Geochemical stratigraphy of lava flows sampled by the Hawaii Scientific Drilling Project

Abstract

Geochemical discriminants are used to place the boundary between Mauna Loa flows and underlying Mauna Kea flows at a depth of about 280 m. At a given MgO content the Mauna Kea flows are lower in SiO2 and total iron and higher in total alkali, TiO2, and incompatible elements than the Mauna Loa lavas. The uppermost Mauna Kea lavas (280 to 340 m) contain alkali basalts interlayered with tholeiites and correlate with the postshield Hamakua Volcanics. In addition to total alkalis, the alkali basalts have higher TiO2, P2O5, Sr, Ba, Ce, La, Zr, Nb, Y, and V relative to the tholeiites and lower Zr/Nb and Sr/Nb ratios. Some of the alkali basalts are extensively differentiated. Below 340 m all the flows are tholeiitic, with compositions broadly similar to the few “fresh” subaerial shield‐building Mauna Kea tholeiites studied to date. High‐MgO lavas are unusually abundant, although there is a wide range (7–28%) in MgO content reflecting olivine control. FeO/MgO relationships are used to infer parental picritic magmas with about 15 wt % MgO. Lavas with more MgO than this have accumulated olivine. The Mauna Loa lavas have compositional trends that are controlled by olivine crystallization and accumulation. They compare closely with trends for historical (1843–1984) flows, tending toward the depleted end of the spectrum. They are, though, much more MgO‐rich (9–30%) than is typical for most historical and young (<30 ka) prehistoric lavas. The unusual abundance of high‐MgO and picritic lavas is attributed to the likelihood that only large‐volume, hot, mobile flows will reach Hilo Bay from the northeast rift zone. FeO/MgO relationships are used to infer parental picritic magmas with about 17 wt % MgO. Again, lavas with more MgO than this have accumulated olivine. Systematic changes in incompatible element ratios are used to argue that the magma supply rate has diminished over time. On the other hand, the relatively constant Zr/Nb and Sr/Nb ratios that compare closely with historical and young (<30 kyr) prehistoric flows are used to argue that the source components for these lavas in the Hawaiian plume have remained relatively uniform over the last 100 kyr.

Ceramic ChemCam Calibration Targets on Mars Science Laboratory

“…All elements (including Na) were measured simultaneously using a Siemens MRS-400 spectrometer. Estimates of accuracy and precision are given in Rhodes (1996) and 1-σ errors are presented in the footnote to Table 2. Sulfur was measured on a Panalytical 2400 sequential X-Ray spectrometer on a separate glass disc that was fused with an excess of lithium nitrate to ensure oxidation and retention of the sulfur as sulfate.…”

“…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.…”

Hf isotopic compositions of the Hawaii Scientific Drilling Project Core and the source mineralogy of Hawaiian basalts

“…About 280 meters of Mauna Loa lavas cap Mauna Kea flows, which constitute the major part of the drill core. The top 50 meters of the Mauna Kea sequence consist of alkali lavas intercalated with tholerites, whereas the remainder consists of tholeiites with occasionally picritic character [Rhodes, 1996].…”

Partitioning of Ni, Co and V between spinel-structured oxides and silicate melts: Importance of spinel composition

“…The variation can be ascribed to progressive liquid evolution during fractionation of 0.6% chromite, 8.4% olivine, 26.0% feldspar and 22.9% pyroxene. Trace element concentrations are calculated using the results of this study (for spinel) and published D's of Green (1994) and Roeder and Reynolds (1991) (Rhodes, 1996;Albarède, 1996). The calculated trends are those resulting from major element modeling using MELTS (Ghiorso and Sack, 1994), and assuming sample R091 as a parental liquid at 5 kb, QFM buffer, between 1500 and 1200 8C.…”