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D.A. Clague

Publications and source records attributed to D.A. Clague.

At least 37 records · Page 2Linked to original sources
USGS1991

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.

Hawaii↗
USGS1991

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.

Hawaii↗
USGS1991

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.

Earth and Planetary Science Letters↗
USGS1990

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.

Hawaii↗
USGS1988

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.

Journal of Petrology↗
USGS1987

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.

Bulletin of Volcanology↗
USGS1986

Carbon isotope systematics of a mantle "hotspot": A comparison of Loihi Seamount and MORB glasses

The carbon isotope geochemistry of glasses from Loihi Seamount has been compared with that of MORB glasses. Stepped heating shows two carbon components in both sample suites: (1) isotopically light carbon ( avg. δ 13 C = −26.3‰ ) released < 600°C, ascribed to surficial contamination, and (2) isotopically heavy carbon released > 600°C, regarded as indigenous. The high-temperature component in MORB samples varied from 52 to 169 ppm C, average δ 13 C = −6.6‰ , consistent with previous studies (overall MORD average δ 13 C = −6.4 ± 0.9‰ ), and new results for Indian Ocean glasses are similar to Atlantic and Pacific Ocean samples. Carbon release profiles produced by stepped heating may be typical of locality, but there are no significant differences in δ 13 C values between MORB samples from different areas. Lower yields (17–110 ppm C) correlated with depth in the Loihi samples suggest that they are partially degassed. This degassing has not affected δ 13 C values significantly (avg. −5.8‰). Loihi tholeiites have higher δ 13 C (avg. −5.6‰) than the alkali basalts (avg. −7.1‰). Carbon abundances correlate well with He concentration data. Comparison of the δ 13 C values with trace element and He, Sr, Nd, and Pb isotope data from the literature suggests that the Loihi samples with highest δ 13 C have high 3 He/ 4 He and possibly the least depleted 143 Nd/ 144 Nd and 87 Sr/ 86 Sr. The carbon isotope data are consistent with previous models for Loihi involving several mantle sources, lithospheric contamination, and mixing. The slightly higher δ 13 C of Loihi tholeiites suggests that the undegassed “plume” component manifested by high 3 He/ 4 He values might have δ 13 C about 1‰ higher than the MORB average.

Earth and Planetary Science Letters↗
USGS1985

The age and origin of felsic intrusions of the Thetford Mines ophiolite, Quebec

The Thetford Mines ophiolite in southern Quebec was obducted in Early Ordovician time during the closing of the proto-Atlantic. The tectonized peridotite lower unit of the ophiolite is intruded by felsic dikes and pods including isolated lenses of massive rodingite, small bodies of strongly deformed diorite, and younger, less deformed quartz monzonite. These intrusions are found only near the base of the ophiolite, do not intrude the surrounding country rock, and are rootless; for these reasons they are considered to have been emplaced in the ophiolite before it reached its present location.The younger group of intrusions consists of biotite–muscovite quartz monzonite and leuco–quartz monzonite. Analyzed samples have high K 2 O contents, high (K 2 O × 100)/(Na 2 O + K 2 O) ratios, and high initial strontium ratios (0.7171–0.7179), indicating that the magma source region was continental and that these felsic rocks formed by partial melting of continental sediments. Whole-rock and mineral isochron ages suggest that the felsic intrusions are about 456 ± 4 Ma old and that they were metamorphosed about 418 ± 7 Ma ago.The detachment of the ophiolite occurred about 491 ± 3 Ma ago and is recorded by the age of the metamorphic aureole beneath the ophiolite. The felsic dikes were intruded some 35 Ma years later during the Taconic Orogeny. The lengthy time between detachment and final nappe emplacement recorded by the felsic dikes may be a requirement for the formation of abundant asbestiform chrysotile.

Quebec↗
USGS1984

Geochemistry of tholeiitic and alkalic lavas from the Koolau Range, Oahu, Hawaii: Implications for Hawaiian volcanism

Lavas of the post-erosional, alkalic Honolulu Volcanics have significantly lower 87 Sr/ 86 Sr and higher 143 Nd/ 144 Nd than the older and underlying Koolau tholeiites which form the Koolau shield of eastern Oahu, Hawaii. Despite significant compositional variation within lavas forming the Honolulu Volcanics, these lavas are isotopically (Sr, Nd, Pb) very similar which contrasts with the isotopic heterogeneity of the Koolau tholeiites. Among Hawaiian tholeiitic suites, the Koolau lavas are geochemically distinct because of their lower iron contents and Sr and Nd isotopic ratios which range to bulk earth values. These geochemical data preclude simple models such as derivation of the Honolulu Volcanics and Koolau tholeiites from a common source by different degrees of melting or by mixing of two geochemically distinct sources. There may be no genetic relationship between the origin and evolution of these two lava suites; however, the trend shown by Koolau Range lavas of increasing 143 Nd/ 144 Nd and decreasing 87 Sr/ 86 Sr with decreasing eruption age and increasing alkalinity also occurs at Haleakala, East Molokai and Kauai volcanoes. A complex mixing model proposed for Haleakala lavas can account for the variations in Sr and Nd isotopic ratios and incompatible element abundances found in lavas from the Koolau Range. This model may reflect mixing and melting processes occurring during ascent of relatively enriched mantle through relatively depleted MORB-related lithosphere. Although two isotopically distinct components may be sufficient to explain Sr and Nd isotopic variations at individual Hawaiian volcanoes, more than two isotopically distinct materials are required to explain variations of Sr, Nd and Pb isotopic ratios in all Hawaiian lavas.

Hawaii↗
USGS1984

Mineralogy and chemistry of massive sulfide deposits from the Juan de Fuca Ridge

Six hydrothermal vent sites and associated benthic communities were located in the axial valley of the southern Juan de Fuca Ridge using transponder-navigated bottom photography. The hydrothermal deposits form ledges and shallow mounds within a central zone characterized by a linear bathymetric depression and numerous collapse features. The flat valley floor adjacent to the central zone consists of ferrobasalt lobate flows and sheet flows; sediment cover is minimal. Vent sites are characterized by concentrations of tube worms, clams, benthic siphonophores, and several unidentified fauna. Two types of massive sulfide were dredged from one of the vent sites. Type A samples are angular slabs of dark gray Zn-rich sulfide with interlayers and a thin, partly oxidized crust of Fe sulfide. These layered sulfide aggregates appear to be fragments of a sulfide wall enclosing an active hydrothermal vent. The outer sulfide wall is composed mainly of colloform Fe sulfide and Fe-poor sphalerite deposited under lower-temperature conditions whereby sea water and hydrothermal fluid mix above the discharge point. With continued sulfide deposition, the wall inhibits mixing of sea water and hydrothermal fluid. Inside the wall, the intensifying hydrothermal system deposits a higher-temperature assemblage of granular Fe-rich sphalerite, wurtzite, pyrite, and minor Cu-Fe sulfide. The zonation in wurtzite from Fe-rich cores to Fe-poor rims may result from a late-stage cooling of the hydrothermal fluid and(or) a change in fluid chemistry. The sulfide wall grows outward where a rupture in it permits the escape of high-temperature fluid and then deposition of a secondary shell over the breakthrough point. As temperature increases, earlier-formed minerals dissolve, and Zn, Fe, and Pb migrate toward the outer sulfide wall. Tube worms flourished in the outer wall of type A samples, and abandoned tube structures served as conduits for the late-stage hydrothermal fluids. Type B sulfide samples are subrounded, spongy-textured fragments composed almost entirely of dendritic aggregates of pale, Fe-poor colloform sphalerite and opaline silica. This type of sulfide is deposited in open space by moderate- to low-temperature fluid discharging at a slow but variable rate; the fluid becomes increasingly oxidizing, resulting in late-stage deposition of hematite, barite, and sulfur. Type B samples show little evidence of burrowing animals; this type of sulfide may be deposited in settings peripheral to sites of focused discharge.

Geological Society of America Bulletin↗
USGS1983

Geochemistry of diverse basalt types from Loihi Seamount, Hawaii: Petrogenetic implications

The wide variety of basalt types, tholeiitic to basanite, dredged from Loihi Seamount have minor and trace element abundances that are characteristic of subaerial Hawaiian basalts, thereby confirming that Loihi Seamount is a manifestation of the Hawaiian “hot spot”. Within the Loihi sample suite there are well-defined positive correlations among abundances of highly incompatible elements (P, K, Rb, Ba, Nb, light REE and Ta) and moderately incompatible elements (Sr, Ti, Zr and Hf) and between MgO, Ni and Cr. However, within the Loihi suite abundance ratios of geochemically similar elements (Zr/Hf, Nb/Ta and La/Ce) vary by factors of 1.2–1.5 and abundance ratios of highly incompatible elements such as P/Ce, P/Th, K/Rb, Ba/Th and La/Nb vary by factors of 1.2–2.5. These abundance ratios are not readily changed by different degrees of fractionation and melting. Therefore, we conclude that these samples are not genetically related by different degrees of melting of a compositionally homogeneous source.

Hawaii↗
USGS1983

Noble gas systematics for coexisting glass and olivine crystals in basalts and dunite xenoliths from Loihi Seamount

Noble gas isotopes including 3 He/ 4 He, 40 Ar/ 36 Ar and Xe isotope ratios were determined for coexisting glass and olivine crystals in tholeiitic and alkalic basalts and dunite xenoliths from Loihi Seamount. Glass and coexisting olivine crystals have similar 3 He/ 4 He ratios (2.8–3.4) × 10 −5 , 20 to 24 times the atmospheric ratio ( R A ), but different 40 Ar/ 36 Ar ratios (400–1000). Based on the results of noble gas isotope ratios and microscopic observation, some olivine crystals are xenocrysts. We conclude that He is equilibrated between glass and olivine xenocrysts, but Ar is not. The apparent high 3 He/ 4 He ratio (3 × 10 −5 ; = 21 R A ) coupled with a relatively high 40 Ar/ 36 Ar ratio (4200) for dunite xenoliths (KK 17-5) may be explained by equilibration of He between MORB-type cumulates and the host magma. Except for the dunite xenoliths, noble gas data for these Loihi samples are compatible with a model in which samples from hot spot areas may be explained by mixing between P (plume)-type and M (MORB)-type components with the addition of A (atmosphere)-type component. Excess 129 Xe has not been observed due to apparent large mass fractionation among Xe isotopes.

Earth and Planetary Science Letters↗