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Provenance Analysis of the Neoproterozoic-Cambrian Nama Group (Namibia)

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Provenance Analysis of the Neoproterozoic-Cambrian Nama Group (Namibia) PROVENANCE ANALYSIS OF THE NEOPROTEROZOIC-CAMBRIAN NAMA GROUP (NAMIBIA) AND THE ARROYO DEL SOLDA*0 GROUP (URUGUAY): IMPLICATIONS FOR THE PALAEOGEOGRAPHIC RECONSTRUCTION OF SW GONDWANA by Gonzalo HomerocBlanco Gaucher) (Gonzalo Blanco4 THESIS presented in fulfilment of the requirements for the degree of PHILOSOPHIAE DOCTOR in GEOLOGY in the FACULTY OF SCIENCE of the UNIVERSITY OF JOHANNESBURG Supervisor Dr. H.M. Rajesh Co-supervisors Dr. U. Zimmermann Prof. G.J.B. Germs October 2008 DECLARATION I declare that this thesis is my own original work, conducted under the supervision of Dr. H.M. Rajesh, and co-supervision of Dr. U. Zimmermann and Prof G.J.B. Germs. It is submitted for the degree of Philosophiae Doctor in Geology to the Faculty of Science at the University of Johannesburg. No part of this research has been submitted in the past, or is being submitted, for a degree or examination at any other University or Institution of higher education. nzalo Blanco 26 P I °°' v-k,61\mle ciSUiter Date Place ACKNOWLEDGEMENTS I would like to express many thanks, To my supervisor, Dr. H.M. Rajesh, for the support and guidance. To my co-supervisor, Prof. Gerard Germs, who introduced me to the geology of Nama Group and to share his knowledge not only on geology but also on life. To the Faculty of Science at the University of Johannesburg for the financial support in the form of a bursary awarded to me as a post-graduate student. To the staff of the Department of Geology at the University of Johannesburg and post-graduate mates from the University of Johannesburg. To the staff (Dr. Willie Oldewage, Dr. Herman van Niekerk and Mr L.L. Coetzee) at SPECTRAU, the Central Analytical Facility of the University of Johannesburg, for permission and help to use various analytical equipments. To Prof Farid Chemale Jr. of the Laboratorio de Geologia Isotopica, Universidade Federal do Rio Grande do Sul, Porto Alegre (Brazil), for help with isotope analyses. To the IGCP project 478 "Neoproterozoic to Early-Palaeozoic events in SW Gondwana". To the external reviewers, Dr. David Chew and Dr. Beverly Saylor, for the constructive and encouraging comments, and corrections on the thesis that certainly improved the quality of scientific material as well as the language used to present it. Special thanks to, Dr. Claudio Gaucher for his advice, collaboration and friendship that lead to the realization of this thesis against many complications. Prof. Peter Sprechmann, Gabriela Martinez and Leticia Chiglino for their valuable help and discussions during fieldworks in Uruguay. My parents and all my family in Uruguay and Argentina. This thesis is dedicated to my mother Nora, who is at the time of penning this down, successfully and courageously fighting against illness. My father Homero. My sister Gabriela. Juan Jose and Rosina. All my friends in Uruguay and overseas, with special mention to my unconditional friends, Federico and Leonardo - good friends from Joburg. For the good advises and support to Paul Balayer. Finally, but not least my wife Paulina, for her full support and love. ii ABSTRACT The amalgamation of SW Gondwana after the break-up of Rodinia supercontinent during the Neoproterozoic-early Palaeozic was one of the most active tectonic periods of the earth history and its geological evolution remains controversial. Recently, diverse hypotheses such as mantle plume activity, orthogonal continent-continent and strike-slip collisions according to different models try to explain the complex evolution of the Pan-African Brasiliano orogens and the associated sedimentary basins. In order to get insight of the SW Gondwana reconstruction, provenance analyses were performed on two Neoproterozoic-early Palaeozic sedimentary units: (1) the Arroyo del Soldado Group representing a —5000 meter thick platform succession unconformably overlying the mainly Archaean to Neoproterozoic rocks of the Rio de la Plata Craton in Uruguay and, (2) the Nama Group, a —2000 meter thick shallow marine to fluvial deposit interpreted as a foreland basin in response to tectonism in the adjacent northern Damara and western Gariep Orogenic Belts and unconformably overlying the mainly Mesoproterozoic rocks of the Kalahari Craton in Namibia. Several techniques including petrography, heavy mineral analysis, geochemistry, Sm-Nd isotope analysis and zircon dating were applied to both sedimentary basins. The petrographic, heavy mineral analyses and geochemical results from the Nama Group indicate a recycled upper crust composition characterized by metamorphic and granitic sources and minor mafic rocks. Palaeocurrent analyses of the chromian spinet bearing sandstones of the Nama Basin point to a volcanic island arc source located in the Damara Belt. Detrital zircon dating of the Nama Group display major peaks of Neoproterozoic and Mesoproterozoic ages suggesting a provenance from the Damara/Gariep Belts and their basements. Palaeocurrents from the west and the dominance of Neoproterozoic-Cambrian detrital zircon ages (76%) in the "Molasse" stage of the foreland evolution probably indicate exhumation of the felsic volcanic arc root which probably occurred after the time indicated by the younger zircon dated at 531 ±9 Ma. The petrographic and geochemical results from the Arroyo del Soldado Group indicate a recycled upper crust composition characterized by source diversity composed of granite-gneissic and mafic-metamorphic rocks. On average, Nd isotopes account for Abstract iii negative ENd values and TDM ages in a range of variation found elsewhere within SW Gondwana. Detrital zircon dating indicate sources dominated by Palaeoproterozoic (1.7-2.0-2.2 Ga) and subordinate Archaean ages (2.5-2.9-3.5 Ga). The scarcity of Mesoproterozoic and Neoproterozoic zircons and palaeocurrent directions towards the east indicate that the Arroyo del Soldado Group was fed by detritus from the Rio de la Plata Craton favouring a passive margin tectonic setting for their deposition. Deformation of the Arroyo del Soldado Group took place ca. 530 Ma, after strike-slip collision with an African affinity terrane. Finally, based on the palaeogeographic evaluation, the provenance of Nama foreland basin and the passive margin deposit of the Arroyo del Soldado basin suggest that continent-continent collision of the Kalahari/Congo Cratons with the Rio de la Plata Craton and the Cuchilla Dionisio Pelotas Terrane most likely occurred due to strike slip accretion related to a component of N—S shortening in the period between 530 and 495 Ma. Abstract iv CONTENTS Chapter 1. Introduction and objectives 1.1 Provenance methodology .1 1.2 Objectives .3 1.3 The Arroyo del Soldado Group 6 1.3.1 The Uruguayan Shield .6 1.3.2 Lithostratigraphy and sedimentology of the Arroyo del Soldado Group 9 1.3.3 The Nico Perez Terrane .11 1.3.4 Age and correlations of the Arroyo del Soldado Group 13 1.4 The Nama Group .16 1.4.1 Damara Orogen ..16 Damara Belt 18 Gariep Belt 19 1.4.2 Stratigraphy, sedimentology and age of the Nama Group 20 1.4.3 Geotectonic setting of the Nama Group 23 1.5 Sampling and analytical methods ..25 1.6 Outline of the thesis 25 Chapter 2. Integrated provenance analyses on "Black Sands": A case study from the Lower Cambrian Fish River Subgroup (Nama Group, Namibia) Abstract 26 2.1 Introduction 27 2.2 Geological setting .29 2.2.1 Sedimentology 32 2.3 Sampling and analytical techniques .33 2.4 Sandstone petrography .34 2.5 Geochemistry 40 2.5.1 Major element chemistry ..40 2.5.2 Alteration and weathering .40 v 2.5.3 Trace element composition 41 2.6 Provenance .44 2.6.1 Framework mineral analyses 45 2.6.2 Detrital zircon dating 45 2.6.3 Heavy mineral analyses 47 2.6.4 Whole rock geochemistry 55 2.7 Discussion 59 2.7.1 Geochemistry and heavy mineral composition 59 2.7.2 Tectonic setting and sources .62 2.8 Concluding remarks 66 Chapter 3. Chemical composition and tectonic setting of chromian spinels of the Ediacaran-early Palaeozoic Nama Group, Namibia Abstract 68 3.1 Introduction 68 3.2 Nama Group ...72 3.3 Sampling and analytical techniques 73 3.4 Sedimentology and petrography of the chromian spinel bearing units 73 3.5 Chemistry of the chromian spinels and pyroxenes 78 3.6 Provenance of the detrital chromian spinels .79 3.7 Geotectonic implications 84 3.8 Concluding remarks 90 Chapter 4. Provenance of the Nama Group (Ediacaran-early Palaeozoic, Namibia): petrography, geochemistry and U-Pb zircon ages Abstract 91 4.1 Introduction 92 4.2 Nama Group 94 4.3 Damara Orogen 99 4.3.1 Damara Belt 99 4.3.2 Gaiep Belt 101 4.4 Sampling and analytical techniques 102 vi 4.5 Petrography 103 4.5.1 Kuibis Subgroup 103 4.5.2 Schwarzrand Subgroup 103 4.5.3 Fish River Subgoup 104 4.6 Geochemistry 105 4.6.1 Major element geochemistry ..105 4.6.2 Alteration 106 4.6.3 Trace elements 109 4.7 U-Pb detrital zircon dating 112 4.8 Discussion .116 4.8.1 Petrography .116 4.8.2 Geochemistry .118 4.8.3 Provenance and basin evolution .122 4.9 Concluding remarks 130 Chapter 5. Provenance of the Arroyo del Soldado Group (Ediacaran-Lower Cambrian, Uruguay): petrography, geochemistry, Nd isotopes and detrital zircon dating Abstract 132 5.1 Introduction 133 5.2 Geological setting 135 5.2.1 Pre- Arroyo del Soldado Group units 135 5.2.2 Lithostratigraphy of the Arroyo del Soldado Group ...137 5.2.3 Age and evolution of the Arroyo del Soldado Group .140 5.3 Sampling and analytical methods 141 5.4 Results ...143 5.4.1 Petrography 143 5.4.2 Geochemistry .144 5.4.3 Nd-isotopes 148 5.4.4 Detrital zircon ages 149 5.5 Discussion 151 5.5.1 Provenance .153 vii 5.5.2 Basin evolution and paleotectonic setting .159 5.6 Concluding remarks .163 Chapter 6.
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