Geology of the Antarctic Peninsula
Encyclopedia
The Antarctic Peninsula
, roughly 650 miles south of South America
is the most northerly portion of the continent of Antarctica. Essentially a continuation of the Andes Mountains subduction
zone, the Antarctic Peninsula exhibits textbook subduction zone tectonic activity. The peninsula has experienced continuous subduction for over 200 million years. The geologic and tectonic history of the peninsula spans millions of years. Throughout this span of time the plate configurations that essentially formed the Antarctic Peninsula
shifted. These shifts changed the orientation of the peninsula itself, as well as the underlying volcanics associated with the subduction zone.
are from this time. They are sedimentary rocks from the Trinity Peninsula Group(TPG). Mostly composed of siliciclastic turbidite deposits ~1200-3000m thick deposited in a marginal marine basin. Unfortunately their age is poorly known, but are most likely from the upper Permian
and Triassic
. The clastic component of these sediments was derived from the weathering, erosion, and subsequent transportation of material from Gondwanaland to the northeast. The sedimentary source assemblage was most likely a mixture of metamorphic, igneous, and sedimentary complexes.
under the Gondwana
supercontinent. As a result, marginal basin clastics were scraped from their oceanic crustal base and subsequently antithetic piling-up of the Trinity Peninsula Group sediments occurred. These were then thrust over the continental margin of Gondwanaland. It is believed that the Trinity Peninsula Group rocks were moved and exhumed from their original oceanic-type basement and were moved over the top of the older metamorphosed crystalline basement rock of the Antarctic Peninsula.
-dacite
lavas, ignimbrites, tuffs, and agglomerates which are all together roughly 215 meters thick. The acidic dykes and sills which intrude the MFF and TPG sediments may have been attributed to the KGF stratovolcano
. The acidic volcanism that created the KGF sequence is caused by plutonic intrusions during the Middle Jurassic
-Early Cretaceous
in the northern Antarctic Peninsula.. These plutonic intrusions could be attributed to the up-doming and rifting in the continental margin of Gondwanaland at the onset of oceanic slab subduction.. This subduction zone is described by Pivoting Subduction, which is due to differences in slab-pull forces acting on the system.
. Similar to the inner magmatic arc, the outer is composed of typical subduction-related acidic volcanism. The outer magmatic arc, like the inner mainland arc is composed of acidic volcanics. A study that focused on the conditions for the generation of andesitic lavas on Alexander Island postulated that either the development of a slab-window due to the subduction of a spreading ridge or the breakup of the subducted slab beneath the fore-arc basin could be the source for the andesitic lava. The South Shetland Islands are dissected by two systems of younger and older strike-slip faults. The older system, parallel with the island arc, was active on King George Island during most of the Tertiary
. This older system of faults is characterized by right-lateral faults, caused by the counterclockwise rotation of the Antarctic Continent with respect to the subduction zone. The younger system of faults displaced the older system, which were also a series of strike-slip faults formed transverse to the island arc.
subduction zone was the opening of the Bransfield Rift
.
The Bransfield Rift undergoes extensional tectonic forces forming a passive continental margin.
This rifting subsequently created the Bransfield back-arc basin during the Oligocene
to present day.
This basin separates the inner magmatic arc(mainland Antarctic Peninsula) from the outer magmatic arc(Shetland Islands). Submarine and terrestrial volcanic activity of alkaline and tholeiitic compositions is associated with this rifting event. The trenchward migration of the spreading center is attributed by the subduction of the Phoenix Plate
under the Antarctic Plate
.
Slab rollback and South Shetland Trench oceanward retreat have led to extensional forces acting on the leading edge of the overriding plate.
The Bransfield Strait
is a result of this extension and is presumed to be 4 million years old or less.
Magnetic anomalies created by the upwelling and formation of new crust are aligned along the axis of the Bransfield Rift. Models of these anomalies indicate that the newly formed oceanic crust in the Bransfield Strait is roughly 1.3 million years old. Unfortunately the blanketing by newly formed sediments and extensive intrusions into the rift render modeling unreliable. Basalts dominate the submarine volcanics in the Bransfield Rift. Isolated occurrences of terrestrial volcanic activity is present, which are predominantly alkaline to tholeiitic in composition.
Antarctic Peninsula
The Antarctic Peninsula is the northernmost part of the mainland of Antarctica. It extends from a line between Cape Adams and a point on the mainland south of Eklund Islands....
, roughly 650 miles south of South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
is the most northerly portion of the continent of Antarctica. Essentially a continuation of the Andes Mountains subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
zone, the Antarctic Peninsula exhibits textbook subduction zone tectonic activity. The peninsula has experienced continuous subduction for over 200 million years. The geologic and tectonic history of the peninsula spans millions of years. Throughout this span of time the plate configurations that essentially formed the Antarctic Peninsula
Antarctic Peninsula
The Antarctic Peninsula is the northernmost part of the mainland of Antarctica. It extends from a line between Cape Adams and a point on the mainland south of Eklund Islands....
shifted. These shifts changed the orientation of the peninsula itself, as well as the underlying volcanics associated with the subduction zone.
Tectonic evolution and geology of the Antarctic Peninsula
The geology of the Antarctic Peninsula has occurred within three different stages:- Pre-subduction stage of marginal basin deposition, later separated by the Gondwanian orogeny,PermianPermianThe PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
-Late TriassicTriassicThe Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events... - The middle subduction phase characterized by the formation of the Antarctic Peninsula (inner) and South Shetland IslandsSouth Shetland IslandsThe South Shetland Islands are a group of Antarctic islands, lying about north of the Antarctic Peninsula, with a total area of . By the Antarctic Treaty of 1959, the Islands' sovereignty is neither recognized nor disputed by the signatories and they are free for use by any signatory for...
(outer) magmatic arcsIsland arcAn island arc is a type of archipelago composed of a chain of volcanoes which alignment is arc-shaped, and which are situated parallel and close to a boundary between two converging tectonic plates....
, middle JurassicJurassicThe Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
-MioceneMioceneThe Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
. - The late subduction phase where the opening of the Bransfield Rift and back-arc basinBack-arc basinBack-arc basins are geologic features, submarine basins associated with island arcs and subduction zones.They are found at some convergent plate boundaries, presently concentrated in the Western Pacific ocean. Most of them result from tensional forces caused by oceanic trench rollback and the...
s occur. This is followed by contemporaneous terrestrial and submarine volcanic activity, OligoceneOligoceneThe Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
-present day.
Pre-subduction history
The oldest rocks found on the Antarctic PeninsulaAntarctic Peninsula
The Antarctic Peninsula is the northernmost part of the mainland of Antarctica. It extends from a line between Cape Adams and a point on the mainland south of Eklund Islands....
are from this time. They are sedimentary rocks from the Trinity Peninsula Group(TPG). Mostly composed of siliciclastic turbidite deposits ~1200-3000m thick deposited in a marginal marine basin. Unfortunately their age is poorly known, but are most likely from the upper Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
and Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
. The clastic component of these sediments was derived from the weathering, erosion, and subsequent transportation of material from Gondwanaland to the northeast. The sedimentary source assemblage was most likely a mixture of metamorphic, igneous, and sedimentary complexes.
Gondwanian orogeny
At this time the Trinity Peninsula Group sediments were folded and slightly metamorphosed, particularly at the peninsula's northernmost point. Retroarc thrusting was also occurring at that time. Both events were most likely caused by incipient stage subduction of the south-east Pacific PlatePacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
under the Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
supercontinent. As a result, marginal basin clastics were scraped from their oceanic crustal base and subsequently antithetic piling-up of the Trinity Peninsula Group sediments occurred. These were then thrust over the continental margin of Gondwanaland. It is believed that the Trinity Peninsula Group rocks were moved and exhumed from their original oceanic-type basement and were moved over the top of the older metamorphosed crystalline basement rock of the Antarctic Peninsula.
Middle subduction phase
Inner magmatic arc
The creation of this magmatic arc was first, making it the older of the two. This arc comprises the mainland of the Antarctic Peninsula and has the higher topographic relief. The creation of the inner magmatic arc is characterized by terrestrial clastic deposition and the early stages of acidic volcanism and plutonism. The Mesozoic clastic sequence (Number 2-Figure 2) consists of the Mount Flora Formation(MFF). Roughly 270 meters thick, these sediments are predominantly plant-bearing coarse sedimentary breccias and conglomerates, with a limited abundance of interbedded sandstones and shales. These clastic beds overlay the TPG sediments, and are separated by angular unconformities. Overlying the MFF clastic sequence are the acid volcanics of the Kenny Glacier Formation (KGF). This volcanic sequence consists of rhyoliteRhyolite
This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...
-dacite
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...
lavas, ignimbrites, tuffs, and agglomerates which are all together roughly 215 meters thick. The acidic dykes and sills which intrude the MFF and TPG sediments may have been attributed to the KGF stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
. The acidic volcanism that created the KGF sequence is caused by plutonic intrusions during the Middle Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
-Early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
in the northern Antarctic Peninsula.. These plutonic intrusions could be attributed to the up-doming and rifting in the continental margin of Gondwanaland at the onset of oceanic slab subduction.. This subduction zone is described by Pivoting Subduction, which is due to differences in slab-pull forces acting on the system.
Outer magmatic arc
An apparent westward migration of the inner magmatic arc, the outer magmatic arc volcanic events created what we now call the South Shetland IslandsSouth Shetland Islands
The South Shetland Islands are a group of Antarctic islands, lying about north of the Antarctic Peninsula, with a total area of . By the Antarctic Treaty of 1959, the Islands' sovereignty is neither recognized nor disputed by the signatories and they are free for use by any signatory for...
. Similar to the inner magmatic arc, the outer is composed of typical subduction-related acidic volcanism. The outer magmatic arc, like the inner mainland arc is composed of acidic volcanics. A study that focused on the conditions for the generation of andesitic lavas on Alexander Island postulated that either the development of a slab-window due to the subduction of a spreading ridge or the breakup of the subducted slab beneath the fore-arc basin could be the source for the andesitic lava. The South Shetland Islands are dissected by two systems of younger and older strike-slip faults. The older system, parallel with the island arc, was active on King George Island during most of the Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
. This older system of faults is characterized by right-lateral faults, caused by the counterclockwise rotation of the Antarctic Continent with respect to the subduction zone. The younger system of faults displaced the older system, which were also a series of strike-slip faults formed transverse to the island arc.
Late subduction phase, opening of the Bransfield Rift
The last and most recent stage in the evolution of the Antarctic PeninsulaAntarctic Peninsula
The Antarctic Peninsula is the northernmost part of the mainland of Antarctica. It extends from a line between Cape Adams and a point on the mainland south of Eklund Islands....
subduction zone was the opening of the Bransfield Rift
Rift
In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....
.
The Bransfield Rift undergoes extensional tectonic forces forming a passive continental margin.
This rifting subsequently created the Bransfield back-arc basin during the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
to present day.
This basin separates the inner magmatic arc(mainland Antarctic Peninsula) from the outer magmatic arc(Shetland Islands). Submarine and terrestrial volcanic activity of alkaline and tholeiitic compositions is associated with this rifting event. The trenchward migration of the spreading center is attributed by the subduction of the Phoenix Plate
Phoenix Plate
The Phoenix Plate was an ancient tectonic plate that existed during the mid-Cretaceous through early Tertiary time. The Phoenix Plate began subducting under the Antarctic Plate. The Phoenix Ridge, a mid-oceanic ridge between the Pacific and the Phoenix Plates which had a spreading rate of 18-20 cm...
under the Antarctic Plate
Antarctic Plate
The Antarctic Plate is a tectonic plate covering the continent of Antarctica and extending outward under the surrounding oceans. The Antarctic Plate has a boundary with the Nazca Plate, the South American Plate, the African Plate, the Indo-Australian Plate, the Scotia Plate and a divergent boundary...
.
Slab rollback and South Shetland Trench oceanward retreat have led to extensional forces acting on the leading edge of the overriding plate.
The Bransfield Strait
Bransfield Strait
Bransfield Strait is a body of water about wide extending for in a general northeast-southwest direction between the South Shetland Islands and Antarctic Peninsula. It was named in about 1825 by James Weddell, Master, Royal Navy, for Edward Bransfield, Master, RN, who charted the South Shetland...
is a result of this extension and is presumed to be 4 million years old or less.
Magnetic anomalies created by the upwelling and formation of new crust are aligned along the axis of the Bransfield Rift. Models of these anomalies indicate that the newly formed oceanic crust in the Bransfield Strait is roughly 1.3 million years old. Unfortunately the blanketing by newly formed sediments and extensive intrusions into the rift render modeling unreliable. Basalts dominate the submarine volcanics in the Bransfield Rift. Isolated occurrences of terrestrial volcanic activity is present, which are predominantly alkaline to tholeiitic in composition.
See also
- Antarctic PeninsulaAntarctic PeninsulaThe Antarctic Peninsula is the northernmost part of the mainland of Antarctica. It extends from a line between Cape Adams and a point on the mainland south of Eklund Islands....
- SubductionSubductionIn geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
- Plate TectonicsPlate tectonicsPlate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
- Andes Mountains
- RiftRiftIn geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....
- Fault (geology)