EES Departmental Seminar: Lord of the Rings: a new interpretation for the origin of ring schlieren in the South Mountain Batholith

Thu, 17 Sep 2026 14:30:00 GMT

Dr. D. Barrie Clarke
Adjunct Professor
Earth and Environmental Sciences, ɫ��ֱ��

Title: Lord of the Rings: a new interpretation for the origin of ring schlieren in the South Mountain Batholith

Abstract: Ring schlieren are enigmatic, metre-scale, alternating melanocratic gradational to leucocratic bands, forming open to closed, nested, circular to elliptical, concentric to eccentric structures, with centres aligned along the major axis or minor axis of the outer ellipse, with a cylindrical form in three dimensions, and in which cross-cutting relations show a younging direction towards the interior of the nested rings. Except for their interiors, the rings are normally devoid of coarse constituents, suggesting that segregation based on grain size has occurred during their formation. Previous interpretations for the origin of ring schlieren include Bagnold dispersive grain pressure, intra-plutonic diapirs, flow in magma tubes, shear flow around rising gas bubbles in a magma mush, and liquid immiscibility. A new interpretation relates ring schlieren to partially melted xenoliths, ascent resulting from Rayleigh-Taylor instabilities, segregation by a combination of Bagnold dispersive grain pressure and particle collisions, evisceration of the core, and reinjection.

Speaker: Dr. D. Barrie Clarke was professor of igneous petrology at ɫ��ֱ�� from 1970-2007. His principal areas of research were on the Paleocene volcanic rocks of Davis Strait and on the Devonian peraluminous granites of Nova Scotia. His one venture into forensic petrology determined the source of the Titanic headstones in Halifax to be an abandoned quarry in SW New Brunswick.

Barrie will not be able to meet with the audience for coffee before his lecture

EES Departmental Seminars: Basement Outcrops as Pathways for Seawater Circulation at the Southern Chilean Trench

Fri, 18 Sep 2026 18:00:00 GMT

Special seminar:
(*Please note the change in time and location)

Dr. Eduardo Contreras Reyes
Professor
Department of Geophysics, Universidad de Chile

Title: Basement Outcrops as Pathways for Seawater Circulation at the Southern Chilean Trench

Abstract: Hydrothermal circulation and faulting in fast-spreading oceanic lithosphere are typically confined to the upper crust, but subduction-related outer-rise bending significantly alters this hydrogeologic regime. We investigate the seismic structure and crustal hydration of the incoming Nazca plate offshore southern Chile (42º-44°S), where sediment thickness reaches up to 2.5 km near the deformation front. Utilizing joint traveltime tomography from wide-angle and multi-channel seismic reflection profiles constrained by P-wave and S-wave (Vp/Vs) data, we evaluate fluid percolation and structural modification across the oceanic crust. Elevated Vp/Vs ratios in layers 2A and 2B indicate high upper-crustal porosity, confirming that fracturing and fluid penetration extend through layer 2A and into layer 2B. Basement outcrops piercing the thick sedimentary blanket act as essential primary conduits, governing active cold seawater infiltration and creating highly heterogeneous Vp/Vs distributions that mark localized regions of fluid inflow and outflow. Conversely, the lower crust exhibits minimal Vp/Vs anomalies, showing significant velocity reductions only in the immediate vicinity of the trench. These findings demonstrate that bending-related faulting and outcropping basement pathways primarily drive extensive fracturing and fluid circulation within the upper oceanic crust prior to subduction.

Speaker: Dr. Eduardo Contreras Reyes is a Professor at Department of Geophysics, Universidad de Chile. He is a geophysicist specializing in marine seismic, geodynamics, and geophysical prospecting. His research focuses on subduction zone processes, oceanic lithosphere hydration, and seismic imaging using refraction and reflection methods.

Dal Events

EES Departmental Seminar: Lord of the Rings: a new interpretation for the origin of ring schlieren in the South Mountain Batholith

EES Departmental Seminars: Basement Outcrops as Pathways for Seawater Circulation at the Southern Chilean Trench