scholarly journals Trace element heterogeneities in-situ diamond inclusion garnets from Siberia

2019 ◽  
Keyword(s):  
Trace Element ◽  
Diamond Inclusion

scholarly journals Parental magma composition of the Main Zone of the Bushveld Complex: Evidence from in-situ LA-ICP-MS trace element analysis of silicate minerals in the cumulate rocks

2020 ◽  
Author(s):  
Shenghong Yang ◽  
Wolfgang D. Maier ◽  
Belinda Godel ◽  
Sarah-Jane Barnes ◽  
Eero Hanski ◽  
...  
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Bushveld Complex ◽  
Trace Element Analysis ◽  
Parental Magma ◽  
Main Zone ◽  
Element Analysis ◽  
Silicate Minerals ◽  
Incompatible Elements

<p>In-situ trace element analysis of cumulus minerals may provide a clue to the parental magma from which the minerals crystallized. However, this is hampered by effects of the trapped liquid shift (TLS). In the Main Zone (MZ) of the Bushveld Complex, the Ti content in plagioclase grains shows a clear increase from core to rim, whereas most other elements (e.g., rare earth elements (REEs), Zr, Hf, Pb) do not. This is different from the prominent intra-grain variation of all trace elements in silicate minerals in mafic dikes and smaller intrusion, which have a faster cooling rate. We suggest that crystal fractionation of trapped liquid occurred in the MZ of Bushveld and the TLS may have modified the original composition of the cumulus minerals for most trace elements except Ti during slow cooling. Quantitative model calculations suggest that the influence of the TLS depends on the bulk partition coefficient of the element. The effect on highly incompatible elements is clearly more prominent ­­than on moderately incompatible and compatible elements because of different concentration gradients between cores and rims of cumulate minerals. This is supported by the following observations in the MZ of Bushveld: 1) positive correlation between Cr, Ni and Mg# of clinopyroxene and orthopyroxene, 2) negative correlation between moderately incompatible elements (e.g., Mn and Sc in clinopyroxene and orthopyroxene, Sr, Ba, Eu in plagioclase), but 3) poor correlation between highly incompatible elements and Mg# of clinopyroxene and orthopyroxene or An# of plagioclase. Modeling suggests that the extent of the TLS for a trace element is also dependent on the initial fraction of the primary trapped liquid, with strong TLS occurring if the primary trapped liquid fraction is high. This is supported by the positive correlation between highly incompatible trace element abundances in cumulus minerals and whole-rock Zr contents.</p><p>We have calculated the composition of the parental magma of the MZ of the Bushveld Complex. The compatible and moderately incompatible element contents of the calculated parental liquid are generally similar to those of the B3 marginal rocks, but different from the B1 and B2 marginal rocks. For the highly incompatible elements, we suggest that the use of the sample with the lowest whole-rock Zr content and the least degree of TLS is the best approach to obtain the parental magma composition. Based on calculation, we propose that a B3 type liquid is the most likely parental magma to the MZ of the Bushveld Complex.</p>

Simultaneous determination of Sm–Nd isotopes, trace-element compositions and U–Pb ages of titanite using a laser-ablation split-stream technique with the addition of water vapor

2021 ◽  
Author(s):  
Le Zhang ◽  
Jia-Lin Wu ◽  
Yanqiang Zhang ◽  
Ya-Nan Yang ◽  
Pengli He ◽  
...  
Keyword(s):  
Rare Earth ◽  
Water Vapor ◽  
Laser Ablation ◽  
Rare Earth Elements ◽  
Trace Element ◽  
Simultaneous Determination ◽  
Nd Isotopes ◽  
Trace Element Contents

Titanite is a widespread accessory nesosilicate with high trace-element contents including rare-earth elements, Th, and U, and is thus suitable for in situ isotopic and trace-element analyses and U–Pb dating....

scholarly journals Differentiating between Inherited and Autocrystic Zircon in Granitoids

2020 ◽  
Vol 61 (8) ◽  
Author(s):  
Hugo K H Olierook ◽  
Christopher L Kirkland ◽  
Kristoffer Szilas ◽  
Julie A Hollis ◽  
Nicholas J Gardiner ◽  
...  
Keyword(s):  
Trace Element ◽  
Source Region ◽  
Wall Rock ◽  
Magma Source ◽  
Trace Element Data ◽  
Element Data ◽  
Age Constraints ◽  
Erroneous Interpretation ◽  
Zircon Fraction

Abstract Inherited zircon, crystals that did not form in situ from their host magma but were incorporated from either the source region or assimilated from the wall-rock, is common but can be difficult to identify. Age, chemical and/or textural dissimilarity to the youngest zircon fraction are the primary mechanisms of distinguishing such grains. However, in Zr-undersaturated magmas, the entire zircon population may be inherited and, if not identifiable via textural constraints, can lead to erroneous interpretation of magmatic crystallization age and magma source. Here, we present detailed field mapping of cross-cutting relationships, whole-rock geochemistry and zircon textural, U–Pb and trace element data for trondhjemite, granodiorite and granite from two localities in a complex Archean gneiss terrane in SW Greenland, which reveal cryptic zircon inheritance. Zircon textural, U–Pb and trace element data demonstrate that, in both localities, trondhjemite is the oldest rock (3011 ± 5 Ma, 2σ), which is intruded by granodiorite (2978 ± 4 Ma, 2σ). However, granite intrusions, constrained by cross-cutting relationships as the youngest component, contain only inherited zircon derived from trondhjemite and granodiorite based on ages and trace element concentrations. Without age constraints on the older two lithologies, it would be tempting to consider the youngest zircon fraction as recording crystallization of the granite but this would be erroneous. Furthermore, whole-rock geochemistry indicates that the granite contains only 6 µg g–1 Zr, extremely low for a granitoid with ∼77 wt% SiO2. Such low Zr concentration explains the lack of autocrystic zircon in the granite. We expand on a differentiation tool that uses Th/U ratios in zircon versus that in the whole-rock to aid in the identification of inherited zircon. This work emphasizes the need for field observations, geochemistry, grain characterization, and precise geochronology to accurately determine igneous crystallization ages and differentiate between inherited and autocrystic zircon.

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