Nb/Ta Fractionation by Amphibole in Hydrous Basaltic Systems: Implications for Arc Magma Evolution and Continental Crust Formation

Li, Liang; Xiong, Xiaolin; Liu, Xingcheng

doi:10.1093/petrology/egw070

Cited by 26 publications

(46 citation statements)

References 75 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As observed in Figure b, Nb/Ta ratios decrease with increasing positive Eu anomalies. Because both pyroxenes and garnets have negligible influence on the fractionation of Nb/Ta during magmatic evolution, only amphibole fractionation has the ability to cause the increase of positive Eu anomalies and decrease of Nb/Ta ratios of the residual melts (Foley et al, ; Li et al, ). We therefore consider the increasing magnitude of the positive Eu anomaly at 3.2–3.0 Ga as a result of amphibole fractionation.…”

Section: Discussionmentioning

confidence: 99%

Generation of Archaean TTG Gneisses Through Amphibole‐Dominated Fractionation

Liou

Guo

2019

JGR Solid Earth

View full text Add to dashboard Cite

The early continental crust is characterized by the tonalite-trondhjemite-granodiorite gneisses (TTG) of Archaean terrains. There is a consensus that TTGs were formed by partial melting of hydrated mafic rocks. High-pressure melts tend to be more trondhjemitic with higher Sr/Y ratios due to the presence of garnet and absence of plagioclase, whereas low-pressure melts are more tonalitic with relatively lower Sr/Y ratios. Here we present a geochemical study of diorites, TTGs, and hornblendites from Eastern Hebei, North China Craton. Geochemical analyses show that dioritic parental magmas may evolve to tonalites and trondhjemites through a maximum of 27% fractional crystallization of amphibole and apatite. We also identified the cumulate apatite-bearing hornblendite, a predicted solid fractionate and chemical complement to the TTGs. Mixing of the trondhjemite and the hornblendite can generate similar chemical compositions to the diorites in this region. The mixing trends are consistent with those predicted for fractional crystallization. Based on these analyses, we conclude that these trondhjemites and tonalites can be formed by fractional crystallization of amphiboles and accessory minerals from the calc-alkaline diorites. Partial melting is not a unique solution to the problem of how to form the Archean TTG gneisses and how to make an Archean continent. Thick crust or lithosphere (in the garnet stability field) is also not a unique requirement. Amphibole fractionation may also cause an abrupt increase of Eu/Eu* of Archean granitoids at 3.2-3.0 Ga, which may be linked to a transition period in tectonic style at~3 Ga in Earth's evolution.

show abstract

Section: Discussionmentioning

confidence: 99%

Generation of Archaean TTG Gneisses Through Amphibole‐Dominated Fractionation

Liou

Guo

2019

JGR Solid Earth

View full text Add to dashboard Cite

show abstract

“…Significant positive correlations between TiO 2 and both Nb (r = 0.58) and Ta (r = 0.61) suggest that Ti-magnetite (ulvöspinel) is the main carrier of Nb and Ta, which contains 23% TiO 2 ( Table 5), implying that this common accessory mineral in the Gercus Basalt (Figures 4a and 4i) has played an important role in Nb/Ta fractionation. All these three elements (Ti, Nb, and Ta) have similar behavior in magmatic processes (Li et al, 2017), which is supported by the positive correlation between them. Binary La/Yb (N) -Dy/Yb (N) ( Figure 11c) and La/Yb -Yb (Figure 11d) diagrams of Shaw et al (2003) indicate that the Gercus Basalt follows the trend of garnet lherzolite melting curves rather than the spinel lherzolite melting curves.…”

Section: Origin Of the Gercus Basaltmentioning

confidence: 54%

“…The Th/U -Rb/Cs binary diagram (from Krienitz et al, 2007) shows that the Gercus Basalt is within the field of mantle-derived magmas (Figure 11a). The binary Nb -Nb/Ta diagram discriminating between terrestrial basalts and continental crustal rocks for various silicate reservoirs, which also shows the possible Nb/Ta fractionation trends caused by key minerals such as biotite, amphibole, and Ti-rich phases (from Li et al, 2017), indicates that the Gercus Basalt samples fall totally within the continental basalt (CB) field and follow the fractionation trend of amphibole and/ or biotite (Figure 11b). Significant positive correlations between TiO 2 and both Nb (r = 0.58) and Ta (r = 0.61) suggest that Ti-magnetite (ulvöspinel) is the main carrier of Nb and Ta, which contains 23% TiO 2 ( Table 5), implying that this common accessory mineral in the Gercus Basalt (Figures 4a and 4i) has played an important role in Nb/Ta fractionation.…”

Section: Origin Of the Gercus Basaltmentioning

confidence: 99%

“…The Sanandaj Cretaceous calc-alkaline volcanic belt of northwestern Iran, which was generated at an active continental margin (Azizi and Moinevazir, 2009), the closest and most complementary to the ophiolites of Krienitz et al, 2007); UCC and LCC are upper-and lower-continental crusts, respectively. (b) Nb -Nb/Ta discriminant diagram between terrestrial basalts (MORB, OIB, CB, and IAB) and continental crustal rocks (bulk CC and Archean TTG for various silicate reservoirs); possible Nb/Ta fractionation trends caused by key minerals (biotite, amphibole, and Ti-rich phases are also indicated by arrows; MORB = midocean ridge basalts; OIB = ocean island basalts; CB = continental basalts; IAB = island arc basalts; AG = Archean greenstones; TTG = tonalite-trondhjemite-granite; CC = continental crust (from Li et al, 2017). (c, d) La/Yb (N) -Dy/Y b(N) and La/Yb -Yb discriminant diagrams between garnet-and spinel-lherzolite melting magma source (Shaw et al, 2003).…”

Section: Origin Of the Gercus Basaltmentioning

confidence: 99%

See 1 more Smart Citation

Petrogenesis, geochemistry, and tectonic setting of a basaltic body within the Gercus Formation of northern Iraq: first record for Eocene anorogenic volcanic activity in the region

Kettanah¹,

Bamarni²

2018

Turkish J Earth Sci

View full text Add to dashboard Cite

Introduction Volcanic activities have not been previously reported in the area where the currently studied basaltic body is described in this study. The studied area is characterized by sedimentary formations ranging in age between Late Campanian and Recent. The newly discovered basaltic body has been named the Gercus Basalt, referring to its location within the Gercus Formation (Middle Late Eocene), which is one of the widely exposed formations in N-NE Iraq and neighboring Turkey and Iran. The volcanic units closest to the studied basalt, are located some 150-250 km to the east on the border of Iraq and Iran, which is part of the Paleogene ophiolites (Figure 1a) of the Iraqi Zagros Suture Zone (Ismail et al., 2014). For this reason, the Gercus Basalt is considered here as a rare and odd occurrence. Other than the ophiolites of northeastern Iraq bordering Iran, there are only two other small-scale volcanic occurrences, some ~300-320 km southeast of the study area and ~100 km northeast of Baghdad, within the southern part of Hemrin South Mountain, which is part of the low-folded zone of Iraq (Figure 1a). These are the Hemrin Basalt and Zarloukh Tuff studied by Abdulrahman (2016) and El-Khafaji (1989), respectively. The Hemrin Basalt occurs as very thin cap (<30 cm thick) on top of a few isolated, linearly arranged hills parallel to the axis of the Hemrin South Anticline, which was previously called burnt hills by Basi (1973) and Basi and Jassim (1974). The Zarloukh Tuff exists as flat-lying beds (~3 m thick) alternating with bentonized horizons filling a few closely spaced depressions exposed on top of the Muqdadiya (Lower Bakhtiari) Formation. The aim of this work is to report the first occurrence of a prominent volcanic body in the Gercus Formation and the surrounding area and to study these basaltic rocks Abstract: An abnormally odd and rare occurrence of a basaltic body has been discovered in the middle of the Gercus Formation within the large, double-plunging NW-SE trending Bekhair Anticline to the north of Duhok city, northern Iraq. This is the first discovery of such a volcanic body within the widely exposed Gercus Formation in northern Iraq, southeastern Turkey, and western Iran. This volcanic body, named by the authors the Gercus Basalt, has a long tabular/lenticular shape with a total length of ~4.5 km and a thickness ranging between 1 to 16 m. It is exposed on both limbs of the anticline and has a conformable relation with the terrigenous beds of the Gercus Formation. The basalt is greenish to grayish black in color, vesicular, amygdaloidal and porphyritic in texture, and consists of feldspar (Ab 85 An 2 Or 13), pyroxene (Wo 49 En 40 Fs 11), olivine (Fo 87.2-Fa 12.6-Tp 0.2), and their alteration products. Postemplacement hydrothermal fluids resulted in pervasive alteration of the Gercus Basalt and introduction of copper mineralization filling joints, fractures, and adjacent vesicles. The alteration processes are dominated by calcitization, zeolitization, serpentinization, chloritization, silicification,...

show abstract

“…Table 1. Run conditions and crystallisation products of published experimental studies used for multiple regression analysis. References cited: Nicholls and Harris 1980;Green and Pearson 1985;Adam et al 1993;Green 1994, 2006;Sisson 1994;LaTourrette et al 1995;Klein et al 1997;Dalpé and Baker 2000;Hilyard et al 2000;Tiepolo et al 2000a;b, 2001Nandedkar et al 2016;Li et al 2017. Table 2.…”

Section: Summary -Extending the Crystal Record To The Lower Crustmentioning

confidence: 99%

Unravelling the complexity of magma plumbing at Mount St. Helens: a new trace element partitioning scheme for amphibole

Humphreys

Cooper

Zhang

et al. 2019

Contrib Mineral Petrol

View full text Add to dashboard Cite

Volcanoes at subduction zones reside above complex magma plumbing systems, where individual magmatic components may originate and interact at a range of pressures. Because whole rock compositions of subduction zone magmas are the integrated result of processes operating throughout the entire plumbing system, processes such as mixing, homogenisation and magma assembly during shallow storage can overprint the chemical signatures of deeper crustal processes. Whereas melt inclusions provide an effective way to study the uppermost 10-15 km of the plumbing system, challenges remain in understanding magma intrusion, fractionation and hybridisation processes in the middle to lower crust (15-30 km depth), which commonly involves amphibole crystallisation. Here, we present new insights into the mid-crustal plumbing system at Mount St Helens, USA, using multiple regression methods to calculate trace element partition coefficients for amphibole 2 phenocrysts, and thus infer the trace element compositions of their equilibrium melts. The results indicate vertically distributed crystal fractionation, dominated by amphibole at higher pressures and in intermediate melts, and by plagioclase at lower pressures. Variations in Nb, Zr and REE concentrations at intermediate SiO 2 contents suggest repeated scavenging of partially remelted intrusive material in the mid-crust, and mixing with material from geochemically diverse sources. Amphibole is an effective probe for deep crustal magmatism worldwide, and this approach offers a new tool to explore the structure and chemistry of arc magmas, including those forming plutonic or cumulate materials that offer no other constraints on melt composition.

show abstract

Nb/Ta Fractionation by Amphibole in Hydrous Basaltic Systems: Implications for Arc Magma Evolution and Continental Crust Formation

Cited by 26 publications

References 75 publications

Generation of Archaean TTG Gneisses Through Amphibole‐Dominated Fractionation

Generation of Archaean TTG Gneisses Through Amphibole‐Dominated Fractionation

Petrogenesis, geochemistry, and tectonic setting of a basaltic body within the Gercus Formation of northern Iraq: first record for Eocene anorogenic volcanic activity in the region

Unravelling the complexity of magma plumbing at Mount St. Helens: a new trace element partitioning scheme for amphibole

Contact Info

Product

Resources

About