Geoscience Colloquia for Fall 2008 Semester

Thursday October 23, 2008 3:00 pm

Dr. Jordi Carreras
Universitat Autònoma de Barcelona (Spain)
Structural Geology
Title: Shear Zones, simple, but complex structures
Lapham Hall 262

Abstract:

Shear Zone

Ductile shear zones are common structures arising from strain localization in mid to deep crustal levels. Most shear zones arise as the result of relative displacement of undeformed or less deformed wall rocks producing deformation bands with strain approaching the simple shear model. In classic models, shear zones grade upwards in the crust to semi-brittle or brittle faults. However shear zones grade also in space and/or time to other ways of deformation accommodation like homogeneous deformation or folding. The spectrum of shear zone types depends on rock properties (isotropic/anisotropic), mechanical behaviour, and other properties. Moreover, real shear zones deviate considerably from the ideal planar simple shear model and, in consequence, complex structures form inside shear zones. An analysis of the complexity of shear zones is exposed on the basis of different case studies, primarily from the Cap the Creus area (NE Iberia).

Thursday November 6, 2008 Noon

Dr. Jim Miller
University of Minnesota- Duluth
Title: "UMD's Precambrian Field Course"
Link: http://www.d.umn.edu/prc/
Lapham Hall 380 (conference room)

Thursday November 6, 2008 4:00 pm

Dr. Jim Miller
University of Minnesota- Duluth
Title: "The Geology and Mineral Deposits of the Duluth Complex - The (second) Largest Mafic Complex on Earth"
Lapham Hall 262

Abstract:

Dr. Jim Miller

The Duluth Complex of northeastern Minnesota is the major exposed plutonic component of the 1.1 Ga Midcontinent Rift and constitutes the second largest mafic intrusive system on the planet. It also hosts the world’s largest reserve of copper and the third largest reserve of nickel. These resources are currently being evaluated by several mining companies for development in the next few years.

This talk will first give a historical account of the geologic studies and exploration activities that gave rise to our current understanding of this enormous system. Then it will summarize our current state of knowledge about the Duluth Complex. Finally, it will point out areas where future research is needed.

Thursday November 20, 2008 4:00 pm

Dr. Steven Wojtal
Oberlin College
Title: "Near surface transpressional deformation along the southern San Andreas fault system"
Lapham Hall 262

Abstract:Dr. Steven Wojtal research

Although commonly portrayed as a single fault with transcurrent motion, the San Andreas fault (SAF) zone is a complex boundary separating the North American and Pacific plates. The southern San Andreas, near the Salton Sea, is an excellent place to study the fault because of the near absence of vegetation and (for now) housing developments. In this locality, the SAF serrated shape, with segments parallel and oblique to the North American-Pacific plate motion vector. The Mecca Hills and at Durmid Hill occur in the segments that are oblique to plate motion, and result from the component of contraction in these areas. The combination of transcurrent motion (wrench deformation) and convergent motion (contraction deformation), is known as wrench-contraction (or transpression). In both locations, the near-surface geology consists of fault-bounded uplifts a few km across and several km long, covered by very young sedimentary strata. In the Mecca Hills, deformation patterns suggest Dr. Steven Wojtal research 2strong strike-slip partitioning, with transcurrent motion accommodated by particulate flow within a narrow fault zone and convergence accommodated by widespread folding of strata between fault strands. At Durmid Hill, deformation of strata between strands accommodates both convergent and transcurrent displacement. In addition, the near-surface deformation at Durmid, both along the fault strands and within the horses, is accommodated by a mix of discrete deformation elements – faults – and distributed deformation – through the formation of folds or boudinage and thickening and thinning of sedimentary layers.