Petrography and geochemistry of the Gross Spitzkoppe Igneous Complex Central-Western Namibia

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dc.contributor.authorFrindt, Stephenen_US
dc.date.accessioned2014-02-07T14:07:51Z
dc.date.available2014-02-07T14:07:51Z
dc.date.issued1997en_US
dc.description.abstracten_US
dc.description.abstractThe Gross Spitzkoppe Igneous Complex of western central Namibia represents an anorogenic magmatic event related to the opening of the South Atlantic ocean during the late Mesozoic period. The magmatic event (Tristan mantle plume?) is characterised by bimodal epizonal emplacement of evolved melt fractions and mafic dyke swarmsen_US
dc.description.abstractThe complex is composed of three subsolvus biotite monzogranites. A medium-grained biotite granite along the margin of the complex hosts mafic enclaves and Stockscheider units. This marginal granite often has a sharp contact with coarse-grained biotite granite, which is marked by schlieren bands and orbicular structures. A gradational contact between the coarse-grained biotite granite and the central porphyritic granite is often marked by small pegmatite pods and schlieren bands. Numerous late stage porphyritic and aplitic dykes cut all intrusive units of the complex, with subhorizontal aplitic dykes cutting the porphyritic graniteen_US
dc.description.abstractThe granites are weakly peraluminous (A/CNK 0, 93 to 1, 09) and are characterised by high silica content (SiO2 74 to 78 wt percent), NajO + K2O (ca. 9 wt percent), F (up to 1, 16 wt percent), Rb (500 to 800 ppm) and Nb (50 to 120 ppm) as well as low MgO ( 0, 01 wt percent), CaO (0, 3 to 0, 70 wt percent) and P ( 0, 04 wt percent). The granites are strongly differentiated with high Rb/Sr (~36) and Rb/Ba (~14) ratios. Chondrite-normalised rare earth patterns show slight enrichment in LREE (La/Yb ~4), and a prominent negative Eu anomaly (Sm/Eu ~ 33) is common to all granites of the complexen_US
dc.description.abstractGeochemically, the granites have A-type character and are probably derived from a low crustal igneous protolith. Tectonomagmatic diagrams indicate a within plate (WPG) tectonic setting related to crustal extension. The granites are composed of perthitic alkali feldspar, quartz, plagioclase (An 5-20) and extremely Fe-rich biotite (annite to siderophyllite). Accessory minerals include, fluorite, topaz, zircon, monazite, magnetite, columbite, thorite and Nb-rutileen_US
dc.description.abstractSubsolidus reactions are common to all intrusive phases, involving exsolution, recrystallisation and alteration of some primary minerals. The transformation of perthitic alkali feldspar to microcline reflects the postmagmatic activity of volatiles, resulting in the development of secondary albite along feldspar grains. The volatile-rich nature of the residual melt is indicated by marginal pegmatites (Stockscheiders), abundant pegmatite pods and hydrothermal veins. Pressure quenching textures along the pluton's periphery are characterised by banded aplites containing dendritic alkali feldspar. These dendritic alkali feldspar nucleated on the country rock and grew towards the center of the complex, reaching lengths of about 20 cm. Undercooling textures are also visible along apical portions of Stockscheider units and along the hanging wall of subhorizontal dykesen_US
dc.description.abstractThough the complex can be classified as tin bearing, no evidence of metal mineralisation was found, this may be attributed to the oxidising conditions of the meltsen_US
dc.description.degreeHelsinkien_US
dc.description.degreeFinlanden_US
dc.description.degreeHelsinki Universityen_US
dc.description.degreeMastersen_US
dc.format.extent100 pen_US
dc.format.extentillen_US
dc.identifier.isisF016-199901139999980en_US
dc.identifier.urihttp://hdl.handle.net/11070/271
dc.language.isoengen_US
dc.masterFileNumber2684en_US
dc.subjectGross spitzkoppe inen_US
dc.subjectGraniteen_US
dc.subjectPetrologyen_US
dc.subjectGeochemistryen_US
dc.subjectPegmatiteen_US
dc.subjectDamaraland i. pen_US
dc.subjectKleine spitzkoppe inen_US
dc.subjectBasalten_US
dc.subjectGeochronologyen_US
dc.subjectBerylen_US
dc.subjectTopazen_US
dc.subjectRhyoliteen_US
dc.subjectDikeen_US
dc.subjectInclusions in igneous rocksen_US
dc.subjectTourmalineen_US
dc.subjectDoleriteen_US
dc.subjectMicaen_US
dc.subjectTrace elementsen_US
dc.subjectReeen_US
dc.subjectMetasomatismen_US
dc.titlePetrography and geochemistry of the Gross Spitzkoppe Igneous Complex Central-Western Namibiaen_US
dc.typeThesisen_US
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