DGSE Lectures—March 7 and 10

A message from Dr. Scott McCoy (phone: 775-682-7205), Department of Geological Sciences and Engineering (DGSE) about upcoming lectures:

1) On Monday, March 7 at 4 PM in DMS 102, Dr. Adam Forte from ASU will give a talk titled: Fold-Thrust Belt Evolution in a Young Orogen: The Eastern Greater Caucasus

Abstract: Understanding how the deformational structures (e.g. faults and folds) within mountain ranges evolve with time, along with forces that influence their spatial and temporal evolution, represents a first-order question within structural geology and tectonics. To fully explore this question in the field within active orogens requires the integration of traditional structural geology with stratigraphy and geomorphology. Here I present a synthesis of some of my work utilizing all three of these disciplines to reconstruct the history of the eastern half of the Greater Caucasus Mountains. The Greater Caucasus lie at the northern edge of the central Arabia-Eurasia collision zone, and in the region between the Black and Caspian Seas, represent the main locus of active convergence between Arabia and Eurasia. The Greater Caucasus are a young (~5 Ma) orogen with excellent exposures of both active structures and foreland stratigraphy, making them an ideal location in which to explore general processes important in the formation and evolution of fold-thrust belt and orogenic systems. Focusing on the eastern half of the range, the results of my work demonstrate a complicated history of both in-sequence (propagation of new structures into the foreland, away from the core of the orogen) and out-of-sequence propagation and/or reactivation of thrust systems on a range of spatial and temporal scales. Field mapping, construction of balanced cross-sections, and analysis of foreland stratigraphy indicates that the current main locus of shortening is within a foreland fold-thrust belt along the southern margin of the eastern Greater Caucasus. Integrating those results with a series of provenance analyses indicates that the initiation of this foreland-fold thrust system was preceded by a protracted history of in-sequence, southward propagation of deformation. However, using the somewhat atypical topography of the core of the eastern Greater Caucasus as a constraint and attempting to reproduce that topography through a series of landscape evolution models, suggests that superimposed within that history of in-sequence, progressively southward propagation, is the out-of-sequence development or reactivation of a significant set of structures within the hinterland of the orogen. This reactivation could relate to changes in either the topography of the orogen or the nature of the underthrusting lithosphere, or could be part of an accretion cycle. Generally, these results represent a unique field view of the early stages of mountain building. Current and future work is focused on further constraining the style and timing of structures and their relation to the topographic and foreland basin development of the Greater Caucasus to refine our view of the structural evolution of this young orogen and develop insights into what aspects of the early history of an orogen may be important for later development.

2) On Thursday, March 10 at 4 PM in DMS 105, Dr. Jessica Shaw from University of Victoria will give a talk titled: Coupled oroclines of the Western European Variscan belt: From recognition to reinterpretation of the processes involved in Pangea amalgamation.

Abstract: An S-shaped pair of coupled oroclines characterizes the Iberian segment of the Western European Variscan belt. The well-exposed northerly Cantabrian orocline is one of the best-studied structures of its kind; the geometry of its southerly partner, the Central Iberian orocline, was only recently constrained. Structural continuity between the Cantabrian–Central Iberian orocline pair suggests that they formed peri-contemporaneously by vertical-axis buckling of an initially linear 2300-km-long segment of the Variscan orogen. However, the requirements for orocline formation are difficult to reconcile within traditional models that interpret the Variscan as the European record of Pangea-forming Gondwana–Laurussia continental collision. A dramatic shift in regional compressive stress is required to initiate buckling following the Late Carboniferous cessation of E-W Variscan shortening, and a maximum 20 My time interval for orocline formation indicates that >1100 km of orogen parallel-shortening was accommodated at translation rates in excess of 5 cm yr-1. Palinspastic restoration of the Iberian coupled oroclines revealing a N-S trending orogen bound on either side by oceanic-sutures is consistent with paleomagnetic data indicating mid-Paleozoic separation of the Variscan autochthon from its north Gondwanan point of origin. Paleomagnetic data further indicate that northward drift of Gondwana persisted through each phase of protected Variscan orogenesis to cease only after a final period of acceleration coincident with oroclinal buckling at the Carboniferous–Permian boundary. The implication that the true record of Pangean amalgamation is not Variscan orogenesis but oroclinal buckling of the orogen itself requires construction of the Variscan orogen through pre-Pangean accretionary processes.

REMINDER: TODAY Friday March 4, GPHS and DGSE are cosponsoring a colloquium by Dr. Mark Engle, a graduate of the GPHS program who now works for the USGS in Texas. He will talk about “Geochemistry and origin of produced waters from shale gas and tight oil reservoirs” in DMS 110 at 4 pm.

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