The Mavuradonha Layered Complex: Neoproterozoic ... - ArchiMeD

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5 Geochemistry 86 indicators for early differentiation processes within the magma chamber because both elements decrease with decreasing MgO concentrations. Scandium displays a general depletion trend with decreasing MgO from relatively high concentrations in metapyroxenites to low concentrations in meta-anorthosites. These trends imply crystallisation of mineral phases such as pyroxene or olivine and opaques from the magma which can incorporate these elements in their crystal lattice. Yttrium, V, Nb, Zn, Sr and Ga show negative correlations with MgO. These negative correlations are restricted to the metagabbros and metapyroxenites. These elements, except Sr and Ga, are generally depleted in the meta-anorthosites. The negative correlation of these elements indicates enrichment in the residual magma. This enrichment of Y, V, Nb, Zn implies the occurrence of Fe-Ti oxides and apatite as additional cumulate phases. The negative Sr and Ga correlation reflects accumulation of plagioclase as the major Sr and Ga-bearing phase (McBirney, 1998). 5.2.2 Nyamhanda Inlier and Chimwaya Hill Inlier Field observations and investigations in thin sections lead to the supposition for a genetic relation between the Chimwaya Hill Inlier and the Mavuradonha Layered Complex rocks. Contrary to this, the Nyamhanda Inlier rocks show a different occurrence in the field, and petrographic investigations demonstrated major differences between the Nyamhanda Inlier and the Mavuradonha Layered Complex metagabbroic rocks, such as the appearance of different corona textures around the mafic phases and the clearly subophitic texture in most of the samples. The results of major and trace element investigations for each rock type which was distinguished in the metagabbros of both inliers during field work are shown in Figure 5-4 and are listed in Appendix IV, Table IV-2. MgO in the metagabbroic samples of the inliers ranges from 2.10 to 13.90 wt. % and SiO2 ranges from 43.76 to 54.26 wt. %. Al2O3 ranges between 13.15 and 24.81 wt. % and Fe2O3 is ranging from 4.39 to 15.61 wt. %. K2O, MnO and P2O5 concentrations are generally higher than those reported from the Mavuradonha Layered Complex. These major elements are enriched in samples with low MgO but high FeO concentrations. Major element trends (Fig. 5-4) are restricted to CaO, TiO2 and Na2O. CaO (8.08 –14.27 wt. %) correlates well with MgO and increases with increasing MgO. TiO2 (2.27 – 3.97 wt. %) and Na2O (0.75 - 4.56 wt. %) are negatively correlated with MgO, whereas CaO/Al2O3 ratios are fairly constant at decreasing MgO. The inlier samples display common trace element characteristics, in which compatible elements are enriched in samples with high MgO concentrations. Negative correlations are visible in HFS and incompatible elements.
5 Geochemistry 87 The trace elements Cr, Ni and Co correlate well with MgO. These three elements decrease with decreasing MgO content, which implies crystallisation of early phases from the mafic magma, e.g. pyroxene and/or olivine as well as opaques. These elements are sensitive indicators of fractionation of these early crystallising minerals. Strontium, Rb, Ba and Ga yield negative correlations with MgO, and all four elements are incompatible elements. They increase with decreasing MgO. This behaviour reflects crystallisation and removal of feldspars from the magma. Y, V, Zr, Nb and Zn show negative correlations with MgO. These elements are enriched mainly in Fe-rich metagabbros and metagabbros containing high Fe2O3 concentrations indicating the presence of Fe-Ti oxides and apatite. 15 13 11 9 CaO [wt. %] 7 0 4 8 12 16 MgO [wt. %] 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 0 4 8 MgO [wt. %] Na O [wt. %] 2 Nyanhanda Inlier metagabbros 12 16 Chimwaya Hill Inlier metagabbros Nyanhanda Inlier ferro-metagabbros Figure 5-4. Selected major and trace element variations versus MgO for metagabbroic rocks of the iNyamhanda Inlier and Chimwaya Hill Inlier.
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The Mavuradonha Layered Complex: Ne
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All views and results presented in
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Table of contents Acknowledgements
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6.2.3.4 Summary and interpretation
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This project was part of the Mainz-
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utile ages ranging from 526 ± 7 to
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Alter von 899 ± 46 Ma untermauert.
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1 Introduction 1 1 Introduction 1.1
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1 Introduction 3 1993). In the West
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1 Introduction 5 Moreover, the stru
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1 Introduction 7 Zambezi Belt Mount
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1 Introduction 9 metamorphosed unde
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1 Introduction 11 on minerals with
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2 Geology of the study areas 13 Zam
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2 Geology of the study areas 15 The
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Plate I Plate I-1: View at the land
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Plate I Plate I-3: Layering in the
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Plate I Plate I-5: Compositional la
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Plate I Plate I-7: Shearzone within
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2 Geology of the study areas 25 def
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2 Geology of the study areas 27 Two
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3 Analytical methods 29 3 Analytica
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3 Analytical methods 31 Mineral sep
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3 Analytical methods 33 U-Pb rutile
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Page 57 and 58: Am II-1 II-2 Pl II-3 Grt Pl Cpx Cpx
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7 Sm-Nd, Rb-Sr and Pb-Pb isotopic s
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8 Petrogenetic and geotectonic impl
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9 Interpretation in the regional co
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References 164 References ARANOVICH
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References 166 COMPSTON, W., WILLIA
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References 168 GRAHAM, C.M. and POW
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References 170 JOHN, T., SCHENK, V.
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References 172 KROGH RAVNA, E. (200
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References 174 MEZGER, K., HANSON,
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References 176 POLLER, U. (1999): A
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References 178 TEERTSTRA, D.K. and
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Appendix 180 Appendix A-I Geology o
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Appendix A-I. Geology of the study
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Appendix A-I. Geology of the study
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Appendix A-II. Analytical methods v
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Appendix A-II. Analytical methods v
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Appendix A-III. Petrology and metam
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Appendix A-III. Petrography and met
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Appendix A-IV. Geochemistry xlviii
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Appendix A-IV. Geochemistry l Table
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Appendix A-IV. Geochemistry lii Tab
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Appendix A-IV. Geochemistry liv Tab
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Appendix A-IV. Geochemistry lvi Tab
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Appendix A-IV. Geochemistry lviii T
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Appendix A-V. Geochronology and cat
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Appendix A-VI. Sm-Nd, Rb-Sr and Pb-
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Appendix A-VI. Sm-Nd, Rb-Sr and Pb-
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Curriculum vitae 181 Curriculum Vit
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