Göttingen, Univ., Diss., 2000. / Computerdatei im Fernzugriff.

Göttingen, Univ., Diss., 2000. / Computerdatei im Fernzugriff.

Göttingen, University, Diss., 2000.

The tectonic region that encompasses Southwestern Montana is a petrologically complex area containing several batholiths and thrust faults, underlined by Precambrian basement rock and capped by sedimentary rocks. Intrusive volcanism of Southwest Montana best represented by the Pioneer and Boulder batholiths is a product of the eastward subduction of the Farallon Plate underneath the North American Plate during the Mesozoic time. Geochemical modeling made evident that the Pioneer and Boulder batholiths have a comagmatic relationship. This conclusion is derived from variation, spider and REE diagrams along with petrographic and geochemical models. The intrusion of these batholiths is likely related to the emplacement of a detached portion of the Idaho batholith known as the Sapphire block. Future models that are outside of the scope of this research must consider the evidence proposed in this document to produce an overarching model for the intrusion of the Pioneer and Boulder batholiths in the incredibly dynamic tectonic setting of the Mesozoic.

The Karakoram Axial Batholith in N. Pakistan records the magmatic development of the Eurasian continental margin since the late Jurassic. Magmatism prior to the collision of India with Eurasia at c.45Ma is represented by subduction-related, calc-alkaline granodiorite plutonism. The chemical variation within these plutons is caused by high-level fractionation processes. However, heterogeneous isotope data suggests that the source of these magmas was the mantle wedge, enriched by87 a subducted slab component, with the melts being contaminated by a Sr-rich crustal component. There are two types of post-collisional leucogranite. The Sumayar pluton is related to restricted partial melting of sillimanite-grade metapelites triggered by fluxing of fluids from the underthrust Indian crust. This water-saturated, minimum melt is considered to be an analogue of the High Himalayan leucogranites. The other Karakoram leucogranites are related by fractionation to a more basic monzogranitic parent, whose geochemistry indicates a lower crustal source. However, melting of typical crust cannot explain the anomalously high large ion lithophile element (LILE) content of the monzogranites. Associated with the granites are ultra- potassic, LILE-enriched lamprophyres. This LILE-enrichment is attributed to alteration of the mantle wedge by fluids and/or siliceous melts from the slab. Amphibole in the resulting metasomatic assemblage acts as a sink for the otherwise incompatible LILE. As a result of heating and thermal relaxation beneath the thickened continental crust, enriched amphibole, stable in the pre-collisional mantle wedge beneath the Karakoram, dehydrated or melted some 20Ma after collision to give the lamprophyres. Fluid precursors to this melting contaminated the source region of the granites selectively enriching it in LILE and triggering/promoting melting. The identification of the above magma-types, which have different generative processes and magmatic triggers, in other collisional environments will lead to information about the evolution of similar orogenic belts.

[No abstract available] / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

>Magister Scientiae - MSc / The late- to post-collisional Cape Granite Suite (CGS) located in the southwest of South Africa is comprised of S-, I-, and A-type granites, mafic intrusives, and volcanic flows. The CGS is interpreted to have formed during the closing of the Adamastor Ocean during the Late-Proterozoic to Early-Cambrian. Recently, the S-type granites have received much attention concerning their petrogenesis and sources. However, the I- and A-type granites remain poorly understood and little studied. Therefore, with new geochemical and isotopic data the petrogenesis, sources, and tectonic settings of I- (Vredenburg Batholith) and A-type (Cape Columbine) granites of the CGS form the focus for this study. The major and trace element data presented in this thesis show that the granites from the Vredenburg Batholith are weakly peraluminous to metaluminous, ferroan, and alkali-calcic. Associated with the granites are metaluminous, magnesian, and calc-alkalic igneous enclaves. Formerly, the granites have been interpreted to have formed by fractionation. However, with new geochemical analyses and reassessment of such models, it can be shown that such processes are incompatible with accounting for the chemical variation displayed by the granites and their enclaves. Moreover, the I-type granites and enclaves exhibit positive linear trends between whole-rock major and trace elements vs. maficity (Fe + Mg), which can be explained by co-entrainment of peritectic and accessory phases. The lithogeochemical characteristics of the enclaves and host granite reflect melting of a heterogeneous source. Moreover, the granite and enclave"s ?Nd(t) values reflect melting of Paleoproterozoic-aged crustal sources. Finally, with tectonomagmatic discrimination diagrams, it can be shown that the tectonic setting of the granites indicates a transition from a collisional to extensional regime which corroborates the inferences of previous studies. The Cape Columbine Granites lithogeochemical characteristics are ferroan, calc-alkalic and weakly peraluminous. They show typical A-type granite characteristics in having high silica content, high Na + K values, REE enrichment as compared to S- and I-type granites and strong negative Eu anomalies. For this thesis, it can be shown that anatexis of quartzofeldspathic protolith in an extensional regime produced the chemical variation of the Cape Columbine Granite. Moreover, their isotope ratios are typically radiogenic, indicative of a crustal origin. With this new geochemical data evidence is provided against and in support of previous inferences made about the petrogenesis of the I- and A-type granites of the CGS. This also betters our understanding of the magmatic processes involved in the construction of the CGS over time.

Two regional scale deformation events are observed in the Kamloops region. A Late Triassic-Early Jurassic southwest directed compressional event and a later Tertiary extensional deformation episode, manifested in the uplift of the Nicola horst. The Nicola horst is bounded to the northeast by the Cherry Creek Tectonic Zone, a northwest striking fault zone that separates schistose footwall rocks of the Nicola horst from relatively undeformed Nicola Group rocks in the hanging wall. The fault is interpreted to have accommodated multiple episodes of movement associated with both compressional and extensional tectonics. A pervasive metamorphic fabric, exposed in the horst and cross-cut by the 144.8 5.9 Ma LeJeune granodiorite, is interpreted to represent a broad, Middle Jurassic shear zone, formed by east-directed translation of the Nicola arc during contractional tectonics inboard of an east dipping subduction zone. Variations in orientation of the fabric suggest subsequent east-directed compression during post-Jurassic, pre-Eocene deformation.

No description available.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1988. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 169-188).