Ultramafic-alkaline-carbonatite complexes as a result of two-stage melting of mantle plume: evidence from the mid-paleoproterozoic Tiksheozero intrusion, Northern Karelia, Russia

2019 ◽  
Vol 486 (4) ◽  
pp. 460-465
Author(s):  
E. V. Sharkov ◽  
A. V. Chistyakov ◽  
M. M. Bogina ◽  
O. A. Bogatikov ◽  
V. V. Shchiptsov ◽  
...  
Keyword(s):  
Fractional Crystallization ◽  
Mantle Plume ◽  
Large Igneous Province ◽  
Intrusive Complex ◽  
Incongruent Melting ◽  
Isotopic Data ◽  
Two Stage ◽  
Similar Composition ◽  
Igneous Province ◽  
Alkaline Magmas

Tiksheozero ultramafic-alkaline-carbonatite intrusive complex, like numerous carbonatite-bearing complexes of similar composition, is a part of large igneous province, related to the ascent of thermochemical mantle plume. Our geochemical and isotopic data evidence that ultramafites and alkaline rocks are joined by fractional crystallization, whereas carbonatitic magmas has independent origin. We suggest that origin of parental magmas of the Tiksheozero complex, as well as other ultramafic-alkaline-carbonatite complexes, was provided by two-stage melting of the mantle-plume head: 1) adiabatic melting of its inner part, which produced moderately-alkaline picrites, which fractional crystallization led to appearance of alkaline magmas, and 2) incongruent melting of the upper cooled margin of the plume head under the influence of CO2-rich fluids  that arrived from underlying zone of adiabatic melting gave rise to carbonatite magmas.

The Tethyan Himalaya igneous province: Early melting products of the Kerguelen mantle plume

2021 ◽  
Author(s):  
Sheng-Sheng Chen ◽  
Wei-Ming Fan ◽  
Ren-Deng Shi ◽  
Ji-Feng Xu ◽  
Yong-Min Liu
Keyword(s):  
Mantle Plume ◽  
Crustal Contamination ◽  
Large Igneous Province ◽  
Mafic Rocks ◽  
Os Isotopes ◽  
Igneous Province ◽  
Break Up ◽  
Low Degrees ◽  
The Relationship ◽  
Tethyan Himalaya

Abstract The Kerguelen large igneous province (LIP) has been related to mantle plume activity since at least 120 Ma. There are some older (147–130 Ma) magmatic provinces on circum-eastern Gondwana, but the relationship between these provinces and the Kerguelen mantle plume remains controversial. Here we present petrological, geochronological, geochemical, and Sr–Nd–Hf–Pb–Os isotopic data for high-Ti mafic rocks from two localities (Cuona and Jiangzi) in the eastern Tethyan Himalaya igneous province (147–130 Ma). Zircon grains from these two localities yielded concordant weighted mean 206Pb/238U ages of 137.25 ± 0.98 and 131.28 ± 0.78 Ma (2σ), respectively. The analyzed mafic rocks are enriched in high field strength elements and have positive Nb–Ta anomalies relative to Th and La, which have ocean island basalt-like characteristics. The Cuona basalts were generated by low degrees of melting (3–5%) of garnet lherzolites (3–5 vol.% garnet), and elsewhere the Jiangzi diabases were formed by relatively lower degrees of melting (1–3%) of garnet lherzolite (1–5 vol.% garnet). The highly radiogenic Os and Pb isotopic compositions of the Jiangzi diabases were produced by crustal contamination, but the Cuona basalts experienced the least crustal contamination given their relatively low γOs(t), 206Pb/204Pbi, 207Pb/204Pbi, and 208Pb/204Pbi values. Major and trace element geochemical and Sr–Nd–Hf–Pb–Os isotope data for the Cuona basalts are similar to products of the Kerguelen mantle plume head. Together with high mantle potential temperatures (>1500°C), this suggests that the eastern Tethyan Himalaya igneous province (147–130 Ma) was an early magmatic product of the Kerguelen plume. A mantle plume initiation model can explain the temporal and spatial evolution of the Kerguelen LIP, and pre-continental break-up played a role in the breakup of eastern Gondwana, given the >10 Myr between initial mantle plume activity (147–130 Ma) and continental break-up (132–130 Ma). Like studies of Re-Os isotopes in other LIPs, the increasing amount of crustal assimilation with distance from the plume stem can explain the variations in radiogenic Os.

Megacrysts of “bubbled” kaersutite in the Neogene-Quaternary of Western Syria: evidence of crystallization in a boiled melt/fluid?

2021 ◽  
Author(s):  
Evgenii Sharkov ◽  
Maria Bogina ◽  
Alexey Chistyakov
Keyword(s):  
Mantle Plume ◽  
Melting Zone ◽  
Mantle Xenoliths ◽  
Large Igneous Province ◽  
Iron Core ◽  
Basaltic Magmatism ◽  
Igneous Province ◽  
Retrograde Boiling ◽  
Thermochemical Plume ◽  
Subordinate Amount

<p>The territory of Syria is a classic area of intraplate Neogene-Quaternary plateau basaltic magmatism (Ponikarov et al., 1969; Sharkov, 2000; Lustrino, Sharkov, 2006; Trifonov et al., 2011, etc.). These basalts belong to the Afro-Arabian large igneous province (LIP) (Ernst, 2014), whose origin, according to geophysical data, is related to the ascent of a mantle thermochemical plume that originated at the liquid iron core-silicate mantle boundary of (Hansen et al., 2012).</p><p>The basalt plateaus of Syria have a similar structure and are formed by numerous basaltic flows, as well as scoria and pyroclastic cones, often containing mantle xenoliths. Approximately 80% of them are represented by green spinel lherzolites and harzburgites, and subordinate amount (~20 %) of xenoliths belong to black series (hornblendite, hornblende clinopyroxenites, clinopyroxenites, phlogopitites, etc., as well as megacrysts of kaersutite, clinopyroxene, ilmenite, sanidine, etc.). Some of the kaersutite megacrysts have unusual “bubbled” structure, containing oval cavities up to 3-4 mm in diameter. We believe that these xenoliths are fragments of the upper cooled margin of the mantle plume above the adiabatic melting zone (Sharkov et al., 2017). Thus, they probe substance of mantle plume and bear important information about the processes within its interior.</p><p>As previously shown (Sharkov et al., 2017), the black series rocks were formed from a melt/fluid released fluid during the incongruent ("secondary") melting of the mantle plume head at the final stage of the magmatic system evolution. The crystallization of this fluid-supersaturated melt could be accompanied by its retrograde boiling, which led to the appearance of "bubbled" crystals.</p><p> </p>

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