Puig de la Garrinada

Puig de la Garrinada
Puig de la Garrinada
height	533  m
location	Catalonia
Mountains	Pyrenees
Coordinates	42 ° 11 ′ 33 "  N , 2 ° 29 ′ 41"  E Coordinates: 42 ° 11 ′ 33 "  N , 2 ° 29 ′ 41"  E
rock	Basanite , alkali basalt
Age of the rock	133,000 years
particularities	The volcanic cone has three craters

The Puig de la Garrinada is an extinct volcano in northeastern Catalonia ( Spain ). It is located in the area of ​​the city of Olot and forms part of the Garrotxa Volcanoes Natural Park . It erupted around 133,000 years ago towards the end of the Middle Pleistocene .

location

The Puig de la Garrinada, also called Volcà de la Garrinada , is only 1500 meters northeast of the city center of Olot, on the left of the nearby Fluvià . The volcanic cone is at 417 meters above sea level in the Olot plain. The directly neighboring volcano Montsacopa (532 meters) almost touches its southwest flank. In the southeast, the lava flow from the Ca l'Isidret and the Bisarroques volcano meets the lapilli of the Garrinada. The expressway from Ripoll to Besalú passes in the north of the volcano .

description

Of the volcanic cones in Olot, the Puig de la Garrinada is the best preserved. The volcano covers an area of ​​0.41 square kilometers with a total volume of 0.012 cubic kilometers, reaches a total height of 533 meters above sea level and towers over its base by 116 meters. Its diameter is 726 meters and the angle of incidence is 26 °. Its cone is not circular, but slightly elliptical - with a maximum axis ratio of 1.5: 1 and a main axis direction of N 036. It has three craters , a central crater ( Cràter Central ) and secondary craters on the north-northwest ( Cràter de la Mosquera ) and on the south-southeast slope ( Cràter del Bufador ). The 300 meter wide central crater is at a height of 474 meters with its base and is elongated according to the N 163. The much smaller Cràter de la Mosquera measures 150 meters in diameter and its base level is 503 meters; he broke out to N 335. The Cràter del Bufador in the south is 275 meters wide and its base is 423 meters high, only 6 meters above the plain of Olot. The three craters are therefore likely to sit on a north-northwest-south-south-east facing eruption crevice, which moreover continues as a lineament further south-south-east.

The volcano also follows, together with the immediately neighboring volcano Montsacopa and the volcanoes Montolivet and Aiguanegra, a north-west-south-east trending lineament that has been known for a long time and is interpreted as a deep break. Stratigraphically, the volcanic cone is superimposed on a lava flow that has emerged at its base and which flowed north in the Olot plain. It is believed that this lava flow and the volcanic cone of the Puig de la Garrinada originate from the same extraction vent.

Course of the eruption

The eruption at Puig de la Garrinada began after the basal lava had flowed out with a Strombolian explosion that filled up the majority of the ash cone . Due to the contact with groundwater that penetrated into the extraction vent from unconsolidated sediments of the Quaternary, the style of eruption finally switched to phreatomagmatic events halfway through . This resulted in several explosion breccias with a high proportion of lithic clasts and pyroclastic density currents; these phreatomagmatic deposits express different proportions of magma to water.

According to Martí and colleagues (2011), the volcanic activity at Puig de la Garrinada ended with further lava flows.

stratigraphy

In a new outcrop on the southeastern edge of the volcano, a reduced, 11-meter-thick sequence can be addressed above the basal lava flow, which can be divided into seven stratigraphic units (from hanging to lying ):

• Relatively powerful unit G (2 meters) of a pyroclastic surge deposit . Only very small grain sizes of fine lapilli and ash.
• Very thin, massive looking unit F (0.5 meters). Lapilli and Scoria. First appearance of scories with oxidized skin.
• Very thin unit E (0.3 meters) of a pyroclastic surge deposit. Has characteristic fluidic pyroclasts. Fine lapilli and coarse ash particles.
• Relatively powerful unit D (2 meters) of a pyroclastic density flow . Striking ocher color. Contains oxidized pyroclasts.
• Small surge deposit of unit C (0.5 meters). Mainly fine grain sizes of the lapilli. Due to the phreatomagmatic character, occasional voluminous blocks could also be transported. Oblique stratification .
• Minor unit B (0.7 meters), which corresponds to an ash flow or a surge deposit. Fine grain sizes of the lapilli and ash particles. First phreatomagmatic action of groundwater.
• Very powerful Strombolian unit A (5 meters), dominated by some very large bombs (> 1 meter), coarse lapilli, scraps of cinder and pyroclasts. The volcanic agglomerate corresponds to the proximal ejection that heaped up the bulk of the volcano. Very badly sorted granulometry.

interpretation

Unit A was deposited in shallow water in which the bombs were suddenly quenched ( English supercooling ). Due to the high emission rate, however, there were no phreatomagmatic explosions, as the magma was protected from the ingress of water by its own ejection. From unit B, however, the influence of the groundwater on the eruption is noticeable, although the Strombolian activity continued, albeit at a reduced rate. Unit C is well sorted and was deposited under relatively "dry" conditions. In it, oxidized scoria appears for the first time. Unit D clearly stands out due to its lighter color and the first appearance of fluidic pyroclasts. It is a very water-rich, very poorly sorted pyroclastic density current.

The transition from unit C to unit D marks a clear break in the magmatic process. It can be assumed that there was a drop in the magma level in the vent, which enabled the groundwater to access rapidly. The final units E, F and G indicate a sharp decrease in the groundwater supply, but also a decrease in the magma supply. For the first time, scories appear with an oxidized skin coating. If units E and G are dry surge deposits, then unit F is difficult to classify due to its uniformly massive character; it may represent the deposits of a fountain of fire. In unit G, the skin coverings then clearly recede and thus indicate the final exhaustion of the groundwater.

mineralogy

Mineralogically, small crystals of olivine , clinopyroxene and plagioclase are found, which are embedded in a glassy matrix rich in iron oxides. Remains of ultramafic mantle rocks and mafic crust magmatites are to be mentioned as xenolites , but occasionally sedimentary fragments also appear.

composition

The chemical composition of the ejecta of the Puig de la Garrinada corresponds to a latite or a sodium-rich alkali basalt .

Main elements

Oxide wt.%	Garrinada Basal Lava	Garrinada bomb	Garrinada Pyroclast	Standard mineral	CIPW standard Basal Lava	CIPW standard bomb	CIPW standard pyroclast
SiO 2	44.32	43.15	44.93	Q
TiO 2	2.55	2.66	2.47	Or	11.78	9.86	10.23
Al 2 O 3	14.46	14.19	14.13	From	13.57	10.27	18.86
Fe 2 O 3	12.15 (dead)	12.26 (dead)	12.44 (dead)	On	18.32	16.91	21.44
FeO				No	9.32	12.84	3.25
MnO	0.18	0.18	0.17	Tuesday	21.13	24.17	17.80
MgO	8.76	9.18	9.42	Oil	13.37	12.95	16.38
CaO	9.63	10.13	9.26	Mt	6.03	6.21	5.93
Na 2 O	3.54	3.90	2.85	Ilm	4.97	5.20	4.83
K 2 O	1.94	1.62	1.68	Ap	1.52	1.60	1.29
P 2 O 5	0.64	0.67	0.54

The SiO ₂ content of the main elements is between 43 and 45 percent by weight, so we are dealing with ultramafic rocks . The sodium content is relatively high at 2.85 to 5.59 percent by weight Na ₂ O, while the potassium content is relatively low. The volcanic rocks are normatively undersaturated in quartz , but instead contain nepheline . The rocks are also olivine normative. The absence of normative hypersthene , leucite and kalsilite is to recognize dss it in the pyroclastic dealing with sodium-rich alkali basalts.

Trace elements

Trace elements ppm	Garrinada Basal Lava	Garrinada bomb	Garrinada Pyroclast
Cr	171	171	182
Ni	124	143	157
Zn	99	92	104
Rb	52	55	47
Sr	797	959	672
Zr	197	204	174
Ba	527	553	492
Ce	78	78	68
W.	148	135	369
V	197	219	209
Co	58	56	85

In the case of trace elements , strontium shows quite high values, which indicates crust contamination. Also, chrome , nickel and zinc are slightly enriched and thus give even the mantle origin of magma to detect. The LILE barium and rubidium and the HFSE cerium and zirconium are depleted .

Age

The lava flow at the base was dated in 1985 by Guérin and colleagues using thermoluminescence to be 133,000 ± 12,000 years BP . The eruption of the Puig de la Garrinada should therefore be almost the same age.

Individual evidence

1. ↑ ^{a b} Gisbert, G., Gimeno, D. and Fernandez-Turiel, JL: Eruptive necks of the Puig De La Garrinada volcano (Olot, Garrotxa volcanic field, Northeastern Spain): A methodological study based on proximal pyroclastic deposits . In: Journal of Volcanology and Geothermal Research . tape 180 , 2009, p. 259-276 .
2. ↑ Cimarelli, C. et al .: Space-time evolution of monogenetic volcanism in the mafic Garrotxa Volcanic Field (NE Iberian Peninsula) . In: Bulletin of Volcanology . tape 75: 758 , 2013, pp. 1-18 , doi : 10.1007 / s00445-813-0758-6 .
3. ↑ Xavier de Bolós Granados: Geological and structural controls on La Garrotxa monogenetic volcanic field (NE Iberia) - doctoral thesis . Universitat de Barcelona, ​​Barcelona 2014.
4. ↑ San Miguel de la Cámara, M. and Marcet Riba, J .: Región Volcánica de Olot, Extracto de la Guía "Cataluña" . In: Excursión C-4, XIV Congreso Geológico Internacional . Imprenta Sobrinas de López Robert y Cia., Barcelona 1926, p. 39-214 .
5. ↑ Mallarach, JM and Riera, M .: Els volcans olotins i el seu paisatge . Editorial Serpa, Barcelona 1981, p. 250 .
6. ↑ Martí, J. and Mallarach, JM: Erupciones hidromagmáticas en el volcanismo cuaternario de Olot (Girona) . In: Estudios geológicos . vol. 43, 1987, pp. 31-40 .
7. ↑ Martí, J. et al .: Complex interaction between Strombolian and phreatomagmatic eruptions in the Quaternary monogenetic volcanism of the Catalan Volcanic Zone (NE of Spain) . In: Journal of Volcanology and Geothermal Research . tape 201 , 2011, pp. 178-193 .
8. ↑ Guérin, G., Benhamou, G. and Mallarach, JM: Un exemple de fusió parcial en medi continental. El vulcanisme quaternari de Catalunya . In: Vitrina 1, 19-26 (Olot) . 1985.