scholarly journals Diffuse spreading, a newly recognized mode of crustal accretion in the southern Mariana Trough backarc basin

Geosphere ◽  
2021 ◽  
Author(s):  
Jonathan D. Sleeper ◽  
Fernando Martinez ◽  
Patricia Fryer ◽  
Robert J. Stern ◽  
Katherine A. Kelley ◽  
...  
Keyword(s):  
Plate Tectonics ◽  
Volcanic Rocks ◽  
High Water ◽  
Threshold Effect ◽  
Philippine Sea Plate ◽  
Spreading Center ◽  
Normal Extension ◽  
Crustal Accretion ◽  
Side Scan Sonar ◽  
Diffuse Spreading

South of the latitude of Guam, the Mariana Trough exhibits both trench-parallel and trench-normal extension. In this study, we examined the locus of trench-normal extension separating the Philippine Sea plate from the broadly deforming Mariana platelet. Along this boundary, we identified three distinct modes of extension and described their distinguishing characteristics using deep- and shallow-towed side-scan sonar and ship multibeam data along with regional geophysical, geochemical, and seismicity data. In the west, the Southwest Mariana Rift is an active tectonic rift exhibiting abundant strong earthquakes up to mb 6.7 and limited evidence of volcanism. In the east, the Malaguana-Gadao Ridge is a seafloor spreading center producing few and weak earthquakes less than mb 5. Between these zones, there is an ~20–40-km-wide and ~120-km-long area of high acoustic backscatter characterized by closely spaced volcano- tectonic ridges and small volcanic cones with distributed intermediate-strength seismicity up to mb 5.7. Fresh-looking volcanic rocks with high water contents and strong arc chemical affinities have been recovered from the high-backscatter zone. We interpret this morphologically and geophysically distinct zone as undergoing diffuse spreading, a distributed form of magmatic crustal accretion where new crust forms within a broad zone tens of kilometers across rather than along a narrow spreading axis. Diffuse spreading appears to be a rheological threshold effect enabled by slow opening rates and a high slab-fluid flux that facilitate the formation of a broad zone of weak hydrous lithosphere, within which new crust is accreted. Our findings describe a poorly understood process in plate tectonics, and observations of similar terrains in other backarc basins suggest that this process is not unique to the Mariana Trough.

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.

Geochemical and metallogenic relations in volcanic rocks of the southern Slave Province: implications for late Neoarchean tectonics

2006 ◽  
Vol 43 (12) ◽  
pp. 1835-1857 ◽  
Author(s):  
A M Goodwin ◽  
M B Lambert ◽  
O Ujike
Keyword(s):  
Plate Tectonics ◽  
Early Stage ◽  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Gold Deposits ◽  
Tectonic Plates ◽  
Slave Province ◽  
Volcanogenic Massive Sulphide ◽  
Lode Gold Deposits ◽  
Volcanic Belts

Late Neoarchean volcanic belts in the southern Slave Province include (1) in the east, the Cameron River – Beaulieu River belts, which are characterized by stratigraphically thin, flow-rich, classic calc-alkaline, arc-type sequences with accompanying syngenetic volcanogenic massive sulphide deposits; and (2) in the west, the Yellowknife belt, which is characterized by stratigraphically thick, structurally complex, pyroclastic-rich, adakitic, back-arc basin-type sequences, with accompanying epigenetic lode-gold deposits. The volcanic belt association bears persuasive chemical evidence of subduction-initiated magma generation. However, the greenstone belts, together with coeval matching patterned belts in Superior Province of the southern Canadian Shield, bear equally persuasive evidence of prevailing autochthonous–parautochthonous relations with respect to component stratigraphic parts and to older gneissic basement. The eastern and western volcanic belts in question are petrogenetically ascribed to a "westerly inclined" (present geography) subduction zone(s) that produced shallower (east) to deeper (west), slab-initiated, mantle wedge-generated, parent magmas. This early stage microplate tectonic process involved modest mantle subduction depths, small tectonic plates, and small sialic cratons. In the larger context of Earth's progressively cooling, hence subduction-deepening mantle, this late Neoarchean greenstone belt development (2.73–2.66 Ga) merged with the massive end-Archean tonalite–trondhjemite–granodiorite–granite (TTGG) "bloom" (2.65–2.55 Ga), resulting in greatly enhanced craton stability. Successive subduction-deepening, plate-craton-enlarging stages, with appropriate metallotectonic response across succeeding Proterozoic time and beyond, led to modern-mode plate tectonics.

How do high school students teach geosciences to elementary students?

2020 ◽  
Author(s):  
Carole Larose
Keyword(s):  
High School ◽  
High School Students ◽  
Young Children ◽  
Plate Tectonics ◽  
School Teacher ◽  
Volcanic Rocks ◽  
School Students ◽  
Earthquake Resistant ◽  
Hands On ◽  
Different Types

<p>I am Biology and Geology teacher in a high school and I teach for students between 15 and 18 years old. Geosciences are not very easy to understand because the concepts are complex. I try to interest my students by using different pedagogical materials including hands-on. At the end of the course, to make sure that they have a good understanding, I sometimes organize a meeting between my students and the children of a primary school. It is a way to assess them because if they are able to explain some geological issues to young children, they must before understand them.</p><p>Before the meeting, the elementary school teacher and I did an educational notebook for young children. We have planned 5 activities on the topic "plate tectonics"</p><ul><li>Explosive and effusive volcanism : children identify different types of volcanism by watching two short videos</li> <li>Study the volcanic rocks : children observe the rocks and look under a polarizing microscope</li> <li>Earthquake-resistant buildings: children use a model to understand how a building can withstand an earthquake</li> <li>The different kind of faults: children use a model to create different types of faults.</li> <li>Identify the movement of Plate tectonics: children use software to do this exercise</li> </ul><p>The meeting lasted two hours. It was a great moment for all the students. My student's job was to help the youngest to answer the questions on their notebooks. They had to explain clearly and simply and it was a very interesting exercise for them because they needed knowledge to do it. Young students asked a lot of questions, they were very curious and interested in this topic.</p><p>Here is an article in French. http://svt.spip.ac-rouen.fr/spip.php?article396</p><p> </p>

Rock and paleomagnetic evidence for the existence and nature of a Cayman Trough spreading center

1978 ◽  
Vol 15 (12) ◽  
pp. 1930-1940 ◽  
Author(s):  
M. J. Clark ◽  
J. M. Hall ◽  
J. W. Peirce
Keyword(s):  
Central Valley ◽  
Spreading Center ◽  
Small Scale ◽  
Low Temperature Oxidation ◽  
Crustal Accretion ◽  
Temperature Oxidation ◽  
Magnetic Parameters ◽  
Mid Atlantic Ridge ◽  
Curie Temperatures

Rock and paleomagnetic measurements have been made on a set of 54 basalts dredged from 17 stations located within the central valley of the Cayman Trough. Seventeen of the samples could be oriented with respect to the in situ vertical by the use of lava cooling ledges and stalactites.Peak remanent intensities in the Cayman Trough are lower than peak Mid-Atlantic Ridge values by a factor of 2 or 3 even after allowance is made for the latitudinal variation in geomagnetic field intensity. This difference is likely to be the result of the combined effects of relatively low saturation magnetization and more advanced low temperature oxidation of titanomagnetite in the Cayman Trough basalts.Five young, reversely magnetized basalts, similar to those found on the Mid-Atlantic Ridge, occur in the Cayman Trough sample set.Plots of the magnetic parameters of the pillow basalts with distance from the axis of the trough show broad highs or lows associated with the axis. Our interpretation is that crustal formation in the central valley has occurred recently, but it has either been rather diffuse or is now much disturbed tectonically on a small scale in comparison with the Mid-Atlantic Ridge. Analysis of the distribution of Curie temperatures suggests that crustal accretion has been slow (0.1–0.4 cm year−1 half-rate) and may have ceased in the area studied at about 0.6 Ma BP.

scholarly journals Crustal accretion at a sedimented spreading center in the Andaman Sea

Geology ◽  
2016 ◽  
Vol 44 (5) ◽  
pp. 351-354 ◽  
Author(s):  
Aurélie Jourdain ◽  
Satish C. Singh ◽  
Javier Escartin ◽  
Yann Klinger ◽  
K.A. Kamesh Raju ◽  
...  
Keyword(s):  
Andaman Sea ◽  
Spreading Center ◽  
Crustal Accretion

scholarly journals Neotectonic mountain uplift and geomorphology

2019 ◽  
pp. 3-26
Author(s):  
C. D. Ollier ◽  
C. F. Pain
Keyword(s):  
Plate Tectonics ◽  
Volcanic Rocks ◽  
Passive Margin ◽  
Continental Margins ◽  
Lateral Compression ◽  
Mountain Building ◽  
Topographic Features ◽  
Active Margins ◽  
The World ◽  
Fold Belts

Mountains are topographic features caused by erosion after vertical uplift or mountain building. Mountain building is often confused with orogeny, which today means the formation of structures in fold belts. The common assumption that folding and mountain building go together is generally untrue. Many mountains occur in unfolded rocks, granites and volcanic rocks, so there is no direct association of folding and mountain building. In those places where mountains are underlain by folded rocks the folding pre-dates planation and uplift. The age of mountains is therefore not the age of the last folding (if any) but the age of vertical uplift. Since mountains are not restricted to folded rocks, lateral compression is not required to explain the uplift. A compilation of times of uplift of mountains around the world shows that a major phase of tectonic uplift started about 6 Ma, and much uplift occurred in the last 2 Ma. This period is known as the Neotectonic Period. It is a global phenomenon including mountains on passive continental margins, and those in deep continental interiors. Several hypotheses of mountain building have problems with this timing. Some fail by being only able to make mountains out of folded rock at continental margins. Many translate the vertical uplift into lateral compression, but vertical uplift alone can create mountains. The Neotectonic Period has important implications for geomorphology, climate and global tectonics. In geomorphology it does not fit into conventional theories of geomorphology such as Davisian or King cycles of erosion. Neotectonic uplift might initiate several cycles of erosion, but most planation surfaces are much older than the Neotectonic Period. The increasing relief associated with Neotectonic uplift affected rates of erosion and sedimentation, and also late Cenozoic climate. The Neotectonic Period does not fit within plate tectonics theory, in which mountains are explained as a result of compression at active margins: mountains in other locations are said to have been caused by the same process but further back in time. This is disproved by the young age of uplift of mountains in intercontinental and passive margin positions. Subduction is supposed to have been continuous for hundreds of millions of years, so fails to explain the world-wide uplifts in just a few million years. Geomorphologists should be guided by their own findings, and refrain from theory-driven hypotheses of plate collision or landscape evolution.

scholarly journals Lithium, Oxygen and Magnesium Isotope Systematics of Volcanic Rocks in the Okinawa Trough: Implications for Plate Subduction Studies

2021 ◽  
Vol 10 (1) ◽  
pp. 40
Author(s):  
Zhigang Zeng ◽  
Xiaohui Li ◽  
Yuxiang Zhang ◽  
Haiyan Qi
Keyword(s):  
Basaltic Andesite ◽  
Subduction Zones ◽  
Okinawa Trough ◽  
Volcanic Rocks ◽  
Philippine Sea Plate ◽  
Material Transfer ◽  
Magma Compositions ◽  
Subduction Input ◽  
Back Arc ◽  
Plate Subduction

Determining the influence of subduction input on back-arc basin magmatism is important for understanding material transfer and circulation in subduction zones. Although the mantle source of Okinawa Trough (OT) magmas is widely accepted to be modified by subducted components, the role of slab-derived fluids is poorly defined. Here, major element, trace element, and Li, O and Mg isotopic compositions of volcanic lavas from the middle OT (MOT) and southern OT (SOT) were analyzed. Compared with the MOT volcanic lavas, the T9-1 basaltic andesite from the SOT exhibited positive Pb anomalies, significantly lower Nd/Pb and Ce/Pb ratios, and higher Ba/La ratios, indicating that subducted sedimentary components affected SOT magma compositions. The δ7Li, δ18O, and δ26Mg values of the SOT basaltic andesite (−5.05‰ to 4.98‰, 4.83‰ to 5.80‰ and −0.16‰ to −0.09‰, respectively) differed from those of MOT volcanic lavas. Hence, the effect of the Philippine Sea Plate subduction component, (low δ7Li and δ18O and high δ26Mg) on magmas in the SOT was clearer than that in the MOT. This contrast likely appears because the amounts of fluids and/or melts derived from altered oceanic crust (AOC, lower δ18O) and/or subducted sediment (lower δ7Li, higher δ18O and δ26Mg) injected into magmas in the SOT are larger than those in the MOT and because the injection ratio between subducted AOC and sediment is always >1 in the OT. The distance between the subducting slab and overlying magma may play a significant role in controlling the differences in subduction components injected into magmas between the MOT and SOT.

A method to estimate the pre-eruptive water content of basalts: Application to the Wudalianchi–Erkeshan–Keluo volcanic field, Northeastern China

2020 ◽  
Vol 105 (2) ◽  
pp. 149-161 ◽  
Author(s):  
Yankun Di ◽  
Wei Tian ◽  
Mimi Chen ◽  
Zefeng Li ◽  
Zhuyin Chu ◽  
...  
Keyword(s):  
Water Content ◽  
Volcanic Rocks ◽  
High Water ◽  
Volcanic Field ◽  
Northeastern China ◽  
Magma Ascent ◽  
High Water Content ◽  
Silica Activity ◽  
Igneous Provinces ◽  
The Difference

Abstract Water plays an important role in the generation and evolution of volcanic systems. However, the direct measurement of the pre-eruption water content of subaerial volcanic rocks is difficult, because of the degassing during magma ascent. In this study, we developed a method to calculate the pre-eruption water content of the basalts from the Cenozoic Wudalianchi–Erkeshan–Keluo (WEK) potassic volcanic field, Northeastern China, and investigated their mantle source. A water-insensitive clinopyroxene–melt thermobarometer and a water-sensitive silica activity thermobarometer were applied to these basalts. Two pressure-temperature (P-T) paths of the ascending magma were calculated using these two independent thermobarometers, with a similar P-T slope but clear offset. By adjusting the water content used in the calculation, the difference between the two P-T paths was minimized, and the water content of the WEK melts was estimated to be 4.5 ± 1.2 wt% at a pressure range of 10.1–13.5 kbar, corresponding to depths of 37–47 km. Degassing modeling shows that during the magma ascent from below the Moho to near the surface, CO2 was predominantly degassed, while the melt H2O content kept stable. Significant H2O degassing occurred until the magma ascended to 5–2 kbar. The silica activity P–T estimates of the most primary WEK samples suggest that the magmas were generated by the melting of convective mantle, which was probably facilitated by a wet upwelling plume from the mantle transition zone. The high water content found in the WEK basalts is similar to the recent reports on Phanerozoic intraplate large igneous provinces (LIPs) and supports the presence of hydrated deep mantle reservoirs as one possible source of the LIPs.

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