K-Ar ages from the eastern Azores group (Santa Maria, São Miguel and the Formigas Islands)

Abdel-Monem, A.A.; Fernandez, L. A.; Boone, Gary M.

doi:10.1016/0024-4937(75)90008-0

Cited by 125 publications

(41 citation statements)

References 9 publications

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“…The maximum elevation (1105 m at Pico da Vara) is located in the eastern part of the island (Fig. The deeply eroded Nordeste mafic shield volcano is the oldest part of the island and is Plio-Pleistocene in age, ranging from 4 to 0.95 Ma (Abdel-Monem et al 1975;Duncan et al 2015). The island comprises three active central volcanoes with summit calderas (Sete Cidades, Fogo and Furnas) linked by volcanic fissure systems (Picos Fissural Volcanic System and Congro Fissural Volcanic System), and two older and inactive volcanic systems in the east, Povoação and Nordeste (Fig.…”

Section: São Miguelmentioning

confidence: 99%

Chapter 3 Active tectonics in the central and eastern Azores islands along the Eurasia–Nubia boundary: a review

Madeira

Silveira

Hipólito

et al. 2015

Memoirs

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The geodynamic setting of the Azores archipelago, straddling the triple junction between the North America, Eurasia and Nubia plates, is reflected in frequent volcanic and tectonic activity. A review of neotectonics is presented for the islands forming the central and eastern groups of the Azores (Faial, Pico, São Jorge, Graciosa, Terceira, São Miguel and Santa Maria). The geometry and kinematics of active faults displacing stratigraphic and geomorphological markers of Pleistocene and Holocene age are presented. Slip-rates were determined using the available ages for the displaced markers. Maximum expected moment magnitudes were estimated using empirical correlations between magnitude and fault length, fault area and maximum observed surface displacement during surfacerupturing palaeoearthquakes. Neotectonic parameters show that the faults are in most cases very to moderately active, with slip-rates usually ranging from a few tenths of millimetres to a few millimetres per year, while maximum expected magnitudes vary from M w 6 to 7. These magnitudes are in agreement with the instrumental and historical seismic record in the region. Neotectonic data define a dextral transtensive stress regime acting on the region and contribute to characterizing the complexity of the geodynamic processes that dominate the western-most segment of the Eurasia-Nubia plate boundary.

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Section: São Miguelmentioning

confidence: 99%

Chapter 3 Active tectonics in the central and eastern Azores islands along the Eurasia–Nubia boundary: a review

Madeira

Silveira

Hipólito

et al. 2015

Memoirs

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“…6.2). The Nordeste Volcanic System is the oldest unit on the island, ranging in age from 4 to 0.95 Ma (Abdel-Monem et al 1975) and corresponds to a basaltic (s.l.) shield volcano incised by marine and fluvial erosion.…”

Section: Povoação and Nordeste Volcanic Systemsmentioning

confidence: 99%

Chapter 6 Volcano-tectonic structures of São Miguel Island, Azores

Carmo

Madeira

Ferreira

et al. 2015

Memoirs

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The Azores archipelago is located at the triple junction between the Eurasia, Nubia and North America lithospheric plates. São Miguel Island, situated at the southeastern part of the western segment of the Azores-Gibraltar Fracture Zone, presents an east-west elongated shape, comprising three quiescent central volcanoes with summit calderas linked by zones of fissure volcanism. The eastern part of the island is older and inactive. Active faulting is represented by prominent fault scarps that constitute important extensional structures, or by linear volcanic structures in fissural volcanic zones, with a dominant NW-SE to WNW-ESE trend. Although less frequent, there are also NNW-SSE to north-south, NE-SW and east-west faults, reflected by some volcanic alignments and linear segments of the drainage system and sea cliffs. The geometric and kinematic data are in agreement with that observed in the rest of the archipelago. However, at eastern São Miguel Island data indicate two distinct groups of conjugated faults characterized by three-dimensional strain: NW-SE to WNW-ESE normal dextral structures are conjugated with NNW-SSE normal left-lateral faults and NW-SE to WNW-ESE normal left-lateral faults are conjugated with NE-SW normal dextral structures, showing the presence of two different stress fields separated in time.

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“…In the central and eastern parts of the island, the remaining volcano‐tectonic structures are offset along an E‐W direction parallel to the East Azores Fracture zone. The formations are Quaternary, with the exception of the Nordeste shield, which is partly Pliocene [ Abdel‐Monem et al, ; Feraud et al, ]. Moreover, according to Johnson et al [] using both bulk fusion and laser incremental heating techniques the alkali‐basalt flow of Lombo Gordo yields a younger radiometric 40 Ar / 39 Ar age of 0.820 to 0.852 Ma.…”

Section: Geological Descriptionmentioning

confidence: 99%

Magma flow pattern in dykes of the Azores revealed by anisotropy of magnetic susceptibility

2015

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The localization of magma melting areas at the lithosphere bottom in extensional volcanic domains is poorly understood. Large polygenetic volcanoes of long duration and their associated magma chambers suggest that melting at depth may be focused at specific points within the mantle. To validate the hypothesis that the magma feeding a mafic crust, comes from permanent localized crustal reservoirs, it is necessary to map the fossilized magma flow within the crustal planar intrusions. Using the AMS, we obtain magmatic flow vectors from 34 alkaline basaltic dykes from São Jorge, São Miguel and Santa Maria islands in the Azores Archipelago, a hot-spot related triple junction. The dykes contain titanomagnetite showing a wide spectrum of solid solution ranging from Ti-rich to Ti-poor compositions with vestiges of maghemitization. Most of the dykes exhibit a normal magnetic fabric. The orientation of the magnetic lineation k 1 axis is more variable than that of the k3 axis, which is generally well grouped. The dykes of São Jorge and São Miguel show a predominance of subhorizontal magmatic flows. In Santa Maria the deduced flow pattern is less systematic changing from subhorizontal in the southern part of the island to oblique in north. These results suggest that the ascent of magma beneath the islands of Azores is predominantly over localized melting sources and then collected within shallow magma chambers. According to this concept, dykes in the upper levels of the crust propagate laterally away from these magma chambers thus feeding the lava flows observed at the surface.

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K-Ar ages from the eastern Azores group (Santa Maria, São Miguel and the Formigas Islands)

Cited by 125 publications

References 9 publications

Chapter 3 Active tectonics in the central and eastern Azores islands along the Eurasia–Nubia boundary: a review

Chapter 3 Active tectonics in the central and eastern Azores islands along the Eurasia–Nubia boundary: a review

Chapter 6 Volcano-tectonic structures of São Miguel Island, Azores

Magma flow pattern in dykes of the Azores revealed by anisotropy of magnetic susceptibility

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