The Complex Vertical Motion of Intraplate Oceanic Islands Assessed in Santiago Island, Cape Verde

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2020-03, Vol.21 (3), p.n/a
• Main Authors: Marques, F. O., Hildenbrand, A., Zeyen, H., Cunha, C., Victória, S. S.
• Format: Article
• Language: English
• Subjects: Altitude; Deformation; Earth Sciences; Environmental Sciences; Eustatic changes; Eustatic sea level changes; Islands; Lava; Lithosphere; Magma; Mantle plumes; Oceanic islands; Paleoshorelines; passage zones; Rock; Rocks; Sciences of the Universe; Sea level; Sea level changes; Seamounts; Shorelines; Subsidence; topography response to isostasy; Uplift; uplift and subsidence rates of oceanic islands; vertical displacement in Santiago Island, Cape Verde; Vertical motion; Volcanic islands
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2019GC008754

Dated paleosea level markers and eustatic sea level changes are necessary but not sufficient information to calculate vertical motion rates on oceanic islands. Therefore, we use a procedure in which we work progressively back in time to incorporate the more recent vertical motion rates implied by the youngest paleoshorelines into the vertical motion history of all older shorelines. Specifically, we calculate the time‐averaged vertical motion rates required to explain the present‐day elevations of the dated sequence of paleoshorelines on Santiago volcanic island (Cape Verde). We thus obtain a vertical motion history consisting of time‐averaged vertical motion rates spanning the five intervening periods between paleoshoreline formation and the present day: (1) 5.06 to 3.29 Ma—seamount growth or island subsidence because all the rocks in this period are submarine; (2) fast uplift (approximately 0.96 mm/a) from 3.29 to 2.87 Ma, mostly responsible for putting submarine lavas currently close to 410 m altitude; (3) relatively fast subsidence (approximately −0.11 mm/a) between 2.87 and 2.18 Ma; (4) stagnation from 2.18 to 0.811 Ma; and (5) relatively fast uplift (approximately 0.14 mm/a) between 0.811 and 0 Ma. We numerically tested top‐down (volcanic loading) and bottom‐up (lithosphere thinning, underplating, and mantle plume) mechanisms to explain the inferred vertical movements, and we conclude that volcanic loading and crustal underplating are capable of producing the observed subsidence and uplift, respectively. Plain Language Summary Oceanic volcanic islands experience vertical movements during their lifetime, which can be the consequence of several mechanisms like bending of the lithosphere due to the island's weight (subsidence) or horizontal intrusion of magma below the volcanic edifice (uplift). In order to discriminate among the possible mechanisms, we must correctly estimate the successive vertical displacements and motion rates. We account for eustatic sea level change and use dated paleoshorelines, working progressively back in time to incorporate the more recent vertical motion rates implied by the youngest paleoshorelines into the vertical motion history of all older shorelines, to obtain a step‐by‐step vertical motion history: (1) 5.06 to 3.29 Ma—seamount growth or island subsidence because all the rocks in this period of time are submarine; (2) fast uplift (approximately 0.96 mm/a) from 3.29 to 2.87 Ma mostly responsible for putting submarine lav