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21.
Delia Rösel Steven David Boger Andreas Möller Birgit Gaitzsch Matthias Barth Jeffrey Oalmann Thomas Zack 《地学学报》2014,26(1):64-71
Provenance studies from Cambro‐Ordovician sediments of the North Gondwana passive margin typically ascribe a North African source, a conclusion that cannot be reconciled with all observations. We present new U‐Pb ages from detrital rutile and zircon from Late Ordovician sediments from Saxo‐Thuringia, Germany. Detrital zircons yield age populations of 500–800 Ma, 900–1050 Ma and 1800–2600 Ma. The detrital rutile age spectra are unimodal with ages between 500 and 650 Ma and likely represent, together with the 500–800 Ma and 1800–2600 Ma zircon populations, detritus sourced predominantly from North Africa. In contrast, the c. 950 Ma zircons, which are persistently found in Cambro‐Ordovician sediments of North Gondwana, have no obvious African source. We propose that these zircons are sourced from the Rayner Complex–Eastern Ghats regions of Antarctica and India. An Indo‐Antarctic source indicates either continental‐scale sedimentary transport from central Gondwana to its peripheries or multiple cycles of sediment reworking and redeposition. 相似文献
22.
Thomas Zack Daniel F. Stockli George L. Luvizotto Matthias G. Barth Elena Belousova Melissa R. Wolfe Richard W. Hinton 《Contributions to Mineralogy and Petrology》2011,162(3):515-530
Rutile is a common accessory mineral that occurs in a wide spectrum of metamorphic rocks, such as in blueschists, eclogites,
and granulites and as one of the most stable detrital heavy minerals in sedimentary rocks. The advent of rutile trace element
thermometry has generated increased interest in a better understanding of rutile formation. This study documents important
analytical advances in in situ LA-ICP-MS U/Pb geochronology of rutile: (1) Matrix matching, necessary for robust in situ dating
is fulfilled by calibrating and testing several rutile standards (R10, R19, WH-1), including the presentation of new TIMS
ages for the rutile standard R19 (489.5 ± 0.9 Ma; errors always stated as 2 s). (2) Initial common lead correction is routinely
applied via 208Pb, which is possible due to extremely low Th/U ratios (usually <0.003) in most rutiles. Employing a 213 nm Nd:YAG laser coupled
to a quadrupole ICP-MS and using R10 as a primary standard, rutile U/Pb concordia ages for the two other rutile standards
(493 ± 10 Ma for R19; 2640 ± 50 Ma for WH-1) and four rutile-bearing metamorphic rocks (181 ± 4 Ma for Ivrea metapelitic granulite;
339 ± 7 Ma for Saidenbach coesite eclogite; 386 ± 8 Ma for Fjortoft UHP metapelite; 606 ± 12 Ma for Andrelandia metepelitic
granulite) always agree within 2% with the reported TIMS ages and other dating studies from the same localities. The power
of in situ U/Pb rutile dating is illustrated by comparing ages of detrital rutile and zircon from a recent sediment from the
Christie Domain of the Gawler Craton, Australia. While the U/Pb age spectrum from zircons show several pronounced peaks that
are correlated with magmatic episodes, rutile U/Pb ages are marked by only one pronounced peak (at ca 1,675 Ma) interpreted
to represent cooling ages of this part of the craton. Rutile thermometry of the same detrital grains indicates former granulite-facies
conditions. The methods outlined in this paper should find wide application in studies that require age information of single
spots, e.g., provenance studies, single-crystal zoning and texturally controlled dating. 相似文献
23.
C. J. Soares S. Guedes J. C. Hadler R. Mertz-Kraus T. Zack P. J. Iunes 《Physics and Chemistry of Minerals》2014,41(1):65-73
We present a novel age-equation calibration for fission-track age determinations by laser ablation inductively coupled plasma mass spectrometry. This new calibration incorporates the efficiency factor of an internal surface, [ηq]is, which is obtained by measuring the projected fission-track length, allowing the determination of FT ages directly using the recommended spontaneous fission decay constant. Also, the uranium concentrations in apatite samples are determined using a Durango (Dur-2, 7.44 μg/g U) crystal and a Mud Tank (MT-7, 6.88 μg/g U) crystal as uranium reference materials. The use of matrix-matched reference materials allows a reduction in the uncertainty of the uranium measurements to those related to counting statistics, which are ca. 1 % taking into account that no extra source of uncertainty has to be considered. The equations as well as the matrix-matched reference materials are evaluated using well-dated samples from Durango, Fish Canyon Tuff, and Limberg as unknown samples. The results compare well with their respective published ages determined through other dating methods. Additionally, the results agree with traditional fission-track ages using both the zeta approach and the absolute approach, suggesting that the calibration presented in this work can be robustly applied in geological context. Furthermore, considering that fission-track ages can be determined without an age standard sample, the fission-track thermochronology approach presented here is assumed to be a valuable dating tool. 相似文献
24.
Ahmad Redaa Juraj Farkaš Sarah Gilbert Alan S. Collins Stefan Löhr Davood Vasegh Marnie Forster Morgan Blades Thomas Zack Andrea Giuliani Roland Maas Andre Baldermann Martin Dietzel Dieter Garbe-Schönberg 《Geostandards and Geoanalytical Research》2023,47(1):23-48
Reference materials (RMs) with well-characterised composition are necessary for reliable quantification and quality control of isotopic analyses of geological samples. For in situ Rb-Sr analysis of silicate minerals via laser ablation inductively coupled plasma tandem mass spectrometry (LA-ICP-MS/MS) with a collision/reaction cell, there is a general lack of mineral-specific and matrix-matched RMs, which limits wider application of this new laser-based dating technique to certain minerals. In this work, pressed nano-powder pellets (NP) of four RMs, GL-O (glauconite), Mica-Mg (phlogopite), Mica-Fe (biotite) and FK-N (K-feldspar), were analysed and tested for in situ Rb-Sr dating, complemented by isotope dilution (ID) MC-ICP-MS Rb-Sr analyses of GL-O and Mica-Mg. In addition, we attempted to develop alternative flux-free and fused ‘mineral glasses’ from the above RMs for in situ Rb-Sr dating applications. Overall, the results of this study showed that among the above RMs only two NP (Mica-Mg-NP and GL-O-NP) were suitable and robust for in situ dating applications. These two nano-powder reference materials, Mica-Mg-NP and GL-O-NP, were thus used as primary RMs to normalise and determine Rb-Sr ages for three natural minerals: MDC phlogopite and GL-O glauconite grains, and also Mica-Fe-NP (biotite). Our in situ analyses of the above RMs yielded Rb-Sr ages that are in good agreement (within 8%) of published ages, which suggests that both Mica-Mg-NP and GL-O-NP are suitable RMs for in situ Rb-Sr dating of phlogopite, glauconite and biotite. However, using secondary RMs is recommended to monitor the quality of the obtained ages. 相似文献
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26.
Chen Zhengle Zhang Yueqiao Chen Xuanhua Wang Xiaofeng Ramon A. S. Zack W. B. 《中国科学:地球科学(英文版)》2001,44(1):103-111
The ENE-striking Altyn Tagh fault (ATF), extending along the northern edge of the Ti-betan Plateau, is one of the major important strike-slip faults, and has been known as one of the key areas to debate the eastward extrusion and crustral shortening models of the Tibetan Plateau during and after India-Asia collision. This paper mainly presents new evidence of Late Cenozoic sedimentary process to reconstruct the slip history of the ATF during the Late Cenozoic. Field measurements and laboratory analyses of the sedimentary characteristics in the Late Cenozoic basins in the central Altyn Tagh fault suggest that Late Cenozoic sedimentary sequence should be divided into three units according to facies changes. The paleo-topography reconstruction shows that the sedimentarion in these basins was tightly related with the fault, indicating that the ATF has experienced at least three stages of strike slipping in the Late Cenozoic. New geological data from the Late Cenozoic sedimentary basins and the formation of the present Suo’erkuli basin provide evidence for the displacement of the fault. The result shows that the 80–100 km left-lateral strike-slip displacement of the fault has been accumulated in the Late Cenozoic.
相似文献27.
28.
Silke Triebold George Luiz Luvizotto Raimon Tolosana-Delgado Thomas Zack Hilmar von Eynatten 《Contributions to Mineralogy and Petrology》2011,161(4):581-596
Investigation by Raman spectroscopy of samples from different geological settings shows that the occurrence of TiO2 polymorphs other than rutile can hardly be predicted, and furthermore, the occurrence of anatase is more widespread than
previously thought. Metamorphic pressure and temperature, together with whole rock chemistry, control the occurrence of anatase,
whereas variation of mineral assemblage characteristics and/or fluid occurrence or composition takes influence on anatase
trace element characteristics and re-equilibration of relict rutiles. Evaluation of trace element contents obtained by electron
microprobe in anatase, brookite, and rutile shows that these vary significantly between the three TiO2 phases. Therefore, on the one hand, an appropriation to source rock type according to Nb and Cr contents, but as well application
of thermometry on the basis of Zr contents, would lead to erroneous results if no phase specification is done beforehand.
For the elements Cr, V, Fe, and Nb, variation between the polymorphs is systematic and can be used for discrimination on the
basis of a linear discriminant analysis. Using phase group means and coefficients of linear discriminants obtained from a
compilation of analyses from samples with well-defined phase information together with prior probabilities of groupings from
a natural sample compilation, one is able to calculate phase grouping probabilities of any TiO2 analysis containing at least the critical elements Cr, V, Fe, and Nb. An application of this calculation shows that for the
appropriation to the phase rutile, a correct-classification rate of 99.5% is obtained. Hence, phase specification by trace
elements proves to be a valuable tool besides Raman spectroscopy. 相似文献
29.
Constraints on the formation environment of two chondrule‐like igneous particles from comet 81P/Wild 2 
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下载免费PDF全文 Zack Gainsforth Anna L. Butterworth Julien Stodolna Andrew J. Westphal Gary R. Huss Kazu Nagashima Ryan Ogliore Donald E. Brownlee David Joswiak Tolek Tyliszczak Alexandre S. Simionovici 《Meteoritics & planetary science》2015,50(5):976-1004
Using chemical and petrologic evidence and modeling, we deduce that two chondrule‐like particles named Iris and Callie, from Stardust cometary track C2052,12,74, formed in an environment very similar to that seen for type II chondrules in meteorites. Iris was heated near liquidus, equilibrated, and cooled at ≤100 °C h‐1 and within ≈2 log units of the IW buffer with a high partial pressure of Na such as would be present with dust enrichments of ≈103. There was no detectable metamorphic, nebular, or aqueous alteration. In previous work, Ogliore et al. (2012) reported that Iris formed late, >3 Myr after CAIs, assuming 26Al was homogenously distributed, and was rich in heavy oxygen. Iris may be similar to assemblages found only in interplanetary dust particles and Stardust cometary samples called Kool particles. Callie is chemically and isotopically very similar, but not identical to Iris. 相似文献
30.
Viable insertion in agribusiness value chains? Seaweed farming after Typhoon Yolanda (Haiyan) in Iloilo Province,the Philippines 下载免费PDF全文
下载免费PDF全文 This article provides one of the first academic assessments of upstream agribusiness value chain and rural livelihood challenges after the November 2013 Typhoon Yolanda (Haiyan), which devastated many coastal communities in the central Philippines. Based on a survey and semistructured interviews among fisherfolk, seaweed farmers and other stakeholders in Iloilo Province, this article lays bare the limited viability of the seaweed value chain as a result of the recurring typhoon threat, other environmental pressures and an ineffective regional political economy. Since Typhoon Yolanda, the marginalized communities have depended on horizontal coordination and support from international civil society. The empirical results show that enhanced information dissemination and public sector cooperation are necessary for the seaweed value chain to become more inclusive. The results could also have a wider significance for rural development in other coastal areas in Southeast Asia, namely in the spheres of adaptive strategies amidst vulnerability, upstream vertical coordination and upgrading. 相似文献