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

Abstract

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.

Geomorphology and Age Constraints of Seamounts in the Cabo Verde Archipelago, and Their Relationship to Island Ages and Geodynamic Evolution

“…This should be taken into account in future detailed investigations of coastline reconstructions. Notwithstanding this regional uplift signal, observations onshore suggest a complex long‐term uplift/subsidence history for the Cabo Verde islands, even if they are subjected to net uplift trends, as it happens with Santiago, São Nicolau, and Brava (Ramalho, 2011; Ramalho et al., 2010a, 2010b; Ramalho, Helffrich, et al., 2010; Madeira et al., 2010; Marques et al., 2020). Moreover, individual islands exhibit different uplift/subsidence histories, demonstrating that isostatic movements are dominated by local processes (such as jacking by intrusive activity at the base of the edifices—see Carvalho et al., 2022) that operate at different times and spatial scales at each individual island (Ramalho et al., 2010a, 2010b; Ramalho, Helffrich, et al., 2010).…”

Some Observations on Phytoplankton Community Structure, Dynamics and Their Relationship to Water Quality in Five Santiago Island Reservoirs, Cape Verde

“…The highest point is Pico de Antónia at 1394 m a.s.l., located in the south-central part of the island. The northern two-thirds of the island is cut by deep valleys, but in certain places (i.e., west of the city of Assomada and the center of the island) there are sloping paleotopographies that can be recognized as comprising large non-conformities covered by younger lavas [50]. Regarding data from [47], the island has an estimated population of 309,372 inhabitants, administratively distributed in nine Municipalities (Tarrafal, Santa Catarina, Santa Cruz, Praia, S. Domingos, S. Miguel, S. Salvador do Mundo, S. Lourenço dos Órgãos, and Ribeira Grande de Santiago).…”

Why do small volcanic ocean islands collapse? Lessons from Santa Maria Island, Azores Triple Junction

“…Similarly to other volcanic ocean islands (e.g. Hildenbrand et al, 2003;Ramalho et al, 2013;Marques et al, 2020b), Santa Maria experienced considerable vertical motions (Marques et al, 2020a), witnessed by submarine lava ows currently outcropping at ca. 200 m above sea level.…”