scholarly journals Origin of potassic postcollisional volcanic rocks in young, shallow, blueschist-rich lithosphere

2021 ◽  
Vol 7 (29) ◽  
pp. eabc0291
Author(s):  
Yu Wang ◽  
Stephen F. Foley ◽  
Stephan Buhre ◽  
Jeremie Soldner ◽  
Yigang Xu
Keyword(s):  
Temporal Trend ◽  
Volcanic Rocks ◽  
Continental Collision ◽  
Mantle Lithosphere ◽  
Source Regions ◽  
Himalayan Belt ◽  
Potassic Rocks

Potassium-rich volcanism occurring throughout the Alpine-Himalayan belt from Spain to Tibet is characterized by unusually high Th/La ratios, for which several hypotheses have brought no convincing solution. Here, we combine geochemical datasets from potassic postcollisional volcanic rocks and lawsonite blueschists to explain the high Th/La. Source regions of the volcanic melts consist of imbricated packages of blueschist facies mélanges and depleted peridotites, constituting a new mantle lithosphere formed only 20 to 50 million years earlier during the accretionary convergence of small continental blocks and oceans. This takes place entirely at shallow depths (<80 km) without any deep subduction of continental materials. High Th/La in potassic rocks may indicate shallow sources in accretionary settings even where later obscured by continental collision as in Tibet. This mechanism is consistent with a temporal trend in Th/La in potassic postcollisional magmas: The high Th/La signature first becomes prominent in the Phanerozoic, when blueschists became widespread.

Evolution of deep mantle sourced carbonated melt in the mantle lithosphere

2020 ◽  
Author(s):  
Guoliang Zhang
Keyword(s):  
Rare Earth ◽  
Field Strength ◽  
Rare Earth Elements ◽  
Lithospheric Mantle ◽  
High Field ◽  
Volcanic Rocks ◽  
Mantle Lithosphere ◽  
High Field Strength ◽  
Alkali Basalts ◽  
Deep Mantle

&lt;p&gt;Deep sourced magmas play a key role in distribution of carbon in the Earth&amp;#8217;s system. Oceanic hotspots rooted in deep mantle usually produce CO&lt;sub&gt;2&lt;/sub&gt;-rich magmas. However, the association of CO&lt;sub&gt;2&lt;/sub&gt; with the origin of these magmas remains unclear. Here we report geochemical analyses of a suite of volcanic rocks from the Caroline Seamount Chain formed by the deep-rooted Caroline hotspot in the western Pacific. The most primitive magmas have depletion of SiO&lt;sub&gt;2&lt;/sub&gt; and high field strength elements and enrichment of rare earth elements that are in concert with mantle-derived primary carbonated melts. The carbonated melts show compositional variations that indicate reactive evolution within the overlying mantle lithosphere and obtained depleted components from the lithospheric mantle. The carbonated melts were de-carbonated and modified to oceanic alkali basalts by precipitation of perovskite, apatite and ilmenite that significantly decreased the concentrations of rare earth elements and high field strength elements. These magmas experienced a stage of non-reactive fractional crystallization after the reactive evolution was completed. Thus, the carbonated melts would experience two stages, reactive and un-reactive, of evolution during their transport through in thick oceanic lithospheric mantle. We suggest that the mantle lithosphere plays a key role in de-carbonation and conversion of deep-sourced carbonated melts to alkali basalts. This work was financially supported by the National Natural Science Foundation of China (91858206, 41876040).&lt;/p&gt;

scholarly journals Linzizong Volcanic Rocks in Linzhou of Tibet: A Volcanic Petrologic Assemblage in Continental Collision Environment

2008 ◽  
Vol 2 (4) ◽  
pp. 128
Author(s):  
Guochen Dong ◽  
Xuanxue Mo ◽  
Zhidan Zhao ◽  
Liang Wang ◽  
Su Zhao
Keyword(s):  
Volcanic Rocks ◽  
Continental Collision ◽  
Special Issue

Himalayan Journal of Sciences Vol.2(4) Special Issue 2004 pp. 128

scholarly journals Probing crustal and mantle lithosphere origin through Ordovician volcanic rocks along the Iberian passive margin of Gondwana

2008 ◽  
Vol 461 (1-4) ◽  
pp. 166-180 ◽  
Author(s):  
J. Brendan Murphy ◽  
G. Gutiérrez-Alonso ◽  
J. Fernández-Suárez ◽  
James A. Braid
Keyword(s):  
Volcanic Rocks ◽  
Passive Margin ◽  
Mantle Lithosphere

scholarly journals A short, sharp pulse of potassium-rich volcanism during continental collision and subduction

Geology ◽  
2019 ◽  
Vol 47 (11) ◽  
pp. 1079-1082 ◽  
Author(s):  
M.R. Palmer ◽  
E.Y. Ersoy ◽  
C. Akal ◽  
İ. Uysal ◽  
Ş.C. Genç ◽  
...  
Keyword(s):  
High Pressure ◽  
Isotope Composition ◽  
Volcanic Rocks ◽  
Continental Collision ◽  
Western Anatolia ◽  
Slab Rollback ◽  
Tectonic Zones ◽  
Geochemical Indices ◽  
Partial Melts ◽  
Potassic Volcanism

Abstract Potassic volcanic rocks are characteristic of collisional tectonic zones, with recycling of continental crust playing an important role in their generation. Potassium-rich partial melts and/or fluids derived from subducted continental material initiate and/or mix with mantle-derived melts and then erupt at the surface with varying degrees of interaction with the overlying lithosphere. The details of how continental material incorporates into mantle melts are, however, uncertain. In particular, the depths from which the potassium-rich fluids and/or melts are released from the continental material and then react with the mantle-derived melts remain a subject of debate. We have measured the boron isotope composition of volcanic rocks from Western Anatolia (Turkey) that erupted between 52 and 0.1 Ma, and span the lifetime of collisional events from initial arc-type eruptions to post-collisional volcanism. These data and other geochemical indices show that ultrapotassic volcanism was mainly confined to a narrow window between ca. 20 and 15 Ma, consistent with recycling of high-pressure phengite, with the timing of the potassic volcanism coincident with slab rollback and breakoff.

Tectonic environments of Cenozoic volcanic rocks in China and characteristics of the source regions in the mantle

1995 ◽  
Vol 14 (4) ◽  
pp. 289-302 ◽  
Author(s):  
Ruoxin Liu ◽  
Guanghong Xie ◽  
Xinhua Zhou ◽  
Wenji Chen ◽  
Qicheng Fan
Keyword(s):  
Volcanic Rocks ◽  
Source Regions ◽  
Tectonic Environments

Geochemical and isotopic evidence for the origin of continental flood basalts with particular reference to the Snake River Plain Idaho, U. S. A

1984 ◽  
Vol 310 (1514) ◽  
pp. 643-660 ◽  
Keyword(s):  
Volcanic Rocks ◽  
Snake River Plain ◽  
Snake River ◽  
Spinel Lherzolite ◽  
Magma Chambers ◽  
Flood Basalts ◽  
Continental Flood Basalts ◽  
Source Regions ◽  
River Plain ◽  
Crustal Magma

Voluminous outpourings of olivine and quartz tholeiite cover vast tracts of the western U.S.A, around the Columbia and Snake Rivers. Voluminous eruptive units within each province are petrographically and chemically homogeneous and generally lack significant lateral or temporal variation. These features suggest relatively homogeneous source regions. A possible scenario for the Snake River Plain involves extraction of tholeiitic melts from enriched spinel lherzolite mantle ( 87 Sr/ 86 Sr > 0.7058, 143 N d/ 144 Nd < 0.51252) which contains at least a component of 2.5 Ga material. Subsequent fractionation of olivine, plagioclase, apatite and magnetite in crustal magma chambers and simultaneous assimilation of crust ( ca . 20%) accounts for the isotopic variability in the more evolved ferrolatites and ferrobasalts. Unlike the olivine tholeiites these evolved volcanic rocks exhibit all the classic elemental and isotopic correlations consistent with an origin involving combined assimilation and fractional crystallization.

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