Provenance of the Neogene to Holocene sediments drilled by IODP Expedition 341 in the Gulf of Alaska. A single grain geochemical and geochronological study of the glacially influenced denudation history of the evolving St. Elias Orogen using heavy minerals
Final Report Abstract
Interactions of climate and tectonics during orogen formation are a subject of ongoing research with many open questions concerning their cause and effect relationship. The southern Alaska continental margin hosts the highest coastal mountain range on earth, the St. Elias Mountains. Its formation during the last ca. 10 Ma coincides with substantial climate alteration leading to strong glaciation, offering prime conditions for research on climate-tectonic interactions. Most of the detritus produced during the formation of this orogen is transported into the Surveyor Fan and its precursor in the Gulf of Alaska that were drilled during IODP expedition 341. In this case study, we performed a multi-method provenance analysis of sediments from two sites in the distal and proximal Surveyor Fan (site U1417 and U1418, respectively) using single grain geochemical analysis of amphibole, garnet, pyroxene and epidote along with zircon U/Pb and (U-Th)/He dating and REE analysis, Ar-Ar dating of amphibole and mica and point counting of light and heavy minerals. These data are compared to results from onshore studies and are interpreted in the context of changes in glaciation and tectonics. Our results are in line with tectonics as prevalent factor in determining the main erosion centers with substantial modifications caused by the changing glacial cover. The recovered Miocene to Pleistocene sediments have been almost exclusively fed from long-term sources on the Chugach, Prince William and Yakutat terranes. Additional input from the Coast Plutonic Complex cannot be excluded but seem to have been minor. Differences in the characteristics of the sediments from the distal and proximal site are in line with the position of the sites in relation to the tributary system of the Surveyor Fan to impact their provenance hampering direct correlation and complementation of the two datasets. The oldest Miocene sediments reveal high amounts of coaly material being very likely fed from the Kulthieth formation. A change in sediment composition implies rising input from the Chugach metamorphic complex from ca. 11 Ma onwards, leaving tectonic processes associated with the collision of the Yakutat terrane as the most likely cause. Input from the Chugach terrane in the late Miocene implies the existence of an effective transport system from the mountain range into the Gulf of Alaska, draining to the south east. Single grain analysis of heavy minerals and zircon age spectra point to a progressive change in provenance from Miocene to Pliocene, very likely triggered by the advancing glaciation and erosion of the nearshore Yakutat terrane areas. This indicates the increasing glaciation to have enhanced erosion in the newly glaciated areas downslope in the spine of the orogen affecting the main area under erosion causing modifications of erosion centers. The provenance affiliations of the sediments are in line with changes associated with the northern hemisphere glaciation at the Plio-Pleistocene transition while a homogenous sediment petrography and geochemistry during the Pleistocene imply climatic changes at the mid- Pleistocene transition did not cause significant changes in the main area under erosion. Glaciers seem to have remained in their topographically defined positions over time.
Publications
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(2015): Denundation history of the St. Elias orogen: working programme of a provenance study of sediments from the Surveyor Fan, Gulf of Alaska.- IODP/ICDP Kolloquium 2015, Bonn, abstracts
Huber, B., Bahlburg, H.
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(2015): Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska.- Proceedings of the National Academy of Sciences 112, 15042-15047
Gulick, S., Jaeger, J., Mix, A., Asahi, H., Bahlburg, H., Christina Belanger, Glaucia B. B. Berbel, Laurel Childress, Ellen Cowan, Laureen Drab, Matthias Forwick, Akemi Fukumura, Shulan Ge, Shyam Gupta, Arata Kioka, Susumu Konno, Leah S. LeVay, Christian März, Kenji Matsuzaki, Erin McClymont, Christopher Moy, Juliane Müller, Atsunori Nakamura, Takanori Ojima, Fabiana R. Ribiero, Kenneth Ridgway, Oscar Romero, Angela Slagle, Joseph Stoner, Guillaume St-Onge, Itsuki Suto, Maureen D. Walczak, Lindsay Worthington, Ian Bailey, Eva Enkelmann, Robert Reece, John Swartz
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(2016): Climate-tectonic interactions in the St. Elias orogen: New geochemical and geochronological provenance data from Surveyor Fan sediments, Gulf of Alaska.- GeoTirol 2016, DGGV Annual Meeting, abstracts
Huber, B., Bahlburg, H.
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(2016): Towards untangling the changing tectonic and climatic influence on deposition on the Surveyor Fan, Gulf of Alaska: A single grain geochemical and geochronological study.- IODP/ICDP Kolloquium 2016, Heidelberg, abstracts
Huber, B., Bahlburg, H., Drewer, C.
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(2017): Orogenic erosion centres in the crossfire of climate and tectonics: Insights from a single grain provenance analysis of Surveyor Fan sediments, Gulf of Alaska, IODP Expedition 341.- IODP/ICDP Kolloquium 2017, Braunschweig, abstracts
Huber, B., Bahlburg, H.
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(2018): Climate-tectonic interactions in the St. Elias orogen: implications from a single grain heavy mineral provenance analysis of Surveyor Fan sediments, Gulf of Alaska.- Sedimentary Geology 372, 173–192
Huber, B., Bahlburg, H., Pfänder, J.
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(2018): Provenance of the Surveyor Fan and Precursor Sediments in the Gulf of Alaska—Implications of a Combined U-Pb, (U- Th)/He, Hf, and Rare Earth Element Study of Detrital Zircons.- Journal of Geology 126, 577-600
Huber, B., Bahlburg, H., Berndt, J., Dunkl, I., Gerdes, A.
