Exploring the mineralogical heterogeneities of the Louisville Seamount Trail

Abstract

Diopside phenocrysts of the Louisville Seamount Trail show an increase in Ti, Al, and Na with decreasing Mg/(Mg + Fe) as is typical for clinopyroxene in alkalic basalts. Chondrite‐normalized REE patterns of calculated liquids from LA‐ICPMS analyses are comparable to whole‐rock and glass values. Exceptions are clinopyroxene crystals from the Rigil Seamount, the second oldest seamount drilled at the northern end of the chain. Some crystals from this site are strongly zoned with distinct compositional boundaries between cores and mantles. The cores have high Mg/(Mg + Fe) and low Al and Ti concentrations compared to the mantles and phenocrysts. Major element, clinopyroxene discrimination diagrams indicate that the clinopyroxene mantles and phenocrysts crystallized from alkalic basalts. In contrast, the Mg‐rich cores have tholeiitic affinities. The REE abundances of the cores are similar to that of clinopyroxene from transitional tholeiites of the Kerguelen Archipelago. Calculated liquid La/Yb values for the cores have ratios that are similar to transitional tholeiites in Hawaii, whereas the mantles have higher La/Yb values similar to Hawaiian alkalic basalts. The major and trace element compositions of clinopyroxene cores from the Rigil seamount suggest that a transitional tholeiitic magma was present, but no evidence for Hawaiian shield‐type tholeiites was found. Plagioclase crystals from the Rigil seamount have 86Sr/86Sr from 0.70306 to 0.70363, within the range of FOZO. The transitional tholeiitic signature of the Mg‐rich clinopyroxene cores probably did not have a distinct source compared to other Louisville magmas, but more likely indicates a higher degree of partial melting (2–5%) of that FOZO source.

Scandium speciation in a world-class lateritic deposit

“…80 ppm; Table S-3) twice as high as those in typical mantle clinopyroxenites (Samson and Chassé, 2016). Similar concentrations (60 ppm to 80 ppm) occur in other 'Alaskan-type' clinopyroxenites (Burg et al, 2009) and in clinopyroxenes from ocean-island basalts (Dorais, 2015). This suggests the accumulation of clinopyroxene in subvolcanic feeder conduits during fractional crystallisation of a mantle-derived melt.…”

Non-Hawaiian lithostratigraphy of Louisville seamounts and the formation of high-latitude oceanic islands and guyots

“…12). However, geochemical data from Louisville indicate that basalts and hyaloclastites from the upper seamount and island stages have alkaline to transitional tholeiitic affinities (Hawkins et al, 1987;Beier et al, 2011;Koppers et al, 2012a;Nichols et al, 2014;Vanderkluysen et al, 2014;Dorais, 2015). This contrasts with the upper seamount and island stages of Hawaiian volcanoes that have a predominant tholeiitic composition (e.g., Feigenson et al, 2003;Rhodes and Vollinger, 2004).…”

“…Apparent absence of an active hotspot at the eastern end of the chain suggests that most Louisville seamounts were produced during waning of a now extinct Louisville hotspot (Lonsdale, 1988). Basalts recovered by dredging and drilling on the seamounts have only yielded alkaline and transitional geochemical affinities, with so far no evidence for tholeiitic magmatism (Hawkins et al, 1987;Beier et al, 2011;Koppers et al, 2012a;Nichols et al, 2014;Vanderkluysen et al, 2014;Dorais, 2015). Drill cores considered in this study were collected during IODP Expedition 330 at the top of 3 guyots along the older (80-50 Ma) segment of the Louisville seamount chain (Koppers et al, 2012a) (Fig.…”

High‐Resolution40Ar/39Ar Geochronology of the Louisville Seamounts IODP Expedition 330 Drill Sites: Implications for the Duration of Hot Spot‐related Volcanism and Age Progressions

“…However, taking a similar modeling approach for a Louisville Seamount is difficult, since we cannot separate the shield, postshield and rejuvenated stages based on petrology and geochemistry. Cored and dredged samples for Louisville Seamounts studied thus far have been dominantly alkali basalts with a homogeneous isotopic composition (Beier et al, ; Vanderkluysen et al, ) and with a hint of transitional tholeiites in Rigil Guyot only, based on the study of clinopyroxene chemistry (Dorais, ). In the remainder of this paper, we develop a different approach based on the premise that we can determine the lifespan of a seamount by investigating the cumulative distribution of ages collected from multiple seamounts along a seamount trail.…”

“…Swell geometry and buoyancy flux analyses (King & Adam, ; Sleep, ) only identify a weak plume. Unlike the Hawaiian‐Emperor seamount trail, none of the whole‐rock or isotopic analyses obtained indicate anything other than a homogeneous mantle source for Louisville magmas of all ages (Beier et al, ; Cheng et al, ; Dorais, ; Hanyu, ; Tejada et al, ; Vanderkluysen et al, ). No tholeiitic lavas have been recovered from hundreds of dredges or from the lava flows cored at the five IODP drill sites (Koppers et al, ).…”