Sökning: "Proterozoic"

Visar resultat 1 - 5 av 36 avhandlingar innehållade ordet Proterozoic.

1. 1. Geochemistry of tin, tungsten and molybdenum in Swedish Proterozoic granitoids : its potential use in regional mineral exploration

   Författare :Karl-Magnus Drake; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Granitoid; lithogeochemistry; Sn; W; Mo; Li; geotectonic - chronologic subdivision; geochemical-statistical grouping; uni- and multivariate statistical analysis; computer programs; metallogenic element distributions; Sn-W-concentration patterns; ore-bearing potential; probability calculations; petrometallogenic element ratios; petrochemical trends; postmagmatic alterations; geochemical variability; normative composition; genesis; absolute age; bibliography; analysis databank; Proterozoic; Sweden; N5600 N6800 E2330 E1120;

   Sammanfattning : The primary aim of this broad regional study is to statistically determine the Li-Sn-W-Mo-bearing potential of various granitoids using geochemical criteria.Computer-based, univariate and multivariate statistical methods are applied to major and trace element data from ca 660 granitic rock samples and over 800 major element analyses, selected from the Swedish geological literature. LÄS MER

3. 2. Evolution of continental crust in the Proterozoic : growth and reworking in orogenic systems

   Författare :Andreas Petersson; Berggrundsgeologi; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; crustal reworking; Proterozoic; O-isotopes; Lu–Hf; U–Pb; zircon; Crustal growth;

   Sammanfattning : To understand the growth of continental crust, the balance between juvenile mantle derived extraction, infracrustal reworking and crustal recycling, needs to be estimated. Since the beginning of the century, the use of coupled in situ zircon U–Pb, Lu–Hf and O isotope analyses as a tool to address these questions have increased exponentially. LÄS MER

4. 3. Phosphate and Arsenic Cycling under Experimental Early Proterozoic Marine Conditions

   Författare :Christoffer Hemmingsson; Iain Pitcairn; Ernest Chi Fru; Per Andersson; Christophe Dupraz; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; DIP; Early Proterozoic; coprecipitation; adsorption; Iron formations; BIF; geokemi; Geochemistry;

   Sammanfattning : Nutrient dynamics in the Archean-Paleoproterozoic oceans strongly influenced primary productivity and the rise of atmospheric O2. Reconstructing the cycling of key nutrients such as dissolved inorganic phosphate (DIP) at this time is important for our understanding of the timing, rate and extent of atmospheric oxygenation at this time. LÄS MER

5. 4. Microfossils of eukaryotic cysts through time : A study of Precambrian-Ordovician organic-walled microbiota

   Författare :Heda Agić; Malgorzata Moczydlowska; Sebastian Willman; Frances Westall; Nicholas Butterfield; Uppsala universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; microfossils; eukaryotes; Proterozoic; reproductive cyst; Earth Science with specialization in Historical Geology and Palaeontology; Geovetenskap med inriktning mot historisk geologi och paleontologi;

   Sammanfattning : .... LÄS MER

7. 5. U-Pb baddeleyite geochronology of Precambrian mafic dyke swarms and complexes in southern Africa - regional scale extensional events and the origin of the Bushveld Complex

   Författare :Johan Olsson; Berggrundsgeologi; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; U-Pb TIMS geochronology; geochemistry; baddeleyite; mafic dyke swarms; mantle plume; Bushveld Complex; Kaapvaal Craton; Zimbabwe Craton; Archean; Proterozoic;

   Sammanfattning : Dolerite dykes are formed when iron- and magnesium-rich (mafic) mantle-derived magmas ascend through the lithosphere (upper part of the mantle) and crystallize as ‘hydro-fractures’ within the crust. Dykes may exist in great numbers to form dyke swarms (linear or radiating), which can be linked to time periods of continental break-up, or attempted break-up events, associated with voluminous volcanism. LÄS MER