K‐Ar ages of Cainozoic volcanic suites,Bowen‐St Lawrence Hinterland,North Queensland (with some implications for petrologic models)     

F. L. Sutherland  D. Stubbs  D. C. Green 《Australian Journal of Earth Sciences》2013,60(7-8):447-460

Thirty K‐Ar dates on Cainozoic volcanic rocks lying at the north end of the Bowen Basin suggest that several episodes of volcanism took place at major structural weaknesses. The oldest volcanism (ca 54 m.y.) was located outside the basin structure. The main volcanism (Nebo and East Clermont Provinces) extended from early Oligocene (34–35 m.y.) to mid‐Cainozoic time (21–22 m.y.?). Isolated Pliocene activity is tentatively suggested by dates on Mt St Martin (ca 3 m.y.).

Dating of the Nebo central volcano (31–33 m.y.) supports the model of Wellman &; McDougall, with volcanic activity related to migration of Australia northwards over a mantle magma source. Consideration of the Nebo dates with those of other central volcanoes in north Queensland, suggests that central felsic activity was surrounded by broad zones of peripheral eruptives, petrologically zoned from outer undersaturated basalts to inner saturated basalts. These zones (super provinces) delineate the size and profile of underlying magma sources and appear to trend back in time and space to sea‐floor spreading episodes in the Coral Sea—southeastern Papua region (55 m.y.).

The basalt dates also assist in fixing periods of lateritization (mid‐Oligocene) and in determining approximate minimum erosion rates in the northern Bowen Basin since the Eocene (3–5m/m.y.).  相似文献   

Radiometric evidence of the Kanimblan Orogeny in southeastern Queensland and the age of the Neranleigh-Fernvale group     

D.C. Green 《Australian Journal of Earth Sciences》2013,60(2):153-160

Abstract

Conventional K-Ar geochronology and the ⁴⁰Ar/³⁹Ar method in which the ratio of radiogenic argon to postassium is determined by measurement of ³⁹Ar produced by neutron irradiation are used to document the occurrence of the Upper Carboniferous Kanimblan Orogeny in the D'Aguilar Block and Beenleigh Block of southeastern Queensland.

Incremental evolution of argon by the heating of an irradiated sample of Neranleigh-Fernvale argillite and ⁴⁰Ar/³⁹Ar measurements on two hornblendes from alaskite clasts in the Neranleigh-Fernvale Group suggest that part of this unit may be as young as Lower Carboniferous.  相似文献   

Thermal history of the Rio Muni (West Africa)–NE Brazil margins during continental breakup     

Jonathan P. Turner  Paul F. Green  Simon P. Holford  Stephen R. Lawrence 《Earth and Planetary Science Letters》2008,270(3-4):354-367

We document the thermal record of breakup of the conjugate Rio Muni (West Africa) and NE Brazil margins using apatite fission track analysis, vitrinite reflectance data and stratigraphic observations from both margins. These results permit determination of the timing of four cooling episodes, and the temperature of samples at the onset of each episode. All samples are interpreted to have experienced higher temperatures in the geological past due to i) elevated basal heatflow (palaeogeothermal gradient in Rio Muni-1 well decaying from 58 °C/km during the Mid Cretaceous to 21.5 °C/km in the Late Cenozoic) and ii) progressive exhumation from formerly greater burial depth. A well constrained history of changing palaeogeothermal gradient allows for much more precise quantification of the thickness of eroded section (exhumation) than if a constant heatflow is assumed. Cooling episodes identified from the palaeotemperature data at 110–95 Ma (both margins) and 85–70 Ma (Rio Muni only) coincide with major unconformities signifying, respectively, the cessation of rifting (breakup) and compressional shortening that affected the African continent following the establishment of post-rift sedimentation (drift). The interval between these separate unconformities is occupied by allochthonous rafts of shallow-water carbonates recording gravitational collapse of a marginal platform. The rift shoulder uplift that triggered this collapse was enhanced by local transpression associated with the obliquely divergent Ascension Fracture Zone, and thermal doming due to the coeval St Helena and Ascension Plumes. The data also reveal a c.45–35 Ma cooling episode, attributed to deep sea erosion at the onset of Eo-Oligocene ice growth, and a c.15–10 Ma episode interpreted as the record of Miocene exhumation of the West African continental margin related to continent-wide plume development. Integration of thermal history methods with traditional seismic- and stratigraphy-based observations yields a dynamic picture of kilometre-scale fluctuations in base level through the breakup and early drift phases of development of these margins. Major unconformities at ocean margins are likely to represent composite surfaces recording not only eustasy, but also regional plate margin-generated deformation, local ‘intra-basinal’ reorganization, and the amplifying effect of negative feedbacks between these processes.  相似文献   

Nannofossil age constraints for the northern KwaZulu-Natal shelf-edge wedge: Implications for continental margin dynamics, South Africa, SW Indian Ocean     

A.N. Green  M. Ovechkina  R. Uken 《Continental Shelf Research》2008,28(17):2442-2449

Samples collected from the shelf-edge wedge using surface grab samples and the Jago submersible constrain the KwaZulu-Natal shelf-edge wedge to a late Pliocene age on the basis of the absence of Gephyrocapsa oceanica s.l. and Discoaster brouweri, and the presence of Calcidiscus macintyrei. This correlates with proposed Tertiary sea-level curves for southern Africa and indicates relative sea-level fall during the late Pliocene coupled with hinterland uplift. Exposed failure scarps in the upper portions of submarine canyons yield sediment samples of early Pleistocene ages, indicating the uppermost age of deposition of clinoform topsets exposed in the scarp walls. Partially consolidated, interbedded silty and sandy deposits of similar age outcrop in the thalweg of Leven canyon at a depth of 150 m. These sediments provide an upper age limit of the shelf-edge wedge of early Pleistocene, giving a sedimentation rate of this wedge of 162–309 m/Ma. The distribution of widespread basal-most Pleistocene sediments on the upper slope indicates that these sediments escaped major reworking during sea-level falls associated with Pleistocene glaciations and remain as relict upper slope veneers. The absence of more recent sediments suggests that this area has been a zone of sediment bypass or starvation since the early Pleistocene. Areas where younger sediments mantle deposits of early Pleistocene ages represent areas of offshore bedload parting, re-distributing younger Holocene sediment offshore and downslope.  相似文献   

Comparison of hypoxia among four river-dominated ocean margins: The Changjiang (Yangtze), Mississippi,Pearl, and Rhône rivers     

C. Rabouille  D.J. Conley  M.H. Dai  W.-J. Cai  C.T.A. Chen  B. Lansard  R. Green  K. Yin  P.J. Harrison  M. Dagg  B. McKee 《Continental Shelf Research》2008

We examined the occurrence of seasonal hypoxia (O₂<2 mg l⁻¹) in the bottom waters of four river-dominated ocean margins (off the Changjiang, Mississippi, Pearl and Rhône Rivers) and compared the processes leading to the depletion of oxygen. Consumption of oxygen in bottom waters is linked to biological oxygen demand fueled by organic matter from primary production in the nutrient-rich river plume and perhaps terrigenous inputs. Hypoxia occurs when this consumption exceeds replenishment by diffusion, turbulent mixing or lateral advection of oxygenated water. The margins off the Mississippi and Changjiang are affected the most by summer hypoxia, while the margins off the Rhône and the Pearl rivers systems are less affected, although nutrient concentrations in the river water are very similar in the four systems. Spring and summer primary production is high overall for the shelves adjacent to the Mississippi, Changjiang and Pearl (1–10 g C m⁻² d⁻¹), and lower off the Rhône River (<1 g C m⁻² d⁻¹), which could be one of the reasons of the absence of hypoxia on the Rhône shelf. The residence time of the bottom water is also related to the occurrence of hypoxia, with the Mississippi margin showing a long residence time and frequent occurrences of hypoxia during summer over very large spatial scales, whereas the East China Sea (ECS)/Changjiang displays hypoxia less regularly due to a shorter residence time of the bottom water. Physical stratification plays an important role with both the Changjiang and Mississippi shelf showing strong thermohaline stratification during summer over extended periods of time, whereas summer stratification is less prominent for the Pearl and Rhône partly due to the wind effect on mixing. The shape of the shelf is the last important factor since hypoxia occurs at intermediate depths (between 5 and 50 m) on broad shelves (Gulf of Mexico and ECS). Shallow estuaries with low residence time such as the Pearl River estuary during the summer wet season when mixing and flushing are dominant features, or deeper shelves, such as the Gulf of Lion off the Rhône show little or no hypoxia.  相似文献   

Frictional sliding in serpentine at very high pressure     

Haemyeong Jung  Yingwei Fei  Paul G. Silver  Harry W. Green 《Earth and Planetary Science Letters》2009,277(1-2):273-279

Using a new four-channel system for detecting acoustic emissions in a multianvil apparatus, we have assessed the pressure–temperature range for such emissions, as well as the role of dehydration, by deforming samples of extensively serpentinized peridotite. We show that in the absence of dehydration and for samples initially faulted at low pressure, acoustic emissions occurred well outside the expected pressure–temperature field of unassisted brittle failure. Emissions were also detected during and after dehydration of serpentine. Microstructures of post-run specimens revealed fault slip with offsets up to ~ 500 μm, regardless of whether or not dehydration took place. Dehydration appears to effectively stop slip on pre-existing faults and create new ones. Analysis of P-wave travel times from the four sensors confirmed that the acoustic emissions originated within the specimen during fault slip. These observations suggest that earthquakes can be triggered by slip along an existing fault containing serpentine under significantly higher pressure and temperature conditions than previously thought possible without dehydration.  相似文献   

An overview of the Tennessee-Tombigbee Waterway     

Samuel R. Green 《Environmental Geology》1985,7(1-2):9-13

When the Tennessee-Tombigbee Waterway of Mississippi and Alabama opened to commercial and recreational traffic on January 16, 1985—some 21 months ahead of schedule—it signaled the completion of the largest Army Corps of Engineers Civil Works project ever undertaken, and perhaps the last of its kind After more than a century of studies and re-studies and major funding battles in Congress, the Tennessee-Tombigbee construction faced, predictably, great opposition on environmental grounds The first major project to be completed under the National Environmental Policy Act, it brought environmental design to the same level of prominence as engineering design.  相似文献   

8- to 13-μm spectra of asteroids     

S.F. Green  N. Eaton  D.K. Aitken  P.F. Roche  A.J. Meadows 《Icarus》1985,62(2):282-288

We present 8- to 13-μm spectra of the main-belt asteroids 1, 2, 6, 7, 10, 16, 45, 51, 56, 65, 78, and 451. None of these exhibit pronounced emission features, and all can be fitted reasonably well using a standard thermal model. We also present wide- and narrowband photometry of 19 Fortuna, which has previously been reported to show an emission feature in this region.  相似文献   

The detection of fast-moving asteroids and comets by IRAS     

S.F. Green  J.K. Davies  N. Eaton  B.C. Stewart  A.J. Meadows 《Icarus》1985,64(3):517-527

The Infrared Astronomical Satellite (IRAS) was used to search for fast-moving objects in the inner Solar System. The selection effects and limitations of the search are examined with particular reference to the objects which may be present in the moving-object data base at JPL. It is shown that the two new Apollo asteroid discoveries are in fair agreement with the discovery rate by ground-based telescopes. IRAS discovered six comets which is also consistent with the discovery rate for ground-based searches. It is estimated that there are 20–30 comets but no Apollo asteroids in the hours-confirmed moving-object data base established by the IRAS project.  相似文献   

A revised reference catalogue of galactic supernova remnants     

D. A. Green 《Astrophysics and Space Science》1988,148(1):3-74

This paper reviews observations made over recent years that have led to the identification of many new galactic supernova remnants (SNRs) and have clarified the nature of several objects that had been thought to be SNRs. A revised reference catalogue of 155 galactic SNRs is presented, complete with notes on the newly identified remnants, those objects no longer thought to be SNRs, the questionable objects in the catalogue, and possible candidate SNRs. The selection effects applicable to the identification of galactic SNRs are discussed, with particular reference to the limitations that they impose upon statistical studies.  相似文献