Multiple P–T–d–t paths reveal the evolution of the final Nuna assembly in northeast Australia     

Silvia Volante  Amaury Pourteau  William J. Collins  Eleanore Blereau  Zheng-Xiang Li  Matthijs Smit  Noreen J. Evans  Adam R. Nordsvan  Chris J. Spencer  Brad J. McDonald  Jiangyu Li  Christina Günter 《Journal of Metamorphic Geology》2020,38(6):593-627

The final assembly of the Mesoproterozoic supercontinent Nuna was marked by the collision of Laurentia and Australia at 1.60 Ga, which is recorded in the Georgetown Inlier of NE Australia. Here, we decipher the metamorphic evolution of this final Nuna collisional event using petrostructural analysis, major and trace element compositions of key minerals, thermodynamic modelling, and multi-method geochronology. The Georgetown Inlier is characterised by deformed and metamorphosed 1.70–1.62 Ga sedimentary and mafic rocks, which were intruded by c. 1.56 Ga old S-type granites. Garnet Lu–Hf and monazite U–Pb isotopic analyses distinguish two major metamorphic events (M1 at c. 1.60 Ga and M2 at c. 1.55 Ga), which allows at least two composite fabrics to be identified at the regional scale—c. 1.60 Ga S1 (consisting in fabrics S1a and S1b) and c. 1.55 Ga S2 (including fabrics S2a and S2b). Also, three tectono-metamorphic domains are distinguished: (a) the western domain, with S1 defined by low-P (LP) greenschist facies assemblages; (b) the central domain, where S1 fabric is preserved as medium-P (MP) amphibolite facies relicts, and locally as inclusion trails in garnet wrapped by the regionally dominant low-P amphibolite facies S2 fabric; and (c) the eastern domain dominated by upper amphibolite to granulite facies S2 foliation. In the central domain, 1.60 Ga MP–medium-T (MT) metamorphism (M1) developed within the staurolite–garnet stability field, with conditions ranging from 530–550°C at 6–7 kbar (garnet cores) to 620–650°C at 8–9 kbar (garnet rims), and it is associated with S1 fabric. The onset of 1.55 Ga LP–high-T (HT) metamorphism (M2) is marked by replacement of staurolite by andalusite (M2a/D2a), which was subsequently pseudomorphed by sillimanite (M2b/D2b) where granite and migmatite are abundant. P–T conditions ranged from 600 to 680°C and 4–6 kbar for the M2b sillimanite stage. 1.60 Ga garnet relicts within the S2 foliation highlight the progressive obliteration of the S1 fabric by regional S2 in the central zone during peak M2 metamorphism. In the eastern migmatitic complex, partial melting of paragneiss and amphibolite occurred syn- to post- S2, at 730–770°C and 6–8 kbar, and at 750–790°C and 6 kbar, respectively. The pressure–temperature–deformation–time paths reconstructed for the Georgetown Inlier suggest a c. 1.60 Ga M1/D1 event recorded under greenschist facies conditions in the western domain and under medium-P and medium-T conditions in the central domain. This event was followed by the regional 1.56–1.54 Ga low-P and high-T phase (M2/D2), extensively recorded in the central and eastern domains. Decompression between these two metamorphic events is ascribed to an episode of exhumation. The two-stage evolution supports the previous hypothesis that the Georgetown Inlier preserves continental collisional and subsequent thermal perturbation associated with granite emplacement.  相似文献   

Using local infrasound arrays to detect plunging snow avalanches along the Milford Road,New Zealand (Aotearoa)     

Watson  Leighton M.  Carpenter  Brad  Thompson  Kevin  Johnson  Jeffrey B. 《Natural Hazards》2022,111(1):949-972

Natural Hazards - Snow avalanches pose a hazard in alpine environments. There is a need to improve monitoring capabilities in order to reliably detect and locate avalanche activity, which will help...  相似文献   

Geostatistical Rock Physics Inversion for Predicting the Spatial Distribution of Porosity and Saturation in the Critical Zone     

Grana  Dario  Parsekian  Andrew D.  Flinchum  Brady A.  Callahan  Russell P.  Smeltz  Natalie Y.  Li  Ang  Hayes  Jorden L.  Carr  Brad J.  Singha  Kamini  Riebe  Clifford S.  Holbrook  W. Steven 《Mathematical Geosciences》2022,54(8):1315-1345

Mathematical Geosciences - Understanding the subsurface structure and function in the near-surface groundwater system, including fluid flow, geomechanical, and weathering processes, requires...  相似文献   

‘Like touching with your roots’: migrants’ children visiting the ancestral homeland     

Brad Ruting 《The Australian geographer》2012,43(1):17-33

Many migrants and their descendants make journeys to their homelands, and these visits form an important part of their ethnic identities, kinship relations and transnational connections. While such journeys have attracted increased attention recently, there has been relatively little exploration of the experiences that migrants’ children have when visiting their parents’ homeland, especially in an exile context when there has been little contact with the homeland for an extended period. This paper examines why the children and grandchildren of Estonian migrants to Australia journey to Estonia, and the experiences they have there. Motivations for visiting are complex and varied, and typically interweaved with parents’ stories, ethnic identities, kinship and curiosity. While visiting was a positive but emotional experience for some, it involved awkward encounters for others. This paper explores how these journeys led to respondents reconceptualising their senses of identity, belonging and home, and how many came to align their identities to both Estonia and Australia simultaneously.  相似文献   

Environmental determinism in Holocene research: causality or coincidence?   总被引：2，自引：0，他引：2  

Paul Coombes  Keith Barber 《Area》2005,37(3):303-311

The past decade has seen a revival of environmental determinism in palaeoenvironmental research, with palaeoclimatic shifts implicated in the collapse of many past civilizations. Implicit in these studies is a belief that the observed cultural transitions can be causally related to the magnitude of climatic change. However, examination of the processes of these declines suggests that many exhibit patterns characteristic of complexity cascading within self-organized systems. If so, the nonlinear nature of these systems' responses to external forcing means that the assumption of causality in many of these cases should be considered questionable.  相似文献   

Identification of base‐excited structures using output‐only parameter estimation     

Brad A. Pridham  John C. Wilson 《地震工程与结构动力学》2004,33(1):133-155

This paper presents a new identification technique for the extraction of modal parameters of structural systems subjected to base excitation. The technique uses output‐only measurements of the structural response. A combined subspace‐maximum likelihood algorithm is developed and applied to a three‐degree‐of‐freedom simulation model. Five ensembles of synthetically generated input signals, representing varying input characteristics, are employed in Monte Carlo simulations to illustrate the applicability of the method. The technique is able to circumvent some of the difficulties arising from short data sets by employing the Expectation Maximization (EM) algorithm to refine the subspace state estimates. This approach is motivated by successful application by previous authors on speech signals. Results indicate that, for certain system characteristics, more accurate pole estimates can be identified using the combined subspace‐EM formulation. In general, the damping ratios of the system are difficult to identify accurately due to limitations on data set length. The applicability of the technique to structural vibration signals is illustrated through the identification of seismic response data from the Vincent Thomas Bridge. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

A reassessment of dynamic characteristics of the Quincy Bayview Bridge using output‐only identification techniques     

Brad A. Pridham  John C. Wilson 《地震工程与结构动力学》2005,34(7):787-805

A reassessment of the dynamic characteristics of the 542 m cable‐stayed Bayview Bridge in Quincy, Illinois, is presented using a newly developed output‐only system identification technique. The technique is applied to an extensive set of ambient vibration response data acquired from the bridge in 1987. Vertical, torsional and transverse modal frequencies of the deck are identified, and uncertainty in damping values are estimated using an automated procedure on several redundant measurements at four locations. Important practical implementation issues associated with the implementation of the procedure and selection of algorithm design parameters for stochastic subspace identification techniques are discussed. An overall mean and standard deviation of damping of 1.0±0.8% is estimated considering all identified vertical, torsional and transverse modes in the 0–2 Hz band. The mean damping for the fundamental vertical mode (0.37 Hz) is identified as 1.4±0.5%, and for the first coupled torsion–transverse mode (0.56 Hz) is identified as 1.1±0.8%. Variability in the damping estimates is shown to decrease as estimated modal RMS acceleration levels increase. Standard deviations on estimated damping range from 0.05% to 2%. The results are shown to be a substantial improvement in the evaluation of damping compared to earlier spectral analysis conducted on the same data set. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Gender-specific local labour market areas in England and Wales     

A.E. Green  M.G. Coombes  D.W. Owen 《Geoforum》1986,17(3-4)

Local labour market areas (LLMAs) are usually defined on the basis of total commuting flows between constituent ‘building block’ areas. Indeed the 1984 revision of Travel-To-Work Areas (TTWAs) was based on aggregate flows between 1981 Census wards. It is widely recognized, however, that various sub-groups of the population have distinctive commuting patterns. TTWAs therefore represent the outcome of an ‘averaging’ of the journey-to-work patterns of different gender, socio-economic and occupational groups. In this preliminary review, the self-containment of TTWAs in England and Wales, which have been generated using aggregate data, is assessed at the simplest level of disaggregation of the commuting data: disaggregation by gender. In accordance with expectations, it is found that TTWAs defined on the basis of total commuting flows are generally more self-contained for females than for males, and that those TTWAs which are insufficiently self-contained to be considered as LLMAs for males are overwhelmingly concentrated in the most urbanized regions. These findings are reinforced by the results of re-running the TTWA regionalization algorithm against 1981 flow data for males and females in order to create gender-specific TTWAs; disparities between Male and Female TTWAs are greatest in the most urbanized regions. Such differences are investigated in greater detail for two Metropolitan Regions (MRs): the combined Liverpool and Manchester MRs in the north-west and the London MR in the south-east.  相似文献   

Modelling the effect of vegetation on channel pattern in bedload rivers     

A. Brad Murray  Chris Paola 《地球表面变化过程与地形》2003,28(2):131-143

We modify a simple numerical stream‐pattern model to examine the effect of sediment stabilization by roots on the channel pattern of bedload rivers. In the model, vegetation enhances bank resistance to erosion, causing the development of a single channel instead of a rapidly changing, multiple channel (braided) pattern. Net aggradation resulting from a high sediment supply, however, causes frequent avulsions that destroy vegetation locally, leading to the development of a multiple‐channel pattern. A stability diagram representing multiple model runs predicts whether a river will exhibit single or multiple channels, based on plant‐enhanced bank strength, and on the time scale of plant development relative to a time scale for change in unvegetated channels. A second stability diagram predicts the way in which the amplitude and period of a fluctuating imposed sediment load influence whether a single or multiple‐channel pattern develops. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Speciation and fate of trace metals in estuarine sediments under reduced and oxidized conditions, Seaplane Lagoon, Alameda Naval Air Station (USA)     

Susan Carroll  Peggy A O'Day  Brad Esser  Simon Randall 《Geochemical transactions》2002,3(1):81-21

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