scholarly journals Nb–Ta Behaviour during Magma-to-Pegmatite Transformation Process: Record from Zircon Megacrysts in Pegmatite

Minerals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1139
Author(s):  
Sheng He ◽  
Ziying Li ◽  
Abdullah Al Jehani ◽  
Dongfa Guo ◽  
Zaben Harbi ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Fractional Crystallization ◽  
Transformation Process ◽  
Arabian Shield ◽  
Magmatic System ◽  
Melt Extraction ◽  
The Core ◽  
Nb Content ◽  
T Values ◽  
Oscillatory Zonation

Due to the absence of early magma records in pegmatites, it is difficult to investigate the behavior of Nb and Ta during the transformation from magma to pegmatite melt. Zircon megacrysts in an NYF-type (Nb-Y-HREE-F) pegmatite from the Arabian Shield could be divided into three phases from core to margin. The Phase Ι zircon in the core of the zircon megacrysts had typical magma oscillatory zonation with ∑REE content from 300 to 400 ppm, Th/U ratios of less than 0.1 and Nb/Ta ratios of less than 1.0. Phase ΙΙ zircon had oscillatory zonation and was enriched with LREEs mostly with Th/U ratios of 0.1–0.2 and Nb/Ta ratios of 1.0–3.0. Phase ΙΙΙ unzoned zircon had the highest ∑REE content, from 8000 to 15,000 ppm, with Th/U ratios higher than 3.0 and Nb/Ta ratios higher than 5.0. The Hf-O isotopic composition was similar in the different phases of zircon with initial 176Hf/177Hf ratios of 0.28258–0.28277, εHf(t) values from 8.0 to 12.0 and δ18OVSMOW from +4.0‰ to +5.0‰. Zircon megacrysts in the NYF-type pegmatite from the Arabian Shield record the transformation from magma to pegmatite melt. Similar Hf-O isotopic compositions mean a closed magmatic system without contamination by external melt, rock or fluid. The proposed modeling shows that magma with low Nb and Ta concentrations and Nb/Ta ratios could evolve into residual pegmatite melt with a high Nb content and superchondrite Nb/Ta ratio during several stages of melt extraction and fractional crystallization of Ti-rich minerals, such as rutile and titanite. The Nb/Ta ratio can be used as an effective indicator of the transformation process from magma to pegmatite melt.

The effects of high-temperature fractional crystallization on calcium isotopic composition

2019 ◽  
Vol 509 ◽  
pp. 77-91 ◽  
Author(s):  
Maria C. Valdes ◽  
Vinciane Debaille ◽  
Julien Berger ◽  
Rosalind M.G. Armytage
Keyword(s):  
High Temperature ◽  
Isotopic Composition ◽  
Fractional Crystallization

scholarly journals Mathematical Modelling of Some Nutrient Losses during Heat Treatment of Stewed Apples

2009 ◽  
Vol 27 (Special Issue 1) ◽  
pp. S23-S26
Author(s):  
F. Courtois ◽  
L. Vedrenne ◽  
S. Georgé
Keyword(s):  
Experimental Data ◽  
Heat Treatment ◽  
Vitamin C ◽  
Mathematical Modelling ◽  
Transformation Process ◽  
Nutrient Losses ◽  
Single Model ◽  
First Order ◽  
The Core

Vitamin C (later noted VITC) and polyphenols (later noted PP) were regarded as main nutritional markers in the transformation process of stewed apples after an <I>in situ</I> measurement campaign at two leading French industrials on that matter. Experiments on pilots with the CTCPA of Avignon made it possible to create a small experimental data base whose treatment is the core of this article. The objective of this work is to check if the experimental data collected at the CTCPA facility can be represented by a single model of 2 separate first order reactions, with or without Arrhenius, under varying processing temperatures.

Computer Simulation Study of the Effects of Copper Precipitates on Dislocation Core Structure in Ferritic Steels

1996 ◽  
Vol 439 ◽  
Author(s):  
T. Harry ◽  
D. J. Bacon
Keyword(s):  
Dislocation Core ◽  
Alloy System ◽  
Lattice Parameter ◽  
Transformation Process ◽  
Core Structure ◽  
Metastable Equilibrium ◽  
Precipitate Size ◽  
Ferritic Steels ◽  
Interatomic Potentials ◽  
The Core

AbstractThe small, coherent BCC precipitates of copper that form during fast neutron irradiation of ferritic steels are an important component of in-service irradiation hardening. Many-body interatomic potentials for the Fe-Cu alloy system have been developed and used to simulate the atomic structure of the ½<111> screw dislocation in both pure a-iron and the metastable BCC phase of copper. In iron, the core has the well-known 3-fold form of atomic disregistry. In BCC copper, however, the core structure depends on the lattice parameter. At the metastable equilibrium value, the core is similar to that in iron, but as the lattice parameter is reduced, as in a precipitate, the core becomes delocalised by transformation of the copper. Simulation of dislocated crystals containing precipitates shows that the extent of this effect depends on precipitate size. The energy changes indicate a significant dislocation pinning effect due to this dislocation-induced precipitate transformation process.

scholarly journals PROTECTING PRIVATE PROPERTY IN CHINA - WHOSE PROPERTY?

2013 ◽  
Vol 25 (1) ◽  
pp. 19-41
Author(s):  
Xiaoyang Zhang
Keyword(s):  
Private Property ◽  
Transformation Process ◽  
Chinese Society ◽  
Chinese History ◽  
The Core ◽  
Modern Chinese ◽  
Modern Chinese History ◽  
Core Value ◽  
The Right

The importance of protecting private property in China has now ascended to the same level as that of safeguarding public assets which has traditionally been a top priority for socialist nations. This article will firstly and heavily expound on the rationale behind the availability and at certain times the marginalisation of protecting private property de jure and de facto during some momentous stages in modern Chinese history. It will then touch on a lingering problem relevant to today’s Chinese society arising from the drainage of state assets, a phenomenon having occurred in the transformation process of China’s economic regimes over the most recent decades. It finally argues that while protecting the right to lawful private property is not a matter in dispute, pursuing the protection of private property shall in no way lead to the weakening of sticking to the core value of justice and egalitarianism, a key to ensuring a sound socialist institution.

scholarly journals Anomalous flow below 2700 m in the EPICA Dome C ice core detected using δ<sup>18</sup>O of atmospheric oxygen measurements

2007 ◽  
Vol 3 (1) ◽  
pp. 63-93 ◽  
Author(s):  
G. B. Dreyfus ◽  
F. Parrenin ◽  
B. Lemieux-Dudon ◽  
G. Durand ◽  
V. Masson-Delmotte ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Northern Hemisphere ◽  
Marine Sediment ◽  
Atmospheric Oxygen ◽  
Ice Core ◽  
The Core ◽  
Sediment Records ◽  
Ice Core Record ◽  
Orbital Precession ◽  
Oxygen Measurements

Abstract. While there are no indications of mixing back to 800 000 years in the EPICA Dome C ice core record, comparison with marine sediment records shows significant differences in the timing and duration of events prior to stage 11 (~430 ka, thousand of years before 1950). A relationship between the isotopic composition of atmospheric oxygen (δ18O of O2, noted δ18Oatm) and daily northern hemisphere summer insolation has been observed for the youngest four climate cycles. Here we use this relationship with new δ18O of O2 measurements to show that anomalous flow in the bottom 500 m of the core distorts the duration of events by up to a factor of 2. By tuning δ18Oatm to orbital precession we derive a corrected thinning function and present a revised age scale for the interval corresponding to Marine Isotope Stages 11–20 in the EPICA Dome C ice core. Uncertainty in the phasing of δ18Oatm with respect to insolation variations in the precession band limits the accuracy of this new agescale to ±6 kyr (thousand of years). The previously reported ~30 kyr duration of interglacial stage 11 is unchanged. In contrast, the duration of stage 15.1 is reduced by a factor of 2, from 31 to 16 kyr.

scholarly journals Decoupling of Sr-Nd Isotopic Composition Induced by Potassic Alteration in the Shapinggou Porphyry Mo Deposit of the Qinling–Dabie Orogenic Belt, China

Minerals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 910
Author(s):  
Jun He ◽  
Xiaochun Xu ◽  
Zhongyang Fu ◽  
Yuhua An ◽  
Tianhu Chen ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Orogenic Belt ◽  
Granite Porphyry ◽  
Quartz Syenite ◽  
Porphyry Cu ◽  
Material Sources ◽  
Dabie Orogenic Belt ◽  
T Values ◽  
Host Rocks ◽  
Nd Isotopic Composition

In our previous study on petrogenesis of quartz syenite and granite porphyry, the host rocks of the Late Mesozoic Shapinggou Mo deposit in the Qinling–Dabie orogenic belt, we found that the initial Sr isotopic composition of the host rocks is strongly affected by the degree of K-alteration. Here, we provide further isotopic evidence of the host rocks and their minerals to investigate the geochemical behaviour of trace elements and isotopes during the alteration and to explain the phenomenon of decoupling of Sr–Nd isotopic composition. The quartz syenite and granite porphyry are altered by K-alteration in varying degrees and have high K2O and Rb contents and low Na2O, CaO, Sr, and Ba contents. Rock samples of both quartz syenite and granite porphyry have variable Rb/Sr ratios and initial 87Sr/86Sr values (even < 0.70) but contain quite homogeneous εNd(t) values (−12.8 to −14.8). Minerals from the rocks of moderate to intense K-alteration have very low initial 87Sr/86Sr values (even < −17), while those from the weakly altered rocks have 87Sr/86Sr(t) values of 0.7044 to 0.7084. The same phenomenon of the decoupling in Sr–Nd isotopic composition can be observed from several Mo deposits within the eastern Qinling–Dabie orogenic belt. This fact suggests similar hydrothermal features and a comparable origin for both the magmatic rocks and hydrothermal fluids in this belt. A comparison between porphyry Mo and porphyry Cu deposits shows that elements and the Rb–Sr isotope system have different behaviours during the K-alteration, implying distinct material sources and igneous rocks for porphyry Mo and porphyry Cu deposits, respectively.

A model involving amphibolite lower crust melting and subsequent melt extraction for leucogranite generation

2021 ◽  
Author(s):  
Liqiang Wang ◽  
Wenbin Cheng ◽  
Teng Gao ◽  
Yong Wang
Keyword(s):  
Rare Earth ◽  
Partial Melting ◽  
Lower Crust ◽  
Melt Extraction ◽  
Southern Tibetan Plateau ◽  
Himalayan Orogenic Belt ◽  
Positive Correlations ◽  
Charge And Radius ◽  
T Values ◽  
Light Rare Earth Elements

In the southern Tibetan Plateau, leucogranites are dominantly distributed in the Himalayan orogenic belt with minor occurrences in the southern Lhasa subterrane. In this paper, we report the first Miocene Anglonggangri leucogranites in the northern Lhasa subterrane. This finding provides important constraints on both leucogranite petrogenesis and the tectono-magmatic evolution of the Lhasa terrane. The Anglonggangri leucogranites include biotite-muscovite granite and slightly younger garnet-muscovite granite and pegmatite. Zircon U-Pb and muscovite 40Ar-39Ar dating of these leucogranites yields Miocene ages of 11.1−10.2 Ma. The biotite-muscovite and garnet-muscovite granites are characterized by high SiO2 (72.3−74.4 wt%) and Al2O3 contents (14.4−15.4 wt%) and are peraluminous. The biotite-muscovite granite displays geochemical signatures with high Sr/Y (29.2−81.0) and (La/Yb)N (37.5−98.9) ratios, low Y (4.30−7.22 ppm) and Yb contents (0.26−0.47 ppm), low to moderate initial (87Sr/86Sr)i ratios (0.7085−0.7192), and moderate εNd(t) values (−10.17 to −6.94). Furthermore, they also exhibit radiogenic Pb isotope and variable zircon εHf(t) values (−9.6 to +4.4) with Proterozoic Nd (1.1−1.4 Ga) and Hf model ages (0.8−1.7 Ga). By comparison, the garnet-muscovite granite has lower CaO, MgO, TiO2, and total FeO contents and is enriched in Rb (380−466 ppm) and depleted in Sr (24.1−38.5 ppm) and Ba (30.7−58.6 ppm) and further characterized by a significant rare earth element (REE) tetrad effect and non-charge and radius-controlled (CHARAC) trace element behaviors. The garnet-muscovite granite shows a negative Eu anomaly and positive correlations among Sr and Eu, Sr and Ba, and Th and light rare earth elements (LREEs). Pegmatite comprising Nb-Ta oxides and cassiterite occurs in the garnet-muscovite granite. Geochronological and geochemical characteristics of the Anglonggangri leucogranites indicate that the magma of the biotite-muscovite granite was derived from partial melting of amphibolite lower crust contaminated with Proterozoic-Archean upper crustal materials. The garnet-muscovite granite was generated through melt extraction from the biotite-muscovite granite crystal mush. These results confirm that partial melting of the amphibolite lower crust not only occurred in the southern and central Lhasa subterranes but also in the northern Lhasa subterrane.

Hafnium isotopic record of crustal maturation during Middle Triassic magmatism in the Southern Alps (Italy)

2020 ◽  
Author(s):  
Julian-Christopher Storck ◽  
Jörn-Frederik Wotzlaw ◽  
Ozge Karakas ◽  
Peter Brack ◽  
Axel Gerdes ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Lower Crust ◽  
Middle Triassic ◽  
Southern Alps ◽  
Crustal Material ◽  
Crustal Melting ◽  
Magmatic System ◽  
Magma Flux ◽  
Lower Crustal ◽  
Over Time

&lt;p&gt;Tracing the origin and evolution of magmas on their pathway through the lithosphere is key to understanding the magmatic processes that eventually produce eruptions. For ancient magmatic provinces, isotope-geochemical tracers are powerful tools to probe the source regions and magma-crust interaction during ascent and storage.&lt;/p&gt;&lt;p&gt;We present new hafnium isotopic compositions of ID-TIMS dated zircons to trace the evolution of the Middle Triassic magmatic province in the Southern Alps (northern Italy) at high temporal resolution [1]. Systematic changes in hafnium isotopic composition with time reveal a coherent temporal evolution from depleted mantle signatures towards crust-dominated signatures within less than four million years. This trend can be ascribed to progressive influence of a crustal source, incorporated into the reservoir from which these zircons crystallized. Towards the end of the magmatic episode, the &amp;#949;Hf compositions abruptly revert within one-million-years back towards more juvenile compositions mainly recorded by the mafic to intermediate intrusive pulses (e.g. Monzoni and Predazzo), the effusive climax of basaltic lavas and the post-intrusive ash beds (e.g. Punta Grohmann) in the Dolomite region. We interpret the variation of Hf-isotopic signatures over time as a protracted contamination signal induced by interaction of the mantle-derived magmas with the lower crust.&lt;/p&gt;&lt;p&gt;The dataset obtained in this study is further implemented into a two-component mixing model employing a range of potential crust and mantle endmember Hf isotope signatures and Hf concentrations which is directly translated into crustal melt/total melt (=sum of crustal and mantle-derived melt) ratios over time. Based on these observations we explored the thermal evolution and crustal melting as a function of time, lithology, water content and magma flux for a lower crustal magmatic system by numerical modelling. Dykes and sills of basaltic composition are incrementally emplaced at the mantle-crust boundary, which leads to changes in crustal over mantle melt ratios over time. Initial intrusions of basaltic dykes into the relatively cold lower crust cause only limited crustal melting and assimilation but ensuing magma injections into progressively hotter crust results in more extensive partial melting and assimilation of crustal material. Subsequent intrusions into the magmatic lower-crustal roots cannibalize previous intrusions with progressively less isotopic contrast due to dilution with mantle-derived magmas. This is potentially accompanied by an increase in magma flux, e.g. by delamination of dense lower crustal cumulates into the subcontinental lithospheric mantle.&lt;/p&gt;&lt;p&gt;The observed trends in hafnium isotopic composition therefore do not necessarily require tectonic re-organizations or changes in mantle sources. Instead these trends may trace variations in mantle-crust interaction during thermally induced chemical maturation of the lower crustal magmatic roots progressively replacing ancient pelitic to mafic lower crustal lithologies by juvenile cumulates.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;[1] Storck, J.-C., Wotzlaw, J.-F., Karakas, O., Brack, P., Gerdes, A., Ulmer, P. Hafnium isotopic record of mantle-crust interaction in an evolving continental magmatic system, Earth and Planetary Science Letters, &lt;em&gt;(in press)&lt;/em&gt;.&lt;/p&gt;

scholarly journals Half a million years of magmatic history recorded in a K-feldspar megacryst of the Tuolumne Intrusive Complex, California, USA

Geology ◽  
2020 ◽  
Vol 48 (4) ◽  
pp. 400-404 ◽  
Author(s):  
Melissa Chambers ◽  
Valbone Memeti ◽  
Michael P. Eddy ◽  
Blair Schoene
Keyword(s):  
Volcanic Rocks ◽  
Trace Element Analysis ◽  
Ionization Mass ◽  
Intrusive Complex ◽  
Magmatic System ◽  
Element Analysis ◽  
Age Progression ◽  
Growth Environment ◽  
The Core ◽  
Magmatic History

Abstract K-feldspars reach megacrystic size (&gt;3 cm) relative to their groundmass in many granitoid plutons and some volcanic rocks. However, the nature of the growth environment and the time scales for megacrystic growth remain poorly constrained. Chemical abrasion–isotope dilution–thermal ionization mass spectrometry with trace-element analysis (CA-ID-TIMS-TEA) U-Pb geochronology was carried out on zircon inclusions from the core and rim of one K-feldspar megacryst sampled from the interior of the Tuolumne Intrusive Complex (TIC), California, USA. Combined with new zircon ages from the groundmass, these data can test if K-feldspar megacrysts are igneous and capable of recycling and transport in the magmatic system or whether they formed by textural coarsening in low-melt-fraction or subsolidus conditions. The zircon ages reveal that the megacryst core is 0.5 m.y. older than the rim, which itself is older than the groundmass. Core ages match zircon dates from the TIC’s porphyritic Half Dome unit, and rim and groundmass ages overlap with the younger Cathedral Peak unit. Trace elements of the zircons from the megacryst core and rim are similar and less evolved than the groundmass zircons. The core-to-rim age progression of zircon inclusions is inconsistent with subsolidus K-feldspar coarsening, but instead indicates that megacrysts in the TIC grew in an igneous environment over at least 0.5 m.y., and that growth likely occurred spanning two or more intrusive episodes. This supports models of an increasingly maturing magmatic system, where crystal recycling from older into younger magma batches is common.

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