8 research outputs found
Impaktkivimite sekundaarne muutumine hüdrotermaalsetes ja diageneesi-murenemise protsessides: Ries’i meteoriidikraater, Saksamaa
No full textVäitekirja elektrooniline versioon ei sisalda publikatsioone.Lõuna-Saksamaal paiknev ligikaudu 24-kilomeetrise läbimõõduga Reis’i meteoriidikraater (14,3–14,5 Ma) on üks paremini säilinud impaktstruktuure, olles heaks mudelstruktuuriks impakti järgsete protsesside uurimisel. Riesi kraater on ühtlasi ka üks esimesi impaktstruktuure, kus on kirjeldatud ja oletatud impakt-indutseeritud hüdrotermaalset mineralisatsiooni. Hüdrotermaalset muutust on seostatud ennekõike süeviitse kompleksiga ning on kirjeldatud detailsemalt Newsom et al. (1986), Osinski (2003,2004) ja Osinski et al (2004) töödes. Kraatrit täitvate süeviitide hüdrotermaalseid muutuseid/ilminguid iseloomustab sekundaarne savimineralisatsioon ja teoliidistumine, millega kaasneb varajane K-metasomatism koos albitiseerumise ning kloritiseerumise ilmingutega temperatuuridel ~200–300°C (Osinski 2005). Samas pole pindmiste süeviitide hüdrotermaalne mineralisatsioon nii selgelt märgatav/eristatav ning seda on seostatud impaktklaasi muutumisel tekkima hakanud montmorilloniidi tüüpi savifaasiga (Newsom et al 1986), mille alusel on hinnatud pindmiste süeviitide muutumistemperatuuriks < 130 °C.
Antud uurimuse mineraloogilised, geokeemilised ja stabiilsete isotoopide analüüsid näitavad, et hüdrotermaalsete protsesside mõju Riesi meteoriidikraatri pindmiste süeviitide muutumisele praktiliselt puudub või ei ole eristatav ning valdav süeviitide muutumine toimub pindmisel murenemisel, madala pH (5–7) ja ioonkontsentratsiooniga (nt sademete vesi) veelises keskkonnas. Erinevalt pindmistest süeviitidest iseloomustavad kraatrit täitvate süeviitide hüdrotermaalseid muutuseid/ilminguid sekundaarne savimineralisatsioon ja tseoliidistumine ning satabiilsete isotoopide uuringud näitavad, et võrreldes pindmiste süeviitidega on nende muutumine toimunud kõrgematemperatuurilises (~100 °C) fluidis, mille pH varieerus >7–8 ning mis võis olla kõrgenenud ioonkontsentratsiooniga. Selline fluidikoostis tõendab sisemiste süeviitide muutumisel tekkinud savimineraalide hüdrotermaalset päritolu anioonhüdrolüütiliselt neutraliseeritud ja lahustuvate komponentide suhtes rikastunud fluidist.The 24-km diameter Ries crater, in Germany, is one of the best-preserved terrestrial complex impact structures; providing a good opportunity to study the evolution of the post-impact cooling in impact craters. The mineralogical, geochemical and stable isotope studies of the surficial and crater- fill suevites from the Ries crater has provided additional constraints on the mineralogical alteration of the Ries impactites and on the origin and evolution of the (geothermal) fluids that were involved in the formation of alteration mineralogy. Previous studies (Newsom et al., 1986; Osinski, 2005) have proposed that the Ries crater suevites have been altered by post-impact aqueous and hydrothermal fluids. Based on mineralogical grounds Newsom et al. (1986) suggested that the surficial suevite was altered at temperatures < 130 °C, and Osinski suggested that the crater-fill suevite was altered at temperatures from 200 – 300 °C.
Our mineralogical, geochemical and stable isotope studies suggests that the alteration in surficial suevites is driven mainly by ambient low-temperature weathering, rather than hydrothermal processes and the alteration occured at lower pH and in slightly acidic environment (percolation of meteoric water), showing that the smectite in surficial suevites precipitated in equilibrium with meteoritic fluids. However, alteration in crater filling sequence occurred in the presence of meteoric water-dominated fluid circulation at higher temperatures (40 to 110 °C) than the surficial suevites, but possibly within a normal thermal gradient. The modeled δ11B composition of crater-fill suevites, on the other hand, indicate that the alteration in the crater-fill suevites took place at elevated pH (>8–9). The elevated pH of the alteration fluids in crater filling suevites is possibly related to the effective removal of the available H+ ions in hydrothermal fluid (evolved meteoric water) through anion hydrolysis of impact glass and primary silicates
Stable isotope composition of smectite in suevites at the Ries crater, Germany: Implications for hydrous alteration of impactites
No full textThe 24-km diameter Ries crater, Germany, exhibits well-preserved crater
filling and surficial melt-rich breccia deposits that are believed to
have been altered by post-impact hydrothermal fluids. The alteration
mineralogy of the crater filling breccias is characterized by clay
(smectite, chlorite) and a zeolite assemblage, and secondary clay phases
(smectite, minor halloysite) in surficial melt-bearing breccia deposits.
Using stable isotope analysis of secondary smectitic clay fractions,
evidence of significant hydrous alteration of impactites at large
water/rock ratios was found. The estimated fluid temperatures, using
data derived by delta(18)O and delta D fractionation, suggest smectite
precipitation in surficial breccias in equilibrium with meteoric fluids
at temperatures 16 +/- 5 degrees C in agreement with the long-term
variation of modern precipitation in the area. The stable isotope
composition of smectite in crater-fill breccia, however, suggests a
trend of monotonously increasing temperatures from 43 to 112 degrees C.
with increasing depth through the breccia sequence. This demonstrates a
different origin of alteration and temperature distribution for the
surficial and crater filling melt-bearing impact breccias in the Ries
crater. Our results suggest that the inverted structure of hydrothermal
systems observed in some terrestrial impact craters, including the Ries
crater, could indicate the initial configuration of a thermal anomaly in
the crater filling sequence, but which is replaced with a normal
hydrothermal convection in crater proper, during the course of
post-impact cooling. (C) 2010 Elsevier B.V. All rights reserved
Establishment of standards for working time related to monolithic structures of the Estonian National Museum
No full textLõputöö autor jälgis konstruktsioonide tootlikkus näitajaid tagasi arvestamise tulemusena ja ka reaalseid tootlikkuse näitajaid. Autori hinnangul ei erinenud kahel viisil välja selgitatud tulemused teineteisest suuresti. Lisaks võib jõuda järeldusele, et püstitatud hüpotees - mida väiksem hind, seda viletsam tulemus ei pidanud paika. Takistused, mis mõjutavad erinevate ettevõtete tootlikust on tarneaegade nihkumised, alamehitatud meeskond, ebapädevad ja erinevate käekirjadega meeskonna liikmed – tekitavad tööde ringi tegemise vajadust, rahaprobleemid, järelevalvega suhtlemise probleemid, probleemid tellijaga ning projekteerijaga. Takistused frontidega – eelnevad tegijad ei ole oma asju veel lõpetanud, või siis on tegemist mõnel juhul mõne sidussüsteemiga, kus asi sõltub kahest ettevõttest. Organiseerimine või siis organiseerimatus – kui nt materjale või mehhanisme pole, siis ei saa enamus juhtudel tööd teostada. Oluliselt mõjutab tootlikkuse efektiivsust tööaja pikkus, vahetustega töö. Autori arvates pikk vahetus ei ole nii efektiivne kui puhanud mehe lühem vahetus. Kindlasti tuleb arvestada puhkepauside ja nende pikkustega - osad suitsetavad pakk päevas, teised aga ei tee suitsu ja teevad terve päev tööd. Autori saadud kogemuse põhjal jälgides kahe erineva alltöövõtja tööprotsesse postide valmistamiseks – peaks postide ehitus brigaadi koosseisus olema kaks inimest, eeldusel, et materjal on ette tellitud ning tõstetehnika on tagatud. Kuid vahest tuleb tööde organiseerimisel opereerida tervik brigaadiga, mis on justkui planeeritud ebaefektiivsus. Olukorras kus tööde mahud ei ole stabiilsed, võib seda ette tulla. Kui on suurem maht ja mehi vähe, võib osutuda kõigile osapooltele kahjulikuks, tähtajad hakkavad venima. Lõputöö koostaja on jõudnud järeldusele, et ettevõttete tootlikus sõltub ettevõtte töökultuurist ning tööprotsessis osalevate inimeste pädevusest ja arvust. Mõnikord suudetakse teha väiksema arvu inimestega rohkem, kui suurema arvu inimeste puhul, sest planeerimistööd, platsil tööde kordineerimine, varustatus jms. on paremini organiseeritud. Samuti määrab tootlikuse ära ka see, kas töölisel on tegemist tunni- või tükitööga. Mõlemal puhul on ITP kaasatus oluline - just koordineeritud tunnitöö on kvaliteedi ja tempo tagamise võti.The author of the diploma thesis examined the productivity indicators for the structures as a result of recalculation as well as actual productivity indicators. In the author's opinion, there were no significant differences in the results established using two methods. Moreover, one may come to the conclusion that the hypothesis defined – the lower the price, the worse the result – was not true. The bottlenecks that affect the productivity of various enterprises include shifts in the delivery dates, undermanned teams, incompetent and differently trained team members – calling for redoing of works, causing financial issues, issues in communication with the supervisory personnel, issues with the contracting authority and the designer. Bottlenecks related to fronts – the previous contractors are yet to complete their works or in some cases the issues are due to a cohesive system where activities depend on two enterprises. Organization or rather a lack of organization – for example, if there are no materials or mechanisms, in most cases it is not possible to perform the required works. The productivity indicators are substantially influenced by the working hours and shift work. In the author's opinion, long shifts are not as effective as shorter shifts by well-rested men. Definitely, rest breaks and their length must be taken into account – some employees smoke a pack per day whilst others do not smoke at all and work all the day long. The author's experience in monitoring the work processes of two different subcontractors for preparing posts shows that the construction team of posts should comprise two people, provided that the material has been pre-ordered and that lifting equipment has been ensured. The compiler of the diploma thesis has come to the conclusion that the productivity of enterprises depends on the work ethics of the enterprise as well as the competence and number of the people involved in the work process. Sometimes more work can be done with a smaller rather than a bigger team since planning, work coordination at the construction site, supplies, etc. have been better organized. Productivity can also be linked to the fact whether employees work on an hourly or piece work basis
Boron isotope composition of secondary smectite in suevites at the Ries crater, Germany: Boron fractionation in weathering and hydrothermal processes
No full textPractical considerations regarding power factor for nonlinear loads
No full textThis material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Brunel University's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. Copyright @ 2004 IEEEThe choice of LC compensator may be constrained by the availability of manufacturers units. To account for this, the capacitor values are chosen from among standard values and for each value the transmission losses is minimized, or power factor is maximized, or transmission efficiency is maximized. The global minimum or maximum is obtained by scanning all local minims or maxims. The performance of the obtained compensator is discussed by means of numerical examples
O in the ancient Martian regolith from Northwest Africa 7034: The important role of Fe oxides
No full textGeologic history of Martian regolith breccia Northwest Africa 7034:Evidence for hydrothermal activity and lithologic diversity in the Martian crust
No full textThe timing and mode of deposition for Martian regolith breccia Northwest Africa (NWA) 7034 were determined by combining petrography, shape analysis, and thermochronology. NWA 7034 is composed of igneous, impact, and brecciated clasts within a thermally annealed submicron matrix of pulverized crustal rocks and devitrified impact/volcanic glass. The brecciated clasts are likely lithified portions of Martian regolith with some evidence of past hydrothermal activity. Represented lithologies are primarily ancient crustal materials with crystallization ages as old as 4.4 Ga. One ancient zircon was hosted by an alkali-rich basalt clast, confirming that alkalic volcanism occurred on Mars very early. NWA 7034 is composed of fragmented particles that do not exhibit evidence of having undergone bed load transport by wind or water. The clast size distribution is similar to terrestrial pyroclastic deposits. We infer that the clasts were deposited by atmospheric rainout subsequent to a pyroclastic eruption(s) and/or impact event(s), although the ancient ages of igneous components favor mobilization by impact(s). Despite ancient components, the breccia has undergone a single pervasive thermal event at 500–800°C, evident by groundmass texture and concordance of ~1.5 Ga dates for bulk rock K-Ar, U-Pb in apatite, and U-Pb in metamict zircons. The 1.5 Ga age is likely a thermal event that coincides with rainout/breccia lithification. We infer that the episodic process of regolith lithification dominated sedimentary processes during the Amazonian Epoch. The absence of pre-Amazonian high-temperature metamorphic events recorded in ancient zircons indicates source domains of static southern highland crust punctuated by episodic impact modification.</p
The Northwest Africa 8159 martian meteorite: Expanding the martian sample suite to the early Amazonian
No full textInternational audienceNorthwest Africa (NWA) 8159 is an augite-rich shergottite, with a mineralogy dominated by Ca-, Fe-rich pyroxene, plagioclase, olivine, and magnetite. NWA 8159 crystallized from an evolved melt of basaltic composition under relatively rapid conditions of cooling, likely in a surface lava flow or shallow sill. Redox conditions experienced by the melt shifted from relatively oxidizing (with respect to known Martian lithologies, similar to QFM) on the liquidus to higher oxygen fugacity (similar to QFM + 2) during crystallization of the groundmass, and under subsolidus conditions. This shift resulted in the production of orthopyroxene and magnetite replacing olivine phenocryst rims. NWA 8159 contains both crystalline and shock-amorphized plagioclase (An(5062)), often observed within a single grain; based on known calibrations we bracket the peak shock pressure experienced by NWA 8159 to between 15 and 23 GPa. The bulk composition of NWA 8159 is depleted in LREE, as observed for Tissint and other depleted shergottites; however, NWA 8159 is distinct from all other martian lithologies in its bulk composition and oxygen fugacity. We obtain a Sm-Nd formation age of 2.37 +/- 0.25 Ga for NWA 8159, which represents an interval in Mars geologic time which, until recently, was not represented in the other martian meteorite types. The bulk rock Sm-147/Nd-144 value of 0.37 +/- 0.02 is consistent with it being derived directly from its source and the high initial epsilon(143)(Nd) value indicates this source was geochemically highly depleted. Cr, Nd, and W isotopic compositions further support a unique mantle source. While the rock shares similarities with the 2.4-Ga NWA 7635 meteorite, there are notable distinctions between the two meteorites that suggest differences in mantle source compositions and conditions of crystallization. Nevertheless, the two samples may be launch-paired. NWA 8159 expands the known basalt types, ages and mantle sources within the Mars sample suite to include a second igneous unit from the early Amazonian.(C) 2017 Elsevier Ltd. All rights reserved
