The nine volcanic islands of this Azores Archipelago (36.9В°NвЂ“39.8В°N, 24.9В°WвЂ“31.3В°W) straddle the triple junction associated with the NorthвЂђAmerican, Eurasian, and Nubian lithospheric dishes into the midвЂђNorth Atlantic Ocean (inset of Figure 1). Pico Island (447 kilometer 2 ) comes with an elongated form with a maximum length of 46 and 16 kilometer, correspondingly. It’s the youngest area regarding the Azores Archipelago (270 В± 150 ka; Demande et al., 1982 ) and it is consists of three volcanic systems: Topo volcano, Planalto da Achada fissure area and Pico volcano (Figure 1). Topo is definitely an extinct volcano situated in the southern the main area this is certainly profoundly eroded and included in more youthful lavas. Planalto da Achada fissure zone corresponds up to A wnwвЂђeseвЂђoriented ridge of scoria cones, в€ј30вЂђkm long, that forms the eastern area of the island. Pico volcano could be the youngest volcano associated with archipelago (53 В± 5 ka; Costa et al., 2014 ) and comprises the western an element of the area. This volcano that is central described as mild reduced slopes with numerous scoria cones, rising as much as 2,351 m being a conical form edifice with high slopes toward the very best (Nunes, 1999 , 2020 ; Zanon et al., 2020 ). The geological record of Pico Island reveals a higher eruptive usually through the Holocene (Nunes, 1999 ). Planalto da Achada fissure area erupted at the very least 13 times within the last 2,000 years and Pico volcano erupted 22 times within the last 1,500 years (Nunes, 1999 ). Following the area became inhabited when you look at the century that is 15th three historic eruptions have now been recorded (Nunes, 1999 ; Zanon et al., 2020 ): Planalto da Achada fissure area in 1562вЂ“1564 advertisement (MistГ©rio da PraГnha); Pico volcano in 1718 advertising along two subaerial eruptive centers (MistГ©rio de Santa Luzia regarding the north flank and MistГ©rio de SГЈo JoГЈo regarding the south flank) and a submarine vent overseas the south coast, and once again in 1720 advertising (MistГ©rio da Silveira).
Location of sampled internet web sites (red icons) on simplified geological map (modified after Nunes ( 1999 )), lava flows are colored by the particular age rages; exact exact same colors are within same age boundaries. The 3 volcanic systems are suggested by the black colored lines that are solid. Inset shows the geographical place of Pico Island (red rectangle) into the Azores Archipelago as well as in the North Atlantic Ocean, the key structural features (NAP, NorthвЂђAmerican plate; MAR, midвЂђAtlantic Ridge; TR, Terceira Rift; EAFZ, East Azores Fracture Zone; GF, GLORIA Fault), plus the places of Terceira and SГЈo Miguel Islands (blue dashed group and egg-shaped).
We sampled 22 web web sites from 21 separate units that are cooling Pico Island (Figure 1 and dining Table 1). For every single site, в€ј10 oriented samples were taken fully to 20 m aside across each cooling device to get a paleodirection that is reliable. For site PI07, the examples had been taken closer together since the outcrop ended up being instead tiny. Standard size paleomagnetic cores (2.5 cm in diameter or over to 15 cm in total) had been gathered employing a petrolвЂђpowered drill. Age constraints for the majority of among these internet web internet sites had been given by either historic documents (PI01, PI02, PI03, PI04, PI07) or radiocarbon relationship of charcoal, turf material, and sediment that is organic Nunes ( 1999 ). We recalibrated the radiocarbon ages utilising the IntCal13 calibration bend (Reimer et al., 2013 ) additionally the MatCal software program (Lougheed & Obrochta, 2016 ) ( dining dining Table 1). Six web internet internet sites (PI10, PI17, PI18, PI20, PI21, PI22) were sampled from lava moves with unknown many years; but, an age that is relative may be constrained from the geological map (Figure 1). These six web sites should be dated with this new PSV curve.
One sigma period
[lower boundвЂђupper bound, relative likelihood]
3 RockвЂђMagnetic Behavior and Microscopic Characterization
To evaluate the suitability associated with the lava flows for paleodirection and paleointensity experiments, we performed both highвЂђfield and lowвЂђfield rockвЂђmagnetic analyses on one test per web site. The magnetization and susceptibility as function of heat had been calculated to test for chemical alteration dominican cupid. also to figure out the Curie conditions (Tc). With the demagnetization that is thermal, it was used to optimize the heat actions when you look at the thermal paleointensity experiments (Figure 2). For every single website, the susceptibility had been calculated as purpose of heat for an AGICO KLYвЂђ3 susceptometer by having a CSвЂђ3 furnace attachment. The examples were heated in seven rounds with approximate top temperatures of 190, 250, 310, 370, 430, and 590 В°C; after every top the heat ended up being lowered 50 В°C to check when it comes to reversibility regarding the signal, i.e., test for chemical alteration associated with the test. The greatest heat that presents reversible behavior is known as the alteration heat, this is basically the greatest heat that will properly be utilized in paleointensity experiments ( dining dining Table 2). The magnetization over heat ended up being calculated on a horizontal translation curie stability (Mullender et al., 1993 ). The Curie heat had been determined because of the two tangent technique and alternation for the test ended up being once more based on the nonreversibility associated with magnetic sign.
Examples agent of seven internet sites reveal at the very least two dominant Curie conditions, for internet internet web sites PI05, PI10, and PI17 the Curie conditions can’t be determined while the magnetization over heat leads to a gradual decay. The alteration heat acquired by the magnetization or susceptibility vs. heat experiments differ somewhat for web web internet sites PI02, PI04, PI05, PI07, PI08, PI09, and PI21 ( dining dining Table 2).