The Heron Lake Stock is a lenticular shaped, pretectonic granitoid complex intruding the Jutten metavolcanics of the Savant Lake Greenstone Belt, Wabigoon Subprovince, Superior Province. Mapping, petrography, and chemical analyses have revealed that the stock is essentially trondhjemitic, with minor quartz diorite, granodiorite and quartz monzonite. The trondhjemites have undergone a high degree of sericitization and saussuritization. The grandiorite unit is characterized by secondary K-feldspar and the quartz monzonites are characterized by perthite formation as a result of K-autometasomation is the late stage potash-rich fluids. Late faulting has imposed a secondary foliation along the stock's southern boundary. K/Rb ratios suggest partial melting of lower crust/ upper mantle material producing a trondhjemitic magma. Chemical variation diagrams suggest a process of magmatic differentiation and fractional crystallization. / Thesis / Bachelor of Science (BSc)

<p> Glamorgan township in southeastern Ontario, is underlain by Precambrian rocks of the Grenville province. Prominent amongst these are migmatite, paragneiss, and granite gneiss, VJhich collectively form a series of rocks (the Glamorgan gneiss aeries). </p> <p> Field work revealed that this series is completely gradational from a geological aspect, and that the geological gradation is complemented by a geochemical gradation. <p> An explanation of these gradational relationships constitutes the main contribution of this study. The conclusions reached are that partial melting of paragneiss produced migmatite and a trondhjemitic melt, which later produced granitic (in the strict sense) derivatives. </p> <p> In developing the main conclusions, a number of subsidiary problems are discussed, chief of which are the possible metavolcanic or metasedimentary o'rigin of the paragneiss and the possible origin of so-called diorite as a differentiate of an alkaline gabbro. Metamorphism was concluded to be of Miyashiro's low pressure intermediate type. </p> <p> By the use of experimentally determined reactions and stability fields a metamorphic grid was devised, which led to the following upper limits of metamorphic conditions: 550 to 650°C and 3 to 6.5 kilobars total pre5sure. These estimates in turn lead to the following limiting geothermal gradients: 25 to 55°C per kilometre. </p> <p> The Glamorgan occurrence was found to share three characteristics with many other Precambrian terrains : 1. migmatisation and emplacement of granite accompanied high grade metamorphism; 2. an early sodium-rich granite was followed by a more potassic one; and 3. the more sodic granite is associated with a small amount of basic igneous rock. These three generalisations were used to formulate a possible model for deep crustal petrogenesis. </p> / Thesis / Doctor of Philosophy (PhD)