Mechanisms of Extensional Strain Localization: An Example from Cordilleran Metamorphic Core Complexes

2020 ◽  
Author(s):  
Drew Levy ◽  
Andrew Zuza
Keyword(s):  
Great Basin ◽  
Strain Localization ◽  
Plate Tectonics ◽  
Electron Backscatter Diffraction ◽  
Plate Boundary ◽  
Crustal Extension ◽  
The North ◽  
Metamorphic Core Complexes ◽  
Extensional Strain ◽  
Metamorphic Core

<p>Crustal extension is a fundamental process in plate tectonics, and understanding its driving mechanisms is critical to our understanding the role of extensional deformation in the evolution of the Earth’s continents. How and why extension localizes into narrow belts versus being distributed across wide orogens remains enigmatic. Here we investigate extensional strain localization in the North American Cordillera (NAC) and Basin and Range province, where early phases of high magnitude strain (>100%) were fairly localized along a ~2500-km long belt of metamorphic core complexes, and subsequent late-stage low-magnitude strain appears to be fairly distributed across the 500-600-km width of the Great Basin. Various forces compete to drive intracontinental extension in the western United States, and we present field-based case studies of the Central NAC core complexes—the Ruby-East Humboldt, Snake Range, and Albion-Raft River-Grouse Creek—to explore strain localization due to plate-boundary stresses, internal body forces (GPE), and/or crustal rheology including thermal weakening from pervasive magmatism. The studied core complexes consist of significant syn-kinematic intrusions, and we demonstrate how the composition, volume and age (i.e., duration and relative timing) of these intrusions affected strain rates. Through a combination of new and synthesized U-Pb geochronology, <sup>40</sup>Ar/<sup>39</sup>Ar thermochronology and electron backscatter diffraction (EBSD) analysis we link transient thermal and rheological evolution of the crust with deformation mechanisms from grain to outcrop to regional scales.  More broadly, we discuss the mechanisms and modes of crustal extension during orogenesis, and whether extension in active orogens is a transient response to modulate GPE gradients, or a precursor to orogenic collapse.</p>

Mid-Miocene volcanic migration in the westernmost Sunda arc induced by India-Eurasia collision

Geology ◽  
2021 ◽  
Author(s):  
Yu-Ming Lai ◽  
Sun-Lin Chung ◽  
Azman A. Ghani ◽  
Sayed Murtadha ◽  
Hao-Yang Lee ◽  
...  
Keyword(s):  
Plate Tectonics ◽  
Volcanic Rocks ◽  
Plate Boundary ◽  
Andaman Sea ◽  
Fundamental Aspect ◽  
Benioff Zone ◽  
The North ◽  
Sunda Arc ◽  
Subduction Zone Processes ◽  
Zone Depth

The migration of arc magmatism that is a fundamental aspect of plate tectonics may reflect the complex interaction between subduction zone processes and regional tectonics. Here we report new observations on volcanic migration from northwestern Sumatra, in the westernmost Sunda arc, characterized by an oblique convergent boundary between the Indo-Australian and Eurasian plates. Our study indicates that in northwestern Sumatra, volcanism ceased at 15–10 Ma on the southern coast and reignited to form a suite of active volcanoes that erupt exclusively to the north of the trench-parallel Sumatran fault. Younger volcanic rocks from the north are markedly more enriched in K2O and other highly incompatible elements, delineating a geochemical variation over space and time similar to that in Java and reflecting an increase in the Benioff zone depth. We relate this mid-Miocene volcanic migration in northwestern Sumatra to the far-field effect of propagating extrusion tectonics driven by the India-Eurasia collision. The extrusion caused regional deformation southward through Myanmar to northwestern Sumatra and thus transformed the oblique subduction into a dextral motion–governed plate boundary. This tectonic transformation, associated with opening of the Andaman Sea, is suggested to be responsible for the volcanic migration in northwestern Sumatra.

Hazards of the Caribbean

2005 ◽  
Author(s):  
Susan Elizabeth Hough ◽  
Roger G. Bilham
Keyword(s):  
United States ◽  
Puerto Rico ◽  
North America ◽  
Plate Tectonics ◽  
Plate Boundary ◽  
The United States ◽  
American Continent ◽  
North American Continent ◽  
The North ◽  
The Caribbean

The Caribbean is a place of romance. Idyllic beaches, buoyant cultures, lush tropical flora; even the Caribbean pirates of yore often find themselves romanticized in modern eyes, and on modern movie screens. Yet it requires barely a moment’s reflection to appreciate the enormous resilience that must exist in a place that is so routinely battered by storms of enormous ferocity. News stories tend to focus on large storms that reach the United States, but many large hurricanes arrive in the United States by way of the Caribbean. Before it slammed into South Carolina in 1989, Hurricane Hugo brushed the Caribbean islands, skimming Puerto Rico and devastating many small islands to its east. Other hurricanes have hit the islands more directly. These include Inez, which claimed some 1,500 lives in 1966, and the powerful Luis, which caused $2.5 billion in property damage and 17 deaths when it pummeled the Leeward Islands and parts of Puerto Rico and the Virgin Islands in 1995. Hurricanes also figure prominently in the pre-20th-century history of the Caribbean—storms that had no names, the sometimes lethal fury of which arrived unheralded by modern forecasts. Most people know that the Caribbean is hurricane country; probably few realize that it is earthquake country as well. After all, the western edge of North America is the active plate boundary; earthquakes occur in the more staid midcontinent and Atlantic seaboard, but far less commonly. What can be overlooked, however, is North America’s other active plate boundary. To understand the general framework of this other boundary, it is useful to return briefly to basic tenets of plate tectonics theory. As discussed in earlier chapters, the eastern edge of North America is known as a passive margin. Because the North American continent is not moving relative to the adjacent Atlantic oceanic crust, in plate tectonics terms, scientists do not differentiate between the North American continent and the western half of the Atlantic ocean.

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