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

10.1130/gsab.s.14892747.v1 ◽

2021 ◽

Author(s):

Liqiang Wang ◽

et. al

Keyword(s):

Trace Element ◽

Lower Crust ◽

Partition Coefficients ◽

Geochemical Modeling ◽

Magma Source ◽

Isotopic Data ◽

Melt Extraction ◽

Isotopic Compositions ◽

Age Determinations

Table S1: Isotopic data of U-Pb age determinations on zircons of the Anglonggangri biotite-muscovite and garnet-muscovite granites; Table S2: 40Ar-39Ar dating results for muscovite from the pegmatite in the Anglonggangri area; Table S3: Whole-rock major and trace element compositions of the Anglonggangri biotite-muscovite and garnet-muscovite granites; Table S4: Whole-rock Pb isotopic compositions of the Anglonggangri biotite-muscovite and garnet-muscovite granites; Table S5: Zircon in situ Lu-Hf isotopic compositions of the Anglonggangri biotite-muscovite granite; Table S6: Partition coefficients and assumed magma source compositions used in geochemical modeling; Table S7: Partition coefficients and assumed compositions used in geochemical modeling and the calculated results.

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Differentiating between Inherited and Autocrystic Zircon in Granitoids

Journal of Petrology ◽

10.1093/petrology/egaa081 ◽

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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Isotopic analyses of clinopyroxene in mantle xenoliths demonstrate the effects of kimberlite melt metasomatism upon the lithospheric mantle

10.5194/egusphere-egu2020-5331 ◽

2020 ◽

Author(s):

Angus Fitzpayne ◽

Andrea Giuliani ◽

Janet Hergt ◽

Jon Woodhead ◽

Roland Maas

Keyword(s):

Trace Element ◽

Lithospheric Mantle ◽

Mantle Metasomatism ◽

Mantle Xenoliths ◽

Isotopic Compositions ◽

Isotopic Analyses ◽

Cretaceous Magmatism

As clinopyroxene is the main host of most lithophile elements in the lithospheric mantle, the trace element and radiogenic isotope systematics of this mineral have frequently been used to characterise mantle metasomatic processes. To further our understanding of mantle metasomatism, both solution-mode Sr-Nd-Hf-Pb and in situ trace element and Sr isotopic data have been acquired for clinopyroxene grains from a suite of peridotite (lherzolites and wehrlites), MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside), and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks from the Kimberley kimberlites (South Africa). The studied mantle samples can be divided into two groups on the basis of their clinopyroxene trace element compositions, and this subdivision is reinforced by their isotopic ratios. Type 1 clinopyroxene, which comprises PIC, wehrlite, and some sheared lherzolite samples, is characterised by low Sr (~100&#8211;200 ppm) and LREE concentrations, moderate HFSE contents (e.g., ~40&#8211;75 ppm Zr; La/Zr < 0.04), and restricted isotopic compositions (e.g., 87Sr/86Sri = 0.70369&#8211;0.70383; &#949;Ndi = +3.1 to +3.6) resembling those of their host kimberlite magmas. Available trace element partition coefficients can be used to show that Type 1 clinopyroxenes are close to equilibrium with kimberlite melt compositions, supporting a genetic link between kimberlites and these metasomatised lithologies. Thermobarometric estimates for Type 1 samples indicate equilibration depths of 135&#8211;155 km within the lithosphere, thus showing that kimberlite melt metasomatism is prevalent in the deeper part of the lithosphere beneath Kimberley. In contrast, Type 2 clinopyroxenes occur in MARID rocks and coarse granular lherzolites, which derive from shallower depths (<130 km), and have higher Sr (~350&#8211;1000 ppm) and LREE contents, corresponding to higher La/Zr of >~0.05. The isotopic compositions of Type 2 clinopyroxenes are more variable and extend from compositions resembling the &#8220;enriched mantle&#8221; towards those of Type 1 rocks (e.g., &#949;Ndi = -12.7 to -4.4). To constrain the source of these variations, in situ Sr isotope analyses of clinopyroxene were undertaken, including zoned grains in Type 2 samples. MARID and lherzolite clinopyroxene cores display generally radiogenic but variable 87Sr/86Sri values (0.70526&#8211;0.71177), which might be explained by the interaction between peridotite and melts from different enriched sources with the lithospheric mantle. In contrast, the rims of these Type 2 clinopyroxenes trend towards compositions similar to those of the host kimberlite and Type 1 clinopyroxene from PIC and wehrlites. These results are interpreted to represent clinopyroxene overgrowth during late-stage (shortly before/during entrainment) metasomatism by kimberlite magmas. Our study shows that an early, pervasive, alkaline metasomatic event caused MARID and lherzolite genesis in the lithospheric mantle beneath the Kimberley area, which was followed by kimberlite metasomatism during Cretaceous magmatism. This latter event is the time at which discrete PIC, wehrlite, and sheared lherzolite lithologies were formed, and MARID and granular lherzolites were partly modified.

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Differentiation and source of the Nipissing Diabase intrusions, Ontario, Canada

Canadian Journal of Earth Sciences ◽

10.1139/e93-095 ◽

1993 ◽

Vol 30 (6) ◽

pp. 1123-1140 ◽

Cited By ~ 20

Author(s):

P. C. Lightfoot ◽

H. de Souza ◽

W. Doherty

Keyword(s):

Trace Element ◽

Crustal Contamination ◽

Primitive Mantle ◽

Magma Source ◽

Magma Type ◽

Ni Content ◽

Chemical Signatures ◽

Mid Ocean Ridge ◽

Ocean Ridge

Major and trace element data are presented for 2.2 Ga Proterozoic diabase sills from across the Nipissing magmatic province of Ontario. In situ differentiation of the magma coupled with assimilation of Huronian Supergroup roof sediments is responsible for the variation in composition between quartz diabase and granophyric diabase seen within many of the differentiated intrusions. Uniform trace element and isotope ratio signatures, such as La/Sm (2.8 – 3.7) and εNdCHUR (−2.7 to −5.9) characterize chilled margins and undifferentiated quartz diabases. These chemical signatures suggest the existence of a single magma source that was parental to intrusions throughout the magmatic province; this magma has higher La/Sm and lower Ti/Y than primitive mantle and is displaced towards the composition of shales. Most chilled diabases and quartz diabases have a similar Mg# (0.64 and 0.60) and Ni content (98 and 127 ppm), and it is argued that the magma differentiated at depth and was emplaced as a uniform low-Mg magma. The Wanapitei intrusion and Kukagami Lake sill are an exception in that although the quartz diabase has La/Sm similar to the Nipissing magma type, which suggests that they came from the same source, the Mg# (0.68–0.71) and Ni content (130–141 ppm) are higher, which may suggest that they are either slightly more primitive examples of the normal Nipissing magma or that cumulus hypersthene has been resorbed. The light rare earth element enriched signature of the Nipissing magmas was perhaps introduced from the continental crust as the magma migrated from the mantle to the surface, but a remarkably constant and large amount (>20%) of crustal contamination would be required. An addition of 1 –3% shale to the source of a transitional mid-ocean ridge basalt type magma can broadly reproduce the compositional features of the Nipissing magma type. The source characteristics were perhaps imparted during subduction accompanying the terminal Kenoran orogeny.

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