Yellow Neapolitan tuff

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The yellow Neapolitan tuff was deposited around 15,000 years ago during a massive volcanic eruption in southern Italy . The effects of the latitic - trachytic - phonotrachytic eruption are likely to have significantly disrupted the climate at the exit of the Vistula high glacial .

designation

Close up of the yellow Neapolitan tuff

The Yellow Neapolitan tuff , even Yellow Neapolitan tuff or C-2 tephra , English. Yellow Neapolitan Tuff or YNT for short , ital. Tufo Giallo Napolitano , was named after its type locality Naples . Yellow is its characteristic color .

characterization

Outcrop wall of the Yellow Neapolitan Tuff in Naples (Piazza San Luigi)

The Yellow Neapolitan Tuff, the second largest eruption in the Campanian Volcanic District and the largest known phreatoplinian eruption of trachytic composition, is a pyroclastite with a predominant matrix . It consists of pumice of various sizes and rock fragments, both of which are embedded in an ash matrix . The Phreatoplinian eruption , which reached a level of 6 in the volcanic explosion index (VEI) with 30 to 50 cubic kilometers of ejected material , was followed by the collapse of the caldera with the formation of the Camaldoli hill and the Posillipo and Rione Terra hills .

Outbreak focus and spread

The outbreak of the Yellow Neapolitan Tuff lies in the Phlegraean Fields of Campania . The ejecta covered a total of more than 1000 square kilometers. The first phase of the eruption took place via a central chimney and pyroclastics were distributed up to 34 kilometers in the vicinity. The second eruption phase produced through several chimneys and only reached 14 kilometers.

In the course of the eruption, a slightly oval, approximately 11 × 10 kilometer collapse caldera with an area of ​​around 90 square kilometers formed within the larger caldera of the Campanian Ignimbrite. Its edge runs from Capo Miseno west of Bacoli to the east bank of Lake Fusaro and the north bank of Lake d'Averno , grazes the south of Quarto and crosses the plains of Pianura and Fuorigrotta . At Nisida , the structure disappears in the bay of Pozzuoli . A good third of the collapse structure is now in the Tyrrhenian Sea . In addition to the hills already mentioned above, there are outcrops of the Yellow Neapolitan Tuff in the city of Naples, near Chiaia , northeast of Marano , in the frame of the Quarto, near Cuma , south of Baia and on Monte di Procida . The northern limit of the unconsolidated facies (Member B) reaches the Lago di Patria and Aversa in the Campanian plain. Fall deposits were distributed much further, for example ash layers can be found at Monticchio on Monte Vulture over 100 kilometers further east (thickness: 3 centimeters), in the central Apennines 200 kilometers further north (thickness: 15 centimeters) and even in the longitudinal lake in Carinthia . The case deposits were generally drifted to the northeast and can also be detected in deep-sea cores (Tyrrhenis, Adriatic Sea ).

Dating

The yellow Neapolitan tuff was dated by Scandone et al. (1991) to be 12,000 radiocarbon years . When calibrated with CalPal, this corresponds to 12,039 years BC. Chr. Correlatable ash layers in the Lago Grande di Monticchio was an age 14,110 to 14,120 years BP v or 12160-12170. Be assigned. The same age is also used for the Tephralage in the Längsee. More recent dating using the argon method by Deino et al. (2004) and Insinga (2004) indicate an age of 14,900 years BP.

stratigraphy

The volcanic activity in Campania dates back at least 315,000 years BP, possibly up to around 2 million years. The eruption of the Yellow Neapolitan Tuff was preceded by the super-eruption of the Campanian ignimbrite by 39,000 years BP , which was then followed by up to 9 smaller eruptions. After the deposition of the yellow Neapolitan tuff, the volcanic activity of the tripartite recent phase was limited to the interior of the two calderas. In total, there were a further 64 eruptive and 3 effusive volcanic eruptions during the recent phase, the last event in 1538 creating the monogenic volcanic cone of Monte Nuovo .

In the vicinity of the eruption focus (periphery of the Phlegraean Fields), the yellow Neapolitan tuff lies discordantly over previous volcanic rocks, but concordantly in the distal area (Campanian plain) . Its internal stratigraphic structure can be divided into two units (from hanging to lying):

  • Member B
  • Member A

Member A consists of a sequence of phreatoplian lapilli layers , which are composed of ash and pumice particles. This underlying unit shows good stratification and can in turn be divided into 13 sub-units, including 6 case deposits . These subunits are to be interpreted as an alternation of density flows with surge deposits and Plinian fall deposits of pumice and ash. The first subunit (A1), a fall deposit, is undoubtedly the most important, as it has a spread of over 1000 square kilometers and covers topographical unevenness with constant thickness. The intermediate density currents are important in that they could often completely erase deposits in the proximal and medial areas.

The yellow-colored member B is made up of layers of ash in which rounded pumice particles are embedded. This is the actual tufo , which makes up the main part of the funding. Its conveying medium was also likely to have been radial density flows. Proximally it is lithified, but in its distal facies as a so-called pozzolana - an unconsolidated, light gray, pumice-bearing cinerite. The overlaying member B, which is rich in lithoclasts, is difficult to classify because of its massive character, but at least six subunits could be eliminated in the Cinerit. At its base there is often coarse, lithoclast-rich scoria, which can be welded in places.

The lithification of the tuff is due to diagenetic zeolitization .

Petrology

Rock type

Rock analyzes revealed three distinct compositions for the Yellow Neapolitan Tuff:

These petrological findings can best be explained with a three-layer magma chamber , the layers of which were gradually filled. Orsi et al. (1995) assume that the very homogeneous, overhead alkali trachyte magma first entered the magma chamber. Trachytic magma then accumulated underneath, the composition of which changes slightly but continuously with increasing depth. The lowest layer came last and is likely to have triggered the explosive outbreak. It is zoned and consists of latite at the base and alkali trachyte in the higher areas.

Chemical composition

The yellow Neapolitan tuff is an intermediate (its SiO 2 content varies from 57.03 to 61.24 wt.%), Belonging to the Shoshonite series of alkaline rocks . Due to its very high potassium content (K 2 O: 7.59 to 8.64 percent by weight, total alkalis K 2 O + Na 2 O: 11.14 to 12.85 percent by weight) it is like the Campanian ignimbrite among the potash-accented Lined up with rocks. The chemical composition of the tuff is shown in the following table, due to the great variability, intervals are given. As a comparison, the Campanian ignimbrite and an average value of the precursor eruptions (10 analyzes) are given:

Oxide
wt.%		 Yellow Neapolitan tuff Campanian ignimbrite precursor CIPW norm
percent		 Yellow Neapolitan tuff Campanian ignimbrite precursor Trace elements
ppm		 Yellow Neapolitan tuff Campanian ignimbrite precursor
SiO 2 55.0 - 61.0 (58.0) 58.0 - 64.0 (61.0) 59.53 Q Pb 38.7-60.0 28.4-52.4 57.9
TiO 2 0.36 - 0.63 (0.50) 0.35 - 0.48 (0.42) 0.415 Or 51.44 47.38 46.01 Nd 49.3-61.1 33.4-77.4 55.9
Al 2 O 3 17.9-18.96 (18.43) 18.5-21.2 (19.85) 17.25 From 18.20 29.05 40.14
Fe 2 O 3 3.6 - 7.9 (5.6) 3.2 - 5.2 (4.2) 2.91 On 7.10 8.91 2.97 V 50-150 5-100 34.7
FeO No 7.51 5.12 2.51 Zr 250-325 125-700 545
MnO 0.11-0.14 (0.13) 0.06-0.28 (0.17) 0.16 Oil 4.07 4.03 1.28 Y 25-44 17-77 51.8
MgO 0.50 - 2.00 (1.25) 0.25 - 1.50 (0.88) 0.34 Mt 1.25 0.90 0.67 Sr 200-1100 0-750 102
CaO 2.2 - 5.4 (3.8) 1.2 - 4.5 (2.85) 1.81 Il 0.99 0.78 0.84 Ba 50-2100 0 - 1150 60.9
Na 2 O 3.0 - 4.6 (3.8) 2.7 - 6.6 (4.65) 5.01 Ap 0.60 0.42 0.14 Rb 253-375 209-457 392
K 2 O 7.59 - 9.6 (8.6) 6.7 - 9.6 (8.15) 7.37 Tuesday 8.67 3.28 5.30 Nb 20-55 18-120 80
P 2 O 5 0.08-0.44 (0.26) 0.03 - 0.32 (0.18) 0.06 Zr 0.06 0.07 0.12 Th 25-32 10 - 32 44
Mg # 0.34 0.33 0.21 87 Sr / 86 Sr 0.707505 0.707316 - 0.707375 0.707442
A '/ F −0.382 −0.199 - 0.466 143 Nd / 144 Nd 0.5124595 0.512510 - 0.512570 0.5124634
Al / K + Na + Ca 0.813 0.917 0.736 206 Pb / 204 Pb 18.926-19.044 19.110-19.190

According to the CIPW standard , the yellow Neapolitan tuff is a quartz - undersaturated, hypoaluminous, nepheline - and olivine - normative rock. Compared to the Campanian ignimbrite and the precursor eruptions, its magma has experienced a significantly higher level of contamination from continental crustal rocks .

conversion

Soil formation processes on yellow Neapolitan tuff produced characteristic andosols as paleo soils .

Individual evidence

  1. ↑ Paterne, M., Guichard, F. and Labeyrie, J .: Explosive activity of the south Italian volcanoes during the past 80,000 years as determined by marine tephrochronology . In: Journal of Volcanology and Geothermal Research . tape 34 , 1988, pp. 153-172 .
  2. ↑ Orsi, G., D´Antonio, M., de Vita, S. and Gallo, G .: The Neapolitan Yellow Tuff, a large-magnitude trachytic phreatoplinian eruption: eruptive dynamics, magma withdrawal and caldera collapse . In: J. Volcanol. Geothermal. Res. Band 53 , 1992, pp. 275-287 .
  3. ↑ Wohletz, K., Orsi, G. and de Vita, S .: Eruptive mechanisms of the Neapolitan Yellow Tuff interpreted from stratigraphic, chemical, and granulometric data . In: Journal of Volcanology and Geothermal Research . 67, Issue 4, 1995, pp. 263-290 .
  4. ↑ Orsi, G., de Vita, S. and Di Vito, M .: The restless, resurgent Campi Flegrei nested caldera (Italy): constraints on its evolution and configuration . In: J. Volcanol. Geothermal. Res. Band 74 , 1996, pp. 179-214 .
  5. ↑ Schmidt, R. et al .: A new Lateglacial chronostratigraphic tephra marker for the south-eastern Alps: The Neapolitan Yellow Tuff (NYT) in Längsee (Austria) in the context of a regional biostratigraphy and palaeoclimate . In: Quaternary International . 88, Issue 1, 2002, pp. 45-56 .
  6. ↑ Scarpati, C., Cole, P. and Perrotta, A .: The Neapolitan Yellow Tuff - A large volume multiphase eruption from Campi Flegrei, Southern Italy . In: Bulletin of Volcanology . tape 55 , 1993, pp. 343-356 .
  7. ↑ Scandone, R., Bellucci, F., Lirer, L. and Rolandi, G .: The structure of the Campanian Plain and the activity of the Neapolitan volcanoes (Italy) . In: Journal of Volcanology and Geothermal Research . tape 48 , 1991, pp. 1-31 .
  8. ↑ Sabine Wulf: The tephrochronological reference profile of the Lago Grande di Monticchio. A detailed stratigraphy of southern Italy's explosive volcanism over the past 100,000 years . In: Dissertation at the Faculty of Mathematics and Natural Sciences at the University of Potsdam . 2000.
  9. ↑ Deino AL, Orsi G., de Vita S. and Piochi M .: The age of the Neapolitan Yellow Tuff caldera forming eruption (Campi Flegrei caldera-Italy) assessed by 40Ar / 39Ar dating method . In: Journal of Volcanology and Geothermal Research . tape 133 , 2004, pp. 157-170 .
  10. ^ De Vivo, B. et al.: New constraints on the pyroclastic eruptive history of the Campanian Volcanic Plain (Italy) . In: Mineralogy and Petrology . tape 73 , 2001, pp. 47-65 , doi : 10.1007 / s007100170010 .
  11. ↑ Di Girolamo, P. et al .: The calcalkaline rocks of the Campanian Plain new mineral chemical data and possibile links with the acidic rocks of the Pontine Islands . In: Periodico di Mineralogia . tape 65 , 1996, pp. 305-316 .
  12. Jump up ↑ Cole, PD and Scarpati, C .: A facies interpretation of the eruption emplacement mechanisms of the upper part of the Yellow Neapolitan Tuff, Campi Flegrei, Southern Italy . In: Bulletin of Volcanology . tape 55 , 1993, pp. 311-326 .
  13. ↑ Orsi, G. et al .: Step-filling and development of a three-layer magma chamber: the Neapolitan Yellow Tuff case history . In: Journal of Volcanology and Geothermal Research . 67, Issue 4, 1995, pp. 291-312 .
  14. ↑ Frezzotti, M. and Narcisi, B .: Late Quaternary tephra-derived paleosols in central Italy's carbonate Apennine Range: stratigraphical and paleoclimatological implications . In: Quaternary International . tape 34-36 , 1996, pp. 147-153 .