40Ar-39Ar geochronology of the active phonolitic Cadamosto Seamount, Cape Verde.

Samrock, Lisa K. , Wartho, Jo-Anne and Hansteen, Thor H. (2019) 40Ar-39Ar geochronology of the active phonolitic Cadamosto Seamount, Cape Verde. Lithos, 344-345 . pp. 464-481. DOI 10.1016/j.lithos.2019.07.003.

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Supplementary data:

Abstract

Highlights

• Extensive set of 170 40Ar39Ar single-crystal ages for Cadamosto Seamount.
• Volcanic eruption ages at Cadamosto Seamount are all young (< 100 ka).
• Three samples dominated by sanidine phenocrysts preserve a 21.04 ± 0.62 ka age.
• Sanidine antecrysts in two samples show complex chemical zonation patterns.
• Antecryst ages suggest long-lived magmatic activity in the seamount, up to 1.52 Ma.

Abstract

Cadamosto Seamount is located in the SW of the Cape Verde Archipelago in the central Atlantic Ocean off the west coast of Africa. Many radiometric dates exist for the islands in the archipelago; however, no geochronological information has been obtained from the numerous seamounts. The timescales for igneous processes in the submarine realm are thus poorly understood.

In this study, we investigated five lavas that were sampled by dredging and ROV (remotely operated vehicle) from the flanks and summit areas of the largely phonolitic Cadamosto Seamount during two different research cruises. Chemical zonation patterns of minerals were determined by electron microprobe, and radiometric ages were obtained from single-crystal total-fusion and single−/multi-grain step-heating 40Ar39Ar analyses of sanidine, nepheline and sodalite-group minerals.

Our 40Ar39Ar results reveal young sanidine eruption ages (all <100 ka) at Cadamosto Seamount: (1) Three western flank/summit lavas have a relatively simple petrology dominated by phenocrysts, and overlap with mean sanidine ages of 20.98 ± 0.87 ka, 21.44 ± 0.80 ka and 22.3 ± 2.0 ka, with a combined mean age of 21.04 ± 0.62 ka from the three samples (all uncertainties are quoted at 2σ). The remaining two samples from the summit/NE flank are dominated by complex zoned sanidines with resorbed antecrystic cores and phenocrystic rims. These samples yield older sanidine ages of 51.8 ± 2.4 ka and 97 ± 14 ka, which are interpreted to be maximum eruption ages. This is due to the dominance of antecrysts in these two samples and the possibility that the analyzed sanidine grains may be a mixture of older antecrystic cores and younger phenocrystic rims.

The older 40Ar39Ar ages of many sanidine and nepheline antecrysts also give us clues regarding older magmatic events at Cadamosto Seamount, despite these grains having undergone resorption and phenocrystic rim overgrowths, resulting in some radiogenic 40Ar loss during entrainment in the subsequent magmas. The antecrysts minimum ages extend back to 1.5215 ± 0.0083 Ma, which supports the age progression of magmatism observed in the southern islands chain of the Cape Verde Archipelago.

The youngest volcanic eruption period (21.14 ± 0.62 ka) occurred during the Last Glacial Maximum, a period of global sea level lowstands. We suggest that the comparatively rapid unloading leading up to the lowstand may have reduced pressure conditions within the Cadamosto Seamount magma plumbing system, and thus led to enhanced submarine eruption activity.

Document Type: Article
Keywords: Cape Verde, Cadamosto Seamount, 40Ar-39Ar, Sanidine, Nepheline, volcanism
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.lithos.2019.07.003
ISSN: 0024-4937
Projects: HOSST
Expeditions/Models/Experiments:
Date Deposited: 10 Jul 2019 06:42
Last Modified: 22 Jul 2019 09:45
URI: http://oceanrep.geomar.de/id/eprint/47148

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