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| Titel |
Towards untangling the changing tectonic and climatic influence on deposition on the Surveyor Fan, Gulf of Alaska: A single grain geochemical and geochronological study |
| VerfasserIn |
Barbara Huber, Heinrich Bahlburg, Christian Drewer |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250124359
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| Publikation (Nr.) |
 EGU/EGU2016-3781.pdf |
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| Zusammenfassung |
| The Surveyor Fan depositional system, Gulf of Alaska, serves as a recorder of onshore
processes in the evolving St. Elias orogen, the highest coastal mountain range on
earth. Here, the relative contribution of tectonics and climate to clast production and
denudation are controversial and need to be determined in detail. Absence of major
onshore sediment traps allows fast transport of orogenic sediment to the ocean,
minimising modifications of the sediment during transport. Exhumation and climatically
controlled variations in glacier type and extent influence denudation rates and the
characteristics of the sediments. We apply diverse tools of single grain geochemical
provenance analysis to Neogene sediments from IODP 341 expedition sites U1417 (distal
Surveyor Fan), U1418 (proximal Surveyor Fan), U1419 (continental slope) and
U1420 (continental shelf). This will allow for deriving information about the relative
contributions of tectonics and climate on rates and locations of exhumation and
denudation as well as their temporal and spatial interplay in the evolving St. Elias
orogen.
Target of the sampling were sands and silts, covering the Miocene to Pleistocene
stratigraphy of the four sites. We apply microprobe analysis for main element geochemistry
on different heavy minerals; cathodoluminescence imaging, U/Pb dating and REE and
trace element measuring on zircons as well as 40Ar/39Ar dating of hornblende and
mica.
First analyses point towards dominant sediment sources in the area of the Chugach
Metamorphic Complex (CMC). U/Pb dating of zircons of samples in different stratigraphic
positions from sites U1417 and U1418 shows peaks in age spectra between ca. 50 and 60 Ma,
the youngest being 25.3 Ma ± 0.6 Ma, the oldest 1305.8 ± 38.1 Ma of age. Additional
analyses of REE and trace elements from the same zircons imply granitoid sources, mainly
granodiorites and tonalites, for most zircons measured. REE and trace element spectra of the
50 to 60 Ma zircons strongly resemble published REE patterns of zircons from the
Sanak-Baranof plutonic belt in the CMC. Microprobe analyses of 450 hornblende
grains of the same samples and additional analyses of samples from sites U1419 and
U1420 show an overall dominance of magnesiohornblende and varying amounts of
actinolite, kaersutite and tschermakite. Similar hornblende compositions have been
published for a belt of metamafic rocks in the CMC. Microprobe data of garnets from
these samples indicate derivation from granites or gneisses and amphibolites of
metamorphic conditions transitional between amphibolite and granulite facies.
This also matches with published information about lithologies in the area of the
CMC.
The Chugach Metamorphic Complex, via the Bering glacier, seems to be one of the main
long time sources of the Surveyor Fan sediments. Shipboard clast and other data indicate
input also from the eastward lying Seward glacier and longshore transfer into the Surveyor
Fan system. Changing amphibole compositions with time of deposition and zircons with ages
older than ca. 50 Ma point to changes in source terranes which will be constrained by future
analysis. |
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