Geology topics

F. Trusdell

Publications and source records attributed to F. Trusdell.

4 recordsLinked to original sources

USGS2009

Diverse lavas from closely spaced volcanoes drawing from a common parent: Emmons Lake Volcanic Center, Eastern Aleutian Arc

Emmons Lake Volcanic Center (ELVC) on the lower Alaskan Peninsula is one of the largest and most diverse volcanic centers in the Aleutian Arc. Since the Middle Pleistocene, eruption of ~ 350 km 3 of basalt through rhyolite has produced a 30 km, arc front chain of nested calderas and overlapping stratovolcanoes. ELVC has experienced as many as five major caldera-forming eruptions, the most recent, at ~ 27 ka, produced ~ 50 km 3 of rhyolitic ignimbrite and ash fall. These violent silicic events were interspersed with less energetic, but prodigious, outpourings of basalt through dacite. Holocene eruptions are mostly basaltic andesite to andesite and historically recorded activity includes over 40 eruptions within the last 200 yr, all from Pavlof volcano, the most active site in the Aleutian Arc. Geochemical and geophysical observations suggest that although all ELVC eruptions derive from a common clinopyroxene + spinel + plagioclase fractionating high-aluminum basalt parent in the lower crust, magma follows one of two closely spaced, but distinct paths to the surface. Under the eastern end of the chain, magma moves rapidly and cleanly through a relatively young (~ 28 ka), hydraulically connected dike plexus. Steady supply, short magma residence times, and limited interaction with crustal rocks preserve the geochemistry of deep crustal processes. Below the western part of the chain, magma moves haltingly through a long-lived (~ 500 ka) and complex intrusive column in which many generations of basaltic to andesitic melts have mingled and fractionated. Buoyant, silicic melts periodically separate from the lower parts of the column to feed voluminous eruptions of dacite and rhyolite. Mafic lavas record a complicated passage through cumulate zones and hydrous silicic residues as manifested by disequilibrium phenocryst textures, incompatible element enrichments, and decoupling of REEs and HFSEs ratios. Such features are absent in mafic lavas from the younger part of the chain, highlighting the importance of plumbing architecture and longevity in creating petrologic diversity. Supplemental Data include 156 major element (XRF) and 128 trace element (ICP-MS) whole-rock analyses, 23 new 40 Ar/ 39 Ar ages, a generalized geologic map with associated unit descriptions and field photographs, and photomicrographs of key petrographic features.

Alaska↗

USGS2006

Cosmogenic 3He production rates revisited from evidences of grain size dependent release of matrix-sited helium

Measurements of the cosmogenic 3 He ( 3 He c ) content of various size aliquots of exposed olivines show that the fine fraction (<140 μm) has 3 He c concentrations between 14 and 100% lower than that of the coarse fractions (0.14–1 mm). Such differences attest to a grain size dependent partial release of 3 He c from the phenocrysts matrix during the preliminary in vacuo crushing. This result might have important implications since most 3 He c measurements have used for ∼20 yr a standard routine based on the fusion of bulk powdered phenocrysts, whatever their grain size. A suite of new data obtained from coarse olivine grains yielded a mean Sea Level High Latitude 3 He c production rate (SLHL P 3 ) of 128±5 and 136±6 at. g −1 yr −1 , depending on the scaling factors used. This new value, which is ∼15% higher than previously published rates, is obtained from 5 ropy flow surfaces of Mt Etna (38°N) and Hawaiian (19°N) volcanoes, at elevations between sea level and 870 m and ranging in age from 1.47±0.05 to 149±23 ka according to independent 14 C or K/Ar dating. 3 He loss during the crushing step might account for the discrepancy between the standard reference value of 110–115 at. g −1 y −1 and the higher SLHL P 3 proposed here. More generally, removal of the powdered fraction before fusion is an important point to consider in further studies in order to avoid any 3 He c systematic underestimates. An altitudinal section has also been sampled on the ropy surface of a ∼1500 yr single flow of Mauna Loa (19°N) which allowed a new empirical atmospheric attenuation length of 149±22 g cm −2 to be documented for 3 He c in olivines between 2400 and 4000 m elevations.

Earth and Planetary Science Letters↗

USGS2005

The May 2003 eruption of Anatahan volcano, Mariana Islands: Geochemical evolution of a silicic island-arc volcano

The first historical eruption of Anatahan volcano began on May 10, 2003. Samples of tephra from early in the eruption were analyzed for major and trace elements, and Sr, Nd, Pb, Hf, and O isotopic compositions. The compositions of these tephras are compared with those of prehistoric samples of basalt and andesite, also newly reported here. The May 2003 eruptives are medium-K andesites with 59–63 wt.% SiO 2 , and are otherwise homogeneous (varying less than 3% 2 σ about the mean for 45 elements). Small, but systematic, chemical differences exist between dark (scoria) and light (pumice) fragments, which indicate fewer mafic and oxide phenocrysts in, and less degassing for, the pumice than scoria. The May 2003 magmas are nearly identical to other prehistoric eruptives from Anatahan. Nonetheless, Anatahan has erupted a wide range of compositions in the past, from basalt to dacite (49–66 wt.% SiO 2 ). The large proportion of lavas with silicic compositions at Anatahan (> 59 wt.% SiO 2 ) is unique within the active Mariana Islands, which otherwise erupt a narrow range of basalts and basaltic andesites. The silicic compositions raise the question of whether they formed via crystal fractionation or crustal assimilation. The lack of 87 Sr/ 86 Sr variation with silica content, the MORB-like δ 18 O, and the incompatible behavior of Zr rule out assimilation of old crust, altered crust, or zircon-saturated crustal melts, respectively. Instead, the constancy of isotopic and trace element ratios, and the systematic variations in REE patterns are consistent with evolution by crystal fractionation of similar parental magmas. Thus, Anatahan is a type example of an island-arc volcano that erupts comagmatic basalts to dacites, with no evidence for crustal assimilation. The parental magmas to Anatahan lie at the low 143 Nd/ 144 Nd, Ba/La, and Sm/La end of the spectrum of magmas erupted in the Marianas arc, consistent with 1–3 wt.% addition of subducted sediment to the mantle source, or roughly one third of the sedimentary column. The high Th/La in Anatahan magmas is consistent with shallow loss of the top ∼ 50 m of the sedimentary column during subduction.

Anatahan volcano, Mariana Islands↗

USGS1997

Chronology of the episode 54 eruption at Kilauea Volcano, Hawaii, from GOES-9 satellite data

The free availability of GOES satellite data every 15 minutes makes these data an attractive tool for studying short-term changes on cloud-free volcanoes in the Pacific basin. We use cloud-free GOES-9 data to investigate the chronology of the January 1997, episode 54 eruption of Kilauea Volcano, Hawaii. Seventy-six images for this effusive eruption were collected over a 60-hour period and show the opening and shutdown of active fissures, the draining and refilling of the Pu'u 'O'o lava lake, and the cessation of activity at the ocean entry. Copyright 1997 by the American Geophysical Union.

Geophysical Research Letters↗