Continental collision zones are primary sites for net continental crust growth — A testable hypothesis

Folded sedimentary rocks (calcareous turbidite sequence) of Carbonferous age at Loughshinny, Ireland. The Variscan orogeny is responsible for the folding. (c) Siim Sepp

Yaoling Niu, Zhidan Zhao, Di-Cheng Zhu, Xuanxue Mo has published a review article about continental collision zones. The abstract of the article is reported below.

The significance of the continental crust (CC) on which we live is self-evident. However, our knowledge remains limited on its origin, its way and rate of growth, and how it has acquired the “andesitic” composition from mantle derived magmas. Compared to rocks formed from mantle derived magmas in all geological environments, volcanic arc rocks associated with seafloor subduction share some common features with the CC; both are relatively depleted in “fluid-insoluble” elements (e.g., Nb, Ta and Ti), but enriched in “fluid-soluble” elements (e.g., U, K and Pb). These chemical characteristics are referred to as the “arc-like signature”, and point to a possible link between subduction-zone magmatism and CC formation, thus leading to the “island arc” model widely accepted for the origin of the CC over the past 45 years. However, this “island–arc” model has many difficulties: e.g., (1) the bulk arc crust (AC) is basaltic whereas the bulk CC is andesitic; (2) the AC has variably large Sr excess whereas the CC is weakly Sr deficient; and (3) AC production is mass-balanced by subduction erosion and sediment recycling, thus contributing no net mass to the CC growth, at least in the Phanerozoic. Our recent and ongoing studies on granitoid rocks (both volcanic and intrusive) formed in response to the India–Asia continental collision (~ 55 ± 10 Ma) show remarkable compositional similarity to the bulk CC with the typical “arc-like signature”. Also, these syncollisional granitoid rocks exhibit strong mantle isotopic signatures, meaning that they were recently derived from a mantle source. The petrology and geochemistry of these syncollisional granitoid rocks are most consistent with an origin via partial melting of the upper ocean crust (i.e., last fragments of underthrusting ocean crust upon collision) under amphibolite facies conditions, adding net mantle-derived materials to form juvenile CC mass. This leads to the logical and testable hypothesis that continental collision produces and preserves the juvenile crust, and hence maintains net CC growth.

Importantly, the history of the Greater Tibetan Plateau from the Early Paleozoic to present manifests the history of “super” continent amalgamation through a series of continental collision events with production and preservation of abundant syncollisional granitoids. Plate tectonics in terms of seafloor spreading and subduction is a continuous process on a global scale since its inception (in the early Archean?), whereas continental collision on regional scales and super-continental formation on a global scale are episodic (vs. continuous). Hence, continental collision with juvenile crust formation/preservation and super-continent amalgamation explains the episodic growth of the CC. We are continuing testing and refining this hypothesis by detailed petrological, geochemical and geochronological studies of syncollisional granitoids along older collision zones in central-west China, especially on the northern Tibetan Plateau in a global context.

More information about the article: Earth-Science Reviews Volume 127, December 2013, Pages 96–110

Authors and affiliations:

Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China

Yaoling Niu

Department of Earth Sciences, Durham University, Durham DH1 3LE, UK

Yaoling Niu

State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China

Yaoling Niu , Zhidan Zhao, Di-Cheng Zhu, Xuanxue Mo

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Tsunami-generated turbidity current of the 2011 Tohoku-Oki earthquake

Effect of the tsunami from the Tōhoku earthquake on a Japanese coast. (c) German Aerospace Center, Rapid Eye

A Japanese scientific team studied relationships between tsunami and turbidity current due to the 2011 Tohoku-Oki earthquake. The article has been recently published on the journal Geology. Here below the abstract.

We show the first real-time record of a turbidity current associated with a great earthquake, the Mw 9.0, 2011 Tohoku-Oki event offshore Japan. Turbidity current deposits (turbidites) have been used to estimate earthquake recurrence intervals from geologic records. Until now, however, there has been no direct evidence for large-scale earthquakes in subduction plate margins. After the 2011 Tohoku-Oki earthquake and tsunami, an anomalous event on the seafloor consistent with a turbidity current was recorded by ocean-bottom pressure recorders and seismometers deployed off Sendai, Japan. Freshly emplaced turbidites were collected from a wide area of seafloor off the Tohoku coastal region. We analyzed these measurements and sedimentary records to determine conditions of the modern tsunamigenic turbidity current. We anticipate our discovery to be a starting point for more detailed characterization of modern tsunamigenic turbidites, and for the identification of tsunamigenic turbidites in geologic records. 

Follow this link for more information about this article: Geology, November 2013, v. 41, p. 1195-1198

Authors and affiliations:

Department of Earth Sciences, Graduate School of Science, Chiba University, 1-33 Yayoicho, Inage-ku, Chiba 263-8522, Japan

Kazuno Arai

Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan

Hajime Naruse

Nippon Marine Enterprises, Ltd., 14-1 Ogawa-cho, Yokosuka, Kanagawa 238-0004, Japan

Ryo Miura

Graduate School of Science and Engineering, Yamaguchi University, 1677-1 Yoshida, Yamaguchi, Yamaguchi 753-8512, Japan

Kiichiro Kawamura

Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 6-6 Aza-Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8578, Japan

Ryota Hino, Yoshihiro Ito

National Research Institute for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba, Ibaraki 305-0006, Japan

Daisuke Inazu

Faculty of Information Science and Technology, Osaka Institute of Technology, 1-79-1 Kitayama, Hirakata, Osaka 576-0196, Japan

Miwa Yokokawa

Department of Civil Engineering, Hokkaido University, Nishi 8, Kita 13, Kita-ku, Sapporo, Hokkaido 060-8628, Japan

Norihiro Izumi

Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku, Kochi 783-8502, Japan

Masafumi Murayama

Institute for Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan

Takafumi Kasaya

On the origin of orogens

The Mont Blanc seen in the afternoon taken from the Rébuffat platform. (c) Nicolas Sanchez, edit by Digon3

The origin of orogens is the topic of this important article published on Geological Society of America Bulletin by R.A. Jamieson and C. Beaumont. Here the abstract.

In order to understand how orogens “work,” a quantitative approach demonstrating proof of concept is essential. Our goal is to reconcile the diverse array of tectonic features observed in natural orogens in the context of “working” numerical models that are consistent with both the underlying physics and first-order geological constraints. We present a simple conceptual temperature-magnitude (T-M) framework for orogenesis in terms of the progression from small-cold to large-hot orogens, and we use forward numerical models to test hypotheses corresponding to specific stages along the T-M spectrum. Small-cold orogens are analyzed using crustal-scale singularity (S) point models, in which suborogenic mantle lithosphere is kinematically subducted beneath crust that deforms by critical wedge mechanics. The transition from oceanic subduction to continental collision, and the subsequent evolution of large-hot orogens, has been investigated using both crustal- and upper-mantle–scale models, the latter including dynamic subduction of suborogenic mantle lithosphere. Large-hot orogens with thick crust are characterized by elevated plateaus with a strong superstructure underlain by hot, weak, lower-crustal infrastructure. Beneath plateaus, tectonic processes are dominated by ductile flow of weak crust in response to differential pressure, while plateau flanks form external thrust-sense wedges. We discuss four topical issues in orogenic tectonics, including the response of the suborogenic mantle lithosphere to convergence, the interaction of climate and tectonics, the current debate concerning wedge versus channel-flow models to explain the Himalayan-Tibetan system, and the interpretation of metamorphic architecture in terms of orogenic processes. We conclude that collisional orogenesis is driven largely by subduction and accretion of material at convergent margins, accompanied by shortening, thickening, and heating of deformed crust.

Follow this link for more information about this article: Geological Society of America Bulletin, November 2013, v. 125, no. 11-12, p. 1671-1702

Affiliations:

Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada

R.A. Jamieson

Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada

C. Beaumont

Recent hydrological and geochemical research for earthquake prediction in Japan

Global earthquake epicenters.  (c)NASA, DTAM project team

The last issue of the journal Natural Hazards is devoted to the topic: earthquake prediction. We have already reported the article "Earthquake prediction: 20 years of global experiment" and now we propose an other article written by Norio Matsumoto, Naoji Koizumi affiliated to the Geological Survey of Japan.
They take into account hydrological and geochemical aspects in earthquake prediction, as the following abstract reports.
Hydrological and geochemical studies for earthquake prediction in Japan during the last two decades are reviewed. Following the 1995 Hyogo-ken Nanbu (Kobe) earthquake, the central approach to research on earthquake prediction was modified. Instead of precursory detection, emphasis was placed on understanding the entire earthquake cycle. Moreover, the prediction program for the anticipated Tokai earthquake was revised in 2003 to include the detection of preslip-related precursors. These changes included the promotion of the following hydrological and geochemical studies for earthquake prediction: (1) development and/or application of statistical methods to extract small fluctuations from hydrological/geochemical data, (2) evaluation of the detectability of preslip-related anomalies in terms of groundwater levels in wells in the Tokai region, and (3) establishment of a new groundwater and borehole strain observation network for Nankai and Tonankai earthquake prediction research. The following basic geochemical studies were carried out: (1) development of a new monitoring system using a quadrupole mass spectrometer, (2) experimental studies on hydrogen generation by the grinding of rock and crystal powders, (3) comprehensive monitoring of groundwater gas and precise crustal deformation, and (4) mantle-derivative helium observation to compare with seismic velocity structures and the distribution of non-volcanic tremors. Moreover, hydrological and geochemical investigations related to the evolution of fault zones were introduced within the framework of fault zone drilling projects.

Follow the link below to go to article website: Natural Hazards    November 2013, Volume 69, Issue 2, pp 1247-1260
 

Affiliations:

Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8567, Japan

Norio Matsumoto, Naoji Koizumi

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Carbon dioxide emission to Earth’s surface by deep-sea volcanism

Submarine volcanic eruption in El Hierro island (Canary) - (c) NASA's Earth Obs

Satoshi Okumura and Naoto Hirano, from Tohoku University (Japan), have published on the journal Geology an interesting article (Open Access) about CO₂ emitted by submarine volcanism. Here below the abstract of the article.

Large amounts of CO₂ are transferred from Earth’s interior to the surface by volcanism. On a geological time scale, the rate of CO₂ emission has controlled the evolution of Earth’s atmosphere and climate, as well as the dynamic processes that take place in the mantle and core. The total rate of natural CO₂ emission from Earth has been estimated on the basis of CO₂ flux from arc, mid-ocean-ridge, and hotspot volcanism. However, previous estimates have overlooked the CO₂ emitted from a recently discovered type of volcanism—petit-spot volcanism—that occurs on the deep-sea floor. Here, we measure the CO₂ and H₂O contents of glassy basalts produced by petit-spot volcanism and estimate the initial contents to be >5 wt% and 1.0–1.1 wt%, respectively. Based on these values and magma flux of petit-spot volcanism, we show that the rate of CO₂ emission from petit-spot volcanoes (2.7–5.4 × 10¹¹ g CO₂ yr^–1) is a few percent of the CO₂ emissions from arc and mid-ocean-ridge volcanism, and up to ∼14% of that from hotspot volcanism. Thus, the contribution to the carbon cycle on Earth of the large amounts of CO₂ that have been emitted from the deep-sea floor by petit-spot volcanism has not previously been recognized.

Follow the link below to read the full article (Open Access)
Geology, November 2013, v. 41, p. 1167-1170

 

Affiliations: 
Division of Earth and Planetary Materials Science, Department of Earth Science, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Satoshi Okumura

Center for Northeast Asian Studies, Tohoku University, Sendai 980-8576, Japan 
Naoto Hirano

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Water and the composition of Martian magmas

(c) NASA/JPL

This article has been written by J. Brian Balta and Harry Y. McSween Jr. affiliated to University of Tennessee - USA.

Shergottites, the most abundant martian meteorites, represent the best source of information about Mars’ mantle and its dissolved water. If the mantle was wet, magmatic degassing could have supplied substantial water to the martian surface early in its history. Researchers have attempted to reconstruct the volatile contents of shergottite parental magmas, with recent analyses confirming that the shergottites contained significant water. However, water is not a passive tracer; it directly affects magma chemistry and physical properties. Deciphering the history of water on Mars requires understanding how that water affected the chemistry of the shergottites and how they fit within Mars’ geologic history. Both topics present difficulties, as no shergottite-like rock has been found in stratigraphic context and there is debate over the timing of eruptions of shergottite-like magmas. Partial melting experiments on terrestrial basalts and new data from orbiters and rovers on Mars provide the information needed to overcome these difficulties and explain the role of water in shergottite magmas. Here we show that shergottite compositions and their martian geologic context can be explained by melting of an originally wet mantle that degassed over time. We also demonstrate that models for the evolution of the martian mantle that do not consider water fail to account for the shergottite compositions, surface distributions, and ages. Finally, we suggest that dehydration of the martian mantle has led to changes in magmatic chemistry over time, with shergottites representing melts of water-bearing mantle and rocks similar to nakhlites representing melts of other mantle sources.

Geology, October 2013, v. 41, p. 1115-1118

Affiliations: 
Department of Earth and Planetary Sciences, University of Tennessee, 1412 Circle Drive, Knoxville, Tennessee 37996, USA
J. Brian Balta
Harry Y. McSween Jr.

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Structural interpretation of the great earthquakes of the last millennium in the central Himalaya

(c) Michel Royon / Wikimedia Commons

The authors of the article are J.-L. Mugnier, A. Gajurel, P. Huyghe, R. Jayangondaperumal, F. Jouanne, B. Upreti. They are affiliated to Université de Savoie - France,
Tribhuvan University - Nepal and Wadia Institute of Himalayan Geology, Dehradun, Uttarakhand - India

A major question about the Himalaya remains open: does a great earthquake (like the Mw ~ 8.1 1934 earthquake) release all the strain stored by the Tibet–India convergence during the preceding interseismic period and only that strain, or can it also release a background store of energy that remained unreleased through one or more earlier earthquakes and so potentially engender giant events or a relatively random sequence of events?

To consider this question, the history of the great earthquakes of the last millennium is investigated here by combining data provided by the historical archives of Kathmandu, trenches through surface ruptures, isoseismal damage mapping, seismites, and the instrumental record. In the Kathmandu basin, the location of the epicenter of the 1934 earthquake was determined from the arrival of high-energy P-waves that caused sedimentary dikes and ground fractures perpendicular to the epicenter azimuth. The epicenter of the Mw ~ 7.6 1833 earthquake can therefore be determined analogously from dike orientation, and its location to the NE of Kathmandu indicates an overlap with the Mw ~ 8.1 1934 rupture. The 1934 earthquake released strain not released by the 1833 earthquake.

Comparison of the historical records of earthquakes in Kathmandu with ¹⁴C ages from paleo-seismic trenches along the Himalayan front suggests that: (1) the 1344 Kathmandu event ruptured the surface as far away as Kumaon and was therefore a giant Mw ≥ 8.6 earthquake; and (2) the 1255 event that destroyed Kathmandu is attested by surface ruptures in central and western Nepal and by seismites in soft sediment as far away as Kumaon.

Geometric and rheologic controls for the different types of ruptures during the medium (Mw ~ 7), great (Mw ≥ 8), and giant (Mw > 8.4) earthquakes are illustrated in structural cross-sections. It is found that the epicenters of great Himalayan earthquakes are located on the basal thrust farther north or close to the locked zone, which is defined from geodetic measurements of regional deformation during the interseismic period; this suggests that great earthquakes initiate in a wide transition zone between exclusively brittle and exclusively creeping regimes, the extent of which depends on the dip of the Main Himalayan Thrust.

The succession of the great earthquakes during the last millennium has released all the 20-m millennial Himalayan convergence; even in the central seismic gap which has been locked since 1505, the millennial seismic release rate is close to the convergence rate. Nonetheless, no evidence of a succession of characteristic earthquakes has been found: the ~ 1100, 1833, and 1934 earthquakes in the eastern Himalaya are characterized neither by constant displacement nor by constant recurrence. Furthermore, some great earthquakes do not release all the strain elastically stored by the Himalayan and Tibetan upper crust: after the 1255 event, there was still the potential for a slip of several meters for the Mw ~ 8.1 1505 event. This suggests a rather random release of seismic energy; great earthquakes could occur anytime and in any part of the central Himalaya. Furthermore, a future giant earthquake of Mw ≥ 8.6 cannot be excluded.

Earth-Science Reviews - Volume 127, December 2013, Pages 30–47

Affiliations:

ISTerre, Université de Savoie, CNRS, Université Joseph Fourier, Batiment les Belledonnes, Université de Savoie, F-73376, Le Bourget du Lac Cedex, France

J.-L. Mugnier

A. Gajurel

P. Huyghe 

F. Jouanne

Department of Geology, Tribhuvan University, Ghantaghar, Kathmandu, Nepal

A. Gajurel

B. Upreti

Wadia Institute of Himalayan Geology, Dehradun, Uttarakhand, India

R. Jayangondaperumal

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