Using monitoring and modeling to define the hazard posed by the reactivated Ferguson rock slide,Merced Canyon,California     

Jerome V. De Graff  Alan J. Gallegos  Mark E. Reid  Richard G. LaHusen  Roger P. Denlinger 《Natural Hazards》2015,76(2):769-789

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New mineral activity–composition relations for thermodynamic calculations in metapelitic systems     

R. W. White  R. Powell  T. J. B. Holland  T. E. Johnson  E. C. R. Green 《Journal of Metamorphic Geology》2014,32(3):261-286

New activity–composition (a–x) relations for minerals commonly occurring in metapelites are presented for use with the internally consistent thermodynamic dataset of Holland & Powell ( 2011 , Journal of Metamorphic Geology, 29 , 333–383). The a–x relations include a broader consideration of Fe₂O₃ in minerals, changes to the formalism of several phases and order–disorder in all ferromagnesian minerals where Fe–Mg mixing occurs on multiple sites. The a–x relations for chlorite, biotite, garnet, chloritoid, staurolite, cordierite, orthopyroxene, muscovite, paragonite and margarite have been substantially reparameterized using the approach outlined in the companion paper in this issue. For the first time, the entire set of a–x relations for the common ferromagnesian minerals in metapelitic rocks is parameterized simultaneously, with attention paid to ensuring that they can be used together to calculate phase diagrams of geologically appropriate topology. The a–x relations developed are for use in the Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–O₂ (NCKFMASHTO) system for both subsolidus and suprasolidus conditions. Petrogenetic grids in KFMASH and KFMASHTO are similar in topology to those produced with earlier end‐member datasets and a–x relations, but with some notable differences. In particular, in subsolidus equilibria, the FeO/(FeO + MgO) of garnet is now greater than in coexisting staurolite, bringing a number of key staurolite‐bearing equilibria into better agreement with inferences from field and petrographic observations. Furthermore, the addition of Fe³⁺ and Ti to a number of silicate phases allows more plausible equilibria to be calculated in relevant systems. Pseudosections calculated with the new a–x relations are also topologically similar to equivalent diagrams using earlier a–x relations, although with many low variance fields shifting in P–T space to somewhat lower pressure conditions.  相似文献   

Constraints on the timing and conditions of high‐grade metamorphism,charnockite formation and fluid–rock interaction in the Trivandrum Block,southern India          下载免费PDF全文

E. Blereau  C. Clark  R. J. M. Taylor  T. E. Johnson  I. C. W. Fitzsimons  M. Santosh 《Journal of Metamorphic Geology》2016,34(6):527-549

Incipient charnockites have been widely used as evidence for the infiltration of CO₂‐rich fluids driving dehydration of the lower crust. Rocks exposed at Kakkod quarry in the Trivandrum Block of southern India allow for a thorough investigation of the metamorphic evolution by preserving not only orthopyroxene‐bearing charnockite patches in a host garnet–biotite felsic gneiss, but also layers of garnet–sillimanite metapelite gneiss. Thermodynamic phase equilibria modelling of all three bulk compositions indicates consistent peak‐metamorphic conditions of 830–925 °C and 6–9 kbar with retrograde evolution involving suprasolidus decompression at high temperature. These models suggest that orthopyroxene was most likely stabilized close to the metamorphic peak as a result of small compositional heterogeneities in the host garnet–biotite gneiss. There is insufficient evidence to determine whether the heterogeneities were inherited from the protolith or introduced during syn‐metamorphic fluid flow. U–Pb geochronology of monazite and zircon from all three rock types constrains the peak of metamorphism and orthopyroxene growth to have occurred between the onset of high‐grade metamorphism at c. 590 Ma and the onset of melt crystallization at c. 540 Ma. The majority of metamorphic zircon growth occurred during protracted melt crystallization between c. 540 and 510 Ma. Melt crystallization was followed by the influx of aqueous, alkali‐rich fluids likely derived from melts crystallizing at depth. This late fluid flow led to retrogression of orthopyroxene, the observed outcrop pattern and to the textural and isotopic modification of monazite grains at c. 525–490 Ma.  相似文献   

Balancing trade‐off issues in land use change and the impact on streamflow and salinity management          下载免费PDF全文

Xiang Cheng  Kurt K. Benke  Craig Beverly  Brendan Christy  Anna Weeks  Kirsten Barlow  Mark Reid 《水文研究》2014,28(4):1641-1662

The south‐west region of the Goulburn–Broken catchment in the south‐eastern Murray–Darling Basin in Australia faces a range of natural resource challenges. A balanced strategy is required to achieve the contrasting objectives of remediation of land salinization and reducing salt export, while maintaining water supply security to satisfy human consumption and support ecosystems. This study linked the Catchment Analysis Tool (CAT), comprising a suite of farming system models, to the catchment‐scale CATNode hydrological model to investigate the effects of land use change and climate variation on catchment streamflow and salt export. The modelling explored and contrasted the impacts of a series of different revegetation and climate scenarios. The results indicated that targeted revegetation to only satisfy biodiversity outcomes within a catchment is unlikely to have much greater impact on streamflow and salt load in comparison with simple random plantings. Additionally, the results also indicated that revegetation to achieve salt export reduction can effectively reduce salt export while having a disproportionately smaller affect on streamflows. Furthermore, streamflow declines can be minimized by targeting revegetation activities without significantly altering salt export. The study also found that climate change scenarios will have an equal if not more significant impact on these issues over the next 70 years. Uncertainty in CATNode streamflow predictions was investigated because of the effect of parameter uncertainty. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

A middle–late Ediacaran volcano‐sedimentary record from the eastern Arabian‐Nubian shield     

David Nettle  Galen P. Halverson  Grant M. Cox  Alan S. Collins  Mark Schmitz  James Gehling  Peter R. Johnson  Khalid Kadi 《地学学报》2014,26(2):120-129

The Ediacaran Jibalah Group comprises volcano‐sedimentary successions that filled small fault‐bound basins along the NW–SE‐trending Najd fault system in the eastern Arabian‐Nubian Shield. Like several other Jibalah basins, the Antaq basin contains exquisitely preserved sedimentary structures and felsic tuffs, and hence is an excellent candidate for calibrating late Ediacaran Earth history. Shallow‐marine strata from the upper Jibalah Group (Muraykhah Formation) contain a diversity of load structures and intimately related textured organic (microbial) surfaces, along with a fragment of a structure closely resembling an Ediacaran frond fossil and a possible specimen of Aspidella. Interspersed carbonate beds through the Muraykhah Formation record a positive δ¹³C shift from ?6 to 0‰. U‐Pb zircon geochronology indicates a maximum depositional age of ~570 Ma for the upper Jibalah Group, consistent with previous age estimates. Although this age overlaps with that of the upper Huqf Supergroup in nearby Oman, these sequences were deposited in contrasting tectonic settings on opposite sides of the final suture of the East African Orogen.  相似文献   

Reach‐scale contributions of road‐surface sediment to the Honna River,Haida Gwaii,BC          下载免费PDF全文

David A. Reid  Marwan A. Hassan  William Floyd 《水文研究》2016,30(19):3450-3465

Gravel road surfaces can be a major source of fine sediment to streams, yet their contribution to channel reach sediment balances remains poorly documented. To quantify the input of road surface material and to compare this input with natural sediment sources at the reach scale, suspended sediment dynamics was examined and a 16‐month sediment balance was developed for a ~35 channel‐width (approx. 425 m) reach of the Honna River, a medium‐size, road‐affected stream located in coastal British Columbia. Of the 105 ± 33 t of suspended material passing through the reach, 18 ± 6% was attributed to the road surface. The high availability of sediment on the road surface appears to limit hysteresis in road run‐off. During rainstorms that increase streamflow, road surface material composed 0.5–15% of sediment inputs during relatively dry conditions from April to the end of September and 5–70% through wetter conditions from October to the end of March, but our data do not show evidence of major sediment accumulation on the riverbed in the reach. A comparison of modelled sediment production on the road surface with observed yields from drainage channels suggests that (1) during low intensity rainfall, ditches and drainage channels may trap sediment from road run‐off, which is subsequently released during events of greater intensity, and/or (2) production models do not effectively describe processes, such as deposition or erosion of sediment in ditches, which control sediment transport and delivery. Our findings further emphasize the risk of unpaved roads in polluting river systems and highlight the continued need for careful road design and location away from sensitive aquatic environments. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Jointing around magmatic dikes as a precursor to the development of volcanic plugs     

Meredith Townsend  David D. Pollard  Kendra Johnson  Cansu Culha 《Bulletin of Volcanology》2015,77(10):1-13

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Inferring air–water temperature relationships from river and catchment properties          下载免费PDF全文

M. F. Johnson  R. L. Wilby  J. A. Toone 《水文研究》2014,28(6):2912-2928

Water temperature (Tw) is a key determinant of freshwater ecosystem status and cause for concern under a changing climate. Hence, there is growing interest in the feasibility of moderating rising Tw through management of riparian shade. The Loughborough University Temperature Network (LUTEN) is an array of 36 water and air temperature (Ta) monitoring sites in the English Peak District set‐up to explore the predictability of local Tw, given Ta, river reach, and catchment properties. Year 1 of monitoring shows that 84%–94% of variance in daily Tw is explained by Ta. However, site‐specific logistic regression parameters exhibit marked variation and dependency on upstream riparian shade. Perennial spring flows in the lower River Dove also affect regression model parameters and strongly buffer daily and seasonal mean Tw. The asymptote of the models (i.e. maximum expected Tw) is particularly sensitive to groundwater inputs. We conclude that reaches with spring flows potentially offer important thermal refuges for aquatic organisms against expected long‐term warming of rivers and should be afforded special protection. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Exhumation history of the Peake and Denison Inliers: insights from low-temperature thermochronology     

J. W. Hall  S. Glorie  A. S. Collins  A. Reid  N. Evans  B. McInnes 《Australian Journal of Earth Sciences》2016,63(7):805-820

Multi-method thermochronology applied to the Peake and Denison Inliers (northern South Australia) reveals multiple low-temperature thermal events. Apatite fission track (AFT) data suggest two main time periods of basement cooling and/or reheating into AFT closure temperatures (～60–120°C); at ca 470–440 Ma and ca 340–300 Ma. We interpret the Ordovician pulse of rapid basement cooling as a result of post-orogenic cooling after the Delamerian Orogeny, followed by deformation related to the start of the Alice Springs Orogeny and orocline formation relating to the Benambran Orogeny. This is supported by a titanite U/Pb age of 479 ± 7 Ma. Our thermal history models indicate that subsequent denudation and sedimentary burial during the Devonian brought the basement rocks back to zircon U–Th–Sm/He (ZHe) closure temperatures (～200–150°C). This period was followed by a renewal of rapid cooling during the Carboniferous, likely as the result of the final pulses of the Alice Springs Orogeny, which exhumed the inlier to ambient surface temperatures. This thermal event is supported by the presence of the Mount Margaret erosion surface, which indicates that the inlier was exposed at the surface during the early Permian. During the Late Triassic–Early Jurassic, the inlier was subjected to minor reheating to AFT closure temperatures; however, the exact timing cannot be deduced from our dataset. Cretaceous apatite U–Th–Sm/He (AHe) ages coupled with the presence of contemporaneous coarse-grained terrigenous rocks suggest a temporally thermal perturbation related with shallow burial during this time, before late Cretaceous exhumation cooled the inliers back to ambient surface temperatures.  相似文献   

Southern Hemisphere strong polar mesoscale cyclones in high-resolution datasets     

Alexandre Pezza  Katherine Sadler  Petteri Uotila  Timo Vihma  Michel D. S. Mesquita  Phil Reid 《Climate Dynamics》2016,46(5-6):1647-1664

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