UVM Theses and Dissertations
Format:
Print
Author:
McAtamney, Janelle Jovanka
Dept./Program:
Geology
Year:
2010
Degree:
MS
Abstract:
The southernmost Andes of Patagonia, south of 51°S latitude, record an orogenic cycle that began during the inversion of the Late Jurassic Rocas Verdes rift basin. This basin is the only Late Jurassic Andean extensional basin (in a series of inverted marginal basins) south of Ecuador that is floored by Cretaceous-Tertiary quasi-oceanic crust with mid ocean ridge affinities. The sedimentary succession preserved in the Magallanes foreland basin and fold-thrust belt of Patagonia records the inversion of the Late Jurassic rift basin during the onset of the Late Cretaceous-Neogene contractional fold-thrust belt development during Andean orogenesis. The purpose of this study is to characterize how and when Andean orogenesis initiated.
I have analyzed the provenance, sedimentology, and sediment dispersal patterns in the Magallanes foreland basin using stratigraphy, sandstone petrography, Rare Earth Element geochemistry, and detrital zircon age spectra through the stratigraphic transition from rift to foreland basin to create a model of the Magallanes foreland basin during Magallanes fold-thrust belt initiation. A transect through my study location and line balanced a viable cross section, estimate shortening of ~3.5 km at 54.5°S latitude. These conservative estimates constrain the original stratigraphic thickness and context of the depositional environment of the southern Magallanes foreland basin.
Changes in sediment composition and transport patterns, and Bouma cycle sedimentology along strike ofthe Andean orogen through time record a shift in depositional environment. In Late Jurassic the depositional environment is that of distal hemipelagic mud deposited by a prograding submarine fan in a moderately shallow horst and graben style marine basin. This environment shifts into a deep marine environment depositing coarse-grained fan channel conglomerates into a subsiding foreland basin by Late Cretaceous time. Petrography and Rare Earth Element fractionations of pre and post inversion sediments, the Zapata and Punta Barrosa formations, respectively, record a provenance shift from compositionally immature, euhedral, volcanic lithic fragments to highly weathered felsic metamorphic lithic fragments. This shift indicates uplift and denudation of new material infilling the foreland basin.
Detrital zircon age spectra yielded ages of between 88.48 ± 0.61 and 82.16 ± 1.4 Ma that are younger than previously reported ages for these units along the strike of the orogen to the north. Variations in maximum depositional ages along strike of the basin, combined with changes in sediment composition and structural style, support an interpretation whereby the basin is filled with multiple submarine fans sourcing material from locally uplifted blocks of the rift basin. Significant uplift and erosion of pre-rift basement and syn-rift volcanic rocks is not identified in the detrital zircon record until after 82.16 ± 1.4 Ma at 54.5°S latitude, suggesting Magallanes fold-thrust belt maturation and foreland crustal loading did not occur here until after 82.16 ± 1.4 Ma.
I have analyzed the provenance, sedimentology, and sediment dispersal patterns in the Magallanes foreland basin using stratigraphy, sandstone petrography, Rare Earth Element geochemistry, and detrital zircon age spectra through the stratigraphic transition from rift to foreland basin to create a model of the Magallanes foreland basin during Magallanes fold-thrust belt initiation. A transect through my study location and line balanced a viable cross section, estimate shortening of ~3.5 km at 54.5°S latitude. These conservative estimates constrain the original stratigraphic thickness and context of the depositional environment of the southern Magallanes foreland basin.
Changes in sediment composition and transport patterns, and Bouma cycle sedimentology along strike ofthe Andean orogen through time record a shift in depositional environment. In Late Jurassic the depositional environment is that of distal hemipelagic mud deposited by a prograding submarine fan in a moderately shallow horst and graben style marine basin. This environment shifts into a deep marine environment depositing coarse-grained fan channel conglomerates into a subsiding foreland basin by Late Cretaceous time. Petrography and Rare Earth Element fractionations of pre and post inversion sediments, the Zapata and Punta Barrosa formations, respectively, record a provenance shift from compositionally immature, euhedral, volcanic lithic fragments to highly weathered felsic metamorphic lithic fragments. This shift indicates uplift and denudation of new material infilling the foreland basin.
Detrital zircon age spectra yielded ages of between 88.48 ± 0.61 and 82.16 ± 1.4 Ma that are younger than previously reported ages for these units along the strike of the orogen to the north. Variations in maximum depositional ages along strike of the basin, combined with changes in sediment composition and structural style, support an interpretation whereby the basin is filled with multiple submarine fans sourcing material from locally uplifted blocks of the rift basin. Significant uplift and erosion of pre-rift basement and syn-rift volcanic rocks is not identified in the detrital zircon record until after 82.16 ± 1.4 Ma at 54.5°S latitude, suggesting Magallanes fold-thrust belt maturation and foreland crustal loading did not occur here until after 82.16 ± 1.4 Ma.