scholarly journals The ca. 2785–2805 Ma High Temperature Ilivertalik Intrusive Complex of Southern West Greenland

Geosciences ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 319 ◽  
Author(s):  
Tomas Næraa ◽  
Thomas F. Kokfelt ◽  
Anders Scherstén ◽  
Andreas Petersson
Keyword(s):  
High Temperature ◽  
Trace Element ◽  
Partial Melting ◽  
Source Region ◽  
Intrusive Complex ◽  
Large Role ◽  
Rock Record ◽  
O Isotope ◽  
Granitoid Intrusions

Ferroan granitoid intrusions are rare in the Archaean rock record, but have played a large role in the evolution of the Proterozoic crust, particular in relation to anorthosite-mangerite-charnockite-granite suites. Here we discuss the petrogenesis of the ca. 2785–2805 Ma ferroan Ilivertalik Intrusive Complex, which has many geochemical similarities to Proterozoic iron rich granitoids. We present major and trace element whole rock chemistry and combined in-situ zircon U-Pb, Hf and O isotope data. The intrusive complex divides into: (i) minor tabular units of mainly diorite-tonalite compositions, which are typically situated along contacts to the host basement and (ii) interior larger, bodies of mainly granite-granodiorite composition. Geochemically these two unites display continuous to semi-continuous trends in Haker-diagrams. Whole rock REE enrichment display increases from Yb to La, from 10–25 to 80–100 times chondrite, respectively. The diorite-tonalite samples are generally more enriched in REE compared to the granite-granodiorite samples. The complex has hafnium isotope compositions from around +1.5 to −2.5 epsilon units and δ18O compositions in the range of 6.3 to 6.6‰. The complex is interpreted to be derived from partial melting in a crustal source region during anomalously high crustal temperatures.

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.

scholarly journals Hidden Archaean and Palaeoproterozoic crust in NW Ireland? Evidence from zircon Hf isotopic data from granitoid intrusions

2009 ◽  
Vol 146 (6) ◽  
pp. 903-916 ◽  
Author(s):  
M. J. FLOWERDEW ◽  
D. M. CHEW ◽  
J. S. DALY ◽  
I. L. MILLAR
Keyword(s):  
Source Region ◽  
Isotope Analysis ◽  
Isotopic Signature ◽  
Detrital Zircons ◽  
Metasedimentary Rocks ◽  
Deep Crust ◽  
Gneiss Complex ◽  
Granitoid Rocks ◽  
Granitoid Intrusions

AbstractThe presence of major crystalline basement provinces at depth in NW Ireland is inferred from in situ Hf isotope analysis of zircons from granitoid rocks that cut structurally overlying metasedimentary rocks. Granitoids in two of these units, the Slishwood Division and the Tyrone Central Inlier, contain complex zircons with core and rim structures. In both cases, cores have average ϵHf values that differ from the average ϵHf values of the rims at 470 Ma (the time of granitoid intrusion). The Hf data and similarity in U–Pb age between the inherited cores and detrital zircons from the host metasedimentary rocks suggests local contamination during intrusion rather than transport of the grains from the source region at depth. Rims from the Slishwood Division intrusions have average ϵHf470 values of −7.7, consistent with a derivation from juvenile Palaeoproterozoic crust, such as the Annagh Gneiss Complex or Rhinns Complex of NW Ireland, implying that the deep crust underlying the Slishwood Division is made of similar material. Rims from the Tyrone Central Inlier have extremely negative ϵHf470 values of approximately −39. This isotopic signature requires an Archaean source, suggesting rocks similar to the Lewisian Complex of Scotland, or sediment derived wholly from it, occurs at depth in NW Ireland.

Olivine, clinopyroxene and orthopyroxene reference materials for Li and O isotope in-situ microanalyses and their trace element compositions

2020 ◽  
Vol 36 (4) ◽  
pp. 1274-1284
Author(s):  
WANG Jing ◽  
◽  
SU BenXun ◽  
TANG GuoQiang ◽  
GAO BingYu ◽  
...  
Keyword(s):  
Trace Element ◽  
Reference Materials ◽  
O Isotope

Olivine, clinopyroxene and orthopyroxene reference materials for Li and O isotope in-situ microanalyses and their trace element compositions

2020 ◽  
Vol 36 (4) ◽  
pp. 1274-1284
Author(s):  
WANG Jing ◽  
◽  
SU BenXun ◽  
TANG GuoQiang ◽  
GAO BingYu ◽  
...  
Keyword(s):  
Trace Element ◽  
Reference Materials ◽  
O Isotope

Geochemistry of Proterozoic granulites from northern Prince Charles Mountains, East Antarctica

1992 ◽  
Vol 4 (1) ◽  
pp. 59-69 ◽  
Author(s):  
N.C. Munksgaard ◽  
D.E. Thost ◽  
B.J. Hensen
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Subduction Zone ◽  
Source Region ◽  
Melting Process ◽  
East Antarctica ◽  
Partial Melting Process ◽  
Proterozoic Basement ◽  
Lower Crustal ◽  
Igneous Layering

The late Proterozoic basement of the Porthos Range northern Prince Charles Mountains, east Antarctica, is dominated by a suite of felsic to mafic granulites derived from igneous and, less importantly, sedimentary protoliths. Compositionally, they are broadly similar to granulites occurring along the Mac. Robertson Land coast and southern Prince Charles Mountains. Ultramafic to mafic orthopyroxene' + clinopyroxene granulites with relict igneous layering occur as lenses within the felsic to mafic granulites, and show compositional evidence of a cumulate origin. The felsic to mafic granulites are intruded by several large charnockite bodies that have similarities to the Mawson Charnockite, and may have formed via a two-stage partial melting process. The charnockite and host granulites are chemically very similar, and both may have been derived from a common middle to lower crustal source region. Undepleted K/Rb ratios suggest retention of original chemistry, with variations being due to fractionation processes. Normalized trace element patterns resembling modern-day arc settings suggest that the Porthos Range granulites were possibly generated in a subduction zone environment.

scholarly journals Using In Situ Trace-Element Determinations to Monitor Partial-Melting Processes in Metabasites

2005 ◽  
Vol 46 (6) ◽  
pp. 1283-1308 ◽  
Author(s):  
A. C. STORKEY ◽  
J. HERMANN ◽  
M. HAND ◽  
I. S. BUICK
Keyword(s):  
Trace Element ◽  
Partial Melting

Geochemistry of a Tertiary continental basalt suite, Red Sea coastal plain, Egypt: petrogenesis and characteristics of the mantle source region

2003 ◽  
Vol 140 (1) ◽  
pp. 11-24 ◽  
Author(s):  
ABDEL-KADER M. MOGHAZI
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Red Sea ◽  
Fractional Crystallization ◽  
Coastal Plain ◽  
Mantle Source ◽  
Source Region ◽  
Rift System ◽  
Mantle Source Region ◽  
Continental Basalt

Major and trace element data on Tertiary continental basalt flows from the Shalatein area, Red Sea coastal plain of Egypt, have been presented and used to obtain more information about their source region and the processes involved in their generation. The rocks are mainly alkali olivine basalt with MgO and Mg no. in the range of 9.8–5 wt % and 65–46, respectively. They display wide variations in incompatible element concentrations, particularly LREE, Zr, Nb, K, Y, Ba and Sr. There is no evidence of significant crustal contamination or a lithospheric mantle signature in these rocks. Normalized trace element patterns and diagnostic elemental ratios are very similar to those of modern ocean-island basalts (OIB) a feature which suggests that the mantle source region was the asthenosphere. Comparison with the different types of OIB indicates that the basalts may be derived from a high U/Pb (HIMU) source with slightly elevated K and Ba contents. The basalts show general trends of increasing incompatible elements (K2O, Nb, Y, Sr and Yb), and decreasing contents of compatible elements (Cr, Ni, Sc and Ca) with decreasing Mg no. Furthermore, TiO2, P2O5, LREE and Th define maxima at about Mg no.=56, suggesting late fractionation of Fe–Ti oxides and apatite. Although these variations are consistent with fractional crystallization processes, the wide variations in LREE contents and the incompatible trace element ratios Ce/Y (1.2–3.8), Zr/Nb (2.3–7.1) and Nb/Y (0.6–4) in the least fractionated samples (Mg no. > 56) suggest that fractional crystallization involving the observed phenocryst assemblage (olivine and clinopyroxene) cannot fully explain such compositional variations. Modelling of the mafic rocks (Mg no. > 56) using REE suggests varying degrees of partial melting of an enriched mantle source region in the garnet stability field. Partial melting is attributed to plume-related mantle upwelling beneath the Red Sea rift system.

scholarly journals U-Pb dating, Lu-Hf isotope systematics and chemistry of zircon from the Morro do Polvilho meta-trachydacite: constraints on sources of magmatism and on the depositional age of the São Roque Group

2018 ◽  
Vol 18 (2) ◽  
pp. 45-56 ◽  
Author(s):  
Renato Henrique-Pinto ◽  
Valdecir De Assis Janasi ◽  
Ginaldo Ademar da Cruz Campanha
Keyword(s):  
High Temperature ◽  
Trace Element ◽  
Metamorphic Grade ◽  
Geochronological Data ◽  
Trace Element Chemistry ◽  
Reducing Conditions ◽  
Metavolcanic Rocks ◽  
Depositional Age ◽  
Isotope Systematics

We present new in situ geochronological data of controversial silicic metavolcanic rocks from the lower terrigenous-metavolcanic sequence of the São Roque Group, Ribeira Belt, confirming that they are older than the rocks of higher-metamorphic grade sequences of the Serra do Itaberaba Group. The age of the Polvilho meta-trachydacite was established at 1760 ± 17 Ma, furthermore the results suggest that the bi-modal volcanism of the Boturuna Formation has parent melts from an old (Archean to Paleoproterozoic) continental crust that was melted in a within-plate environment. Trace-element chemistry of zircon, suggests similarities with high-temperature melts (T Zrsat = 900–915ºC) similar to A-type granites (high negative EuN/EuN* and moderate positive CeN/CeN*) from continental sources under reducing conditions.

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