mutual agreement among the West African nations because the impacts of reforestation do not recognize political boundaries. 相似文献
9.
The controls and development of early-post-rift, deep-water depositional systems are poorly understood due to their commonly deeply-buried nature. As a consequence, in the subsurface there is usually a lack of well penetrations and/or weak seismic imaging. At outcrop, early post-rift strata have commonly been deformed beyond reasonable recognition by later inversion tectonics. In contrast to these systems, the North Viking Graben shows a well-imaged Cretaceous early post-rift package with good well control and little effect from inversion. Therefore, this paper examines the early post-rift, deep-water depositional systems of the North Viking Graben to determine the controls on their stratigraphic position, geometry and evolution, and thus provide an analogue for comparable systems. Greater understanding of such systems will allow for the enhanced prediction of reservoir units in the subsurface and development of new play models since post-rift intervals are generally under-explored.The basin configuration inherited by the Cretaceous early post-rift in the northern North Sea was set up by Permo-Triassic and Late Jurassic rifting. In the North Viking Graben this established considerable along-strike variability, resulting in a northern basin segment surrounded by steep slopes and faulted-bounded structural highs and a southern basin segment margined by slopes with noticeably gentler gradients. Associated with the Cretaceous post-rift is an overall transgressional trend, which drowned local source areas, resulting in prevalent carbonate and hemipelagic mudstone deposition in the basins. In the North Viking Graben, the uplifted Oseberg fault-block provided the sub-aerial clastic source area until it was submerged in the early Upper Cretaceous.The early post-rift infill of the North Viking Graben was divided into four key seismic stratigraphic units (K1, K2, K3 and K4) using an integration of seismic and well data. Inside this stratigraphic framework, the depositional systems within each K-unit were resolved from characteristic seismic facies, amplitude anomalies, relationship with adjacent reflections, and geomorphologies. In the northern basin segment, the early post-rift stratigraphy contains basin-floor fans, a channel complex and a shoreline-like geometry, whereas the southern basin segment is solely characterised by hemipelagic and carbonate deposition. This spatial variability indicates that one of the dominant controls on the development of the early post-rift depositional systems in the North Viking Graben was the inherited syn-rift fault-controlled topography. The steep slopes bounding the northern basin segment aided the delivery of sediment from the sub-aerial Oseberg source area to the graben whereas the submerged, gentle slopes in the southern basin segment were relatively sediment-starved.Long- and short-term changes in relative sea-level also heavily influenced the evolution of the early post-rift basin stratigraphy. Short-term relative sea-level fall allowed basin-floor fan emplacement whereas short-term relative sea-level stand-still favoured deposition of a channel complex. Deposition of the shoreface-like geometry is associated with a short-term relative sea-level rise. This temporal difference in the style and scale of the depositional systems is also interpreted to reflect the gradual denudation and drowning of the Oseberg source area. Regional short-term trangressive and anoxic events in the northern North Sea further influenced the early post-rift strata, resulting in the deposition of stratigraphic units that can be correlated across the North Sea. 相似文献
10.
Remote Observation of the Spatial Variability of Surface Waves Interacting With an Estuarine Outflow
Brian K. Haus Rafael J. Ramos Hans C. Graber Lynn K. Shay Zachariah R. Hallock 《Oceanic Engineering, IEEE Journal of》2006,31(4):835-849
This paper explores the application of phased-array high-frequency (HF) radars to identify locations of enhanced local waveheights. Measurements of the near-surface current velocities and waveheights were obtained from HF radars deployed near the mouth of the Chesapeake Bay in the fall of 1997. The radar-derived near-surface velocities were compared with the upper bin (2-m depth) of four upward-looking acoustic Doppler current profilers (ADCPs). The slopes of the linear correlations were close to one and the root-mean-square (rms) differences were similar to previous studies. Significant waveheight (Hs) estimates from both radars were compared with a laser height gauge. The largest differences were observed during low winds due to overestimates at one of the radar stations and during storms when the laser measurement failed. Further analysis focused on the HF radar results from the more reliable of the two sites. The rms difference between this radar and the in situ sensor was 0.29 m. Synoptic observations of Hs over the Chesapeake Bay revealed regions of current-induced wave shoaling and refraction. Hs over the estuarine outflow increased between 19-50% relative to the incident Hs in light onshore winds (~5 m/s). In stronger winds (>10 m/s), Hs also increased by up to 25% when there was a tidal outflow in the surface layer, although the near-surface currents were responding to both the wind and the ebbing tide. Hs was not enhanced when the outflow was below a thicker layer (>5 m) of wind-forced onshore flow 相似文献
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