Date of Award

1-1-2010

Document Type

Campus Access Dissertation

Department

Earth and Ocean Sciences

Sub-Department

Geology

First Advisor

David L Barbeau

Abstract

Though southern South America and the Antarctic Peninsula were previously connected through a Paleozoic-Mesozoic subduction system on the western margin of Gondwana, this connection was tectonically disrupted in the Cenozoic by forming the Drake Passage in the Scotia Sea. Heavy mineral composition data from the eastern Magallanes basin of southernmost South America indicate that Campanian to middle Eocene sediments had a mafic/ophiolitic provenance which is interpreted as being derived from the Patagonian-Fuegian magmatic arc and the mafic floor of the preceding Rocas Verdes marginal basin. Upper middle Eocene to lower Miocene heavy minerals, on the other hand, indicate a metamorphic/metasedimentary provenance, which suggest being derived from the Cordillera Darwin metamorphic complex. While the rare earth element patterns of all of these samples are typical to those of average post-Archean upper continental crustal types, the younger middle-upper Eocene and lower Oligocene samples contain a higher concentration of the light REE (LaN/SmN) ratio compared to the older upper Cretaceous to middle Eocene samples suggesting an eastern Andean metamorphic complex provenance for younger sediments. Trace elements plot of stratigraphically older samples exhibit a lower Th/Sc ratio compared to the younger samples suggesting a mafic origin. Nd isotope data show a shift in eNd values from a less negative to a more negative value also during the middle to late Eocene. Together, these data indicate an abrupt shift in sediment provenance in middle to late Eocene time, thereby corroborating recent interpretations of the basin's detrital-zircon geochrononology and thermochronology, and providing further support for temporal and possibly genetic relationships between development of the Patagonian orocline, the opening of Drake Passage and the Oi-1 glaciation of Antarctica.

Quantifying the relative abundance of different framework mineral components of sandstone is a common practice in the determination of sedimentary provenance. This study describes a Microsoft Excel-based method of constructing sandstone provenance and classification related ternary diagrams. The technique demonstrated in this chapter stores sandstone point-count data, generate ternary diagrams with provenance and classification related internal fields, and generate publication-quality scientific diagrams, all in a single step only requiring widely available programs such as Microsoft Excel.

TernaryPlotterzahidbarbeau.xls (953 kB)
Ternary plotter for chapter 4

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