Palaeomagnetic and potassium‐argon dating studies of the Tasmanian Dolerites     

P. W. Schmidt  Ian McDougall 《Australian Journal of Earth Sciences》2013,60(5-6):321-328

The stable magnetizations of the Tasmanian Dolerites are shown to fall into two distinct groups depending upon their directions and the geographical region of the dolerites. It has been suggested that this could be a result of significant age differences between the dolerites of these groups. A series of K‐Ar determinations indicates that there is no detectable systematic age differences and the average of the five bodies dated is 170.5 ± 8.0 m.y. (not significantly different from previous K‐Ar dates from a single body). A re‐appraisal of the palaeomagnetic data, in the light of the distinct groupings of the directions, yields two significantly different pole positions‐ Lat 50.7°S, Long. 174.5°E (A_9r, = 5.2°) and Lat. 47.7 °S, Long. 123.5° (A₉₅ = 9.5°)’. The former of these is in excellent agreement with pole positions from other Lower to Middle Jurassic rocks of Australia but the significance of the latter remains obscure.  相似文献   

Reply: Palaeomagnetic and potassium‐argon dating studies of the Tasmanian dolerites     

P. W. Schmidt  Ian McDougall 《Australian Journal of Earth Sciences》2013,60(5-6):366-367

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Impact of changing climate and land use on the hydrogeology of southeast Australia ∗     

I. Cartwright  I. Simmonds 《Australian Journal of Earth Sciences》2013,60(8):1009-1021

Anthropogenic climate change is the Earth's most serious large-scale environmental concern. While the projected changes of global temperatures, rainfall and surface water have been modelled in a sophisticated manner, the impact on groundwater resources is much less well constrained. In southeast Australia, the decrease in rainfall amount and an increase in temperature that are predicted by climate models are generally assumed to reduce the amount of recharge to the groundwater systems. However, the increase in recharge that has resulted from clearing of the native vegetation will almost certainly produce a greater impact on the groundwater system, increasing quantity and potentially improving quality. Additionally, the impact on recharge of changes to rainfall frequency rather than just total amount is not well documented. Overall our understanding of the impacts of climate change on groundwater systems is insufficiently advanced to make firm predictions. Indirect impacts of climate change, particularly the projected increased demand for groundwater or surface water to supplement surface water supplies also will have a major impact that may be greater than the direct effect of climate change.  相似文献   

Zircon U-Pb age, geochemical, and Sr-Nd-Pb isotopic constraints on the origin of alkaline intrusions in eastern Shandong Province, China     

Shen Liu  Caixia Feng  Ruizhong Hu  Shan Gao  Tao Wang  Guangying Feng  Youqiang Qi  Ian M. Coulson  Shaocong Lai 《Mineralogy and Petrology》2013,107(4):591-608

Alkaline intrusions in the eastern Shandong Province consist of quartz monzonite and granite. U-Pb zircon ages, geochemical data, and Sr-Nd-Pb isotopic data for these rocks are reported in the present paper. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon analyses yielded consistent ages ranging from 114.3?±?0.3 to 122.3?±?0.4 Ma for six samples of the felsic rocks. The felsic rocks are characterised by a wide range of chemical compositions (SiO₂?=?55.14–77.63 wt. %, MgO?=?0.09–4.64 wt. %, Fe₂O₃?=?0.56–7.6 wt. %, CaO?=?0.40–5.2 wt. %), light rare earth elements (LREEs) and large ion lithophile elements (LILEs) (i.e., Rb, Pb, U) enrichment, as well as significant rare earth elements (HREEs) and heavy field strength (HFSEs) (Nb, Ta, P and Ti) depletion, various and high (⁸⁷Sr/⁸⁶Sr) _i ranging from 0.7066 to 0.7087, low ε _Nd (t) values from ?14.1 to ?17.1, high neodymium model ages (T_DM1?=?1.56–2.38Ga, T_DM2?=?2.02–2.25Ga), ²⁰⁶Pb/²⁰⁴Pb?=?17.12–17.16, ²⁰⁷Pb/²⁰⁴Pb?=?15.44–15.51, and ²⁰⁸Pb/²⁰⁴Pb?=?37.55–37.72. The results suggested that these rocks were derived from an enriched crustal source. In addition, the alkaline rocks also evolved as the result of the fractionation of potassium feldspar, plagioclase, +/? ilmenite or rutile and apatite. However, the alkaline rocks were not affected by crustal contamination. Moreover, the generation of the alkaline rocks can be attributed to the structural collapse of the Sulu organic belt due to various processes.  相似文献   

U-Pb Zircon Age,Geochemical, and Sr-Nd-Pb Isotopic Constraints on the Age and Origin of Mafic Dykes from Eastern Shandong Province,Eastern China   总被引：1，自引：0，他引：1  

LIU Shen  HU Ruizhong  FENG Caixi  GAO Shan  FENG Guangying  LAI Shaocong  QI Youqiang  Ian M. COULSON  YANG Yuhong  YANG Chaogui  and TANG Liang 《《地质学报》英文版》2013,87(4):1045-1057

U-Pb zircon age, geochemical, and Sr-Nd-Pb isotopic data of mafic dykes from eastern Shandong Province, eastern China is reported herein. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon analyses of two samples from the investigated mafic dykes yield consistent ages ranging from 121.9 Ma ± 0.47 Ma to 122.9 Ma ± 0.61 Ma. The mafic dykes are characterized by high (87Sr/86Sr) i ranging from 0.7087 to 0.7089, low εNd(t) values ranging from -16.9 to -17.8, 206Pb/204Pb = 17.15 to 17.17, 207Pb/204Pb = 15.45 to 15.47, and 208Pb/204Pb = 37.59 to 37.68. Results from the current study suggest that the mafic dykes are derived from partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from foundered lower crustal eclogite. The mafic dykes may have been generated through subsequent insignificant crystal fractionation and very minor crustal contamination during magma ascent. Combined with previous studies, the current findings provide new evidence that the intense lithospheric thinning beneath the eastern Shandong Province of eastern China occurred at ~120 Ma, and that this condition was caused by the removal of the lower lithosphere (mantle and lower crust).  相似文献   

The augen gneisses of the Peloritani Mountains (NE Sicily): Granitoid magma production during rapid evolution of the northern Gondwana margin at the end of the Precambrian     

Patrizia Fiannacca  Ian S. Williams  Rosolino Cirrincione  Antonino Pezzino 《Gondwana Research》2013,23(2):782-796

The medium- to high-grade polymetamorphic basement rocks of the Peloritani Mountains, northern Sicily, include large volumes of augen gneiss of controversial age and origin. By means of a geochemical and SHRIMP zircon study of representative samples, the emplacement age of the original granitoid protoliths of the augen gneisses and the most likely processes and sources involved in that granitoid magmatism have been determined. U–Pb dating of three samples from widely spaced localities in the Peloritani Mountains yielded igneous protolith ages of 565 ± 5, 545 ± 4 and 545 ± 4 Ma, respectively. These late Ediacaran/early Cambrian ages are much older than was previously assumed on geological grounds, and are typical of the peri-Gondwanan terranes involved in the geodynamic evolution of the northern Gondwana margin at the end of the Avalonian–Cadomian orogeny. Major and trace element compositions and Sr–Nd isotopic data, in combination with zircon inheritance age patterns, suggest that the granitoid protoliths of the Sicilian and coeval Calabrian augen gneisses were generated by different degrees of mixing between sediment- and mantle-derived magmas. The magmas forming the ca. 545 Ma inheritance-rich granitoids appear to have had a significant contribution from partial melting of paragneiss that is the dominant rock type in the medium- to high-grade Peloritanian basement. The closeness of the inferred deposition age of the greywacke protoliths of the paragneisses with the intrusion age of the granitoids indicates rapid latest Precambrian crustal recycling involving erosion, burial, metamorphism to partial melting conditions, and extensive granitoid magmatism in less than ca. 10 Ma.  相似文献   

A midge-salinity transfer function for inferring sea level change and landscape evolution in the Hudson Bay Lowlands,Manitoba, Canada     

Trapper R. Dickson  Darren G. Bos  Marlow G. Pellatt  Ian R. Walker 《Journal of Paleolimnology》2014,51(3):325-341

We compared water chemistry and environmental data with midge assemblage data, using multivariate analysis to assess the environmental gradients that limit midge (Chironomidae, Chaoboridae and Ceratopogonidae) distributions in the Hudson Bay Lowlands, northeastern Manitoba, Canada. Midge remains, comprising 62 taxa, were obtained from surficial sediments of 63 ponds. Ponds were sampled to maximize the salinity gradient. Specific conductance ranged from 46 to 29,000 μS cm^?1. Proximity to the coast was a principal determinant of pond salinity, with ponds closer to Hudson Bay shoreline more saline that those farther away. Multivariate analysis indicated that midge distributions have a significant relationship ( $ {\text{r}}_{\text{boot}}^{2} = 0.68 $ ) with salinity in the data set. This work will allow paleolimnological inferences of midge community responses to changing sea level (i.e. salinity) via isostatic rebound within the Hudson Bay Lowlands, and will provide essential limnological information to scientists and managers in a region where understanding of aquatic ecosystems is limited. One undescribed midge taxon was dominant in ponds with the highest salinities and may be a key indicator for inferring highly saline environments.  相似文献   

Big Ben: a new wide-bore piston corer for multi-proxy palaeolimnology     

Ian R. Patmore  Carl D. Sayer  Ben Goldsmith  Thomas A. Davidson  Ruth Rawcliffe  Jorge Salgado 《Journal of Paleolimnology》2014,51(1):79-86

We present a design for a large diameter piston corer, deployed from a raft that is suitable for use in shallow lakes. The piston corer, known as Big Ben, consists of a core tube, a piston on a rope and a corer head, to which rods are attached to drive the tube into the sediment. A core catcher, which aids the support of the core tube when full of sediment, has been incorporated into the design. To extrude the sediment, a framework has been designed to keep the core tube upright and stationary and a modified bottle jack is used to push the piston upwards during the extrusion process. The practical operation of the Big Ben coring system from setting up a coring platform to collecting and safely extruding a core is detailed. Finally we summarise recent experiences of deploying the corer and highlight its potential uses in the developing field of multi-proxy palaeolimnology.  相似文献   

Book Reviews     

Ian M. Dunham  Alec Foster 《The Professional geographer》2013,65(1):132-157

Books reviewed:

Pyne, Stephen J., How The Canyon Became Grand: A Short History

Gibson, Clark C., Politicians and Poachers: The Political Economy of Wildlife Policy in Africa

Voeks, Robert A., Sacred Leaves of Candomblé: African Magic, Medicine, and Religion in Brazil

Grossman, Lawrence S., The Political Ecology of Bananas: Contract Farming, Peasants and Agrarian Change in the Eastern Caribbean

Fennell, David A., Ecotourism: An Introduction

Soffer, Arnon, Rivers of Fire: The Conflict Over Water in the Middle East

Light, Andrew and Smith, Jonathan M., Philosophy and Geography II: The Production of Public Space

Davies, Richard O., Main Street Blues: The Decline of Small-Town America

Driver, Felix and Gilbert, David, Imperial Cities: Landscape, Display and Identity

Baldassare, Mark, California in the New Millennium: The Changing Social and Political Landscape

Herzog, Lawrence A., From Aztec to High Tech: Architecture and Landscape Across the Mexico-United States Border

Cowie, Jefferson, Capital Moves: RCA’s Seventy-Year Quest for Cheap Labor

Aiken, Charles, The Cotton Plantation South Since the Civil War

Smith, Steven D., Crass, David, and Zierden, Martha A., The Southern Colonial Backcountry: Interdisciplinary Perspectives on Frontier Communities

Hoelscher, Steven D., Heritage of Stage: The Invention of Ethnic Place in America’s Little Switzerland

Bradley, Betsy Hunter, The Works: The Industrial Architecture of the United States  相似文献   

Error‐sensitive historical GIS: Identifying areal interpolation errors in time‐series data     

Ian N. Gregory  Paul S. Ell 《International journal of geographical information science》2013,27(2):135-152

Historical GIS has the potential to re‐invigorate our use of statistics from historical censuses and related sources. In particular, areal interpolation can be used to create long‐run time‐series of spatially detailed data that will enable us to enhance significantly our understanding of geographical change over periods of a century or more. The difficulty with areal interpolation, however, is that the data that it generates are estimates which will inevitably contain some error. This paper describes a technique that allows the automated identification of possible errors at the level of the individual data values.  相似文献