Bransfield Basin: Difference between revisions
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===Glacial processes=== |
===Glacial processes=== |
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Glacial processes have deposited a subglacial deformation [[till]]. The sediment that makes up this unit |
Glacial processes have deposited a subglacial deformation [[till]]. The sediment that makes up this unit is derived from pressure melting of the glacier and from the substrate the glacier passed over. The subglacial deformation till unit is composed of a matrix-supported diamicton.<ref name="Marga Garcia" /> |
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===Glacialmarine processes=== |
===Glacialmarine processes=== |
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Glacialmarine processes have deposited two different units within the region. One of the processes is a proglacial debris flows have deposited a matrix-supported diamicton with interbeds of [[Lamination (geology)|laminated]] [[mud]] on the lower portion of the [[Continental margin|continental slope]]. The other process is a mixture of rain out from the ice from either melting or instantaneous dumping from the surface of an overturned portion of ice, and from marine rain out. The terrigenous and and biogenic material compounds together to form sandy muds with sparse clasts.<ref name="Marga Garcia" /> |
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===Open Marine processes=== |
===Open Marine processes=== |
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Open marine processes have deposited three units within the region. One of the units is a fining-upwards [[turbidity current]] deposit can be observed within the lower slope of the basin. Layers of volanic ash around 1 to 4 cenitmeters thick are within the deposit. Another unit is a contorted/disturbed mud that makes up a slide unit. This unit is distinct because its angular contacts and disturbed structures that form from sediment reworking and plastic deformation from sliding. The third unit is a stratified mud with clast layers at the lower slope's foot. This unit is deposited from [[Contourite|contour currents]], and differences in clast size is attributed to shifting current conditions.<ref name="Marga Garcia" /> |
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==Magmatism== |
==Magmatism== |
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Revision as of 05:16, 22 February 2015
| Bransfield Basin | |
|---|---|
 This map of Antarctica and the bottom portion of South America shows the locations of Bransfield Strait, Drake Passage, and Scotia Arc. | |
| Type | Back-arc basin |
| Location | |
| Region | Northwest of the Antarctic Peninsula |
| Type section | |
| Country | Antarctica |
The Bransfield Basin is a Back-arc rift basin located off the Northern tip of the Antarctic Peninsula. The basin lies within a Northeast and Southwest trending strait that separates the peninsula from the nearby South Shetland Islands to the Northwest.[García 1]The basin extends for more than 500 kilometers from Smith Island to a portion of the Hero Fracture Zone.[1] The basin can be subdivided into three basins: Western, Central, and Eastern.[2] The Western basin is 130 kilometers long by 70 kilometers wide with a depth of 1.3 kilometers, the Central basin is 230 kilometers long by 60 kilometers wide with a depth of 1.9 kilometers, and the Eastern basin is 150 kilometers long by 40 kilometers wide with a depth of over 2.7 kilometers.[2]The three basins are separated by the Deception Island and Bridgeman Island.[García 1]
Tectonic Development
The Bransfield Basin is considered to be a back-arc basin that is located behind the South Shetland Islands. The Islands are believed to have formed from a subduction event that occurred between the Phoenix Plate and the Antarctic plate roughly 200 million years ago during the Mesozoic.[3] [4][5] It is believed that the Pheonix plate stopped subducting under the Antarctic plate at least 4 million years ago during the Pliocene.[2][3][4][5]. Once the subduction event ceased, it is believed that the extension that created the basin was initiated. Aeromagnetic surveys have provided evidence that the extension occurred 1.8 Million years ago during the Pleistocene at a rate of 0.25 to 0.75 cenimeters per year. [5]
It is widely accepted that the Bransfield basin formed from extension caused by slab rollback.[2][3][4][5] New geophysical and structural data contradicts previously believed theories about slab rollback being the main mechanism for the opening of the basin.[García 1][1] A newer theory for the opening of the basin is attributed to sinistral strike-slip motion between the Scotia Plate and Antarctic plates.[1][6] It is theorized that the trench between the the Phoenix and Antarctic plates is locked in place and there is not any motion within the trench. The new data suggests trench retreat is not attributed as a mechanism for extension because there is a lack of seismic activity in the South Shetland Trench area, and that slab rollback is not a mechanism for extension too because if it were then Northwest-Southeast extension should be observed in the entire South Shetland region but instead compression can be observed.It is proposed that the motion between the Scotia plate and Antarctic plate are pushing the Phoenix plate to the Northwest creating compression.[1] [6]
Geology
The main factor that controls deposition inside the Bransfield basin is Glacial cyclicity. Additional contributing factors include Phyiography, tectonics, and oceanography.[García 1][7] Three Stratigraphic units have been identified on the margins. The oldest unit is an over- consolidated diamicton from subglacial processes. The middle unit is a pebbly-sandy stratified mud from the proximal-ice or sub-ice shelf. The youngest unit consists of diatmaceous mud originating from open marine conditions. Sedimentary systems occur on the margins that are related to glacial and glacialmarine, mass wasting, seabed fluid-escape, and countour current processes.[7]
Glacial processes
Glacial processes have deposited a subglacial deformation till. The sediment that makes up this unit is derived from pressure melting of the glacier and from the substrate the glacier passed over. The subglacial deformation till unit is composed of a matrix-supported diamicton.[7]
Glacialmarine processes
Glacialmarine processes have deposited two different units within the region. One of the processes is a proglacial debris flows have deposited a matrix-supported diamicton with interbeds of laminated mud on the lower portion of the continental slope. The other process is a mixture of rain out from the ice from either melting or instantaneous dumping from the surface of an overturned portion of ice, and from marine rain out. The terrigenous and and biogenic material compounds together to form sandy muds with sparse clasts.[7]
Open Marine processes
Open marine processes have deposited three units within the region. One of the units is a fining-upwards turbidity current deposit can be observed within the lower slope of the basin. Layers of volanic ash around 1 to 4 cenitmeters thick are within the deposit. Another unit is a contorted/disturbed mud that makes up a slide unit. This unit is distinct because its angular contacts and disturbed structures that form from sediment reworking and plastic deformation from sliding. The third unit is a stratified mud with clast layers at the lower slope's foot. This unit is deposited from contour currents, and differences in clast size is attributed to shifting current conditions.[7]
Magmatism
See Also
References
- ^ a b c d González-Casado, José; Jorge, Giner-Robles; Jerónimo, López-Martínez (November 2000). "Bransfield Basin, Antarctic Peninsula: Not a normal backarc basin". Geology. 28 (11): 1043–1046.
- ^ a b c d Schreider, Al.; Schreider, A.; Evsenko, E. (2014). "The Stages of the Development of the Basin of the Bransfield Strait". Oceanology. 54 (3): 365–373.
- ^ a b c Lawver, Lawrence; Keller, Randall; Fisk, Martin; Strelin, Jorge (1995). Backarc Basins: Tectonics and Magmatism. New York: Plenum Press. pp. 316–342.
- ^ a b c Galindo-Zaldivar, Jesus; Gamboa, Luiz; Maldonado, Andres; Nakao, Seizo; Bochu, Yao (2006). Antarctica: Contributions to global earth sciences. New York: Spring-verlag. pp. 243–248.
- ^ a b c d Gracia, Eulalia; Canals, Miquel; Farran, Marcel; Prieto, Maria; Sorribas, Jordi; Team, Gebra (1995). "Morphostructure and Evolutionn of the Central and Eastern Bransfield Basins (NW Antarctic Peninsula". Marine Geophysical Researches. 18: 429–448.
- ^ a b Fretzdorff, Susanne; Worthington, Time; Haase, Karsten; Hekinian, Roger; Franz, Leander; Keller, Randall; Stoffers, Peter (2004). "Magmatism in the Bransfield Basin:Rifting of the South Shetland Arc?". Journal of Geophysical Research. 109: 1–19.
- ^ a b c d e Garcia, Marga; Ercilla, Gemma; Alonso, Belen; Casas, David; Dowdeswell, Julian (2011). "Sediment lithofacies, processes and sedimentary models in the central Bransfield Basin, Antarctic Peninsula, since the Last Glacial Maximum". Marine Geology: 1–16.
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