scholarly journals Secular variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary: Was mélange melting involved?

Geosphere ◽  
2021 ◽  
Author(s):  
Antonio Castro ◽  
Carmen Rodriguez ◽  
Carlos Fernández ◽  
Eugenio Aragón ◽  
Manuel Francisco Pereira ◽  
...  
Keyword(s):  
Magma Source ◽  
Isotopic Ratios ◽  
Secular Evolution ◽  
The North ◽  
Secular Variations ◽  
Magma Sources ◽  
Geochemical Variations ◽  
Subduction Erosion ◽  
Ultramafic Cumulates ◽  
Trench Sediments

This study of Sr-Nd initial isotopic ratios of plutons from the North Patagonian batholith (Argentina and Chile) revealed that a secular evolution spanning 180 m.y., from the Jurassic to Neogene, can be established in terms of magma sources, which in turn are correlated with changes in the tectonic regime. The provenance and composition of end-member components in the source of magmas are represented by the Sr-Nd initial isotopic ratios (87Sr/86Sr and 143Nd/144Nd) of the plutonic rocks. Our results support the interpretation that source composition was determined by incorporation of varied crustal materials and trench sediments via subduction erosion and sediment subduction into a subduction channel mélange. Subsequent melting of subducted mélanges at mantle depths and eventual reaction with the ultramafic mantle are proposed as the main causes of batholith magma generation, which was favored during periods of fast convergence and high obliquity between the involved plates. We propose that a parental diorite (= andesite) precursor arrived at the lower arc crust, where it underwent fractionation to yield the silicic melts (granodiorites and granites) that formed the batholiths. The diorite precursor could have been in turn fractionated from a more mafic melt of basaltic andesite composition, which was formed within the mantle by complete reaction of the bulk mélanges and the peridotite. Our proposal follows model predictions on the formation of mélange diapirs that carry fertile subducted materials into hot regions of the suprasubduction mantle wedge, where mafic parental magmas of batholiths originate. This model not only accounts for the secular geochemical variations of Andean batholiths, but it also avoids a fundamental paradox of the classical basalt model: the absence of ultramafic cumulates in the lower arc crust and in the continental crust in general.

scholarly journals Supplemental Material: Secular variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary: Was mélange melting involved?

2021 ◽  
Author(s):  
A. Castro ◽  
et al.
Keyword(s):  
Magma Source ◽  
The North ◽  
Secular Variations

<div>Geochemical and geochronologic data.<br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div>

scholarly journals Isotopic evolution of prehistoric magma sources of Mt. Etna, Sicily: Insights from the Valle Del Bove

2021 ◽  
Vol 176 (7) ◽  
Author(s):  
P. D. Kempton ◽  
A. Spence ◽  
H. Downes ◽  
J. Blichert-Toft ◽  
J. G. Bryce ◽  
...  
Keyword(s):  
Isotopic Signature ◽  
Mount Etna ◽  
Magma Source ◽  
Spinel Lherzolite ◽  
Isotopic Evolution ◽  
Ne Sicily ◽  
Magma Sources ◽  
Mt Etna ◽  
Geochemical Variations ◽  
Tectonic Position

AbstractMount Etna in NE Sicily occupies an unusual tectonic position in the convergence zone between the African and Eurasian plates, near the Quaternary subduction-related Aeolian arc and above the down-going Ionian oceanic slab. Magmatic evolution broadly involves a transition from an early tholeiitic phase (~ 500 ka) to the current alkaline phase. Most geochemical investigations have focussed on either historic (> 130-years old) or recent (< 130-years old) eruptions of Mt. Etna or on the ancient basal lavas (ca. 500 ka). In this study, we have analysed and modelled the petrogenesis of alkalic lavas from the southern wall of the Valle del Bove, which represent a time span of Mt. Etna’s prehistoric magmatic activity from ~ 85 to ~ 4 ka. They exhibit geochemical variations that distinguish them as six separate lithostratigraphic and volcanic units. Isotopic data (143Nd/144Nd = 0.51283–0.51291; 87Sr/86Sr = 0.70332–0.70363; 176Hf/177Hf = 0.28288–0.28298; 206Pb/204Pb = 19.76–20.03) indicate changes in the magma source during the ~ 80 kyr of activity that do not follow the previously observed temporal trend. The oldest analysed Valle del Bove unit (Salifizio-1) erupted basaltic trachyandesites with variations in 143Nd/144Nd and 87Sr/86Sr ratios indicating a magma source remarkably similar to that of recent Etna eruptions, while four of the five subsequent units have isotopic compositions resembling those of historic Etna magmas. All five magma batches are considered to be derived from melting of a mixture of spinel lherzolite and pyroxenite (± garnet). In contrast, the sixth unit, the main Piano Provenzana formation (~ 42–30 ka), includes the most evolved trachyandesitic lavas (58–62 wt% SiO2) and exhibits notably lower 176Hf/177Hf, 143Nd/144Nd, and 206Pb/204Pb ratios than the other prehistoric Valle del Bove units. This isotopic signature has not yet been observed in any other samples from Mt. Etna and we suggest that the parental melts of the trachyandesites were derived predominantly from ancient pyroxenite in the mantle source of Etna.

scholarly journals Supplemental Material: Secular variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary: Was mélange melting involved?

2021 ◽  
Author(s):  
A. Castro ◽  
et al.
Keyword(s):  
Magma Source ◽  
The North ◽  
Secular Variations

<div>Geochemical and geochronologic data.<br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div>

scholarly journals Late Cenozoic Uguumur and Bod-Uul Volcanic Centers in Northern Mongolia: Mineralogy, Geochemistry, and Magma Sources

Minerals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 612
Author(s):  
Alexander Perepelov ◽  
Mikhail Kuzmin ◽  
Svetlana Tsypukova ◽  
Yuri Shcherbakov ◽  
Sergey Dril ◽  
...  
Keyword(s):  
Basaltic Magma ◽  
Magma Source ◽  
Depth Range ◽  
Late Cenozoic ◽  
Central Mongolia ◽  
Cenozoic Volcanism ◽  
Northern Mongolia ◽  
Magma Sources ◽  
Response To Stress ◽  
Isotope Systematics

The paper presents new data on mineralogy, geochemistry, and Sr-Nd-Pb isotope systematics of Late Cenozoic eruption products of Uguumur and Bod-Uul volcanoes in the Tesiingol field of Northern Mongolia, with implications for the magma generation conditions, magma sources, and geodynamic causes of volcanism. The lavas and pyroclastics of the two volcanic centers are composed of basanite, phonotephrite, basaltic trachyandesite, and trachyandesite, which enclose spinel and garnet peridotite and garnet-bearing pyroxenite xenoliths; megacrysts of Na-sanidine, Ca-Na pyroxene, ilmenite, and almandine-grossular-pyrope garnets; and carbonate phases. The rocks are enriched in LILE and HFSE, show strongly fractioned REE spectra, and are relatively depleted in U and Th. The low contents of U and Th in Late Cenozoic volcanics from Northern and Central Mongolia represent the composition of a magma source. The presence of carbonate phases in subliquidus minerals and mantle rocks indicates that carbon-bearing fluids were important agents in metasomatism of subcontinental lithospheric mantle. The silicate-carbonate melts were apparently released from eclogitizied slabs during the Paleo-Asian and Mongol-Okhotsk subduction. The parent alkali-basaltic magma may be derived as a result from partial melting of Grt-bearing pyroxenite or eclogite-like material or carobantized peridotite. The sources of alkali-basaltic magmas from the Northern and Central Mongolia plot different isotope trends corresponding to two different provinces. The isotope signatures of megacrysts are similar to those of studied volcanic centers rocks. The P-T conditions inferred for the crystallization of pyroxene and garnet megacrysts correspond to a depth range from the Grt-Sp phase transition to the lower crust. Late Cenozoic volcanism in Northern and Central Mongolia may be a response to stress propagation and gravity instability in the mantle associated with the India-Asia collision.

Early Cretaceous Xiuyan adakitic granitoids in the Liaodong Peninsula, eastern China: petrogenesis and implications for lithospheric thinning of the North China Craton

2021 ◽  
Vol 58 (1) ◽  
pp. 50-66
Author(s):  
Yang Dong ◽  
Jingdang Liu ◽  
Yanfei Zhang ◽  
Shiyong Dou ◽  
Yanbin Li ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
North China Craton ◽  
Lower Crust ◽  
North China ◽  
Eastern China ◽  
Lithospheric Thinning ◽  
The North ◽  
Magma Sources ◽  
Liaodong Peninsula ◽  
T Values

Mesozoic magmatic rocks are widely distributed in the North China Craton (NCC) and are crucial to understanding the timing, location, and geodynamic mechanisms of lithospheric thinning of the NCC. In this study, we report geochronological, petrogeochemical, and Lu–Hf isotopic data for adakitic granitoids from different parts of Xiuyan pluton in the Liaodong Peninsula, aiming to constrain their magma sources, petrogenesis, and tectonic implications. The adakites are metaluminous to weakly peraluminous and are classified as high-K calc-alkaline I-type granite with Early Cretaceous zircon U–Pb ages of 129–126 Ma. They exhibit adakite-like geochemical characteristics, such as high Sr content and low Yb and Y contents, coupled with high Sr/Y and no pronounced Eu anomalies. They are enriched in Rb, U, and light rare-earth elements and are depleted in Ta, Nb, P, and Ti. The adakites from the eastern part of the pluton have low εHf(t) values (–8.5 to –4.0) with old TDM2 ages (1.57–1.31 Ga), indicating they were derived from the lower crust containing juvenile mantle-derived materials. In contrast, adakites from the northern part of the pluton have lower εHf(t) values (–19.7 to –16.6) with older TDM2 ages (2.21–2.03 Ga), indicating that they were derived mainly from an ancient crust. Our results show that both adakitic magmas were derived from partial melting of delaminated lower crust. Their relatively high MgO and Ni contents and Mg# values indicate that the melts interacted with mantle peridotites. The lower crust delamination beneath the Liaodong Peninsula resulted from paleo-Pacific plate subduction during the Early Cretaceous, which resulted in thinning of Mesozoic crust in the Xiuyan area.

Geochemistry of Middle Triassic gabbros from northern Liaoning, North China: origin and tectonic implications

2008 ◽  
Vol 146 (4) ◽  
pp. 540-551 ◽  
Author(s):  
XIAOHUI ZHANG ◽  
HONGFU ZHANG ◽  
MINGGUO ZHAI ◽  
SIMON A. WILDE ◽  
LIEWEN XIE
Keyword(s):  
North China ◽  
Orogenic Belt ◽  
Shrimp Dating ◽  
The North ◽  
Magmatic Underplating ◽  
Granitic Intrusions ◽  
Ultramafic Cumulates ◽  
Geochronological Dating ◽  
T Values ◽  
Continental Interior

AbstractThe Xiaofangshen mafic stock is a hornblende gabbroic body emplaced in the Faku dome of northern Liaoning within the continental interior of the North China–Mongolian plate. Zircon U–Pb SHRIMP dating yields an emplacement age of 241 ± 6 Ma. These gabbroic rocks exhibit strong enrichment in large ion lithophile elements (e.g. Th, U) and light REE, slightly negative Eu anomalies, and pronounced depletion in high field strength elements (e.g. Nb, Ta, Zr, Ti). They show a relatively narrow range of isotopic compositions with initial 87Sr/86Sr ratios of 0.7053 to 0.7055, ϵNd(t) values of +0.40 to +0.68 and zircon ϵHf(T) values from +5.0 to +7.4. These geochemical features suggest that they might have been derived from partial melting of a subduction-related metasomatized lithospheric mantle source, which is tectonically affiliated to the Xing-Meng orogenic belt. Combined with our previous geochronological dating on the predominantly granitic intrusions from the Faku dome, it is inferred that the northern Liaoning block has a tectonic affinity with the Phanerozoic accretionary orogenic belt. This revelation further leads to the proposition that the Chifeng–Kaiyuan fault likely represents the Mesozoic lithospheric boundary between the North China craton and the Xing-Meng orogenic belt in northern Liaoning. The Xiaofangshen gabbros, together with the Triassic mafic–ultramafic cumulates and granulite xenoliths and the Triassic alkaline intrusions within the continental interior of the newly amalgamated North China–Mongolian Plate, constitute an important post-orogenic to within-plate anorogenic magmatic province, in response to the continued magmatic underplating caused by lithospheric delamination and hot asthenosphere upwelling.

scholarly journals Seismic structure of the north-central Chilean convergent margin: Subduction erosion of a paleomagmatic arc

2014 ◽  
Vol 41 (5) ◽  
pp. 1523-1529 ◽  
Author(s):  
Eduardo Contreras-Reyes ◽  
Juan Becerra ◽  
Heidrun Kopp ◽  
Christian Reichert ◽  
Juan Díaz-Naveas
Keyword(s):  
Seismic Structure ◽  
Convergent Margin ◽  
North Central ◽  
The North ◽  
Subduction Erosion

Caledonian magmatism record within Hebridean Terrane? Loch Roag dyke (Lewis Island, northern Scotland) non-peridotitic xenoliths and megacrysts as messengers from deep lithosphere.

2020 ◽  
Author(s):  
Daniel Buczko ◽  
Magdalena Matusiak-Małek ◽  
Brian J. G. Upton ◽  
Theodoros Ntaflos ◽  
Sonja Aulbach ◽  
...  
Keyword(s):  
North Atlantic ◽  
Parental Magma ◽  
Geological Structure ◽  
Trace Element Composition ◽  
Isotopic Ratios ◽  
The North ◽  
Source Regions ◽  
Mantle Sources ◽  
History Of ◽  
North Atlantic Craton

&lt;p&gt;The northernmost part of Scotland &amp;#8211; the Hebridean Terrane &amp;#8211; is formed of Archean rocks originally being part of the Laurentian North Atlantic Craton. The geological history of the terrane is well recognised, however details of its internal structure remain unknown. The Eocene (Faithfull et al. 2012, JGS) Loch Roag monchiquite (Lewis Island) sampled deep-seated lithologies, providing insight on evolution and geological structure of the deeper lithosphere of the Hebridean terrane. The monchiquite comprises abundant xenoliths of ultramafic, mafic and felsic rocks. The peridotitic xenoliths represent pieces of Archean mantle underlying marginal parts of the North Atlantic Craton, whereas the origin of non-peridotitic lithologies is uncertain.&lt;/p&gt;&lt;p&gt;The studied suite of samples comprises two groups: 1) &amp;#8220;xenoliths&amp;#8221; of diorites (plagioclase, clinopyroxene, orthopyroxene, apatite, opaques) and biotite clinopyroxenites (+apatite), 2) &amp;#8220;megacrysts&amp;#8221; of clinopyroxene and K-feldspar, both with inclusions of clinopyroxene, biotite and apatite. Megacrysts of alkali-rich feldspar associated with corundum and HFSE-bearing minerals, and composite xenoliths formed of pyroxenite and K-feldspar-rich lithology have also been described from this locality (Menzies et al., 1986, Geol. Soc. Australia Spec. Pub.; Upton et al., 2009, Mineral. Mag.).&lt;/p&gt;&lt;p&gt;We interpret the &amp;#8220;xenoliths&amp;#8221; as products of crystallization of fractionated mafic melt(s). The primary character of Sr isotopic ratios in plagioclase (&lt;sup&gt;87&lt;/sup&gt;Sr/&lt;sup&gt;86&lt;/sup&gt;Sr &lt;0.702) suggests that parental melt of those lithologies originated from melting of depleted lithospheric mantle sources. The &amp;#8220;megacrysts&amp;#8221; represent fragments of disintegrated alkaline pegmatite(s) formed from melt of plausible mantle origin, possibly enriched (&lt;sup&gt;87&lt;/sup&gt;Sr/&lt;sup&gt;86&lt;/sup&gt;Sr in feldspar &gt;0.704).&lt;/p&gt;&lt;p&gt;Trace element composition, similar Sr isotopic ratios of minerals and textural features of &amp;#8220;xenoliths&amp;#8221; and &amp;#8220;megacrysts&amp;#8221; groups suggest their close genetic relationship. This geochemical resemblance may reflect crystallisation from primarily similar melt(s) and source regions affected by similar metasomatism. Petrographic features observed in rocks described by Upton et al., (2009) imply that the parental magma of megacrysts might have intruded the rocks forming the xenoliths group. Moreover, the Rb-Sr ages of xenoliths (Der-Chuen et al., 1993, GCA) indicate crystallisation during (or shortly after) Caledonian orogeny. Preliminary age relationship between groups will be determined by on-going Rb-Sr dating of megacrysts.&lt;/p&gt;&lt;p&gt;Xenoliths similar to diorites from Loch Roag were reported by Badenszki et al. (2019, JoP) from the Midland Valley terrane (&amp;#8220;metadiorites&amp;#8221; of protolith ages ca. 415 Ma). They were interpreted as products of alkaline syn-/post-collisional Caledonian magmatism. Our study shows that non-peridotitic xenoliths from Loch Roag dyke might represent a record of similar (or the same) magmatism in the northernmost, &amp;#8220;Laurentian&amp;#8221; part of Scotland. This study presents the first report of such Caledonian magmatism record within the Hebridean Terrane.&lt;/p&gt;&lt;p&gt;Founded by Polish National Science Centre grant no. UMO-2016/23/B/ST10/01905, part of the data was obtained thanks to the Polish-Austrian project no. WTZ PL 08/2018.&lt;/p&gt;

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