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==Basin Tectonics and Evolution== |
==Basin Tectonics and Evolution== |
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[[File:Tyrrhenian Basin Opening.jpg|thumb|Schematic |
[[File:Tyrrhenian Basin Opening.jpg|thumb|Schematic illustrating episodicity of back-arc extension in the Tyrrhenian basin. Vo is the horizontal velocity of the overriding plate and Vr is the horizontal velocity with which the hinge zone moves seaward, both positive to the right. Modified from Kastens and Mascle, 1988.]] |
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===Temporal Onset of Rifting=== |
===Temporal Onset of Rifting=== |
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It is widely agreed that extension in the Tyrrhenian basin began in the late [[Miocene]], as shown by the recognition in seismic reflection profiles of pre-evaporitic (i.e. pre-Messinian) sediments in the western Tyrrhenian and by age estimates based on the overall lithospheric thickness, basement relief, and heat flow.<ref name=Sartori /><ref name="Malinverno and Ryan" /><ref name=Sartori2 /><ref name="Kastens and Mascle" /> [[K-Ar dating]] of peripheral oceanic basalts, drilled at the southeast edge of the Vavilov plain, estimates the beginning of extension to be 7.3 ± 1.3 Ma.<ref name=Barberi>{{cite journal|last1=Barberi et al.|title=Age and nature of basalts from the Tyrrhenian abyssal plain|journal=Deep Sea Drilling Project Initial Reports|date=1978|volume=42|issue=1|pages=509-514|accessdate=22 February 2015}}</ref> Basalts recovered near the spreading center, in middle of the Vavilov plain, yielded ages of 3.4-3.6 Ma.<ref name="Kastens and Mascle" /> This means that back-arc extension in this part of the basin occurred approximately between the late Tortonian and the middle Pliocene. However, in the Marsili plain, the oldest basaltic crust was found to be 2.1 Ma.<ref name="Malinverno and Ryan" /><ref name="Kastens and Mascle" /> This lower age limit, along with the presence of a saddle containing continental crust (the "Issel bridge") between the Vavilov and Marsili plains, implies that there were two distinct episodes of back-arc extension. |
It is widely agreed that extension in the Tyrrhenian basin began in the late [[Miocene]], as shown by the recognition in seismic reflection profiles of pre-evaporitic (i.e. pre-Messinian) sediments in the western Tyrrhenian and by age estimates based on the overall lithospheric thickness, basement relief, and heat flow.<ref name=Sartori /><ref name="Malinverno and Ryan" /><ref name=Sartori2 /><ref name="Kastens and Mascle" /> [[K-Ar dating]] of peripheral oceanic basalts, drilled at the southeast edge of the Vavilov plain, estimates the beginning of extension to be 7.3 ± 1.3 Ma.<ref name=Barberi>{{cite journal|last1=Barberi et al.|title=Age and nature of basalts from the Tyrrhenian abyssal plain|journal=Deep Sea Drilling Project Initial Reports|date=1978|volume=42|issue=1|pages=509-514|accessdate=22 February 2015}}</ref> Basalts recovered near the spreading center, in middle of the Vavilov plain, yielded ages of 3.4-3.6 Ma.<ref name="Kastens and Mascle" /> This means that back-arc extension in this part of the basin occurred approximately between the late Tortonian and the middle Pliocene. However, in the Marsili plain, the oldest basaltic crust was found to be 2.1 Ma.<ref name="Malinverno and Ryan" /><ref name="Kastens and Mascle" /> This lower age limit, along with the presence of a saddle containing continental crust (the "Issel bridge") between the Vavilov and Marsili plains, implies that there were two distinct episodes of back-arc extension. |
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Revision as of 22:50, 22 February 2015
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The Tyrrhenian Basin is a sedimentary basin located in the eastern Mediterranean Sea. It is bounded by Sardinia to the west, Corsica to the northwest, Sicily to the southeast, and peninsular Italy to the northeast. The Tyrrhenian basin displays an irregular seafloor marked by several seamounts and two distinct sub-basins - the Vavilov and Marsili basins. The Vavilov deep plain contains the deepest point of the Tyrrhenian basin at approximately 3785 meters.[1] The basin trends roughly northwest-southeast with the spreading axis trending northeast-southwest.
Regional Geologic Setting
The Tyrrhenian basin is located in a geologically complex portion of the Mediterranean Sea. The basin is partially encircled by several orogenic belts, including the Apennines to the northeast, the Alps to the north, and the Atlas mountains to the southwest. It is also bounded by a convergent boundary and associated trench to the southeast. Deep reflection seismic lines near the trench clearly show oceanic lithosphere from the African plate flexing beneath Calabria to join a seismogenic slab that extends down to 500 km beneath the Tyrrhenian basin.[1][2] Between the upper slope of the trench and Calabria are a number of small fore-arc basins that developed through extensional listric faulting during the Tortonian.[1] These basins subsequently subsided between the late Pliocene and Quaternary and are now infilled with mélange.[1]
The Aeolian Islands north of Calabria and Sicily represent the volcanic arc of the convergent system. The volcanism associated with these islands occurs at the northeast closure of the downgoing slab and began approximately during the late Pliocene to early Pleistocene (1.5-1.7 Ma).[1]
The Tyrrhenian basin lies to the northwest of the Aeolian Islands and represents a back-arc basin formed from tensional forces associated with the northwest subduction of the African plate beneath the Eurasian plate. Similar to other back-arc basins, the Tyrrhenian basin displays a shallowing of the Moho discontinuity towards the central part of the basin, a Wadati Benioff zone, abnormally high heat flow (exceeding 200 mW/m² in some places), and an active volcanic belt on the arc-ward edge of the basin.[3][4]
Basement Structure
Tyrrhenian basement rocks consist of late Paleozoic granites derived from the Hercynian orogeny.[5] Basement rocks in the southeastern portion of the basin were reactivated during the Alpine orogeny while those to the northwest were undisturbed.[5]
Stratigraphy
Upper Sardinia Margin
The Upper Sardinia Margin is a fault-bounded passive margin located northwest of the Vavilov Basin. Seismic reflection surveys across the Upper Sardinia Margin exhibit a stratigraphic geometry suggestive of pre-rift, syn-rift, and post-rift sequences.[6] Drill cores penetrating to the base of the syn-rift sediments identified a transgressive sequence related to subsidence of the continental crust during the rifting stage of the Tyrrhenian Basin opening.[6] At the base of the syn-rift sequence are 60 meters of Tortonian conglomerate with subrounded clasts derived from metamorphosed carbonate and quartzitic basement.[6] It is inferred that this conglomerate formation was deposited in a high-energy subaerial environment like an alluvial fan. Overlying the conglomerate formation are oyster-bearing glauconitic sandstones deposited in a nearshore environment.[6] Late Tortonian to Early Messinian calcareous ooze and claystone with benthic foram assemblages overlays the sandstone formation; this indicates that water depth increased,[6] perhaps due to subsidence at the end of the syn-rift period. The boundary between the syn-rift and post-rift periods is believed to be located in a 50 meter section of late Messinian gypsum that overlays the calcareous ooze and claystone formations. At the top of the stratigraphic section are 243 meters of Pliocene to Pleistocene post-rift sediment containing calcareous mud with occasional terrigenous clastics and volcanic ash.[6]
Lower Sardinia Margin
The Lower Sardinia Margin lies near the transition between continental and oceanic crust. This is the easternmost point on the margin where pre-rift, syn-rift, and post-rift sediments can be clearly discerned on seismic reflection profiles.[6] A drill core to the base of the syn-rift sediments revealed 533 meters of thinly-bedded, calcareous, siltstone and sandstone with dispersed detrital gypsum grains and anhydrite nodules. The entire sequence is reversely magnetized, which when placed in the context of the adjacent stratigraphy, suggests that it was deposited during the reversed polarity event of the Gilbert epoch (between 4.79 and 5.41 Ma).[6] The environment of deposition for this section is uncertain; however, due to the presence of thin, well-graded layers and a lack of marine fossils, it is possible that the formation was deposited in a closed lacustrine setting. Overlaying the syn-rift sediments are 200 meters of Pliocene to Pleistocene hemipelagic marine sediment with intermittent volcanic glass. This sediment layer is believed to be deposited after the end of rifting due to its subhorizontal seismic reflection profile.[6]
Vavilov Basin
The basement rock in the Vavilov Basin consists of strongly serpentinized peridotite with both high and low-temperature phases of deformation.[6] The peridotite is overlain by 120 meters of tholeiitic pillow basalt containing carbonate-filled veins.[6] Nannofossils and planktonic foraminifera within the carbonate veins constrain the age of emplacement between 3.1-3.6 Ma.[6] Immediately above the basalt is a 100-meter-thick section of Pleistocene sedimentary cover, consisting primarily of nannofossil-rich mud with occasional reworked volcanogenic debris.[6]
Marsili Basin
The basement rock of the Marsili Basin is vesicular basalt.[6] Due to the abundance (10%-30% of rock volume) and size (up to 3 or 4 mm) of the vesicles, it is likely that the basalt was emplaced as a flow rather than a sill. Overlaying the basement is 250 meters of calcareous mud and ooze with interbedded volcanoclastic layers. Benthic foraminifera and magnetic anomaly data from the base of this section constrain the terminus of rifting between 1.67 to 1.87 Ma.[6] At the top of the stratigraphic section are 350 meters of volcanoclastic turbidites.[6]
Basin Tectonics and Evolution
Temporal Onset of Rifting
It is widely agreed that extension in the Tyrrhenian basin began in the late Miocene, as shown by the recognition in seismic reflection profiles of pre-evaporitic (i.e. pre-Messinian) sediments in the western Tyrrhenian and by age estimates based on the overall lithospheric thickness, basement relief, and heat flow.[1][3][5][6] K-Ar dating of peripheral oceanic basalts, drilled at the southeast edge of the Vavilov plain, estimates the beginning of extension to be 7.3 ± 1.3 Ma.[7] Basalts recovered near the spreading center, in middle of the Vavilov plain, yielded ages of 3.4-3.6 Ma.[6] This means that back-arc extension in this part of the basin occurred approximately between the late Tortonian and the middle Pliocene. However, in the Marsili plain, the oldest basaltic crust was found to be 2.1 Ma.[3][6] This lower age limit, along with the presence of a saddle containing continental crust (the "Issel bridge") between the Vavilov and Marsili plains, implies that there were two distinct episodes of back-arc extension.
Mechanism of Development
Episodicity of back-arc development is observed in intra-oceanic settings, as in the Western Pacific Ocean, due to changes in the configuration of the retreating slab with time.[1]
Rates of Extension and Subsidence
The extension factor β, which is the ratio between the present and original width of the extended section, of the Tyrrhenian
Hydrocarbon Potential
References
- ^ a b c d e f g Sartori, R. (2003). "The Tyrrhenian back-arc basin and subduction of the Ionian lithosphere" (PDF). Episodes. 26 (3): 217–221. Retrieved 15 February 2015.
- ^ Anderson and Jackson (1987). "The deep seismicity of the Tyrrhenian Sea". Geophysical Journal International. 91: 613–637. Retrieved 17 February 2015.
- ^ a b c Malinverno, A., and Ryan, W. (1986). "Extension in the Tyrrhenian Sea and shortening in the Apennines as result of arc migration driven by sinking of the lithosphere". Tectonics. 5 (2): 227–245. Retrieved 18 February 2015.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Della Vedova; et al. (1984). "Geothermal structure of the Tyrrhenian Sea". Marine Geology. 55: 271–289. Retrieved 18 February 2015.
{{cite journal}}: Explicit use of et al. in:|last1=(help) - ^ a b c Sartori; et al. (2001). "Neogene evolution of the southwestern Tyrrhenian Sea (Sardinia Basin and western Bathyal plain)". Marine Geology. 175: 47–66. doi:10.1016/S0025-3227(01)00116-5.
{{cite journal}}:|access-date=requires|url=(help); Explicit use of et al. in:|last1=(help) - ^ a b c d e f g h i j k l m n o p q r s Kastens, K. and Mascle, J. (1988). "ODP Leg 107 in the Tyrrhenian Sea: Insights into passive margin and back-arc basin evolution". Geological Society of America Bulletin. 100 (7): 1140–1156. Retrieved 16 February 2015.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Barberi; et al. (1978). "Age and nature of basalts from the Tyrrhenian abyssal plain". Deep Sea Drilling Project Initial Reports. 42 (1): 509–514.
{{cite journal}}:|access-date=requires|url=(help); Explicit use of et al. in:|last1=(help)