The Mavuradonha Layered Complex: Neoproterozoic ... - ArchiMeD

More documents

Recommendations

Info

4 Petrology and metamorphic evolution 36 4 Petrology and metamorphic evolution This chapter describes the petrology and metamorphic evolution of the Zambezi Allochthonous Terrain, the structurally highest terrain in the Zambezi belt (Barton et al. 1991; 1993). As mentioned in chapter 1, previous studies assumed that this part of the Zambezi belt was overprinted under granulite-facies conditions (Carney et al. 1991). The PT calculations in this chapter were carried out in order to unravel the evolution of the Mavuradonha Metamorphic Suite (Barton, 1991; 1993), which forms the structurally highest part of the Zambezi Allochthonous Terrain. Additional work was undertaken to describe the different layered sequences of the Mavuradonha Layered Complex. The terminology for the description of cumulate rocks used in this study follows terminology of Irvine (1982). This author redefined the terminology of Wager & Brown (1968), which is now available without relations to processes that lead to the formation of the cumulate rocks. Additionally a brief petrographic description of the metagabbroic rocks in the Nyamhanda and Chimwaya Hill Inliers and the Ocellar Gneisses is given. 4.1 Petrography - mineral assemblages and textures 4.1.1 Mavuradonha Layered Complex The first part of this chapter provides a description of the petrology of the different rock types and mineral phases occurring in the Mavuradonha Layered Complex in order to distinguish these rocks by their petrography. The mineral chemistry for garnet-bearing samples of the upper meta-anorthosite suite (e.g. metagabbros and meta-anorthosites), which were taken for thermobarometry, is described in greater detail. Special attention is given to corona textures associated with pyroxenes in the metagabbros. These textures are used to derive PT estimates for the retrograde part of the PT-path. The second part discusses the results of the thermobarometric estimates of each investigated sample. The results, in combination with the observed textures, were taken to deduce a PT-path. Samples of the different rock types exposed in the Mavuradonha Layered Complex were taken along sections across the mountain range, whenever a marked change in the mineral assemblage was observed. A complete description of the mineral assemblages of the investigated samples is given in Table III-1 in Appendix III. Photographs of thin sections are presented in Plate II.
4 Petrology and metamorphic evolution 37 The samples can be subdivided into eight groups according to their mineral assemblage. The following types can be distinguished: - serpentinite - metapyroxenites - garnet-bearing and garnet-free amphibolites - fine-grained metagabbros with variable amounts of hornblende and plagioclase - coarse-grained metagabbros - garnet-bearing metagabbros - leuco-metagabbros and leuco-amphibolites - meta-anorthosites, with variable amounts of garnet, clinopyroxene and hornblende - pegmatites The most common rock types in the Mavuradonha Layered Complex are garnet- bearing amphibolites at the base of the complex and coarse-grained metagabbros. The mineral assemblage plagioclase + clinopyroxene + garnet is restricted to the northern side of the Mavuradonha Mountain range and appears in the upper meta-anorthosite suite. Meta-anorthosites are restricted to two large suites but also occur in small layers within the layering of the metagabbro sequences. The term meta-anorthosite is used only to describe those rocks which occur within the two suites. Those that appear within the layered sequences of variable scale are termed ‘leuco’, because of the larger amounts of pyroxene pods and the limited scale of their occurrence. 4.1.1.1 Serpentinite A serpentinite (ZZB 55) is exposed on the southern side of the Mavuradonha Mountain range within the sequence of the main metagabbro. The serpentinite consists of equigranular serpentine associated with opaque minerals and small amphiboles. 4.1.1.2 Metapyroxenites Typical metapyroxenites are restricted to the circular structure of Nanuta and to the small hills north of Mavuradonha Mission. Metapyroxenites are always associated with coarse-grained metagabbros and show an equigranular interlobate texture. The metapyroxenites are monomineralic rocks consisting almost exclusively of clinopyroxene; rutile and ilmenite are the only accessory mineral phases. They often occur as exsolved grids within clinopyroxene. Clinopyroxene is partly replaced by green and brown
Page 1 and 2: The Mavuradonha Layered Complex: Ne
Page 3 and 4: All views and results presented in
Page 5 and 6: Table of contents Acknowledgements
Page 7 and 8: 6.2.3.4 Summary and interpretation
Page 9 and 10: This project was part of the Mainz-
Page 11 and 12: utile ages ranging from 526 ± 7 to
Page 13 and 14: Alter von 899 ± 46 Ma untermauert.
Page 15 and 16: 1 Introduction 1 1 Introduction 1.1
Page 17 and 18: 1 Introduction 3 1993). In the West
Page 19 and 20: 1 Introduction 5 Moreover, the stru
Page 21 and 22: 1 Introduction 7 Zambezi Belt Mount
Page 23 and 24: 1 Introduction 9 metamorphosed unde
Page 25 and 26: 1 Introduction 11 on minerals with
Page 27 and 28: 2 Geology of the study areas 13 Zam
Page 29 and 30: 2 Geology of the study areas 15 The
Page 31 and 32: Plate I Plate I-1: View at the land
Page 33 and 34: Plate I Plate I-3: Layering in the
Page 35 and 36: Plate I Plate I-5: Compositional la
Page 37 and 38: Plate I Plate I-7: Shearzone within
Page 39 and 40: 2 Geology of the study areas 25 def
Page 41 and 42: 2 Geology of the study areas 27 Two
Page 43 and 44: 3 Analytical methods 29 3 Analytica
Page 45 and 46: 3 Analytical methods 31 Mineral sep
Page 47 and 48: 3 Analytical methods 33 U-Pb rutile
Page 49: 3 Analytical methods 35 microscopic
Page 53 and 54: 4 Petrology and metamorphic evoluti
Page 57 and 58: Am II-1 II-2 Pl II-3 Grt Pl Cpx Cpx
Page 63 and 64: Plate III 49 Plate III-8: Corona te
Page 65 and 66: Pl III-4 Am III-5 III-6 Am Pl Am Op
Page 93 and 94: 5 Geochemistry 79 a) Gabbro / Norit
Page 95 and 96: 5 Geochemistry 81 Chimwaya Hill Inl
Page 97 and 98: 31 28 25 22 19 16 13 10 2.5 1.6 1.4
Page 99 and 100: 5 Geochemistry 85 25 20 15 10 5 Ga
Page 101 and 102:
5 Geochemistry 87 The trace element
Page 103 and 104:
5 Geochemistry 89 1000 900 800 700
Page 105 and 106:
5 Geochemistry 91 600 500 400 300 2
Page 107 and 108:
5 Geochemistry 93 proposed for gabb
Page 109 and 110:
5 Geochemistry 95 1000 900 800 700
Page 111 and 112:
6 Geochronology and zircon-cathodol
Page 113:
Page 116 and 117:
6 Geochronology and zircon cathodol
Page 120 and 121:
Page 122 and 123:
Page 125 and 126:
6 Geochronology and zircon cathodol
Page 127:
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
7 Sm-Nd, Rb-Sr and Pb-Pb isotopic s
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Page 154 and 155:
Page 156 and 157:
8 Petrogenetic and geotectonic impl
Page 158 and 159:
Page 160 and 161:
Page 162 and 163:
Page 164 and 165:
Page 166 and 167:
Page 168 and 169:
Page 170 and 171:
Page 172 and 173:
9 Interpretation in the regional co
Page 174 and 175:
Page 176 and 177:
Page 178 and 179:
References 164 References ARANOVICH
Page 180 and 181:
References 166 COMPSTON, W., WILLIA
Page 182 and 183:
References 168 GRAHAM, C.M. and POW
Page 184 and 185:
References 170 JOHN, T., SCHENK, V.
Page 186 and 187:
References 172 KROGH RAVNA, E. (200
Page 188 and 189:
References 174 MEZGER, K., HANSON,
Page 190 and 191:
References 176 POLLER, U. (1999): A
Page 192 and 193:
References 178 TEERTSTRA, D.K. and
Page 194 and 195:
Appendix 180 Appendix A-I Geology o
Page 196 and 197:
Appendix A-I. Geology of the study
Page 198 and 199:
Appendix A-I. Geology of the study
Page 200 and 201:
Appendix A-II. Analytical methods v
Page 202 and 203:
Appendix A-II. Analytical methods v
Page 204 and 205:
Appendix A-III. Petrology and metam
Page 206 and 207:
Page 208 and 209:
Page 210 and 211:
Page 212 and 213:
Page 214 and 215:
Page 216 and 217:
Page 218 and 219:
Page 220 and 221:
Page 222 and 223:
Page 224 and 225:
Appendix A-III. Petrography and met
Page 226 and 227:
Page 228 and 229:
Page 230 and 231:
Page 232 and 233:
Page 234 and 235:
Page 236 and 237:
Page 238 and 239:
Page 240 and 241:
Page 242 and 243:
Appendix A-IV. Geochemistry xlviii
Page 244 and 245:
Appendix A-IV. Geochemistry l Table
Page 246 and 247:
Appendix A-IV. Geochemistry lii Tab
Page 248 and 249:
Appendix A-IV. Geochemistry liv Tab
Page 250 and 251:
Appendix A-IV. Geochemistry lvi Tab
Page 252 and 253:
Appendix A-IV. Geochemistry lviii T
Page 254 and 255:
Appendix A-V. Geochronology and cat
Page 256 and 257:
Page 258 and 259:
Page 260 and 261:
Page 262 and 263:
Appendix A-VI. Sm-Nd, Rb-Sr and Pb-
Page 264 and 265:
Appendix A-VI. Sm-Nd, Rb-Sr and Pb-
Page 266:
Curriculum vitae 181 Curriculum Vit
show all

The Mavuradonha Layered Complex: Neoproterozoic ... - ArchiMeD

Create successful ePaper yourself

Delete template?

Save as template?