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The African continent is unique in that it has escaped widespread orogenic activity after the Pan African orogenic event. Therefore, the African Plate provides the world's best example of the relationship between extensional magmatism and structural setting. This first complete and up-to-date review, written by leading scientists, discusses the evolutionary model and offers a new and reliable basis for scientists working on plate tectonics and extensional areas in other continents.
T is atlas is intended primarily for anybody who is in-some background for the arrangement of how the terested in basic geology of Africa. Its originality lies atlas was done. T e second chapter is devoted to the in the fact that the regional geology of each African history of geological mapping in Africa, necessary nation or territory is reviewed country-wise by maps for a fuller appreciation of why this work in Africa is and text, a view normally not presented in textbooks worth doing. Chapter 3 provides an executive s- of regional geology. It is my belief, that there has long mary on the stratigraphy and tectonics of Africa as a been a need in universities and geological surveys, whole, i. e. in the context of no political boundaries. both in Africa and in the developed world, for sum- T e main part of the atlas lies in Chapter 4, where in marizing geological maps and an accompanying basic alphabetical order each African country or territory text utilising the enormous fund of knowledge that is presented by a digitized geological overview map has been accumulated since the beginning of geologi- and an accompanying text on its respective strat- th cal research in Africa in the mid-19 century. I hope raphy, tectonics, economic geology, geohazards and that, in part, the present atlas may satisfy this need. geosites. A short list of relevant references is also a- ed.
Author : William R. Dickinson Publisher : Geological Society of America Page : 130 pages File Size : 28,47 MB Release : 1991 Category : Science ISBN : 9780813722641
Mid-Tertiary strata exposed as tilted homoclines along the flanks of the San Pedro trough and across broad uplands north of the Catalina core complex are assigned to the following formations, each of which includes informal local members and facies: (a) Mineta Formation, mid-Oligocene redbeds including both conglomeratic fluvial and finer-grained lacustrine deposits; (b) Galiuro Volcanics, including lavas and domes, air-fall and ash-flow tuffs, and intercalated volcaniclastic strata of late Oligocene to earliest Miocene age; (c) Cloudburst Formation, also of late Oligocene and earliest Miocene age but including a sedimentary upper member of conglomeratic strata as well as a volcanic lower member correlative with part of the Galiuro Volcanics; and (d) San Manuel Formation, composed of lower Miocene alluvial fan and braidplain deposits that display contrasting clast assemblages in different areas of exposure. Generally correlative Oligocene-Miocene strata exposed south of the Catalina core complex are assigned to the Pantano Formation, which contains similar lithologic components. Less-deformed Neogene strata of post-mid-Miocene basin fill are assigned to the Quiburis Formation along the San Pedro trough, but stratigraphic equivalents elsewhere lack adequate nomenclature. High benchlands mantled by paleosols mark the highest levels of Neogene aggradation. Successive stages of subsequent erosional dissection are recorded by multiple terrace levels incised into basin fill. Key exposures of syntectonic mid-Tertiary sedimentary sequences in several local subareas reveal typical structural and stratigraphic relationships. Multiple fault blocks expose pre-Tertiary bedrock overlain by tilted mid-Tertiary strata confined to intervening half-grabens. Bounding syndepositional faults dip southwest and associated homoclines dip northeast. Fanning dips and buttress unconformities reflect progressive tilt and burial of eroding fault blocks. Dips of block-bounding faults are inversely proportional to the ages of the faults. Steeper dips for younger faults suggest either progressive erosion of successive listric faults or progressive rotation of successive planar faults. Uniformly moderate to steep dihedral angles between fault surfaces and offset homoclinal bedding imply that the faults dipped more steeply near the surface when syntectonic mid-Tertiary strata were subhorizontal. Although the inference of listric faulting best links apparent strands of the Catalina detachment system, the alternate interpretation of rotational normal faulting is compatible with local structural relationships including tilt of porphyry copper orebodies. Within the San Pedro trough, multiple homo clines of mid-Tertiary strata are exposed locally in tilt-blocks exhumed by Neogene erosion from beneath nearly flat-lying basin fill of the Quiburis Formation. Faults bounding the mid-Tertiary exposures include backtilted strands of the Catalina detachment system, somewhat younger listric or rotational normal faults, and steeper basin-range normal faults that display offsets both synthetic and antithetic to the flanks of the San Petro trough. In Cienega Gap, flanking the Tucson Basin, multiple tilt-blocks of the Pantano Formation form part of the upper plate of the Catalina detachment system. Initial construction of alluvial fans by generally westward paleoflow was followed by ponding of lacustrine environments along the foot of secondary breakaway scarps that also generated massive megabreccia deposits. In summary, syntectonic Oligocene to Miocene sedimentation succeeded a prominent pulse of polymodal mid-Tertiary volcanism and was coeval with mylonitic deformation and detachment faulting along the flank of the Catalina core complex. The headwall rupture for the detachment system migrated westward from an initial position along the range front of the Galiuro Mountains. After mid-Miocene time, accumulation and subsequent dissection of essentially undeformed basin fill was accompanied by basin-range block faulting. The most challenging structural issue is whether fault strands of the Catalina detachment system are interconnected or are disconnected rotational segments.
This volume contains papers giving an interdisciplinary review of 12 major rift systems from North and South America, Africa, Europe and Asia. These papers are written by an international group of academic and industrial specialists each of whom is most knowledgeable about the respective rift. The analyzed rifts were selected on the basis of availability of an as-complete-as-possible geological and geophysical data base. Thirteen papers deal with geodynamic processes governing the evolution of rifts. A comprehensive digest of the available stratigraphic, structural, geophysical and petrological data, together with an extensive list of references, is provided for each of the analyzed rift systems. The megatectonic setting and dynamics of evolution of each basin is discussed. Geodynamic models are tested against the record of the analyzed rifts. The question of "active" as against "passive" rifting is addressed. The rifts analyzed range in age from Precambrian to Recent and cover a wide spectrum of megatectonic settings. There is discussion of the evolution of rifts in a plate-tectonic frame. The case histories are followed by discussions addressing the global setting of rifts and geodynamic processes active during the development of rifted basins.
Author : Mark R. Hudson Publisher : Geological Society of America Page : 516 pages File Size : 14,47 MB Release : 2013-01-01 Category : Science ISBN : 0813724945
"Extending from Colorado, USA, on the north to the state of Chihuahua, Mexico, on the south, the Rio Grande rift divides the Colorado Plateau on the west from the interior of the North American craton on the east. This volume focuses on the Rio Grande rift's upper crustal basins and is organized geographically with study areas progressing from north to south. Nineteen chapters cover a variety of topics, including sedimentation history, rift basin geometries and the influence of older structure on rift basin evolution, faulting and strain transfer within and among basins, relations of magmatism to rift tectonism, and basin hydrogeology"--Provided by publisher.
Meso-Cenozoic Brazilian Offshore Magmatism: Geochemistry, Petrology and Tectonics presents detailed studies from different points-of-view on the geological—particularly magmatic—evolution of the Brazilian and South Atlantic Ocean offshore areas. This comprehensive book on geological events will help readers understand the holistic evolution of the area across geographical boundaries. Each chapter consists of an introduction, regional and local geology, methods, results, discussions, conclusions and supplementary material related to the geological development in island and seamounts in the Brazilian Platform and seafloor. Integrates independent studies and research of the Brazilian offshore magmatism and tectonics into a single book Includes new seamount and island data that was previously unavailable to the public Introduces case studies to provide real-world examples of volcanism and scientific evolution
The variety of volcanic activity in the Solar System is widely recognised, yet the majestic sequences of magmatic processes that operate within an active planet are much less well known. Providing an exposition of igneous rocks, magmas and volcanic erupsions, this book brings together magnetic and volcanic data from different tectonic settings, and planets, with explanations of how they fit together. It systematically examines composition, origin and evolution of common igneous rocks, yet also examines a variety of rare magnetic rocks that play a crucial role in the global magma/igneous rock system.
Although geodetic monitoring techniques have been widely used in areas of seismic or volcanic activity, the difficulty inherent to their discrete nature means that they must be deployed carefully to ensure the best possible detection or sensitivity of these points (see e. g. , BALDI and UNGUENDOLI, 1987; JOHNSON and WYATT, 1994; SEGALL and MATTHEWS, 1997; Yu et al. , 2000). In many cases, a more global monitoring method, is required yet at the same time one that offers the highest level of sensitivity which enables detection of the phenomenon. Interferometry radar (InSAR) techniques have been shown to play an important role in seismic and volcanic monitoring because they cover large areas (100 x 100 km) and can be easily systematized in monitoring (see e. g. , MASSONNET and FEIGL, 1998; BDRGMANN et al. , 2000; MASSONNET and SIGMUNDSON, 2000; HANSSEN, 2001). The limitations inherent to the GPS and InSAR techniques (mainly observations at discrete surface points in the case of GPS and existence of non-coherent areas and the fact that, at present, the three displacement components cannot be obtained in SAR interferometry) can be overcome by using them together or other techniques (e. g. , PUGLISI and COLTELLI, 2001; RODRiGUEZ-VELASCO et al. , 2002; FERNANDEZ et al. , 2003).