Geology topics
D.A. Clague
Publications and source records attributed to D.A. Clague.
Noble gases in submarine pillow basalt glasses from Loihi and Kilauea, Hawaii: A solar component in the Earth
Noble gas elemental and isotopic abundances have been analysed in twenty-two samples of basaltic glass dredged from the submarine flanks of two currently active Hawaiian volcanoes, Loihi Seamount and Kilauea. Neon isotopic ratios are enriched in 20 Ne and 21 Ne by as much as 16% with respect to atmospheric ratios. All the Hawaiian basalt glass samples show relatively high 3 He 4 He "> 3He4He ratios. The high 20 Ne 22 Ne "> 20 Ne 22 Ne values in some of the Hawaiian samples, together with correlations between neon and helium systematics, suggest the presence of a solar component in the source regions of the Hawaiian mantle plume. The solar hypothesis for the Earth's primordial noble gas composition can account for helium and neon isotopic ratios observed in basaltic glasses from both plume and spreading systems, in fluids in continental hydrothermal systems, in CO 2 well gases, and in ancient diamonds. These results provide new insights into the origin and evolution of the Earth's atmosphere.
Ages, rare-earth element enrichment, and petrogenesis of tholeiitic and alkalic basalts from Kahoolawe Island, Hawaii
Kahoolawe Island, Hawaii (18×11 km), is a basaltic shield volcano with caldera-filling lavas, seven identified postshield vents, and at least two occurrences of apparent rejuvenated-stage eruptive. We examined 42 samples that represent all stages of Kahoolawe volcano stratigraphy for their petrography, whole-rock major-and trace-element contents, mineral compositions, and K−Ar ages. The two oldest shield samples have an average age of 1.34±0.08 Ma, and four postshield samples (3 are alkalic) average 1.15±0.03 Ma; ages of 1.08 and 0.99 Ma for two additional tholeiitic samples probably are minimum ages. Whole-rock major- and trace-element and mineral compositions of Kahoolawe shield and caldera-fill laves are generally similar to the lavas forming Kilauea and Mauna Loa tholeiitic shields, but in detail, Kahoolawe shield lavas have distinctive compositions. An unusual aspect of many postshield Ka-hoolawe lavas is anomalously high REE and Y abundances (up to 200 ppm La and 175 ppm Y) and negative Ce anomalies. These enrichments reflect surficial processes, where weathering and soil development promoted REE-Y transport at the weathering front. Major element abundances (MgO, 10–6 wt.%) for shield and caldera-fill basalts are consistent with fractionation of ol+px+pl in frequently replenished magma reservoirs. In general, tholeiitic basalts erupted from late vents are higher in SiO 2 than the shield lavas, and temporal differences in parental magma compositions are the likely explanation. Alkalic basalts that erupted from vents are comparable in composition to those at other Hawaiian volcanoes. Trace-element abundance ratios indicate that alkalic basalts represent either relatively lower degrees of melting of the shield source or a distinct source. Apparent rejuvenated-stage basalts (i.e., emplaced after substantial Kahoolawe erosion) are tholeiitic, unlike the rejuvenated-stages at other Hawaiian volcanoes (alkalic). Kahoolawe, like several other Hawaiian volcanoes, has intercalated tholeiitic and alkalic basalts in the postshield stage, but it is the only volcano that appears to have produced tholeiitic rejuvenated-stage lavas.
The ten-year eruption of Kilauea Volcano
The Pu'u 'O' o-Kupaianaha eruption now ranks as the longest-lived historic eruption on the East Rift Zone and the most destructive in Kilauea's recent history. About 1 km 3 of lava erupted during the first 0 years of the eruption. Lava flows have destroyed 181 houses and severed the coastal highway along the volcano's south flank, severely restricting transportation on this part of the island of Hawaii. the eruption consisted of many distinct episodes characterized by activity at different vents and by different eruptive styles. the following summarizes the first 10 years of the eruption, starting with the initial outbreak in 1983.
Geology and petrology of Mahukona Volcano, Hawaii
The submarine Mahukona Volcano, west of the island of Hawaii, is located on the Loa loci line between Kahoolawe and Hualalai Volcanoes. The west rift zone ridge of the volcano extends across a drowned coral reef at about-1150 m and a major slope break at about-1340 m, both of which represent former shoreines. The summit of the volcano apparently reached to about 250 m above sea level (now at-1100 m depth) did was surmounted by a roughly circular caldera. A econd rift zone probably extended toward the east or sutheast, but is completely covered by younger lavas from the adjacent subaerial volcanoes. Samples were vecovered from nine dredges and four submersible lives. Using subsidence rates and the compositions of flows which drape the dated shoreline terraces, we infer that the voluminous phase of tholeiitic shield growth ended about 470 ka, but tholeiitic eruptions continued until at least 435 ka. Basalt, transitional between tholeiitic and alkalic basalt, erupted at the end of tholeiitic volcanism, but no postshield-alkalic stage volcanism occurred. The summit of the volcano apparently subcided below sea level between 435 and 365 ka. The tholeiitic lavas recovered are compositionally diverse.
Possible solar noble-gas component in Hawaiian basalts
The noble-gas elemental and isotopic composition in the Earth is significantly different from that of the present atmosphere, and provides an important clue to the origin and history of the Earth and its atmosphere. Possible candidates for the noble-gas composition of the primordial Earth include a solar-like component, a planetary-like component (as observed in primitive meteorites) and a component similar in composition to the present atmosphere. In an attempt to identify the contributions of such components, we have measured isotope ratios of helium and neon in fresh basaltic glasses dredged from Loihi seamount and the East Rift Zone of Kilauea 1–3 . We find a systematic enrichment in 20 Ne and 21 Ne relative to 22 Ne, compared with atmospheric neon. The helium and neon isotope signatures observed in our samples can be explained by mixing of solar, present atmospheric, radiogenic and nucleogenic components. These data suggest that the noble-gas isotopic composition of the mantle source of the Hawaiian plume is different from that of the present atmosphere, and that it includes a significant solar-like component. We infer that this component was acquired during the formation of the Earth.
Picritic glasses from Hawaii
Estimates of the MgO content of primary Hawaiian tholeiitic melts range from 8wt% to as high as 25wt% (refs 1, 2). In general, these estimates are derived from analysis of the whole-rock composition of lavas, coupled with the compositions of the most magnesian olivine phenocrysts observed. But the best estimate of magma composition comes from volcanic glass, as it represents the liquid composition at the time of quenching; minimal changes occur during the quenching process. Here we report the discovery of tholeiitic basalt glasses, recovered offshore of Kilauea volcano, that contain up to 15.0 wt% MgO. To our knowledge, these are the most magnesian glasses, and have the highest eruption temperatures ( ∼ 1,316 ° C), yet found. The existence of these picritic (high-MgO) liquids provides constraints on the temperature structure of the upper mantle, magma transport and the material and thermal budgets of the Hawaiian volcanoes. Furthermore, picritic melts are affected little by magma-reservoir processes, and it is therefore relatively straightforward to extrapolate back to the composition of the primary melt and its volatile contents.
Low sulfur content in submarine lavas: An unreliable indicator of subaerial eruption
Low S content (<250 ppm) has been used to identify subaerially erupted Hawaiian and Icelandic lavas. Large differences in S content of submarine-erupted lavas from different tectonic settings indicate that the behavior of S is complex. Variations in S abundance in undegassed, submarine-erupted lavas can result from different source compositions, different percentages of partial melting, and crystal fractionation. Low S concentrations in highly vesicular submarine lavas suggest that partial degassing can occur despite great hydrostatic pressure. These processes need to be evaluated before using S content as an indicator of eruption depth.
Cruise report, Hawaiian GLORIA cruise F12-89-HW
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Geochronology and petrogenesis of MORB from the Juan de Fuca and Gorda ridges by 238U230Th disequilibrium
A highly precise mass spectrometric method of analysis was used to determine 238 U 234 U 230 Th 232 Th in axial and off-axis basalt glasses from Juan de Fuca (JDF) and Gorda ridges. Initial 230 Th activity excesses in the axial samples range from 3 to 38%, but generally lie within a narrow range of 12 to 15%. Secondary alteration effects were evaluated using δ 234 U and appear to be negligible; hence the 230 Th excesses are magmatic in origin. Direct dating of MORB was accomplished by measuring the decrease in excess 230 Th in off-axis samples. 238 U 230 Th ages progressively increase with distance from axis. Uncertainties in age range from 10 to 25 ka for U Th ages of 50 to 200 ka. The full spreading rate based on U Th ages for Endeavour segment of JDF is 5.9 ± 1.2 cm/yr, with asymmetry in spreading between the Pacific ( 4.0 ± 0.6 cm/yr) and JDF ( 1.9 ± 0.6 cm/yr) plates. For northern Gorda ridge, the half spreading rate for the JDF plate is found to be 3.0 ± 0.4 cm/yr. These rates are in agreement with paleomagnetic spreading rates and topographic constraints. This suggests that assumptions used to determine ages, including constancy of initial 230 Th/ 232 Th ratio over time, are generally valid for the areas studied. Samples located near the axis of spreading are typically younger than predicted by these spreading rates, which most likely reflects recent volcanism within a 1–3 km wide zone of crustal accretion. Initial 230 /Th/ 232 Th ratios and 230 Th activity excesses were also used to examine the recent Th/U evolution and extent of melting of mantle sources beneath these ridges. A negative anomaly in 230 Th/ 232 Th for Axial seamount lavas provides the first geochemical evidence of a mantle plume source for Axial seamount and the Cobb-Eickelberg seamount chain and indicates recent depletion of other JDF segment sources. Large 230 Th activity excesses for lavas from northern Gorda ridge and Endeavour segment indicate formation from a lower degree of partial melting than other segments. An inverse correlation between 230 Th excess and 230 Th/ 232 Th for each ridge indicates that these lower degree melts formed from slightly less depleted sources than higher degree melts. Uniformity in 230 Th excess for other segments suggests similarity in processes of melt formation and mixing beneath most of the JDF-Gorda ridge area. The average initial 230 Th/ 232 Th activity ratio of 1.31 for the JDF-Gorda ridge area is in agreement with the predicted value of 1.32 from the Th Sr isotope mantle array.
Pliocene and Pleistocene alkalic flood basalts on the seafloor north of the Hawaiian islands
The North Arch volcanic field is located north of Oahu on the Hawaiian Arch, a 200-m high flexural arch formed by loading of the Hawaiian Islands. These flood basalt flows cover an area of about 25, 000 km 2 ; the nearly flat-lying sheet-like flows extend about 100 km both north and south from the axis of the flexural arch. Samples from 26 locations in the volcanic field range in composition from nephelinite to alkalic basalt. Ages estimated from stratigraphy, thickness of sediment on top of the flows, and thickness of palagonite alteration rinds on the recovered lavas, range from about 0.75–0.9 Ma for the youngest lavas to somewhat older than 2.7 Ma for the oldest lavas. Most of the flow field consists of extensive sheetflows of dense basanite and alkalic basalt. Small hills consisting of pillow basalt and hyaloclastite of mainly nephelinite and alkalic basalt occur within the flow field but were not the source vents for the extensive flows. Many of the vent lavas are highly vesicular, apparently because of degassing of CO 2 . The lavas are geochemically similar to the rejuvenated-stage lavas of the Koloa and Honolulu Volcanics and were generated by partial melting of sources similar to those of the Koloa Volcanics. Prior to eruption, these magmas may have accumulated at or near the base of the lithosphere in a structural trap created by upbowing of the lithosphere.
Composition of Basaltic glasses dredged from seven seamounts offshore Southern California on R/V Farnella cruise F7-87-SC
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Age and petrology of alkalic postshield and rejuvenated-stage lava from Kauai, Hawaii
At the top of the Waimea Canyon Basalt on the island of Kauai, rare flows of alkalic postshield-stage hawaiite and mugearite overlie tholeiitic flows of the shield stage. These postshield-stage flows are 3.92 Ma and provide a younger limit for the age of the tholeiitic shield stage. The younger Koloa Volcanics consist of widespread alkalic rejuvenated-stage flows and vents of alkalic basalt, basanite, nephelinite, and nepheline melilitite that erupted between 3.65 and 0.52 Ma. All the flows older than 1.7 Ma occur in the west-northwestern half of the island and all the flows younger than 1.5 Ma occur in the east-southeastern half. The lithologies have no spatial or chronological pattern. The flows of the Koloa Volcanics are near-primary magmas generated by variable small degrees of partial melting of a compositionally heterogeneous garnet-bearing source that has about two-thirds the concentration of P2O5, rare-earth elements, and Sr of the source of the Honolulu Volcanics on the island of Oahu. The same lithology in the Koloa and Honolulu Volcanics is generated by similar degrees of partial melting of distinct source compositions. The lavas of the Koloa Volcanics can be generated by as little as 3 percent to as much as 17 percent partial melting for nepheline melilitite through alkalic basalt, respectively. Phases that remain in the residue of the Honolulu Volcanics, such as rutile and phlogopite, are exhausted during formation of the Koloa Volcanics at all but the smallest degrees of partial melting. The mantle source for Kauai lava becomes systematically more depleted in 87Sr/86Sr as the volcano evolves from the tholeiitic shield stage to the alkalic postshield stage to the alkalic rejuvenated stage: at the same time, the lavas become systematically more enriched in incompatible trace elements. On a shorter timescale, the lavas of the Koloa Volcanics display the same compositional trends, but at a lower rate of change. The source characteristics of the Koloa Volcanics, considered along with those of the Honolulu Volcanics, support a mixing model in which the source of rejuvenated-stage lava represents large-percent melts of a plume source mixed with small amounts of small-percent melts of a heterogeneous mid-ocean-ridge source. ?? 1988 Springer-Verlag.
Petrology of ultramafic xenoliths from Loihi Seamount, Hawaii
Ultramafic xenoliths were recovered in four alkalic lava flows from Loihi Seamount at depths between 2200 and 1400m. No xenolith bearing flows were sampled near the summit despite a concentrated dredge program. The flows, three of alkalic basalt and one of basanite, contain common olivine megacrysts and small xenoliths of dunite, rarer harzburgite, and a single wehrlite. Olivine megacrysts as large as 8 mm are Fo 84–88 6 and contain magnesiochromite inclusions with 1·1–3·5 wt.% TiO 2 Dunite contains Fo 83 5–88·5 olivine, magnesiochromite with l·5–6·9 wt.% TiO 2 (avg. 3·2 wt.%), and extremely rare chrome-rich diopside. The wehrlite contains euhedral Fo 85 9 olivine and magnesiochromite with 1·9–4·7 wt.% TiO 2 poikilitically enclosed in chrome-rich diopside (Wo 45 4 En 48 0 Fs 6·6 ).Most of the olivine megacrysts, dunite, and the wehrlite are cumulates of Loihi alkalic lavas that accumulated in a magma storage zone located at least 16km below sea level. The rarity of dunite related to tholeiitic magmas supports the interpretation that the alkalic lavas at Loihi generally predate the tholeiitic lavas. The harzburgite xenoliths have cataclastic textures and contain Fo 89 5–92 6 olivine, enstatite (Wo 2 0–2·7 En 90·0–88 7 Fe 8·0–8·6 ), Cr-rich endiopside (Wo 43 4–44 5 En 52 0–50 0 Fs 4 6–4 5 ), and translucent red-brown magnesiochromite. The harzburgite xenoliths, which have 2-pyroxene temperatures of 1066 ± 35°C, originated in the uppermost mantle in a region of high strain rate, probably near the boundary between the mantle and the overlying ocean crust. The presence of upper mantle xenoliths indicates that the magma storage zone is located below the base of the ocean crust within the uppermost mantle.
Shipboard report for Hawaii GLORIA ground-truth cruise F2-88-HW, 25 Feb.-9 March, 1988
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Hawaiian xenolith populations, magma supply rates, and development of magma chambers
Hawaiian volcanoes pass through a sequence of four eruptive stages characterized by distinct lava types, magma supply rates, and xenolith populations. Magma supply rates are low in the earliest and two latest alkalic stages and high in the tholeiitic second stage. Magma storage reservoirs develop at shallow and intermediate depths as the magma supply rate increases during the earliest stage; magma in these reservoirs solidifies as the supply rate declines during the alkalic third stage. These magma storage reservoirs function as hydraulic filters and remove dense xenoliths that the ascending magma has entrained. During the earliest and latest stages, no magma storage zone exists, and mantle xenoliths of lherzolite are carried to the surface in primitive alkalic lava. During the tholeiitic second stage, magma storage reservoirs develop and persist both at the base of the ocean crust and 3-7 km below the caldera; only xenoliths of shallow origin are carried to the surface by differentiated lava. During the alkalic third stage, magma in the shallow subcaldera reservoir solidifies, and crustal xenoliths, including oceanic-crustal rocks, are carried to the surface in lava that fractionates in an intermediate-depth reservoir. Worldwide xenolith populations in tholeiitic and alkalic lava may reflect the presence or absence of subvolcanic magma storage reservoirs. ?? 1987 Springer-Verlag.