Geodynamics in the Bamble area during Gothian- and Sveconorwegian times: A comparative petrological study of two gabbros

Continents started to grow already at an early stage of the earth history. Some of these early continents were preserved from major destroying forces and are now recognized as cratons. What make these cratons unique is that they contain useful information about the continent building mechanism at an early time of the earth history. I focus in this thesis on such continent building mechanism occurring in the southwestern part of the Baltic Shield, the Bamble area, in a period between 1.8 Ga and 0.9 Ga ago. This area is one of the youngest parts of the Baltic Shield and exhibits two distinct periods of continental growth. The oldest is known as the Gothian period (between 1.75 Ga and 1.50 Ga); the youngest as the Sveconorwegian (between 1.25 and 0.9 Ga). The method I used to investigate this continent building mechanism at late proterozoic times is by comparing the geology of two gabbros i.e. the Jomasknutene and Dale gabbro. The Jomasknutene gabbro has been dated at 1.77 Ga ±0.19 Ga and must contain information about the Gothian and Sveconorwegian period. The Dale gabbro has been dated at 1.11 Ga ±0.14 Ga and must contain information about the Sveconorwegian period only. In the period the Bamble area was subjected to continental growth, between 1.75 Ga and 0.9 Ga ago, the reigning metamorphic conditions in this area were characterized by a continuous high heat flow from the area below. In terms of geotectonic setting, this can be interpreted as a discontinuous active rift system. At least two periods of gabbroic intrusions were initialized in this rift environment. True rifting was probably opposed by, compressional, orogenic activity. That the geotectonic setting in the Bamble area did not change much between 1.75 Ga and 0.9 Ga ago is accentuated by the geological similarity between the Gothian Jomasknutene and the Sveconorwegian Dale gabbro. They appear to have a similar whole rock chemistry, magmatic fractionation trend, magmatic and, in less extent, metamorphic mineralogy. The most prominent results of this study, based on the comparison of the two gabbros, are listed below

Dynamics of lithospheric extension: a modeling study

Much of the work on continental margins and sedimentary basins has been directed at quantifying parameters of the pure shear extension model (or stretching model) (McKenzie, 1978). This is surprising, since a sound physical basis of this kinematic model is lacking. Alternative kinematic models, like the simple shear model (Wernicke, 1981) have been proposed which, at least in some basins, explain the surface observations equally welL In terms of asymmetry, the pure shear model and the simple shear model represent end-members of a spectrum of kinematic models for continental extension (Figure 1). The central issue of this thesis is to determine -by numerical modeling- whether the pure shear model and the simple shear model are physically plausible and to gain insight in the physical conditions which control the style of extension

Magnetic minerals in Pliocene and Pleistocene marine marls from Southern Italy: rock magnetic properties and alteration during thermal demagnetization

The rock magnetic properties of two different Pliocene to Pleistocene marine marls from southern Italy are studied. Different conditions during sedimentation have led to two completely different magnetic mineralogies in these marls. Chapters 2, 3 and 4 examine the rock magnetic properties of the Early Pliocene marine marls of the Trubi formation sampled at Eraclea Minoa in the Caltanissetta basin on southern Sicily (photo 1). These pelagic marls are characterized by a high carbonate content (60-80%), a sedimentation rate of 4-5 cm/ky and a cyclic lithology related to the Earth's orbital cycles. Magnetite is the primary remanence carrier in the Trubi marls. In chapters 5, 6 and 7 rock magnetic results for the Late Pliocene-Early Pleistocene marine marls of the Vrica section are presented (photo 2). The Vrica section is the Pliocene-Pleistocene boundary stratotype, situated in the Crotone-Spartivento basin of northern Calabria. The marls were deposited in shallower water with a sedimentation rate between 25 and 50 cm/ky and they have a carbonate content of only 15-25%. In these marls the climatic fluctuations caused by the Earth's orbital cycles are expressed as frequently occurring sapropelitic layers. Magnetic sulphides are the main magnetic minerals in the Vrica marls

Growth structures: examples of integrated sedimentological and structural-geological basin analysis

This thesis is based on research in the interface oftwo geological disciplines, sedimentology (the study of sediments, like sandstone and limestone) and structural geology (the study of rock deformation). Sedimentation is influenced by cosmic and climatological processes, sea-level change, and deformation of the earth's crust. Prerequisites for the generation of sediments are uplift and erosion in source areas, and subsidence and deposition in basins. Contrary to these vertical motions, deformation is often acting (sub)parallel to the earth's surface, i.e., horizontally (tension, compression, wrenching). To understand the influence of the deformation on sedimentation, the horizontal effects of deformation have to be translated into vertical ones. Growth structures are deformations active during sedimentation. They cause irregularities in the pattern of basin infilling. They represent the first deformation of sediments, and are generally overprinted by several later phases of deformation. It, therefore, requires stepwise restoration and elimination of these later structures to detect the growth structures. Since sediments can be dated, in a relative sense with fossils and absolutely (with the decay of radioactive elements in minerals), growth structures can be calibrated chronologically. This allows to determine variations in the rate of displacement, direction, and intensity of the deformation process, which is often difficult to detect directly by structural analysis. The study of growth structures, therefore, comprises both the analysis of the mechanism of sedimentation and that of deformation. This kind of research is generally done separately by different scientists with diverse aims, and at different scales. Combination in retrospect of such data easily leads to misinterpretations. The thesis emphasizes the advantage of integrated analysis from the very beginning of a research project in the combined fields of sedimentology and structural geology. The printed part considers that interrelationship with examples from research in mobile belts of a wide range of ages, carried out with colleagues and many MSc students: the early Archaean (± 3450 million years ago) of NW Australia (Pilbara) and South Africa (Barberton Mountains), the Proterozoic (± 1750 Ma) of the Mount Isa area in Queensland (NE Australia), the Carboniferous (± 300 Ma) of the Cantabrian Mountains in NW Spain, and the Eocene of the southern Pyrenees (± 50 Ma). The results of these studies have been published in the period 1989- 1998. A choice of five articles forms, on CD, part of this thesis

Coastal plain and fluvial deposits in the tertiary of central and northern Spain

The Ebro Basin represents purely fluvial deposition with a relatively high, but steady tectonic activity in relation to uplift of the Pyrenees and thrust fault activity. The cyclic pattern in the fluvial deposits can be attributed to Milankovitch related climatological changes. In the Loranca Basin both tectonic activity and climatological conditions controlled the style of the alluvial channels and the alluvial facies distribution. Also in the Tremp-Graus Basin both tectonic activity and climate influenced the alluvial deposition and caused cyclic alluvial deposition, while, moreover, the depositional system was influenced by changes of relative sea level.. The aim of this study is to recognize cyclic patterns in the alluvial sedimentary successions in the three above mentioned areas in Spain. Moreover, the depositional cycles will be interpreted in terms of changes in tectonic activity, in climatological conditions and in sea level

Geodynamic evolution and mantle structure

With the advent of plate tectonic theory a framework has become available in which many observed features of the structure of the Earth can be understood. The theory can explain the geological processes that have resulted in terranes as diverse as oceans, mid-oceanic ridges, mountain belts, and intracontinental basins. However, despite its explanatory power plate tectonic theory is rarely used for its predictive properties, which should after all be an important aim of any scientific theory. In this research I will address some implications of the plate tectonic concepts, by using plate tectonic theory, to predict thermal and elastic properties of the interior of the Earth which were not used to formulate the theory. This prediction is made by forward numerical modelling of lithosphere scale tectonic processes. The work will focus on the Alpine-Mediterranean region, but the method described is applicable to any part of the Earth where Mesozoic or later plate collision processes can be reconstructed with sufficient detail from geological observations

Provenance and dispersal of sand-sized sediments: reconstruction of dispersal patterns and sources of sand-sized sediments by means of inverse modelling techniques

Sedimentary provenance studies attempt to link spatial and temporal patterns of compositional variation in basin fills to the evolution of source areas. The aim of this thesis is to propose a general framework for the study of spatial and temporal patterns of compositional variation of sand-sized sediments by means of quantitative methods. A number of techniques is presented which aim at providing a concise summary and/or explanation of compositional variation observed in natural sedimentary systems. This field of research is sometimes referred to as "provenance modelling"

Evolution of passive continental margins and initiation of subduction zones

The initiation of subduction is a key element in plate tectonic schemes for the evolution of the Earth's lithosphere. Nevertheless, up to present, the underlying mechanism has not been very well understood (e.g. Dickinson and Seely, 1979; Hager, 1980; Kanamori, 1980). The insight into the initiation of subduction process has lagged far behind the progress made in the last few years in the study of other aspects of plate tectonics, making this topic an outstanding problem'in geodynamics (Dziewonski and Boschi, 1980; Flinn, 1982). Vlaar and Wortel (Vlaar, 1975; Vlaar and Wortel, 1976; Wortel, 1980) have shown that a fundamental parameter in lithospheric studies is provided by the age of the oceanic lithosphere. It was, therefore, decided to investigate whether the age-dependence of lithospheric properties might provide a clue to better understanding of the initiation of the subduction process (Cloetingh et al., 198l). It is the aim of this thesis to give a systematic investigation into the mechanical conditions under which the initiation of a subduction zone can take place

Evidence for groundwater contamination by heavy metals through soil passage under acidifying conditions

The research reported here is aimed at improving the knowledge of the mobility of the heavy metals cadmium and zinc in vulnerable soil types. We use the term vulnerable with reference to vulnerability of groundwater for contamination by soil leaching. At diffuse soil immissions of heavy metals, accumulation is often supposed to occur mainly in the topsoil. Binding of heavy metals in this soil compartment is relatively strong, because of de presence of soil organic matter, clay-minerals and sesquioxides. If soil contains little organic matter and no clay minerals a reduced accumulation in the topsoil and an increased leaching of heavy metals to the groundwater is expected. Also the pH of the soil is of influence on this leaching. Cadmium contamination of the environment has drawn attention since the sixties. The most important occasion was an environmental calamity in Japan where rice paddy was irrigated by cadmium contaminated river water. The pollution was originated from an upstream situated mine. Also in the Netherlands concern exists about pollution of the environment by cadmium. Especially in the Dutch-Belgian Kempen elevated cadmium contents are found in soils and plants, as a result of industrial pollution. This study particulary addresses the questions whether or when the diffuse metal immissions breakthrough in the groundwater of the Kempen