Keski-Mosambikin jurakautisten ryoliittien U-Pb zirkoni-iänmääritykset ja Lu-Hf-isotooppikoostumus : viitteitä monivaiheisesta felsisestä Karoo-magmatismista

• Main Author: Puttonen, Riina
• Other Authors: Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta, Geotieteiden ja maantieteen laitos, University of Helsinki, Faculty of Science, Department of Geosciences and Geography, Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten, Institutionen för geovetenskaper och geografi
• Format: Master Thesis
• Language: Finnish
• Published: Helsingfors universitet 2016
• Subjects: Geology; Geologia; Geologi; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/10138/230459

The Karoo large igneous province is situated in southern Africa, Antarctica and Falkland islands and its formation has been connected to the break-up of Gondwana supercontinent. According to previous studies the formation of the Karoo LIP happened during a short period of time, ca. 182 Ma. There have been found also older volcanic rocks from Antarctica (ca. 189 Ma). In this study the felsic volcanic rocks from central Mosambique were dated using the U-Pb zircon method. Zircons from four samples were analyzed using Secondary Ion Mass Spectrometry. The weighted U-Pb ages of the samples are between 182-186 Ma and it was possible to distinguish zircon populations of different ages. The ages of the populations were ca.189–190 Ma, ca. 184–185 Ma and ca. 181–182 Ma. There were also inherited zircons in two samples (385–903 Ma, 2680–2760 Ma and 1950–2450 Ma). From the age results it is possible to conclude that at ca. 188–189 Ma there was crystallizing melt in the magma chamber. At ca. 184–185 Ma and ca. 181–182 Ma more melt was separated from the crystal mush. Of the same samples Lu-Hf isotope composition was also analyzed using Laser Ablation Inductively Couples Mass Spectrometry. From the εHf values of the samples it is possible to conclude that the parental material of the felsic volcanic rocks of central Mozambique was a partial melt of the felsic crust rather than fractional crystallization of Karoo basalts. Karoon suuri magmaprovinssi sijaitsee eteläisen Afrikan, Etelämantereen ja Falklandinsaarten alueilla. Sen muodostumiseen on liitetty Gondwanan supermantereen hajoaminen. Aikaisempien U-Pb-ikätutkimusten mukaan provinssi on muodostunut nopeasti, noin 182 Ma sitten. Etelämantereelta on löydetty myös tätä vanhempia Karoo-vulkaniitteja, jopa 189 Ma vanhoja. Tässä työssä tutkittiin Keski-Mosambikin felsisiä vulkaniitteja. Alueelta ei ole aikaisempia ikätuloksia. Yhteensä neljälle näytteelle suoritettiin U-Pb zirkoni-iänmääritys sekundääri-ionimassaspektrometrimenetelmällä. Näytteiden painotetut keskiarvoiät ...