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1.
Three large-scale instrumented waste rock piles were constructed at the Diavik Diamond Mine in the Northwest Territories, Canada. These experimental waste rock piles (test piles) are 15 m high and are part of an integrated field and laboratory research program to characterize and compare low-sulfide waste rock and drainage at various scales. During test pile construction, samples of the <50 mm fraction of waste rock were collected from two types of waste rock that are segregated during mining operations based on S content. The samples were analyzed for S content and particle size distribution. One test pile contained waste rock with an average of 0.035 wt.% S in the <50 mm fraction, within the operational S target of <0.04 wt.% S for the lower S waste rock type. The second test pile contained waste rock with an average of 0.053 wt.% S in the <50 mm fraction, lower than the operational S target of >0.08 wt.% S for the higher S waste rock type. The third test pile has a low permeability till layer and a low sulfide waste rock thermal layer covering a core of waste rock with average 0.082 wt.% S in the <50 mm fraction, which is within the operational S target of >0.08 wt.% S for the higher S waste rock. Particle size distributions for the lower and higher S waste rock are similar, but the higher S waste rock has a higher proportion of fine-grained particles. Sulfur determinations for discrete particle sizes of the <50 mm fraction illustrate higher S concentrations in smaller particles for both the lower S waste rock and the higher S waste rock. Similarly, S concentrations calculated for the >10 m scale, from composite blast hole cuttings, are lower than those calculated for the <50 mm scale. Acid–base accounting using standard methods and site-specific mineralogical information was used to calculate the ratio of neutralization potential to acid generating potential. A comparison of calculation approaches to pH and alkalinity data from humidity cell and test pile effluent suggest that ratios are very sensitive to the calculation method. The preferred calculation method was selected by comparing calculation results to pH and alkalinity data from humidity cell effluent collected over 95 weeks and test pile effluent collected over five field seasons. The preferred acid–base accounting values were obtained by calculating the average neutralization potential divided by the average acid potential of a sample set. This approach indicates that waste rock with >0.05 wt.% S is of uncertain acid-generating potential and effluent data indicate this waste rock generates acidic effluent; whereas lower S waste rock does not produce acidic effluent, consistent with the acid–base accounting predictions.  相似文献   

2.
The coastline along the southern Arabian Gulf between Al Jubail, Kingdom of Saudi Arabia, and Dubai, UAE, appears to have risen at least 125 m in the last 18,000 years. Dating and topographic surveying of paleo-dunes (43–53 ka), paleo-marine terraces (17–30 ka), and paleo-marine shorelines (3.3–5.5 ka) document a rapid, > 1 mm/a subsidence, followed by a 6 mm/a uplift that is decreasing with time. The mechanism causing this movement remains elusive but may be related to the translation of the coastal area through the backbasin to forebulge hinge line movement of the Arabian plate or, alternatively, by movement of the underlying Infracambrian-age Hormuz salt in response to sea-level changes associated with continental glaciation. Independent of the mechanism, rapid and episodic uplift may impact the design of engineering projects such as nuclear power plants, airports, and artificial islands as well as the interpretation of sedimentation and archeology of the area.  相似文献   

3.
《Quaternary Science Reviews》2003,22(10-13):1339-1343
The Wangsan fault is exposed at Kyeongju, Korea. The andesite is unconformably covered by Quaternary alternating conglomerate and sandstone deposits. The unconformity is cut by the thrust fault which displaces a hanging wall block of about 30 m. Exposed at the surface of this fault is a light gray and brown fault gouge, about 40–120 cm thick. In order to test the consistency of ESR ages from a single fault gouge zone, we collected six gouge samples systematically along and across the Wangsan fault. We found that six samples collected from the same gouge zone show consistent ESR date estimates (average 550 ka). Because fault rock is rare along faults in unconsolidated sediments due to low confining stress near the surface, we consider that this fault gouge has been moved up with the hanging wall block along the fault. The estimated average uplift rate of the hanging wall block is about 0.04 cm/year based on the age of the displaced Quaternary deposits (vertical separation; about 20 m) dated by OSL dating methods. The depth of the fault gouge at the time of reactivation, which was estimated from uplift rate and the ESR ages, is about 220 m. Therefore, we conclude that the results of ESR age estimates represent the time of reactivation of the fault gouge at a depth of 220 m in the past during fault movement, because later movements which occurred during uplift near the surface may not have zeroed ESR signals significantly for ESR dating of fault movements.  相似文献   

4.
《Applied Geochemistry》1998,13(5):651-671
Highly saline fluids were encountered during the German Continental Deep Drilling Project (KTB) from depths ranging between 2 and 3 km to about 9 km. The most reliable data were obtained from samples extracted during a long-term pumping test in the 4000-m deep KTB pilot hole. Some 460 m3 Ca–Na–Cl brines with about 68 g l−1 total dissolved solids (TDS) and some 270 m3 associated gases, mainly N2 and CH4 were pumped to the surface from the main fracture system situated near the bottom of the pilot hole. Geochemical and isotopic data support the hydraulic tests which suggest the presence of an open and large fluid reservoir at depth. The pumped fluids from this main fracture system were released from a deep reservoir situated at more than 5500 m depth which is hydraulically connected with the 9101 m deep KTB main hole, drilled some 250 m to the northeast of the pilot hole.While Ca and Sr contents of the extracted brines may be the result of water–rock interaction, Cl is most likely of external origin. The Cl is hypothesized to derive from geotectonic processes rather than to descending infiltration of paleo-seawater (evaporitic brines). The sampled fluids have probably migrated from a deeper reservoir to their present position since the Cretaceous–Tertiary period due to tectonic activity. However, several isotopic studies have identified an admixture of descending paleowaters down to more than 4000 m depth. The high 36Cl/Cl ratio of the fluids sampled during the long-term pumping test point to a host rock highly enriched in U–Th, unlike the sampled KTB country rocks. The fluid reservoir is believed to be in contact with the Falkenberg granite massif situated about 2 km to the E of the KTB holes, capable of supplying sufficient neutron flux for considerable subsurface production of 36Cl. The Na–Cl–(K-, SO4) precursor fluids of the Ca–Na–Cl brines were produced in the course of extensive tectonic processes since the Late Caledonian within the Bohemian Massif.  相似文献   

5.
The Upper Paleozoic section contains a tight gas sandstone reservoir (of 2.75 × 1012 m3) in the Ordos Basin, central China. The measured porosities (< 10%) and permeabilities (generally < 1 mD) are the result of significant mechanical and chemical compaction and precipitation of carbonate, quartz and authigenic clay cements. Fluid inclusion geochemistry and kinetic modeling (generation of gaseous components and δ13C1) were integrated to constrain the timing of gas charge into the tight reservoir. The modeling results indicate that the natural gases in the present reservoir are similar to gases liberated from quartz inclusions in both composition and stable carbon isotope values and also similar to gas generated from Upper Paleozoic coal. The similar geochemistry suggests that an important phase of quartz cementation must have occurred after gas emplacement in the reservoirs during regional uplift at the end of the Cretaceous. The latest carbonate cement, postdating quartz cementation, consumed most of the late CO2 generated from coal at high maturity (RO > 1.7%) and reduced the reservoir quality dramatically. On the contrary, tight sandstones from non-producing areas have fluid inclusions that were trapped in quartz cements much earlier. These data indicate that natural gas migrated into the Upper Paleozoic reservoir when it still retained high porosity and permeability. The reservoir continued to experience porosity and permeability reduction from continued quartz and carbonate cementation after gas charging due to low gas saturation. Comparison of the relative timing of gas charging with that of sandstone cementation can help to predict areas of risk during tight gas exploration and development.  相似文献   

6.
The Qaidam Basin is the largest intermontane basin of the northeastern Tibetan Plateau and contains a continuous Cenozoic sequence of lacustrine sediments. A ~ 1000-m-deep drilling (SG-1) with an average core recovery of ~ 95% was carried out in the depocenter of the Chahansilatu playa (sub-depression) in the western Qaidam Basin, aimed to obtain a high-resolution record of the paleoenvironmental evolution and the erosion history. Stepwise alternating field and thermal demagnetization, together with rock magnetic results, revealed a stable remanent magnetization for most samples, carried by magnetite. The polarity sequence consisted of 16 normal and 15 reverse zones which can be correlated with chrons 1n to 2An of the global geomagnetic polarity time scale. Magnetostratigraphic results date the entire core SG-1 at ~ 2.77 Ma to ~ 0.1 Ma and yielded sediment accumulation rate (SAR) ranging from 26.1 cm/ka to 51.5 cm/ka. Maximum SARs occurred within the intervals of ~ 2.6–2.2 Ma and after ~ 0.8 Ma, indicating two episodes of erosion, which we relate to pulse tectonic uplift of the NE Tibetan Plateau with subsequent global cooling.  相似文献   

7.
The original spectral features of felsic rocks are often intermingled with other surface objects, which results in difficulty of detecting felsic rocks using remote sensing techniques. Few felsic rock indices were proposed and visual interpretation with RGB false color composition is widely used to detect felsic rocks. This paper aims to construct a two-dimensional spectral feature space model to extract felsic rocks using ASTER thermal infrared radiance data. The study area is located in northern Qinghai Province, western China with average altitude of approximately 4200 m. A large number of training pixels of mafic–ultramafic rock, quartz-rich rock, felsic rock, carbonate rock and vegetation were selected from the ASTER images as samples of these surface objects. Then we used a quartz-rich rock index (QI, QI = band14 − 0.844 × band12 − 1.897) and a mafic–ultramafic rock index (MI, MI = 0.915 × band10 − band13 + 1.437) to generate a two-dimensional scatter plot. The plot was named after quartzose–mafic spectral feature space (QMFS). The samples show an approximate triangular shape in the QMFS. Mafic–ultramafic rock, quartz-rich rock and carbonate rock are located in separate locations in the three vertex regions, respectively, while felsic rock is located in the central region of the triangle. Next, we calculated a linear belt of silicate rocks in which silicate rocks vary regularly by using a linear regression analysis in the QMFS. Statistical characteristics of the felsic rock samples are analyzed. Afterwards, a polygon which delineates the distribution of felsic rock samples was constructed from the linear belt of silicate rocks. Then we generated a system of inequalities based on the equations of the edges of the polygon. The application of the inequalities to the ASER images shows a good performance of the QMFS for extracting felsic rocks.  相似文献   

8.
The Southern Alps of New Zealand are part of an active collisional orogen where metamorphism, hydrothermal fluid flow and the formation of orogenic gold deposits are ongoing. The Southern Alps are forming due to transpressional collision between continental crust fragments on the Pacific and Australian tectonic plates. The plate tectonic rates and geometries, the sources of fluid and broad-scale fluid pathways in the hydrogeological system, and the geochemical compositions of the Torlesse Terrane rock that is being advected through the orogen are well defined so that a mass balance of metal mobility during active orogenic processing in the Southern Alps of New Zealand can be calculated. Advection of a 10 km wide × 5 km deep section of Torlesse rock through the orogen at tectonic rates (0.01 m/yr) that is then metamorphosed up to amphibolite facies causes mobilisation of over 11,27 t Au, 10.1 Mt As, 47,000 t Hg, 560,000 t Sb and 14,000 Mt H2O in 1 Myrs. The masses of elements mobilised at the same rate along the length of the Southern Alps (> 200 km) for 5 Myrs would be more than 100 times greater. The metals were mobilised by the metamorphic fluid produced during the orogenic processing of the Torlesse Terrane rocks and the concentrations of Au, As, Hg and Sb in this fluid are calculated to be 0.08, 711, 3, and 40 mg/kg, respectively. The mobilised metals form the orogenic gold deposits that occur in the Southern Alps. Different styles of gold deposits form contemporaneously during the active orogenesis of the Southern Alps, including those with a fluid temperature > rock temperature that may appear to have formed after the peak of metamorphism but are instead just the product hydrothermal fluid mineralising rocks on their retrograde metamorphic path. The mass balance shows that there has been orders of magnitude more metal mobilised in the orogen than resides in the currently known deposits. There is a clear potential for large gold deposits occurring in the yet to be uplifted parts of the Southern Alps if there have been efficient enough fluid focusing and metal precipitation mechanisms occurring under the Southern Alps.  相似文献   

9.
Palaeomagnetic and magnetomineralogical results are reported from charnockites in basement terrane at the eastern sector of the WSW–ENE granulite belt of South India. Magnetite is the dominant ferromagnet identified by rock magnetic and optical study; it is present in several phases including large homogeneous titanomagnetites and disseminated magnetite in microfractures linked to growth stages ranging from primary charnockite formation to uplift decompression and exhumation within the interval ～2500–2100 Ma. Several components of magnetization are resolved by thermal demagnetization and summarized by four pole positions; in the northern (Pallavaram) sector these are P1 (33°N, 99°E, dp/dm = 8/9°) and P2 (79°N, 170°E, dp/dm = 3/6°), and in the southern (Vandallur) sector they are V1 (23°N, 116°E, dp/dm = 8/9°) and V2 (26°S, 136°E, dp/dm = 5/10°). These magnetizations are linked to uplift cooling of the basement and unblocking temperature spectra suggest acquisition sequences P1 → P2 and V1 → V2 in each case implying movement of the shield from higher to lower palaeolatitudes sometime between 2500 and 2100 Ma. Palaeomagnetic poles from the cratonic nuclei of Africa, Australia and India all identify motion from higher to lower palaeolatitudes in Early Palaeoproterozoic times, and this is dated ～2400 and ～2200 Ma in the former two shields. The corresponding apparent polar wander (APW) segments match the magnetization record within the charnockite basement terranes of southern India to yield a preliminary reconstruction of the ‘Ur’ protocontinent, the oldest surviving continental protolith with origins prior to 3000 Ma. Although subject to later relative movements these nuclei seem to have remained in proximity until the Mesozoic break-up of Gondwana.  相似文献   

10.
Narraguinnep Reservoir in southwestern Colorado is one of several water bodies in Colorado with a mercury (Hg) advisory as Hg in fish tissue exceed the 0.3 μg/g guideline to protect human health recommended by the State of Colorado. Concentrations of Hg and methyl-Hg were measured in reservoir bottom sediment and pore water extracted from this sediment. Rates of Hg methylation and methyl-Hg demethylation were also measured in reservoir bottom sediment. The objective of this study was to evaluate potential sources of Hg in the region and evaluate the potential of reservoir sediment to generate methyl-Hg, a human neurotoxin and the dominant form of Hg in fish. Concentrations of Hg (ranged from 1.1 to 5.8 ng/L, n = 15) and methyl-Hg (ranged from 0.05 to 0.14 ng/L, n = 15) in pore water generally were highest at the sediment/water interface, and overall, Hg correlated with methyl-Hg in pore water (R2 = 0.60, p = 0007, n = 15). Net Hg methylation flux in the top 3 cm of reservoir bottom sediment varied from 0.08 to 0.56 ng/m2/day (mean = 0.28 ng/m2/day, n = 5), which corresponded to an overall methyl-Hg production for the entire reservoir of 0.53 g/year. No significant point sources of Hg contamination are known to this reservoir or its supply waters, although several coal-fired power plants in the region emit Hg-bearing particulates. Narraguinnep Reservoir is located about 80 km downwind from two of the largest power plants, which together emit about 950 kg-Hg/year. Magnetic minerals separated from reservoir sediment contained spherical magnetite-bearing particles characteristic of coal-fired electric power plant fly ash. The presence of fly-ash magnetite in post-1970 sediment from Narraguinnep Reservoir indicates that the likely source of Hg to the catchment basin for this reservoir has been from airborne emissions from power plants, most of which began operation in the late-1960s and early 1970s in this region.  相似文献   

11.
《Journal of Structural Geology》2001,23(6-7):1031-1042
The Eastern Highlands shear zone in Cape Breton Island is a crustal scale thrust. It is characterized by an amphibolite-facies deformation zone ∼5 km wide formed deep in the crust that is overprinted by a greenschist-facies mylonite zone ∼1 km wide that formed at a more shallow level. Hornblende 40Ar/39Ar plateau ages on the hanging wall decrease towards the centre of the shear zone. In the older zone (over 7.8 km from the centre), the ages are between ∼565 and ∼545 Ma; in the younger zone (within 4.5 km of the centre), they are between ∼425 and ∼415 Ma; and in the transitional zone in between, they decrease abruptly from ∼545 to ∼425 Ma. Pressures of crystallization of plutons in the hanging wall, based on the Al-in-hornblende barometer and corresponding to depth of emplacement, increase towards the centre of the shear zone and indicate a differential uplift of up to ∼28 km associated with movement along the shear zone. The age pattern is interpreted to have resulted from the differential uplift. The pressure data show that rocks exposed in the younger zone were buried deep in the crust and did not cool through the hornblende Ar blocking temperature (∼500°C) until differential uplift occurred. The 40Ar/39Ar ages in the zone (∼425–415 Ma) thus date shear zone movement or the last stage of it. In contrast, rocks in the older zone were more shallowly buried before differential uplift and cooled through the blocking temperature soon after the emplacement of ∼565–555 Ma plutons in the area, long before shear zone movement. The transitional zone corresponds to the Ar partial retention zone before differential uplift. The 40Ar/39Ar age pattern thus reflects a Neoproterozoic to Silurian cooling profile that was exposed as a result of differential uplift related to movement along the shear zone. A similar K–Ar age pattern has been reported for the Alpine fault in New Zealand. It is suggested that such isotopic age patterns can be used to help constrain the ages, kinematics, displacements and depth of penetration of shear zones.  相似文献   

12.
The Hujiayu Cu deposit, located in the Zhongtiao Mountains district of southern North China Craton, is hosted by graphite schist and dolomitic marble with disseminated to veinlet (stage I) and thick vein (stage II) mineralization. Stage I mineralization, characterized by stratabound, disseminated pyrite and chalcopyrite within the graphite schist host rock, formed at the syn-metamorphic stage. Graphite geothermometry showed that the host rock was subjected to an upper-greenschist to lower amphibolite metamorphism at a temperature range of 486 to 596 °C, averaging of 546 ± 35 °C (1 σ, n = 19). Stage II mineralization, consisting of brecciated dolomitic thick veins cemented by quartz-sulfide assemblages, was a product of metamorphic hydrothermal activity. This thick vein was subdivided into an early hydrothermal dolomitic alteration composing of dolomitic breccia with some cobaltiferous pyrite (stage IIa) and a late siliceous-copper mineralization consisting of quartz-sulfide assemblages (stage IIb). A clausthalite–siegenite–sphalerite–chalcopyrite mineral assemblage was observed in stage IIb, constraining the sulfur fugacity and selenium fugacity within − 18.7 to − 11.7 and − 21.7 to − 14.7, respectively. It was inferred stage IIb was marked by a drop in sulfur fugacity and a substantial increase in selenium fugacity after the major chalcopyrite precipitation. Calculations based on the compositions of cobaliterous pyrite and sphalerite reveal that the mineral assemblage at stage IIa formed at an approximately temperature range of 400 to 300 °C, whereas the minerals in stage IIb occurred at temperature of 256 ± 9 °C (1 σ, n = 7). Sulfides from stage I have δ34S value ranging from 10.1 to 22.2‰ with an average value of 16.9 ± 3.4‰ (1 σ, n = 27), supporting the model that sulfides precipitated through thermochemical reduction of sulfate at sedimentary stage followed by metamorphic homogenization of δ34S isotopic signatures. Sulfides from the stage II have δ34S values in highly variable ranging from 3.4 to 19.2‰, indicating a rather complex source. Four chalcopyrite samples yielded a weighted model age of 1952 ± 39 Ma (1 σ, MSWD = 1.5), suggesting that the copper mineralization formed synchronously with regional metamorphism (1970–1850 Ma) and hence a Paleoproterozoic metamorphogenic copper mineralization is implicated. Therefore, we envisaged disseminated-veinlet mineralization formed during a metamorphic peak and the major hydrothermal copper mineralization occurred during the retrograde cooling.  相似文献   

13.
The May 12, 2008, Mw 7.9 Wenchuan earthquake was induced by failure of two of the major faults of the Longmen Shan thrust fault zone along the eastern margin of Tibet Plateau. Our study focused on trenches across the Yingxiu–Bichuan fault, the central fault in the Longmen Shan belt that has a coseismic surface break of more than 200 km long. Trenching excavation across the 2008 earthquake rupture on three representative sites reveals the styles and amounts of the deformation and paleoseismicity along the Longmen Shan fault. Styles of coseismic deformation along the 2008 earthquake rupture at these three sites represent three models of deformation along a thrust fault. Two of the three trench exposures reveal one pre-2008 earthquake event, which is coincident with the pre-existing scarps. Based on the observation of exposed stratigraphy and structures in the trenches and the geomorphic expressions on ground surface, we interpret the 2008 earthquake as a characteristic earthquake along this fault. The interval of reoccurrence of large earthquake events on the Central Longmen Shan fault (the Yingxiu–Beichuan fault) can be inferred to be about 11,000 years according to 14C and OSL dating. The amounts of the vertical displacement and shortening across the surface rupture during the 2008 earthquake are determined to be 1.0–2.8 m and 0.15–1.32 m, respectively. The shortening rate and uplift rate are then estimated to be 0.09–0.12 mm/yr and 0.18–0.2 mm/yr, respectively. It is indicated that the deformation is absorbed mainly not by shortening, but by uplift along the rupture during the 2008 earthquake.  相似文献   

14.
The porosity and permeability of core rocks were studied by X-ray tomography. This method has a high potential for studying petrophysical properties of rocks, because it permits not only a general quantitative estimation of the void volume but also visualization of the rock texture, including pores, cavities, cracks, and zones of different densities in the matrix. X-ray tomography permits detailed studies of rock inhomogeneity, which are necessary for the elaboration of reliable porosity-permeability models for hydrocarbon pools. The investigations at Perm State National Research Polytechnic University have shown that X-ray tomography of core samples has a wide spectrum of applications in petroleum geology. Nikon Metrology XT H 225 X-ray computed tomography makes it possible to examine samples with a standard diameter (30 mm) and whole core samples (100 mm). The structure of voids in carbonate and terrigenous rocks was studied on samples with standard and full diameters; the results of hydrochloric acid treatment of carbonate reservoir rocks were visualized; and the mechanical properties of rock salts were studied. Three-dimensional models for the structure of voids and mineral matrix of the core samples have been constructed with the use of the Avizo Fire software.  相似文献   

15.
To constrain the provenance of the Ordos Basin and the evolution history of the Qinling Orogen Belt from the Triassic to the Jurassic, 10 samples from the Dongsheng area and 28 samples from the Yan’an area were analyzed for U–Pb ages and Lu–Hf and Sm–Nd isotopic compositions. The results indicate that Middle Jurassic sediments in the Dongsheng area were derived from the Khondalite Belt, Langshan Mountain and the Yinshan Terrane. Mesozoic sediments in the Yan’an area consist of two parts. One part is derived from the North China Craton (NCC), which has U–Pb age groups of ∼1.8 Ga and ∼2.5 Ga, and Hf model ages of ∼2.8 Ga. The other part is derived from the Qilian–Qinling Orogenic Belt, which has U–Pb age groups of 600–1500 Ma and 100–500 Ma, and Nd and Hf isotopic model ages of less than 2.2 Ga. Combining the U–Pb ages with the Hf and Nd isotopic model ages, Mesozoic detrital zircons with U–Pb age groups of ∼1.8 Ga and ∼2.5 Ga in the Yan’an area are found to also be derived from the Khondalite Belt, Langshan Mountain and the Yinshan Terrane, not from the Trans-China Orogen Belt. From the late–Late Triassic sediments of the Yan’an area, the low average values of the Hf (2.03 Ga) and Nd (2.03 Ga) model ages and the characteristic age population of 600–1500 Ma reveal that the main collision or continental subduction between the NCC and the South China Craton (SCC) occurred in the late–Late Triassic. After the main collision or continental subduction, the proportion of sediments from the Qinling–Qilian Orogenic Belt began to decrease (recorded in the early Jurassic samples), which may be in response to the gradual slowing of the uplift speed of the Qinling Orogenic Belt. In the early-middle Jurassic, the sediments have a main U–Pb age population of 100–500 Ma, low detrital zircon Hf model ages (average value is 1.17 Ga) and low whole rock Nd model ages (average value is 1.13 Ga), which suggests that the Qilian–Qinling Orogenic Belt may have a fast uplift history in the early-middle Jurassic.  相似文献   

16.
《Quaternary Science Reviews》2007,26(7-8):920-940
Sea-level records from the Gulf of Mexico at the Last Glacial Maximum, 20 ka, are up to 35 m higher than time-equivalent sea-level records from equatorial regions. The most popular hypothesis for explaining this disparity has been uplift due to the forebulge created by loading from Mississippi River sediments. Using over 50 new radiocarbon dates as well as existing published data obtained from shallow-marine deposits within the northern Gulf of Mexico and numerical models simulating the impact of loading due to the Mississippi Fan and glacio-hydro-isostasy, we test several possible explanations for this sea-level disparity. We find that neither a large radiocarbon reservoir, sedimentary loading due to the Mississippi Fan, nor large-scale regional uplift can explain this disparity. We do find that with an appropriate model for the Laurentide Ice Sheet, the observations from the Gulf of Mexico can be explained by the process of glacio-hydro-isostasy. Our analysis suggests that in order to explain this disparity one must consider a Laurentide Ice Sheet reconstruction with less ice from 15 ka to its disappearance 6 ka and more ice from the Last Glacial Maximum to 15 ka than some earlier models have suggested. This supports a Laurentide contribution to meltwater pulse 1-A, which could not have come entirely from its southern sector.  相似文献   

17.
The competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain. Most of recent studies have attributed terrace formation to climatic changes and held that, even in tectonically active settings, climate variations control cycles of terrace planation and abandonment. Based on field investigations of loess-paleosol sequences, magnetostratigraphy and optically stimulated luminescence (OSL) dating, we develop a new chronology for a spectacular flight of terraces along the Yellow River near Lanzhou, China over past 1.24 Ma. All the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads, suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates. However, the ages of terraces cluster in two relatively short time periods (1.24–0.86 Ma and 0.13 Ma – present). During the intervening time between 0.86 Ma and 0.13 Ma, terraces either did not form or were not preserved. We suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation/preservation. Thus, our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision.  相似文献   

18.
《Quaternary Research》2014,81(3):400-423
The way in which the NE Tibetan Plateau uplifted and its impact on climatic change are crucial to understanding the evolution of the Tibetan Plateau and the development of the present geomorphology and climate of Central and East Asia. This paper is not a comprehensive review of current thinking but instead synthesises our past decades of work together with a number of new findings. The dating of Late Cenozoic basin sediments and the tectonic geomorphology of the NE Tibetan Plateau demonstrates that the rapid persistent rise of this plateau began ~ 8 ± 1 Ma followed by stepwise accelerated rise at ~ 3.6 Ma, 2.6 Ma, 1.8–1.7 Ma, 1.2–0.6 Ma and 0.15 Ma. The Yellow River basin developed at ~ 1.7 Ma and evolved to its present pattern through stepwise backward-expansion toward its source area in response to the stepwise uplift of the plateau. High-resolution multi-climatic proxy records from the basins and terrace sediments indicate a persistent stepwise accelerated enhancement of the East Asian winter monsoon and drying of the Asian interior coupled with the episodic tectonic uplift since ~ 8 Ma and later also with the global cooling since ~ 3.2 Ma, suggesting a major role for tectonic forcing of the cooling.  相似文献   

19.
We have synthesized new and existing relative sea-level (RSL) data to produce a quality-controlled, spatially comprehensive database from the North Carolina coastline. The RSL database consists of 54 sea-level index points that are quantitatively related to an appropriate tide level and assigned an error estimate, and a further 33 limiting dates that confine the maximum and minimum elevations of RSL. The temporal distribution of the index points is very uneven with only five index points older than 4000 cal a BP, but the form of the Holocene sea-level trend is constrained by both terrestrial and marine limiting dates. The data illustrate RSL rapidly rising during the early and mid Holocene from an observed elevation of ?35.7 ± 1.1 m MSL at 11062–10576 cal a BP to ?4.2 m ± 0.4 m MSL at 4240–3592 cal a BP.We restricted comparisons between observations and predictions from the ICE-5G(VM2) with rotational feedback Glacial Isostatic Adjustment (GIA) model to the Late Holocene RSL (last 4000 cal a BP) because of the wealth of sea-level data during this time interval. The ICE-5G(VM2) model predicts significant spatial variations in RSL across North Carolina, thus we subdivided the observations into two regions. The model forecasts an increase in the rate of sea-level rise in Region 1 (Albemarle, Currituck, Roanoke, Croatan, and northern Pamlico sounds) compared to Region 2 (southern Pamlico, Core and Bogue sounds, and farther south to Wilmington). The observations show Late Holocene sea-level rising at 1.14 ± 0.03 mm year?1 and 0.82 ± 0.02 mm year?1 in Regions 1 and 2, respectively. The ICE-5G(VM2) predictions capture the general temporal trend of the observations, although there is an apparent misfit for index points older than 2000 cal a BP. It is presently unknown whether these misfits are caused by possible tectonic uplift associated with the mid-Carolina Platform High or a flaw in the GIA model. A comparison of local tide gauge data with the Late Holocene RSL trends from Regions 1 and 2 support the spatial variation in RSL across North Carolina, and imply an additional increase of mean sea level of greater than 2 mm year?1 during the latter half of the 20th century; this is in general agreement with historical tide gauge and satellite altimetry data.  相似文献   

20.
Key parameters in the evolution of the oceanic crust in the little-known Tonian period of the Brasiliano Orogen are presently established through the finding and characterization of zircon in chloritite and tourmalinite enclosed in serpentinite. The Ibaré and Palma ophiolites were selected for the study and both are from the juvenile São Gabriel terrane, Rio Grande do Sul state, Brazil. U-Pb and Lu-Hf isotopic analyses of zircon from metasomatites and a volcanoclastic rock with laser ablation indicate similar ages in both ophiolites, respectively 726 ± 2 Ma and 722 ± 3 Ma (metasomatites) and 758 ± 4 Ma (volcanoclastic rock). Other three representative ages recorded in the metasomatites are 880 ± 12, 836 ± 6 and 780 ± 5 Ma, interpreted as successive serpentinization events. Mantle Hf isotope compositions of zircon in the metasomatites range from εHf = + 12.1 to + 1.4 and in the volcanoclastic rock the sample displays εHf = + 11.7 to + 6.7. Zircon geochemistry is close to the mantle array. This direct dating of ophiolites sets new limits to the evolution of the Brasiliano Orogen during formation of Gondwana. The youngest possible age for ophiolite accretion is 722 Ma.  相似文献   

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