Corsican Magma Province

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The Corsican Magmenprovinz is a Magmenprovinz the Neogene . It is the oldest of the circum-Tyrrhenian magma provinces, which arose as a result of the expansion of the crust in the ridge of the collapsing Apennine Orogen .

Geography and occurrence

The Zenobito volcano on Capraia with a tower

The Corsican Magma Province includes the eastern edge of Corsica , the northeast coast of Sardinia , Capraia in the north and the Seamount Cornacya in the south. Its eastern border almost reaches Elba . With a width of around 50 kilometers, it thus reaches around 450 kilometers in a north-south direction. Several deposits have been discovered offshore just a few kilometers off the east coast of Corsica and Sardinia. In Corsica, the Sisco-Lamproit should be mentioned. The composite volcanic structure of Capraia is sometimes counted as part of the neighboring Tuscan Magma Province .

Timeframe

The magmatism sat in Langhian in Corsica 14.2 million years BP with the Lamproite of Sisco one. It was followed by submarine magmatic activities on the Cornacya Seamount around 12 million years ago in the Serravallian . In the Messinian , the composite volcano on Capraia was formed 7.2 million years ago, followed by the Zenobito volcano after a long break in production in the Zancleum by 4.8 million years , but which differs from its predecessor in petrological terms.

Petrology

The magmatites formed in the period 14.2 to 4.8 million years BP ( Miocene and Pliocene ) on the eastern edge of the Corso-Sardinian microplate are generally ultrapotassic , shoshonitic or calcareous ; they are distinguished by the absence of leucite .

The Sisco lamproite dike is rich in MgO and SiO 2 . The Cornacya seamount consists of Shoshonite volcanic rocks. The composite volcano of Capraia is made up of potassium-rich calcareous rocks.

The igneous rocks formed in the first igneous period, ranging from 14.2 to 7.2 million years BP, are lamproites, shoshonites, olivine-latites , trachytes , potassium-rich andesites , potassium-rich dazites, and rhyolites . What is noticeable here is the decreasing potassium content over time. The ultrapotassic rocks are characterized by parageneses with olivine , phlogopite and clinopyroxene as phenocrystals (but no leucite or plagioclase ) and contain sanidine and rare potassium-rich Richterite in the matrix . Plagioclase then becomes an important mineral phase in the shoshonites and calcareous-alkali stones that are already poorer in K 2 O and richer in Al 2 O 3 .

All rocks of the first magma series are enriched in incompatible trace elements , which correlate positively with the respective K 2 O content. Compared to thorium , LREE and LILE there is a fractionation of titanium, tantalum and niobium , which is characteristic of magmatites of the volcanic arches and orogen zones and is explained by sediment recycling during the subduction process.

The second magmatic period followed with a hiatus of 3 million years. They created the alkali basalts and trachy basalts of the monogenic Zenobito volcano on Capraia. Compared to the first series of magmas, their fractionation of Ti, Ta and Nb is much more indistinct.

Magma formation

Characteristic of the Corsican magma province and other circumtyrrhenian magma provinces is their temporary succession of lamproit-shoshonite-calcareous alkaline stones, which is linked to a gradual decrease in the K 2 O content. Two models serve as an explanation:

  • Heterogeneous sub-lithospheric mantle
  • Mixture of two magma components

The model of the heterogeneous sub-lithospheric mantle assumes that the upper mantle is interspersed with cross-linked metasomatic areas along deep faults initiated by the subduction below the Apennine orogen that has been ongoing since the beginning of the Miocene . When the pressure is released, these continentally influenced (and in particular potassium and silicon-rich), phlogopite- bearing areas melt preferentially (with a relatively low partial melting rate) and ultrapotassic magmas (such as the lamproite) are formed. With increasing temperature, the melting rate increases and the surrounding mantle mother rocks, which are depleted in trace elements, are more and more melted on themselves, so that the potassium content in the melt drops noticeably. Shoshonites are now formed followed by calcareous-alkali stones.

The mixture model is based on two parent magmas with different chemical compositions - alkaline and sub-alkaline , with the sub-alkaline calcareous alkaline magma gaining the upper hand over time over the ultrapotassic magma.

Geodynamics

The western Mediterranean region is the result of a very complex geodynamic development that started BP around 35 to 30 million years ago and can be seen in the overarching context of Africa's rapprochement with Eurasia . After the general expansion phase of the Oligocene , the Corso-Sardinian microcontinent had separated from mainland Europe by 19 million years BP in the Lower Miocene and carried out a counterclockwise eastward drift during the Burdigali . As a result of the expansion of the crust, the Liguro-Provençal Basin emerged in its back, which is partly underlain by oceanic crust and can be understood as a backarc basin . During the Miocene, the east drift resulted in crust narrowing in the upstream Adriatic spur of the Apulian microplate with subduction in a south- westerly direction and simultaneous formation of the Apennine nappes. At the end of the Middle Miocene ( Serravallian ) around 13 million years BP, the Corso-Sardinian microcontinent had roughly reached its current north-south trending position. The backarc stretching movement that was set in motion did not end here. Starting from the southeastern edge of the Corso-Sardinian microcontinent (with the formation of the Cornacya Seamount), it continued in the southern Tyrrhenian Sea (which now emerged as a deep-sea basin), slowly migrated southeast and reached the Vavilov Basin in the end of the Messinian / beginning Pliocene and in the late Pliocene / beginning of the Pleistocene the Marsili basin . A consequence was that the offshore Calabrian island arc was strongly narrowed and curved.

The fairly rapid opening of the two backarc basins due to the rotational movement of the Corso-Sardinian microcontinent on the one hand and the south-east migration of the Calabrian continental block on the other hand is closely related to a generally south-easterly evasive movement of the Adriatic / Ionian subduction zone, which dips from north-west to west.

Individual evidence

  1. ↑ L. Civetta, G. Orsi, P. Scandone, R. Pece: Eastward migration of theTuscan Anatectic magmatism due to anticlockwise rotation of the Apennines . In: Nature . tape 276 , 1978, pp. 604-606 .
  2. ↑ GH Mascle, including: Evolution of the Sardinia Channel (Western Mediterranean): new constraints from a diving survey on Cornacya seamount off SE Sardinia . In: Marine Geology . tape 179 , 2001, p. 179-202 .
  3. ↑ M. Gasparon, G. Rosembaum, J. Wijbrans, P. Manetti: The transition from subduction arc to slab tearing: Evidence from Capraia Iceland, northern Tyrrhenian Sea . In: Journal of Geodynamics . tape 47 , 2009, p. 30–38 , doi : 10.1016 / j.jog.2008.06.004 .
  4. ↑ a b S. Conticelli, among others: Trace elements and Sr – Nd – Pb isotopes of K-rich, shoshonitic, and calc-alkaline magmatism of theWestern Mediterranean Region: genesis of ultrapotassic to calc-alkaline magmatic associations in a post-collisional geodynamic setting . In: Lithos . tape 107 , 2009, p. 68-92 .
  5. ^ C. Wagner, D. Velde: The mineralogy of K-richterite bearing lamproite . In: American Mineralogist . tape 71 , 1986, pp. 17-37 .
  6. ↑ L. Chelazzi, inter alia: A lamproitic component in the high-K calc-alkaline volcanic rocks of the Capraia Island, Tuscan Magmatic Province: evidence from clinopyroxene crystal chemical data . In: Periodico di Mineralogi . tape 75 , 2006, pp. 75-94 .
  7. ↑ Tim Elliott: Tracers of the slab . In: John Eiler (Ed.): Inside the Subduction Factory (=  Geophysical Monograph . Volume 138 ). American Geophysical Union, Washington DC 2003, p. 23–45 , doi : 10.1029 / GM138 , bibcode : 2003GMS ... 138 ... 23E .
  8. ↑ S. Conticelli, M. D'Antonio, L. Pinarelli, L. Civetta: Source contamination and mantle heterogeneity in the genesis of Italian potassic and ultrapotassic volcanic rocks: SrNd-Pb Isotope data from Roman Province and Southern Tuscany . In: Mineral. Petrol. tape 74 , 2002, pp. 189-222 .
  9. ↑ Sandro Conticelli, Richard W. Carlson, Elisabeth Widom, Giancarlo Serri: Chemical and isotopic composition (Os, Pb, Nd, and Sr) of Neogene to Quaternary Calcalkalic, shoshonitic and Ultrapotassic mafic rocks from the Italian Peninsula: inferences on the nature of their mantle sources . In: L. Beccaluva, G. Bianchini, M. Wilson (Eds.): Cenozoic volcanism in the Mediterranean area (=  Geological Society of America, Special Paper . Volume 418 ). 2006, p. 171-202 , doi : 10.1130 / 2007.2418 (09) .
  10. ^ M. Mattei, F. Cifelli, N. D'Agostino: The evolution of the Calabrian Arc: evidence from paleomagnetic and GPS observations . In: Earth and Planetary Science Letters . tape 263 , 2007, p. 259-274 .
  11. ↑ F. Speranza, among others: Age of the Corsica - Sardinia rotation and Liguro - Provencal Basin spreading: new paleomagnetic and Ar / Ar evidences . In: Tectonophysics . tape 347 , 2002, pp. 231-25 .