Trace Element Contents of Mantle-Derived Magmas Through Time

Abstract

A large compilation of quality-curated major and trace element data has been assembled to investigate how trace element patterns of mafic and ultramafic magmas have varied with time through particular settings from the Archean to the Phanerozoic, the primary objective being to recognise at what times particular patterns of variation emerge, and how similar these are to baseline data sets representing tectonic settings in the modern Earth. The most informative element combinations involve Nb, Th and the REE, where REE are represented by “lambda” parameters describing slope and shape of patterns. Combinations of the ratios of Th, Nb, La and lambda values from Archean and early Proterozoic basalts and komatiites reveal a distinctive pattern that is common in most well-sampled terranes, defining a roughly linear trend in multi-dimensional space from compositions intermediate between modern n-MORB and primitive mantle at one end, towards compositions approximating middle-to-upper continental crust at the other. We ascribe this “Variable Th/Nb” trend in most instances to varying degrees of crustal contamination of magmas with similar compositions to modern oceanic plateau basalts. Komatiites had slightly more depleted sources than basalts, consistent with the hypothesis of derivation from plume tails and heads, respectively. The most significant difference between Precambrian and Phanerozoic plume-derived basalts is that the distinctive OIB-like enriched source component appears to be largely missing from the Archean and Proterozoic geologic record, although isolated examples of OIB-like trace element characteristics are evident in datasets from even the oldest preserved greenstones. Phanerozoic intra-cratonic LIPs, such as the 260 Ma Emeishan in China, have fundamentally different geochemical characteristics to Archean and Paleoproterozoic assemblages; the oldest Proterozoic LIP we have identified that has this type of “modern” signal is the Midcontinent Rift at 1100 Ma. The data are consistent with plume tail sources having changed from being dominantly depleted in the Archean Earth to dominantly enriched in the Phanerozoic Earth, while plume head sources have hardly changed at all. Trace element patterns considered to be diagnostic of subduction are locally present but rare in Archean terranes and become more prevalent through the Proterozoic, although this conclusion is tempered by the large degree of overlap in compositional space between continental arc magmas and continental flood basalts. This overlap reflects the difficulty of distinguishing the effects of supra-subduction metasomatism and flux melting from those of crustal contamination. Additional factors must also be borne in mind, particularly that trace element partitioning systematics may have been different in all environments in a hotter planet, and large-scale asthenospheric overturns might have been predominant over modern-style plumes in the Archean Earth. Some basaltic suites in particular Archean terranes, notably the western parts of both the Yilgarn and Pilbara cratons in Western Australia and parts of the Superior Craton, have restricted but locally predominant suites of basalts with characteristics akin to modern oceanic arcs, suggesting that some process similar to modern subduction was preserved in these particular belts. Ferropicrite magmas with distinctive characteristics typical of modern OIBs and some continental LIPs (notably Emeishan) are rare but locally predominant in some Archean and early Proterozoic terranes, implying that plume sources were beginning to be fertilised by enriched, probably subducted, components as far back as the Mesoarchean. We see no evidence for discontinuous secular changes in mantle-derived magmatism with time that could be ascribed to major mantle reorganisation events. The Archean-Proterozoic transition appears to be entirely gradational from this standpoint. The transition from Archean-style to Phanerozoic-style plume magmatism took place somewhere between 1900 Ma (age of the Circum-Superior komatiitic basalts suites) and 1100 Ma (age of the Midcontinent Rift LIP).

Secular Evolution of Continents and the Earth System

“…Komatiites are a distinctive but volumetrically minor component of the belts. They are characterized by low alkalis and high Mg contents, and have been divided into Al-depleted and Al-undepleted types for a given MgO (or TiO 2 ) content, with the latter thought to become more common after 3 Ga (Barnes & Arndt, 2019, and references therein; Barnes et al, 2021), although Sossi et al (2016) did not find any temporal variation in the distribution of the two types. Spinifex textures involving bladed olivine and clinopyroxene within komatiites indicate rapid crystallization from a high temperature magma and have played an important role in constraining the thermal evolution of the Earth's early mantle (Herzberg et al, 2010;Nisbet et al, 1993).…”

“…Komatiites are a distinctive but volumetrically minor component of the belts. They are characterized by low alkalis and high Mg contents, and have been divided into Al‐depleted and Al‐undepleted types for a given MgO (or TiO 2 ) content, with the latter thought to become more common after 3 Ga (Barnes & Arndt, 2019, and references therein; Barnes et al., 2021), although Sossi et al. (2016) did not find any temporal variation in the distribution of the two types.…”

Lithogeochemistry in exploration for intrusion-hosted magmatic Ni-Cu-Co deposits

“…This claim has been criticised on these and other grounds by (Arndt 2013). Here I further test the concept using a suite of lithophile and chalcophile trace elements from the extensive database of (Barnes et al 2021a) and (Barnes et al 2015), starting with lithophile trace elements. Chalcophile elements are discussed below.…”

“…The elements Nb, Yb, Th and the REE, along with Zr and Y, are commonly used as petrogenetic proxies and as indicators of tectonic setting. The latter application has been heavily criticised by a number of recent publications (Condie 2015;Li et al 2015a;Barnes et al 2021a), but the relative proportions of these elements are nonetheless important indicators of petrogenetic processes. Barnes et al (2021b) show that most of the useful variance in the entire suite can be captured in the commonly used plot of Th/Yb vs Nb/Yb devised by Pearce (Pearce 2008(Pearce , 2014 and we apply that approach here.…”

Reactivity of Basaltic Minerals for CO2 Sequestration via In Situ Mineralization: A Review

“…Although present in smaller quantities, these elements exert significant influence on various processes, including CO 2 storage. Examples of trace elements found in basalt include chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), and cobalt (Co) [89][90][91]. The presence and distribution of these trace elements offer insights into the origins and evolution of basaltic magma and the potential interactions with CO 2 during storage.…”