Petrography and geochemistry of the Gross Spitzkoppe Igneous Complex Central-Western Namibia select="/dri:document/dri:meta/dri:pageMeta/dri:metadata[@element='title']/node()"/>

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Show simple item record Frindt, Stephen en_US 2014-02-07T14:07:51Z 2014-02-07T14:07:51Z 1997 en_US
dc.description.abstract en_US
dc.description.abstract The 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 swarms en_US
dc.description.abstract The 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 granite en_US
dc.description.abstract The 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 complex en_US
dc.description.abstract Geochemically, 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-rutile en_US
dc.description.abstract Subsolidus 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 dykes en_US
dc.description.abstract Though 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 melts en_US
dc.format.extent 100 p en_US
dc.format.extent ill en_US
dc.language.iso eng en_US
dc.subject Gross spitzkoppe in en_US
dc.subject Granite en_US
dc.subject Petrology en_US
dc.subject Geochemistry en_US
dc.subject Pegmatite en_US
dc.subject Damaraland i. p en_US
dc.subject Kleine spitzkoppe in en_US
dc.subject Basalt en_US
dc.subject Geochronology en_US
dc.subject Beryl en_US
dc.subject Topaz en_US
dc.subject Rhyolite en_US
dc.subject Dike en_US
dc.subject Inclusions in igneous rocks en_US
dc.subject Tourmaline en_US
dc.subject Dolerite en_US
dc.subject Mica en_US
dc.subject Trace elements en_US
dc.subject Ree en_US
dc.subject Metasomatism en_US
dc.title Petrography and geochemistry of the Gross Spitzkoppe Igneous Complex Central-Western Namibia en_US
dc.type Thesis en_US
dc.identifier.isis F016-199901139999980 en_US Helsinki en_US Finland en_US Helsinki University en_US Masters en_US
dc.masterFileNumber 2684 en_US

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