Composition of basaltic lavas sampled by phase‐2 of the Hawaii Scientific Drilling Project: Geochemical stratigraphy and magma types

Abstract

[1] This paper presents major and trace element compositions of lavas from the entire 3098 m stratigraphic section sampled by phase-2 of the Hawaii Scientific Drilling Project. The upper 245 m are lavas from Mauna Loa volcano, and the lower 2853 m are lavas and volcanoclastic rocks from Mauna Kea volcano. These intervals are inferred to represent about 100 ka and 400 ka respectively of the eruptive history of the two volcanoes. The Mauna Loa tholeiites tend to be higher in SiO 2 and lower in total iron, TiO 2 , alkalis, and incompatible elements at a given MgO content than Mauna Kea lavas. The transition from Mauna Loa to Mauna Kea lavas is all the more pronounced because the Mauna Loa tholeiites overlie a thin sequence of postshield Mauna Kea alkalic to transitional tholeiitic lavas. The Mauna Loa tholeiites display welldeveloped coherent trends with MgO that are indistinguishable in most respects from modern lavas. With depth, however, there is a slight decline in incompatible element abundances, and small shifts to depleted isotopic ratios. These characteristics suggest small changes in melt production and source components over time, superimposed on shallow melt segregation. The Mauna Kea section is subdivided into a thin, upper 107 m sequence of postshield tholeiites, transitional tholeiites and alkali basalts of the Hamakua volcanics, overlying four tholeiitic magma types that are intercalated throughout the rest of the core. These four magma types are recognized on the basis of MgO-normalized SiO 2 and Zr/Nb values. Type-1 lavas (high SiO 2 and Zr/Nb) are ubiquitous below the postshield lavas and are the dominant magma type on Mauna Kea. They are inter-layered with the other three lava types. Type-2 lavas (low SiO 2 but high Zr/Nb) are found only in the upper core, and especially above 850 m. Type-3 lavas (low SiO 2 and Zr/Nb) are very similar to tholeiites from Loihi volcano and are present only below 1974 m. There are only 3 discrete samples of type-4 lavas (high SiO 2 and low Zr/Nb), which are present in the upper and lower core. The differences between these magma types are inferred to reflect changes in melt production, depth of melt segregation, and differences in plume source components over about 400 ka of Mauna Kea's eruptive history. At the start of this record, eruption rates were high, and two distinct tholeiitic magmas (type-1 and 3) were erupting concurrently. These two magmas require two distinct source components, one similar to that of modern Loihi tholeiites and the other close to that of Kilauea magmas. Subsequently, the Loihilike source of the type-3 magmas was exhausted, and these lavas are absent from the remainder of the core. For the next 200 ka or so, the eruptive sequence consists of inter-layered type-1 and -2 lavas that are derived from a common Mauna Kea source, the major difference between the two being the depth at which the melts segregated from the source. At around 440 ka (corresponding with the transition in the core from submarine to subaerial lavas) eruption rates bega...

Ceramic ChemCam Calibration Targets on Mars Science Laboratory

“…All the other XRF data in Tables 1 and 2 were measured in the XRF lab at the University of Massachusetts using standard operating procedures (Rhodes 1996;Rhodes and Vollinger 2004). For the XRF analysis of major elements, samples were prepared as fused La-bearing lithium borate glass discs using the methods of Norrish and Hutton (1969), though each sample was first ignited at 1040°C for several hours in order to oxidize the iron to Fe 3+ and remove volatiles.…”

On some fundamentals of igneous petrology

“…The chemical diversity of the lavas encountered in drilling is large, as is illustrated by Fig. 8a (after Rhodes and Vollinger 2004); the variation in MgO alone spans nearly 30 wt%. This style of variation is typical for Hawaii not only for the long-term eruptive record (Peterson and Moore 1987) but also for recent voluminous eruptions as already mentioned in building Kilauea Iki lava lake.…”

“…Bowen's usual reaction series resides and thus Fig. 8 a The variation of MgO in lavas encountered in the 3 km Hilo drill hole covering *500,000 years of eruptive history (after Rhodes and Vollinger 2004). The strong variation in MgO reflects the modal abundance of primocrystic olivine, which varies in accord to the magnitude of the eruptive flux.…”

“…The final horizon of magma is displaced downward due to the effect of hydrothermal cooling in the upper crust from rainfall, and be reminded that the true aspect ratio is that of a slice of bread Fig. 6 The variation in CaO and MgO in lavas encountered in the 3 km Hilo, Hawaii drill hole covering a time span of *500,000 years (after Rhodes and Vollinger 2004). The large range in MgO content reflects a similar range in modal olivine.…”

Submarine radial vents on Mauna Loa Volcano, Hawai'i

“…[21] XRF major and trace element analyses were made on 53 tholeiitic submarine radial vent lava samples (Table 4; see also auxiliary material 1 Table S1) at the University of Massachusetts following 2005GC001086 methods described by Rhodes and Vollinger [2004]. The weakly phyric nature of most of these rocks (<2 vol.% phenocrysts; Table 2) suggests that the whole rock compositions are indicative of liquid compositions.…”