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Igneous Petrology and the Nature of Magmas
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
We can divide elements in igneous rocks and magmas into two groups: those that tend to remain in a magma until the later stages of crystallization (and consequently become enriched in the magma as crystallization takes place), and those that are easily incorporated into early growing crystals (and consequently become depleted in a magma quickly). Elements that tend to remain in the magma are said to be incompatible, and those that enter crystals quickly are compatible. Petrologists use these terms, incompatible and compatible, most commonly to describe trace elements, but they apply equally well to major and minor elements. Some elements behave as compatible elements in some magma types but as incompatible in others, because the specific minerals that crystallize vary with magma composition. Trace elements, however, both compatible and incompatible, are especially useful as trackers of magma evolution. Incompatible elements include the rare earth elements, elements 57 through 71 (La–Lu), but their degree of incompatibility varies with atomic number. The rare earths and other incompatible elements are highlighted in the periodic chart of Figure 5.50.
Geochemistry of elements
Published in Aleksey B. Ptitsyn, Lectures in Geochemistry, 2018
Fersman’s classification explains the term “incompatible elements,” whose behavior is somewhat specific. Incompatible elements are those not included in minerals of the upper mantle. The cause of their incompatibility lies in a large ionic radius or a high charge of the ion. The rare-earth elements (17 of them: scandium, yttrium, and the lanthanides) are a typical example of incompatible elements.
The isotope geochemistry of host rocks of the late Archean Guandi and Banshigou banded iron formations, southern Jilin Province: temporal and tectonic significance
Published in Australian Journal of Earth Sciences, 2023
The primitive-mantle-normalised incompatible element patterns of the PHG–BSG and PA–GD samples are characterised by Nb, Ta, and Ti troughs (Figure 14). These features can be explained by either of the following two petrogenetic models: (1) the samples are from mantle-derived magmas that were contaminated by crustal material (Puchtel et al., 1998); or (2) the samples were formed by the partial melting of a mantle source that was metasomatised by slab-derived fluid or melt (McKenzie, 1989). As stated above, samples PA–GD and PA–BSG are contaminated by crustal material, but we cannot dismiss the possibility of input from slab-derived fluids or metasomatising melts. PA–GD has εHf(t) values of −1.3 to +2.8, and PHG–BSG has εHf(t) values of −1.5 to +2.7 (Figure 17). While there is a relatively wide range of εHf(t) values across the CHUR line, most are relatively close to the depleted mantle array. Generally, for mantle-sourced basaltic rocks, Hf model age that approaches the magmatic crystallisation age indicates a depleted mantle source. An Hf model age greater than the magmatic crystallisation age indicates that the source was either contaminated by crustal materials or derived from an enriched mantle (Wu et al., 2007). PA–GD has TDM(Hf) values of 2903 to 2750 Ma, and PHG–BSG yields TDM(Hf) values of 2914 to 2751 Ma. These values indicate that the protoliths were contaminated, which is consistent with the observed enrichment in LREE.
Mid-Devonian basaltic magmatism and associated sedimentation: the Ooloo Hill Formation, central-eastern South Australia
Published in Australian Journal of Earth Sciences, 2023
C. Wade, A. J. Reid, E. A. Jagodzinski, M. J. Sheard
Ooloo Hill Formation basalts and andesite sit above the mid-ocean ridge basalt (MORB)–ocean island basalt (OIB) array and below the metasomatised mantle array on the Th/Yb–Nb/Yb diagram (Figure 12a). Eruptive sequences #1, #2 and #4 form a trend parallel to the MORB–OIB array, consistent with within-plate evolution of mantle sources (e.g. Liu et al., 2021), whereas eruptive sequence #3 has an apparent, although tenuous, vertical trend toward the metasomatised mantle array (Elliott et al., 1997; Hawkesworth et al., 1997). Differing evolutionary trends are also highlighted on Figure 12b, suggesting eruptive sequences #1 and #2 had an asthenospheric mantle source, possibly derived from OIB, and potentially share a common source region to eruptive sequence #4 that underwent differentiation. The separate but parallel offset in eruptive sequence #3 suggests it was derived from a more enriched OIB-like intraplate parent (Figure 12b). The lithospheric component in this eruptive sequence may be linked to slab-melt contributions into the mantle source or lithospheric contamination of a plume-derived source (Xia & Li, 2019). The mantle source components for Ooloo Hill Formation were therefore likely to be a heterogeneous OIB-like intraplate parent magma derived from the asthenospheric mantle. Different magma sources for Ooloo Hill Formation are demonstrated by incompatible element ratios (Figure 12b, c) suggesting a dynamic magmatic plumbing system.
The geological history and hazards of a long-lived stratovolcano, Mt. Taranaki, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2021
Shane J. Cronin, Anke V. Zernack, Ingrid A. Ukstins, Michael B. Turner, Rafael Torres-Orozco, Robert B. Stewart, Ian E. M. Smith, Jonathan N. Procter, Richard Price, Thomas Platz, Michael Petterson, Vince E. Neall, Garry S. McDonald, Geoffrey A. Lerner, Magret Damaschcke, Mark S. Bebbington
The increasingly incompatible-element rich andesitic magmas at Mt. Taranaki may reflect a progressive modification of the crust, especially the crust-mantle boundary. Over time, beneath Mt. Taranaki, crustal underplating by successive magmas generates high-K magmas that ascend and pond at various levels in the crust, crystallising clinopyroxene + titanomagnetite + amphibole and plagioclase before erupting a range of evolved compositions. The compositions of individual lavas or pyroclastics are strongly related to the crystal cargo, with glass compositions often being often out of equilibrium with the crystals. Gaps in our understanding of this magma generation model include tight constraints on the depths/pressures and water contents of the magmas in storage regions and the extent of connection or mixing between individual melt batches. It is also important to try to characterise the rates of recharge of this system and whether its character changes (e.g. an active crystal mush vs. crystallised cumulates) depending on magma supply rates. It is further very important to apply a range of petrological experimental approaches to establish a link between the pre-eruption storage depth (and age) of magmas that give rise to the range of eruption types seen at Mt. Taranaki.