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

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.

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Hazards of the Caribbean

After the Earth Quakes ◽

10.1093/oso/9780195179132.003.0011 ◽

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

10.5194/egusphere-egu2020-6221 ◽

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

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&#8217;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&#8212;the Ruby-East Humboldt, Snake Range, and Albion-Raft River-Grouse Creek&#8212;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, 40Ar/39Ar 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. &#160;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.

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Across-arc variations in Mo isotopes and implications for subducted oceanic crust in the source of back-arc basin volcanic rocks

Geology ◽

10.1130/g48754.1 ◽

2021 ◽

Author(s):

Xiaohui Li ◽

Quanshu Yan ◽

Zhigang Zeng ◽

Jingjing Fan ◽

Sanzhong Li ◽

...

Keyword(s):

Subduction Zone ◽

Oceanic Crust ◽

Volcanic Rocks ◽

Isotope Ratios ◽

Oceanic Lithosphere ◽

Magma Source ◽

Benioff Zone ◽

Subduction Zone Processes ◽

Subducted Oceanic Crust ◽

Back Arc

Molybdenum (Mo) isotope ratios provide a potential means of tracing material recycling involved in subduction zone processes. However, the geochemical behavior of Mo in subducted oceanic crust remains enigmatic. We analyzed Mo isotope ratios of arc and back-arc basin lavas from the Mariana subduction zone (western Pacific Ocean), combining newly obtained element and Sr-Nd-Pb-Li isotope data to investigate subduction zone geochemical processes involving Mo. The Mo isotope ratios (δ98/95MoNIST3134; U.S. National Institute of Standards and Technology [NIST] Mo standard) of the volcanic rocks showed clear across-arc variations, decreasing with increasing depth to the Wadati-Benioff zone. The high δ98/95Mo values in the Mariana Islands (–0.18‰ to +0.38‰) correspond to high 87Sr/86Sr, low 143Nd/144Nd, and radiogenic Pb isotope ratios, suggesting that altered upper oceanic crust played an important role in the magma source. The low δ98/95Mo values in the Central Mariana Trough (–0.65‰ to –0.17‰) with mantle-like Sr-Nd-Pb but slightly low δ7Li values provide direct evidence for the contribution of deep recycled oceanic crust to the magma source of the back-arc basin lavas. The isotopically light Mo magmas originated by partial melting of a residual subducted slab (eclogite) after high degrees of dehydration and then penetrated into the back-arc mantle. This interpretation provides a new perspective with which to investigate the deep recycling of subducted oceanic lithosphere and associated magma petrogenesis.

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Author response for "Devonian bimodal volcanic rocks from the northeastern margin of the North China Block: Implications for post‐collisional extension and orogen‐craton boundary"

10.1002/gj.3805/v2/response1 ◽

2020 ◽

Author(s):

Qi‐Qi Zhang ◽

Shuan‐Hong Zhang ◽

Yue Zhao ◽

Guo‐Hao Shui

Keyword(s):

North China ◽

Volcanic Rocks ◽

Author Response ◽

North China Block ◽

The North

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A new volcanic province: evidence from glacial erratics in western North Greenland

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/ggub.v186.5213 ◽

2000 ◽

pp. 35-41 ◽

Cited By ~ 1

Author(s):

Peter R. Dawes ◽

Bjørn Thomassen ◽

T.I. Hauge Andersson

Keyword(s):

Volcanic Rocks ◽

Iron Formation ◽

Banded Iron Formation ◽

Common Component ◽

Volcanic Province ◽

North West ◽

North East ◽

The North ◽

Surficial Deposits ◽

North Greenland

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Dawes, P. R., Thomassen, B., & Andersson, T. H. (2000). A new volcanic province: evidence from glacial erratics in western North Greenland. Geology of Greenland Survey Bulletin, 186, 35-41. https://doi.org/10.34194/ggub.v186.5213 _______________ Mapping and regional geological studies in northern Greenland were carried out during the project Kane Basin 1999 (see Dawes et al. 2000, this volume). During ore geological studies in Washington Land by one of us (B.T.), finds of erratics of banded iron formation (BIF) directed special attention to the till, glaciofluvial and fluvial sediments. This led to the discovery that in certain parts of Daugaard-Jensen Land and Washington Land volcanic rocks form a common component of the surficial deposits, with particularly colourful, red porphyries catching the eye. The presence of BIF is interesting but not altogether unexpected since BIF erratics have been reported from southern Hall Land just to the north-east (Kelly & Bennike 1992) and such rocks crop out in the Precambrian shield of North-West Greenland to the south (Fig. 1; Dawes 1991). On the other hand, the presence of volcanic erratics was unexpected and stimulated the work reported on here.

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Morphotectonic Analysis along the Northern Margin of Samos Island, Related to the Seismic Activity of October 2020, Aegean Sea, Greece

Geosciences ◽

10.3390/geosciences11020102 ◽

2021 ◽

Vol 11 (2) ◽

pp. 102

Author(s):

Paraskevi Nomikou ◽

Dimitris Evangelidis ◽

Dimitrios Papanikolaou ◽

Danai Lampridou ◽

Dimitris Litsas ◽

...

Keyword(s):

Fault Zone ◽

Seismic Activity ◽

Volcanic Rocks ◽

Active Tectonics ◽

Normal Fault ◽

Aegean Sea ◽

Northern Margin ◽

The North ◽

Eastern Aegean ◽

Half Graben

On 30 October 2020, a strong earthquake of magnitude 7.0 occurred north of Samos Island at the Eastern Aegean Sea, whose earthquake mechanism corresponds to an E-W normal fault dipping to the north. During the aftershock period in December 2020, a hydrographic survey off the northern coastal margin of Samos Island was conducted onboard R/V NAFTILOS. The result was a detailed bathymetric map with 15 m grid interval and 50 m isobaths and a morphological slope map. The morphotectonic analysis showed the E-W fault zone running along the coastal zone with 30–50° of slope, forming a half-graben structure. Numerous landslides and canyons trending N-S, transversal to the main direction of the Samos coastline, are observed between 600 and 100 m water depth. The ENE-WSW oriented western Samos coastline forms the SE margin of the neighboring deeper Ikaria Basin. A hummocky relief was detected at the eastern margin of Samos Basin probably representing volcanic rocks. The active tectonics characterized by N-S extension is very different from the Neogene tectonics of Samos Island characterized by NE-SW compression. The mainshock and most of the aftershocks of the October 2020 seismic activity occur on the prolongation of the north dipping E-W fault zone at about 12 km depth.

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