Topic: The Return of Eruptive Activity to the Reykjanes Peninsula, SW Iceland: A Saga of Tectonic-Magmatic Interaction atan Oblique Spreading Center
Speaker: Dr. Simon Kattenhorn, Associate Dean, UAA
The Reykjanes Peninsula (RP) marks the SW subaerial point of entry of the mid-Atlantic ridge system into Iceland, a geologically young (<16 Ma)landmass created where the mid-ocean ridge system interacted with the Iceland hotspot. The RP has been an active spreading center since 6–7 Ma. The oldest rocks at the surface are Tertiary lavas, Pleistocene hyaloclastites (formed in subglacial eruptions) and interglacial basaltic lava flows. In the axial rift zone these are mostly covered by basaltic lavas of Holocene age (∼12ka–1240 AD), the products of early post-glacial shield eruptions and episodic fissure eruptions. Eruptive fissures have been grouped into distinct swarms arranged in a right-stepping, en echelon pattern and are spaced approximately 5km apart, with an average strike of N40°E. The plate boundary is oriented~N75°E whereas the plate spreading direction is oriented at 105° at ~20 mm/yr(Keiding et al., 2008), implying that the RP is an oblique spreading ridge with plate motions oriented at 30° to the plate boundary. As a result of this obliquity, the structural architecture of the RP is complex, with a combination of normal faults, oblique-slip faults, and strike-slip faults. Individual faults show variable slip histories, indicating that they may be active in both magmatic and amagmatic periods associated with different strain fields (Clifton and Kattenhorn, 2006). GPS measurements between 1993 and 1998 (Hreinsdóttir etal., 2001) showed primarily left-lateral transcurrent motion parallel to the currently active plate boundary, at a rate of 16.8 ± 0.9 mm/yr. The expected8.5 ± 0.9 mm/yr component of extension was not observed, suggesting that the “missing” rifting component is accommodated along normal faults and eruptive fissures during so-called “rifting episodes” or magmatic events. The last such event onshore was in the 13th century, with the last confirmed eruption ending781 years ago in 1240. In February 2021, however, the RP experienced a seismic crisis with thousands of earthquakes up to M5.6 rocking the peninsula, including the metropolitan area of Reykjavik. It soon became apparent that magma was being emplaced below the peninsula. By mid-March, magma ascent was confirmed in the form of a dike intruding into the central portion of the peninsula, culminating with a fissure-fed eruption on March 19th, 2021.Sustained effusion rates of 5-10 m3/s have resulted in the accumulation of>30 m thickness of lava in the Geldingadalir basin, with spillover into adjacent valleys, from at least 7 aligned cones along the erupting fissure. Whether or not this first eruption on the RP in 781 years marks the beginning of the next magmatic cycle (which could last hundreds of years) and perhaps the transition to the accommodation of the “missing” rifting component of long-term plate spreading remains to be seen.
Speaker Bio: Dr. Simon Kattenhorn, Associate Dean, UAA Dr Kattenhorn is a Professor and Director in the Department of Geological Sciences and serves as the Associate Dean of Math & Natural Sciences and Social Sciences at UAA. He teaches courses in structural geology, geomechanics, and geohazards. His research considers tectonic and volcanic processes in developing extensional fault systems such as continental rifts and mid-ocean spreading centers, with application to hydrocarbon systems and geohazards. His planetary geoscience research considers the tectonic evolution of solid surfaces throughout the Solar System, particularly icy moons of the outer solar system such as Europa and Enceladus.
Because of Physical Distancing our luncheons will be virtual until further notice.
VIRTUAL MEETING ONLINE
TIME: Virtual doors open at 11:30 (Alaska Time), Announcements start at 11:45, Talk starts at 12:00