60Fe–60Ni systematics in the eucrite parent body: A case study of Bouvante and Juvinas     

Ghylaine Quitté  Christopher Latkoczy  Maria Schönbächler  Alex N. Halliday  Detlef Günther 《Geochimica et cosmochimica acta》2011,75(23):7698-7706

Eucrites are basaltic meteorites that cooled rapidly but are in many instances thermally metamorphosed and impact brecciated. The exact timing of these events remains unclear. In this study, Ni isotopic compositions and Fe/Ni elemental ratios are presented for two non-cumulate eucrites, Bouvante and Juvinas, including mineral separates from the latter. The samples are characterized by variable, well-resolved ⁶⁰Ni-excesses consistent with the former presence of live ⁶⁰Fe (t_1/2 = 2.62 Ma) at the time of eucrite crystallization. A significant fraction of Ni with a terrestrial-like composition appears to be surface correlated. This Ni may be the product of terrestrial contamination or was introduced by a chondritic impactor during brecciation. Altogether, the data provide evidence for a complex and probably multi-stage history of Fe and/or Ni redistribution, which impedes the interpretation of the chronological data.  相似文献   

Uranium–lead ages of apatite from iron oxide ores of the Bafq District,East-Central Iran     

Heinz-Günter Stosch  Rolf L. Romer  Farahnaz Daliran  Dieter Rhede 《Mineralium Deposita》2011,46(1):9-21

Iron oxide–apatite (IOA) deposits, often referred to as Kiruna-type iron ore deposits, are known to have formed from the Proterozoic to the Tertiary. They are commonly associated with calc–alkaline volcanic rocks and regional- to deposit-scale metasomatic alteration. In the Bafq District in east Central Iran, economic iron oxide–apatite deposits occur within felsic volcanic tuffs and volcanosedimentary sequences of Early Cambrian age. In order to constrain the age of formation of these ores and their relationship with the Early Cambrian magmatic event, we have determined the U–Pb apatite age for five occurrences in the Bafq District. In a ²⁰⁶Pb/²³⁸U vs. ²⁰⁷Pb/²³⁵U diagram, apatite free of or poor in inclusions of other minerals plots along the Concordia between 539 and 527 Ma with four out of five samples from one deposit clustering at the upper end of this range. For this deposit, we interpret this cluster to represent the age of apatite formation, whereas the spread towards younger ages may reflect either minor Pb loss or several events of IOA formation. Apatite with inclusions of monazite (±xenotime) yields disturbed systems with inclusions having developed after formation of the iron ore–apatite deposits, possibly as late as 130–140 Ma ago. Obtained apatite ages confirms that (IOA) and the apatite-rich rocks (apatites) of the Bafq district formed coevally with the Early Cambrian magmatic (-metasomatic) events.  相似文献   

西藏甲玛铜多金属矿区成矿斑岩的岩浆混合作用:石英及长石斑晶新证据   总被引：6，自引：3，他引：3  

彭惠娟  汪雄武  Müller Axel  秦志鹏  侯林  周云 《矿床地质》2011,30(2):249-265

西藏甲玛矿区斑岩内石英和长石斑晶的阴极发光(CL)特征及元素含量变化有效记录了岩浆演化、混合及补给事件.石英斑晶的显微生长结构表明,原始岩浆经历过2次铁镁质岩浆混合作用.根据石英斑晶中Ti含量的变化可知,在2次溶蚀前后,石英结晶温度分别增高了约110℃和80℃.此外,斜长石斑晶的反环带及其Ba、Sr、Fe等元素的浓度梯...  相似文献   

Chemical composition of spinel from Uralian-Alaskan-type Mafic–Ultramafic complexes and its petrogenetic significance     

J. Krause  G. E. Brügmann  E. V. Pushkarev 《Contributions to Mineralogy and Petrology》2011,161(2):255-273

Uralian-Alaskan-type mafic–ultramafic complexes are recognized as a distinct class of intrusions regarding lithologic assemblage, mineral chemistry and petrogenetic setting. In the present study, we discuss new data on the distribution of major elements in minerals of the spinel group in rocks from Uralian-Alaskan-type complexes in the Ural Mountains, Russia. Cr-rich spinel (Cr₂O₃ = 20–53 wt%) in dunite with interstitial clinopyroxene and in wehrlite cumulates indicate that it reacted with interstitial liquid resulting in the progressive substitution of Al₂O₂ and Cr₂O₃ by Fe₂O₃ and TiO₂. A distinct change in the spinel chemistry in dunite (Cr₂O₃ = 47–53 wt%), towards Al₂O₃- and Cr₂O₃-poor but Fe₂O₃-rich compositions monitors the onset of clinopyroxene fractionation in wehrlite (Cr₂O₃ = 15–35 wt%, Al₂O₃ = 1–8 wt%, Fe₂O₃ = 25–55 wt%). In more fractionated mafic rocks, the calculated initial composition of exsolved spinel traces the sustained crystallization of clinopyroxene by decreasing Cr₂O₃ and increasing FeO, Fe₂O₃ and fO₂. Finally, the initiation of feldspar crystallization buffers the Al₂O₃ content in most of the spinels in mafic rocks at very low Cr₂O₃ contents (<5 wt%). The fractionation path all along and the reaction with interstitial liquid are accompanied by increasing Fe₂O₃ contents in the spinel. This likely is caused by a significant increase in the oxygen fugacity, which suggests closed system fractionation processes. Spinel with Cr₂O₃ < 27 wt% is exsolved into a Fe₂O₃-rich and an Al₂O₃-rich phase forming a variety of textures. Remarkably, exsolved spinel in different lithologies from complexes 200 km apart follows one distinct solvus line defining a temperature of ca. 600°C. This indicates that the parental magmas were emplaced and eventually cooled at similar levels in the lithosphere, likely near the crust–mantle boundary. Eventually, these 600°C hot bodies were rapidly transported into colder regions of the upper crust during a regional tectonic event, probably during the major active phase of the Main Uralian Fault.  相似文献   

Holocene monsoon climate documented by oxygen and carbon isotopes from lake sediments and peat bogs in China: a review and synthesis   总被引：1，自引：0，他引：1  

Jiawu Zhang  Fahu Chen  Jonathan A. Holmes  Hui Li  Xiaoyan Guo  Junlan Wang  Shuang Li  Yanbin Lü  Yan Zhao  Mingrui Qiang 《Quaternary Science Reviews》2011,30(15-16):1973-1987

There has been much recent debate about Holocene climate variation in the monsoon region of China, especially the temporal pattern of variations in precipitation, the time-transgressive nature of the Holocene precipitation maximum, and the extent to which variations in regions influenced by the Indian Summer Monsoon (ISM) and the East Asian Summer Monsoon (EASM) have been synchronous. We summarize and compare carbonate oxygen-isotope records (δ¹⁸O_carb) from ten lakes within the present-day ISM region. We discuss their paleoclimate significance considering the present-day moisture source, isotopic composition of precipitation and the hydrological setting. The δ¹⁸O_carb records are controlled mainly by the isotopic composition of lake water, which in turn is a function of regional Precipitation/Evaporation (P/E) balance and the proportion of precipitation that is monsoon-derived. We normalized the δ¹⁸O_carb data and used these records to generate an integrated moisture index. This index, along with oxygen-isotope records from speleothems and carbon-isotope records (δ¹³C_org) from peats within the monsoon region, suggests that Holocene climate was broadly synchronous across the monsoon region and, within the limits of accuracy of the existing age models, provides no strong evidence for previously-proposed anti-phasing of the ISM and the EASM. Stable-isotope records from lake sediments and peat bogs have excellent potential for providing high-quality paleoclimate data for monsoon Asia, and complement high-resolution speleothem sequences, which are only found in certain localities.  相似文献   

Behavior of Gd-DTPA in simulated bank filtration     

Peter Möller  Andrea KnappePeter Dulski  Asaf Pekdeger 《Applied Geochemistry》2011,26(1):140-149

The behavior of Gd-DTPA during bank filtration was simulated in a 30 m column filled with Pleistocene sand and flushed by surface water from a lakeside in Berlin, Germany. The surface water is about a 1:1 mixture of river water and effluents from a sewage treatment plant. Throughout 34 days this water was continuously spiked with Gd-DTPA at a level of 60 μg/L. The broad plateau of the Gd-DTPA pulse declined by 15.4% within 34 days by transmetallation. Nine percentage of the total decline is caused by Y and rare earth elements; the remaining part is attributed to Cu²⁺ which is the most influential metal in surface water. All other metals also contributing to transmetallation are combined with Cu to Cu equivalents because only the rate constant of transmetallation of Cu²⁺ is known. The analytical results of the column effluents prove the pseudo-first-order kinetics of transmetallation based on reversible sorption of metals by pools in the column sediment and disprove biodegradation at noticeable levels. The mass ratio of water to tracer is <10¹⁰.  相似文献   

Pliocene climate change of the Southwest Pacific and the impact of ocean gateways     

Cyrus Karas  Dirk Nürnberg  Ralf Tiedemann  Dieter Garbe-Schönberg 《Earth and Planetary Science Letters》2011,301(1-2):117-124

The transition from the early Pliocene “Warmhouse” towards the present “Icehouse” climate and the role of Gateway dynamics are intensively debated. Both, the constrictions of the Central American Seaway and the Indonesian Gateway affected ocean circulation and climate during the Pliocene epoch. Here, we use combined δ¹⁸O and Mg/Ca ratios of planktonic foraminifera (marine protozoa) from surface and subsurface levels to reconstruct the thermal structure and changes in salinities from the Southwest Pacific Deep Sea Drilling Project (DSDP) Site 590B from 6.5 to 2.5 Ma. Our data suggest a gradual cooling of ~ 2 °C and freshening of the sea surface during ~ 4.6–4 Ma with an increased meridional temperature gradient between the West Pacific Warm Pool and the Southwest Pacific when the closing of the Central American Seaway reached a critical threshold. After ~ 3.5 Ma, the restricted Indonesian Gateway might have amplified the East Australian Current, allowing enhanced heat transport towards the Southwest Pacific with reduced meridional temperature gradients when the global climate gradually cooled. At the same time our data suggest a cooling and freshening of Subantarctic Mode Water (SAMW) or/and an increased northward flow of SAMW towards Site 590B, possibly a first step towards the present Antarctic Frontal System.  相似文献   

Erosion rates and mechanisms of knickzone retreat inferred from 10Be measured across strong climate gradients on the northern and central Andes Western Escarpment     

Luca M. Abbühl  Kevin P. Norton  John D. Jansen  Fritz Schlunegger  Ala Aldahan  Göran Possnert 《地球表面变化过程与地形》2011,36(11):1464-1473

A steep escarpment edge, deep gorges and distinct knickzones in river profiles characterize the landscape on the Western Escarpment of the Andes between ~5°S and ~18°S (northern Peru to northern Chile). Strong north–south and east–west precipitation gradients are exploited in order to determine how climate affects denudation rates in three river basins spanning an otherwise relatively uniform geologic and geomorphologic setting. Late Miocene tectonics uplifted the Meseta/Altiplano plateau (~3000 m a.s.l.), which is underlain by a series of Tertiary volcanic‐volcanoclastic rocks. Streams on this plateau remain graded to the Late Miocene base level. Below the rim of the Meseta, streams have responded to this ramp uplift by incising deeply into fractured Mesozoic rocks via a series of steep, headward retreating knickzones that grade to the present‐day base level defined by the Pacific Ocean. It is found that the Tertiary units on the plateau function as cap‐rocks, which aid in the parallel retreat of the sharp escarpment edge and upper knickzone tips. ¹⁰Be‐derived catchment denudation rates of the Rio Piura (5°S), Rio Pisco (13°S) and Rio Lluta (18°S) average ~10 mm ky^?1 on the Meseta/Altiplano, irrespective of precipitation rates; whereas, downstream of the escarpment edge, denudation rates range from 10 mm ky^?1 to 250 mm ky^?1 and correlate positively with precipitation rates, but show no strong correlation with hillslope angles or channel steepness. These relationships are explained by the presence of a cap‐rock and climate‐driven fluvial incision that steepens hillslopes to near‐threshold conditions. Since escarpment retreat and the precipitation pattern were established at least in the Miocene, it is speculated that the present‐day distribution of morphology and denudation rates has probably remained largely unchanged during the past several millions of years as the knickzones have propagated headward into the plateau. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Artificial light at night: implications for early life stages development in four temperate freshwater fish species   总被引：1，自引：0，他引：1  

Anika Brüning  Franz Hölker  Christian Wolter 《Aquatic Sciences - Research Across Boundaries》2011,73(1):143-152

Flora and fauna have both evolved under a natural cycle of light and dark. But especially in urban areas, the night is now increasingly disturbed by artificial light. Many traits and behaviours in fish are triggered by a circadian clock, for example hatching and swim bladder inflation, which predominantly take place at dusk or night. As lighting becomes brighter and extends farther into rural areas, the distinction between day and night becomes increasingly blurred. Therefore, the loss of diurnal trigger by artificial light at night was hypothesized having deleterious effects on these traits and impact fish reproduction. To assess these effects, eggs of four native freshwater fishes, Eurasian perch Perca fluviatilis, roach Rutilus rutilus, bleak Alburnus alburnus and chub Leuciscus cephalus, were incubated under two different light conditions: a photoperiod of 14 h light:10 h darkness (LD) and continuous illumination (LL). The time to hatch and swim bladder inflation was recorded. The species showed inconsistent reactions to the light treatments. In roach and bleak, the time to 50% hatch was longer in LL, whereas continuous lighting had an accelerating effect in chub. Incubation in LL elongated the hatching period in perch and roach and, in perch, the onset of darkness seemed to trigger hatching. The swim bladder inflation was significantly promoted by continuous light in chub and bleak but was not affected in roach. In conclusion, nocturnal artificial illumination could have an effect on hatching and initial swim bladder filling by masking the day–night-change and thereby diminish the trigger effect. However, the reactions were species specific and the increase in variation indicated a lack of diurnal triggering, whilst a general deleterious effect of artificial light at night has not been identified on early life stages.  相似文献   

Erratum: Oxidation and emission of methane in a monomictic lake (Rotsee,Switzerland)     

C. J. Schubert  F. S. Lucas  E. Durisch-Kaiser  R. Stierli  T. Diem  O. Scheidegger  F. Vazquez  B. Müller 《Aquatic Sciences - Research Across Boundaries》2011,73(1):183-183

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