Lakehead University Geology - Journal Yearbook (Thunder Bay, Ontario Canada)

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Moreover there was an interesting point about the metamorphism of the volcanic system: the intensity of metamorphism was steadily decreasing from the bottom to the top (very weakly metamorphic pillows) . I suggested an eventual direct relationsnip between the depth of the crustal segment and a kind of late-magmatic auto alteration (deuteric alteration). These are the reasons why I remain personally interested in the results of dredging operations, close to any mid-oceanic ridge. If there were some metamorphic rocks already there, they may well be attributed to some process of alteration of that kind. As soon as you are occupied by such questions, generally many other interesting problems arise. Studying recently, in collaboration with the Bedford Canadian Oceanic Institute, a set of dredged specimens, I momentarily shift toward another topic of interest: the origin of the dredged serpentinized ultrabic fragments. Among many interesting and mysterious facts, we found evidence of an intense pre-serpentinization cataclasis, probably due to a creeping process at the base of the crust, and presumably related to the oceanic floor spreading. Many metamorphic specimens from N. lat. on the Mid Atlantic Ridge are still waiting for an investigation; we may say already that they uniformly belong to the green schist facies only. It is fascinating to meet, near Thunder Bay, in the heart of the Canadian Shield, greenstone belts showing perfectly preserved relics of submarine basic lavas, exactly similar to the one formed very recently. It is extremely promising to compare their detailed petrological properties, with those recent equivalent rocks, because we may suppose some kind of difference between now and 3 billion years ago in the superficial environment and in the relations between continents, oceanic crust and mantle. In this comparison, as a petrologist, I foresee the possibility of detecting an evolution of the earth ' s crust, evolution about which we do not even have a serious hypothetical model yet. The geology school at Lakehead has therefore, a wonderful field of investigations for a long and sucessful future o BONGARD LESLIE GO. LTD. 204 ARTHUR ST. THUNDER BAY (P), ONT. STOCKBROKERS BOND DEALERS MUTUAL FUNDS D. F. BARON MGR. W. N. AUBRY S. MALINOSKI J. M. SCOTT TELEPHONE 344-6618

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Dr. Henri Loubat Geological Engineer, PhD., Geneva Assistant Professor, Lakehead University I became particularly attracted by petrology in 19ol when I found the opportunity of studying a set of metamorphic rocks from California. These rocks belonged to the glaucophane-schist and eclogite facies of metamorphism. At that time, I was fascinated by two problems exhibited by these classic Californian types: the process of diaphtoresis , and the phenomenon of converging facies. The glaucophane-schist may be due to a particular regional metamorphism acting on greywackes and ophiolites; but frequently it results from a retrograde process of modification from a high degree of metamorphism (amphibolite or eclogite) toward lower degrees of alteration. Both these glaucophane-bearing types are to be found, closely associated, in California, and they exemplify very well the retroinorphosis ( diaphthoresis) and facies convergence . It is easy to realize the interest of the study of those facies, if we know that eclogite themselves are not always considered as metamorphic rocks.... Soon after, receiving a grant from the University of Geneva I studied briefly greenstones, sediments and serpentines from Cuba. The degree of alteration of my samples was somewhat discouraging for a sucessful petrographical and geochemical investigation, but this was a first contact with igneous submarine rocks. During the next four years my main petrographic activity was devoted to surveying the Versoyen region - this area of the Alps is geologically very attractive. We should know that the Alps are subdivized longitudinally by a major tectonic thrust plane, the trace of which is called the Pennic front thrust . This line runs parallel to the chain, subdivizing it into two equal bands: the internal Alps (toward Italy) and the external Alps (toward France and Switzerland). The former is very rich in ophiolites, strongly metamorphic and intensely disturbed by the tectonic. The latter is not metamorphic, lacking ophiolites, and gently folded. The Versoyen, which is located exactly on the border between France and Italy, is the last ophiolitic area we could find when leaving the internal Alps going toward France, ’with this marginal location, this area offers the weakest degree of metamorphism we could have in the Alps for submarine volcanic rocks. A study based on field, microscopic and chemical investigations leads to the following conclusions: ' We have there a well-preserved submarine volcanic complex composed of the piling of various related units; at the bottom, along with slabs of aplitic granites and gneiss (fragments of the Alpine basement?), thin layers of serpentinites . Above, thick lenses of diff erenciated gabbros; still above, a set of sills, inter-bedded with black schists. At the top, an enormous amount of pillow-lavas. This rather logical sequence so well known by anglo-saxon geologists, was never recognized before anywhere in the Alps, although it is quite probable that it is actuall ' omnipresent, but was always disturbed by complex diastrophism. Petrology 17

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Dr. James M. Franklin, B.Sc. (Carleton); M.Sc. (Carleton); Ph.D. (Western) . Background Geologist for G.S.C. Assistant Professor, Lakehead University- Research Metallogeny of the Lake Superior Crustal Traverse, Shebandowan to Pickle Lake Origin of low temperature silver deposits, Thunder Bay area Stratigraphy of the Sibley Group, Thunder Bay District Metallogeny, Its Concepts and Uses Two concepts of metallogenesis are (l) the genesis of a single metal in a variety of geological environments, and (2) the examination of all mineral deposits within a geologically or geographic- ally defined region. The single metal concept does not facilitate documentation of variations in mode of occurrence with time, and may preclude comparison or integration of genetic ideas related to one metal with with those related to another. This concept does, however, allow for complete examination of the chemistry of concentration of a metal in all geological processes. For example, Gross (1965) in his study of iron deposits, is able to document the processes operative in concentrating iron in igneous (iron-titanium deposits associated with Grenville anorthosites), metamorphic (contact meta somatic deposits of Vancouver Island) and sedimentary (Algoma, Superior and Minette type deposits) bodies. Such a study contributes much to fundamental geochemistry, but may, in certain circumstances, be of less significance in deposit exploration. For example, in searching for copper, the exact nature of the chemical control on deposition of the metal is less important than the stage of development of a eugeocyncline or facies of cratonic cover sediments affiliated with copper deposition. Recognition of the appropriate lithofacies associated with a deposit is a fundamental factor in delineating new areas of exploration. The second metallogenetic concept involves examination of variations in mineral deposit type within a time-stratigraphic, litho stratigraphic or petrogenetic province. Basically an accurate inter- pretation of source and time of deposition of mineral deposits is integrated with a regional tectonic history including geosynclinal and post-orogenic evolution. Clearly, a prime difficulty in such a study is. selecting useful co-incident geographic and geologic limits. All lithological and structural variations in any time— unit should be included within the geographic bounds of the study. The area must have adequately outlined mineral deposit genesis, paleogeographic and tectonic reconstruction. Convenient geologic limits might be set by systemic boundaries and orogenic events. For example, the Aphebian era is defined at its initiation by the Kenoran orogeny, and at its end by the Penokean and Hudsonian orogeny. The Helikian era is defined by the latter orogenies at its inception, but the termination of dominant continental volcanism and sedimentation at its end. Together these eras include many conventional tectonic elements. The problem is to select an area in which the complete geosynclinal, mountain building, and continental deposition events are preserved. The Lake Superior and Central Labrador areas meet these requirements. A metallogenic scheme for the former region is outlined in Table 1. 19