Geology topics

Aaron J. Pietruszka

Publications and source records attributed to Aaron J. Pietruszka.

7 recordsLinked to original sources

USGS2026

Osmium isotope constraints on Mauna Loa–Kilauea magmatic connectivity, Island of Hawai‘i

The Hawaiian volcanic chain exhibits a long-recognized double track of volcanism defined by the Loa and Kea trends, which erupt chemically and isotopically distinct lavas. Mauna Loa and Kīlauea, the two most frequently active volcanoes of the Loa and Kea trends, produce distinct endmember compositions. However, historical periods of compositional convergence have prompted debate regarding a potential magmatic connection between the two adjacent volcanoes. Proposed links include a shallow edifice-level plumbing system, a common magma source at ∼40 km depth, or a deeper asthenospheric source. In the latter scenario, based on correlated Sr–Nd–Pb isotopes and trace-element systematics, a “shared” mantle source supplies melt alternately to both volcanoes on multi-decadal timescales. Here, we use Os isotopes to evaluate the proposed connections. We measured Os isotopes in eight historical Mauna Loa tholeiites along with three Kīlauea tholeiites (1832 summit eruption; Uēkahuna Bluff; 2000 Pu‘u‘ō‘ō eruption) previously identified as isotopically intermediate between Mauna Loa and Kīlauea endmembers. We found that the acidic bromide leachates of all samples yield more radiogenic 187 Os/ 188 Os than corresponding bulk residues, with the labile Os-bearing phase comprising ∼0.4–27% of bulk Os. Mauna Loa tholeiites display nearly constant 187 Os/ 188 Os over the past ∼200 years (0.134–0.136; mean = 0.1357 ± 0.0013, n = 8, 2SD), despite large variations in total [Os] ranging from ∼30 pg/g (2022 tholeiite) to ∼966 pg/g (1868 picrite). The Kīlauea 1832 sample has 187 Os/ 188 Os = 0.1302 ± 0.0008, slightly higher than the Kīlauea endmember (0.1285 ± 0.0008), whereas the Uēkahuna Bluff and Pu‘u‘ō‘ō samples exhibit more elevated ratios (0.1314 ± 0.0008 and 0.1327 ± 0.0008, respectively). We conclude that the “shared” mantle source exerts negligible control on Mauna Loa Os isotope systematics. In contrast, the Kīlauea mantle source is more heterogeneous, with contributions from small-scale recycled domains with variable time-integrated Re/Os ratios.

Hawaii↗

USGS2026

Magmatic source of the opening phase of Kīlauea’s 2018 Lower East Rift Zone eruption

The 2018 eruption of Kīlauea volcano in its Lower East Rift Zone began with the discharge of evolved high-Ti basalt as weak lava fountains and short, slow-moving lava flows. The lavas were quickly geochemically recognized as being derived from magmas stored within the rift zone and remobilized by a new intrusion, a sequence that is common at Kīlauea. This initial phase of the 2018 eruption, referred to as phase 1a, lasted for 6 days and was followed by extrusion of mixed magma after a 3-day pause. Even though remobilization of older rift zone magmas is common within Kīlauea’s rift zones, it is difficult to determine which past intrusion(s) may have initially emplaced those stored magmas. This difficulty stems from the tendency for Kīlauea magmas to follow very similar differentiation paths without significant variations in major, minor, or even trace element chemistry. We investigate possible magma sources for the lavas erupted during phase 1a of the 2018 eruption using whole-rock, mineral, and glass major and trace element compositions from historical East Rift Zone eruptions with adjacent fissures. We consider two primary hypotheses for the phase 1a source: magmas associated with the 1955 Lower East Rift Zone eruption or the nine eruptions in the Middle and Upper East Rift Zone during the 1960s. Our results suggest that magma associated with the earliest phases of Kīlauea’s 1955 eruption was the most likely source of the 2018 phase 1a remobilized magma. We determine volatile saturation pressures from melt inclusion chemistry and find similar storage depths for the 2018 phase 1a and early 1955 magmas. The phase 1a and early 1955 lavas are nearly indistinguishable in all of the compositional criteria considered, implying that the leftover 1955 magma body barely cooled and differentiated in the 63 years between eruptions (cooling rates of ~0.1 °C/year). This study sheds light on the potential for protracted storage of eruptible magmas in rift zones at Kīlauea, and highlights some of the challenges and solutions to identifying genetic relationships between magmas at Kīlauea.

Hawaii↗

USGS2024

Awakening of Maunaloa linked to melt shared from Kilauea’s mantle source

Maunaloa—the largest active volcano on Earth—erupted in 2022 after its longest known repose period (~38 years) and two decades of volcanic unrest. This eruptive hiatus at Maunaloa encompasses most of the ~35-year-long Puʻuʻōʻō eruption of neighboring Kīlauea, which ended in 2018 with a collapse of the summit caldera and an unusually voluminous (~1 km 3 ) rift eruption. A long-term pattern of such anticorrelated eruptive behavior suggests that a magmatic connection exists between these volcanoes within the asthenospheric mantle source and melting region, the lithospheric mantle, and/or the volcanic edifice. The exact nature of this connection is enigmatic. In the past, the distinct compositions of lavas from Kīlauea and Maunaloa were thought to require completely separate magma pathways from the mantle source of each volcano to the surface. Here, we use a nearly 200-yr record of lava chemistry from both volcanoes to demonstrate that melt from a shared mantle source within the Hawaiian plume may be transported alternately to Kīlauea or Maunaloa on a timescale of decades. This process led to a correlated temporal variation in 206 Pb/ 204 Pb and 87 Sr/ 86 Sr at these volcanoes since the early 19th century with each becoming more active when it received melt from the shared source. Ratios of highly over moderately incompatible trace elements (e.g., Nb/Y) at Kīlauea reached a minimum from ~2000 to 2010, which coincides with an increase in seismicity and inflation at the summit of Maunaloa. Thereafter, a reversal in Nb/Y at Kīlauea signals a decline in the degree of mantle partial melting at this volcano and suggests that melt from the shared source is now being diverted from Kīlauea to Maunaloa for the first time since the early to mid-20th century. These observations link a mantle-related shift in melt generation and transport at Kīlauea to the awakening of Maunaloa in 2002 and its eruption in 2022. Monitoring of lava chemistry is a potential tool that may be used to forecast the behavior (e.g., eruption rate and frequency) of these adjacent volcanoes on a timescale of decades. A future increase in eruptive activity at Maunaloa is likely if the temporal increase in Nb/Y continues at Kīlauea.

Hawaii↗

USGS2017

Evaluation of laser ablation double-focusing SC-ICPMS for “common” lead isotopic measurements in silicate glasses and mineral

An analytical method for the in situ measurement of “common” Pb isotope ratios in silicate glasses and minerals using a 193-nm excimer laser ablation (LA) system with a double-focusing single-collector (SC)-ICPMS is presented and evaluated as a possible alternative to multiple-collector (MC)-ICPMS. This LA-SC-ICPMS technique employs fast-scanning ion deflectors to sequentially place a series of flat-topped isotope peaks into a single ion-counting detector at a fixed accelerating voltage and magnetic field strength. Reference materials (including NIST, MPI-DING, and USGS glasses) are used to identify two analytical artifacts on the Pb isotope ratios (expressed here as heavier/lighter isotopes) when corrected for mass bias relative to NIST SRM610. The first artifact is characterized by anomalously low Pb isotope ratios (~0.1%/AMU) when SRM610 is analyzed in raster mode as an unknown at small spot sizes (<25 µm), which may indicate that (1) SRM610 is isotopically heterogeneous on a small length scale and/or (2) there is a non-spectral matrix effect on the Pb isotope ratios related to differences in spot size. The second artifact is characterized by anomalously high Pb isotope ratios (<0.1%/AMU) for NIST SRM612 (in raster mode) and some Fe-rich glass reference materials (BCR-2G, GOR132-G, and T1-G). These offsets are thought to be caused by one or more non-spectral matrix effects related to differences in the ablation behavior, composition, or physical properties of these reference materials compared to the bracketing SRM610 standard. The precision (±2SD) of our LA-SC-ICPMS Pb isotopic measurements is similar to ( 207 Pb/ 206 Pb and 208 Pb/ 206 Pb, or 20X Pb/ 206 Pb) or better than ( 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb, or 20X Pb/ 204 Pb) a series of published studies that used a different type of SC-ICPMS and obtained a factor of ~3-4 higher sensitivity for Pb. An increase in the sensitivity of our LA-SC-ICPMS would likely improve the precision of the 20X Pb/ 206 Pb and 20X Pb/ 204P b ratios for low-Pb materials (<5 ppm), possibly making the technique broadly similar to LA-MC-ICPMS (particularly compared to methods that rely upon at least one ion-counting detector). Further improvement in the precision of the 20X Pb/ 206 Pb and 20X Pb/ 204 Pb ratios for high-Pb materials (>5 ppm) by LA-SC-ICPMS is unlikely, and in this case, LA-MC-ICPMS remains the preferable analytical technique.

Journal of Analytical Atomic Spectrometry↗

USGS2015

A review of the recent geochemical evolution of Piton de la Fournaise volcano (1927-2010)

Between 1927 and 2010, more than one hundred eruptions of Piton de la Fournaise produced ~1 km 3 of lava, and the volcano’s summit collapsed twice (in 1931 and 2007). These lavas display, respectively, 20 and 65 % of the Sr–Nd and the Pb isotope ranges reported for La Réunion volcanoes over their known eruptive record (3.8 Ma). Variations in major and trace element concentrations and Sr–Pb isotopes do not define a temporal trend at the scale of the century, but display systematic short-term cyclic fluctuations. The positive correlation between 87 Sr/ 86 Sr and ratios of trace elements that are more versus less incompatible during partial melting of the mantle (e.g., Nd/Sm, La/Sm) probably results from the sampling of small-scale heterogeneities within the plume source. Changes in the degree of melting and/or crystallization are debated, but these appear ultimately linked to source properties. Lead isotopes do not co-vary with Sr isotopes, in part because of the partitioning of Pb into dense metallic phases that are preferentially sampled during high-flux eruptions. Taken together, Sr–Nd–Pb–Os–Th isotopes do not support contamination of magma with genetically unrelated components, such as the underlying Indian oceanic crust, mantle lithosphere, seawater, or seawater-altered lavas. Yet, in some rare cases (e.g. the 1998 Hudson eruption), the compositional patterns suggest that the parental magma assimilated older volcanic products within the edifice, such as crystal cumulates and/or interstitial differentiated melts. The geochemical fluctuations over the 1927–2010 time period constrain the residence time of magma in the shallow reservoir to 10–30 years and its size to 0.1–0.3 km 3 . The magma residence time during the course of the long-lived 1998 eruption is estimated to be an order of magnitude shorter, but the reservoir was probably of similar size. Instead, the shorter magma residence for the 1998 eruption was probably due to a higher magma flux.

Book chapter↗

USGS2015

Two magma bodies beneath the summit of Kilauea Volcano unveiled by isotopically distinct melt deliveries from the mantle

The summit magma storage reservoir of Kīlauea Volcano is one of the most important components of the magmatic plumbing system of this frequently active basaltic shield-building volcano. Here we use new high-precision Pb isotopic analyses of Kīlauea summit lavas—from 1959 to the active Halema‘uma‘u lava lake—to infer the number, size, and interconnectedness of magma bodies within the volcano's summit reservoir. From 1971 to 1982, the 206 Pb/ 204 Pb ratios of the lavas define two separate magma mixing trends that correlate with differences in vent location and/or pre-eruptive magma temperature. These relationships, which contrast with a single magma mixing trend for lavas from 1959 to 1968, indicate that Kīlauea summit eruptions since at least 1971 were supplied from two distinct magma bodies. The locations of these magma bodies are inferred to coincide with two major deformation centers identified by geodetic monitoring of the volcano's summit region: (1) the main locus of the summit reservoir &sim;2–4 km below the southern rim of Kīlauea Caldera and (2) a shallower magma body <2 km below the eastern rim of Halema‘uma‘u pit crater. Residence time modeling suggests that the total volume of magma within Kīlauea's summit reservoir during the late 20th century (1959–1982) was exceedingly small (&sim;0.1–0.5 km 3 ). Voluminous Kīlauea eruptions, such as the ongoing, 32-yr old Pu‘u ‘Ō‘ō rift eruption (>4 km 3 of lava erupted), must therefore be sustained by a nearly continuous supply of new melt from the mantle. The model results show that a minimum of four compositionally distinct, mantle-derived magma batches were delivered to the volcano (at least three directly to the summit reservoir) since 1959. These melt inputs correlate with the initiation of energetic (1959 Kīlauea Iki) and/or sustained (1969–1974 Mauna Ulu, 1983-present Pu‘u ‘Ō‘ō and 2008-present Halema‘uma‘u) eruptions. Thus, Kīlauea's eruptive behavior is partly tied to the delivery of new magma batches from the volcano's source region within the Hawaiian mantle plume.

Hawaii↗

USGS2014

Uranium series, rates of basaltic melt generation and transport

No abstract available.

Book chapter↗