Emergence and evolution of Santa Maria Island (Azores)—The conundrum of uplifted islands revisited

Ricardo Dos Santos Ramalho, George Helffrich, José Madeira, Michael Cosca, Christine Thomas, Rui Quartau, Ana Hipólito, Alessio Rovere, Paul J. Hearty, S. P. Ávila

Research output: Contribution to journalArticle (Academic Journal)peer-review

54 Citations (Scopus)
334 Downloads (Pure)

Abstract

The growth and decay of ocean island volcanoes is intrinsically linked to vertical movements; whilst the causes for subsidence are better understood, uplift mechanisms remain enigmatic. Santa Maria Island in the Azores Archipelago is an ocean island volcano resting on top of young lithosphere, barely 480 km away from the Mid-Atlantic Ridge. Like most other Azorean islands, Santa Maria should be experiencing subsidence. Yet, several features indicate an uplift trend instead. In this paper we reconstruct the evolutionary history of Santa Maria with respect to the timing and magnitude of its vertical movements, using detailed fieldwork and 40Ar/39Ar geochronology. Our investigations revealed a complex evolutionary history spanning ~6 m.y., with subsidence up to ca. 3.5 Ma followed by uplift extending to the present day. The fact that an island located in young lithosphere experienced a pronounced uplift trend is remarkable and raises important questions concerning possible uplift mechanisms. Localized uplift in response to the tectonic regime affecting the southeastern tip of the Azores Plateau is unlikely since the area is under transtension. Our analysis shows that the only viable mechanism able to explain the uplift is crustal thickening by basal intrusions, suggesting that intrusive processes play a significant role even on islands standing on young lithosphere, such as in the Azores.
Original languageEnglish
Pages (from-to)372-390
Number of pages20
JournalGeological Society of America Bulletin
Volume129
Issue number3-4
Early online date21 Oct 2016
DOIs
Publication statusPublished - 1 Mar 2017

Keywords

  • Azores
  • Santa Maria
  • uplift
  • subsidence
  • isostasy
  • intrusions
  • relative sea level

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