Hawaiian Volcanism Research Articles

Overlapping volcanoes: The origin of Hilo Ridge, Hawaii

The submarine Hilo Ridge has been interpreted as a part of Mauna Kea volcano, but is crossed at ∼1100 m depth by a submerged shoreline terrace composed of basalts that are isotopically distinct from those of Mauna Kea and similar to those of Kohala volcano. This terrace evidently is a product of Kohala instead of Mauna Kea. Almost all of Hilo Ridge below the terrace therefore must predate the principal growth of Mauna Kea, which has superficially isolated the ridge from its Kohala source by overlapping its proximal segment. The Mauna Kea section penetrated by the Hawaii Scientific Drilling Project is predicted to be thinner than expected previously, owing to the overlap. Similar overlaps are suspected among other volcanoes and may cause significant changes in the understanding of Hawaiian volcanism.

The dynamical origin of Hawaiian volcanism

We study the dynamics of melting in the Hawaiian plume using a 3D variable-viscosity convection model outfitted with a melting parameterization that permits calculation of the local melting rate and the distribution of buoyant depleted residual material. From a suite of 45 steady-state numerical experiments, we derive complete scaling laws for the total rate of melting M and the height H and width W of the topographic swell as functions of the lithospheric thickness zl and the plume's maximum potential temperature θi, thermal buoyancy flux B, and minimum viscosity ηp. Assuming 1500°C<θi<1600°C, the observed values of M, H and W can only be matched if zl≤89 km, 2200 kg s−1 ≤B≤3500 kg s−1, and ηp≥5×1017 Pas. We study a reference Hawaiian model satisfying these constraints. The depletion anomaly is narrower than the thermal anomaly, and carries 24% of the total (thermal plus depletion) buoyancy flux. Its buoyancy contributes 350 m of the uplift along the swell axis, and reduces the geoid/topography ratio by 16% relative to a model without depletion buoyancy. All the material that melts comes from the hottest central part of the plume, and no direct melting of the asthenosphere or lithosphere occurs. Melting occurs both in a primary melting zone above the plume stem and in a weaker secondary melting zone 300–500 km downstream, separated by an interval where no melting occurs. We propose that the preshield-, shield-, and postshield stages of Hawaiian volcanism are generated by the primary melting zone, and the rejuvenated stage by the secondary melting zone.

The emergence of a Galápagos shield volcano, Roca Redonda

Roca Redonda volcano is a mostly submarine shield volcano that rises nearly 3 km from the adjacent seafloor. Over twenty lava flows and palagonite tuff are exposed in a 60 meter high oblong outcrop above sea level, and several other flows are exposed in the shallow water surrounding the islet. Thick, slightly alkaline picritic flows form the base of the section. Thinner picrites interbedded with sparsely porphyritic alkali-olivine basaltic pahoehoe toes characterize the upper section. The subaerial section probably records the filling of a palagonite tuff cone with younger lavas. Numerous fumaroles that may have a magmatic component are present in the shallow ( MgO > 14%, high-Mg basalts with MgO of about 9%, and low-Mg basalts with MgO of about 6%. The Sr and Nd isotopic ratios of the three lava types are within analytical uncertainty. Olivine compositions indicate that the picrites are basaltic liquids that have accumulated olivine whose composition is in equilibrium with the host basaltic liquid. Apparently, basaltic magmas percolated through dunite and troctolite that had crystallized from slightly older Roca Redonda basaltic magma. Lavas from Roca Redonda have enriched trace element contents and isotopic ratios relative to nearby Wolf volcano, but they are quite similar to lavas from Cerro Azul and Ecuador volcanoes. The common characteristic of these volcanoes is that they lie on the periphery of the archipelago and are in a stage of subaerial growth. This suggests that Galapagos volcanoes may go through a juvenile alkaline stage before a mature tholeiitic stage, analogous to the Loihi stage of Hawaiian volcanism. A low 3He/4He ratio in olivine from one of the picrites indicates a small contribution by the Galapagos mantle plume.

Hawaii bibliographic database

The Hawaii bibliographic database has been created to contain all of the literature, from 1779 to the present, pertinent to the volcanological history of the Hawaiian-Emperor volcanic chain. References are entered in a PC- and Macintosh-compatible EndNote Plus bibliographic database with keywords and abstracts or (if no abstract) with annotations as to content. Keywords emphasize location, discipline, process, identification of new chemical data or age determinations, and type of publication. The database is updated approximately three times a year and is available to upload from an ftp site. The bibliography contained 8460 references at the time this paper was submitted for publication. Use of the database greatly enhances the power and completeness of library searches for anyone interested in Hawaiian volcanism.

Mantle Reservoirs and Mantle Convection: Lessons from the Hawaiian Plume

The Hawaiian plunae has long played a central role in conceptual, theoretical, geophysical and geochemical studies of mantle convection. Over the past 80 million years, the Hawaiian hotspot has been the site of the most voluminous intraplate basaltic volcanism on the Earth's surface, and still provides the strongest evidence to date for the presence of active upwelling in the upper mantle. There are several fundamental observations about Hawaiian volcanism which pertain to mantle convection on regional and global scales. Though geophysical studies are increasingly focused on looking for relative hotspot motions, the Hawaiian plume has remained essentially stationary (-t-100 km) over the past 80 Ma. Distinct structural lineaments ( 'Loa' and 'Kea' trends) along the youngest Hawaiian islands erupt compositionally distinct lavas, though there is a certain amount of overlap. Adjacent active Hawaiian volcanoes, separated by as little as 25 km, erupt compositionally distinct shield lavas, which places some limits on the lateral scale of source heterogeneity (Frey and Rhodes, 1993). Finally, there exist at least three (and possibly fouO compositionally distinct components in Hawaiian lavas, all of which are different in composition from the upper mantle source of MORB. Any model of mantle convection must be able to reproduce the thermal and chemical perturbations which are exemplified by the Hawaiian plume and its volcanic expression.

Unspiked K-Ar dating of young volcanic rocks from Loihi and Pitcairn hot spot seamounts

A geochronological study of volcanically active seamounts from the Pitcairn and Hawaii hot spots successfully utilized the unspiked K-Ar technique to obtain ages for young volcanic rocks. These ages were used to calculate lava production rates for the youthful stage for the Hawaiian volcanic chain. The lavas from Pitcairn seamounts have ages ranging from 3 ± 1 to 344 ± 32 ka. The reliably dated lavas from Loihi are from a 500 m thick section on the east flank of the volcano and they range in age from 5 ± 4 to 102 ± 13 ka. These lavas are all alkalic and are from the preshield stage of volcanism. These ages yield lava accumulation rates that increase from 3.5 mm/a for the dominantly alkalic lower section to 7.8 mm/a for the predominantly tholeiitic upper part of the volcano. These values are consistent with those obtained for other Hawaiian volcanoes. The duration of the transition from tholeiitic to alkalic lava during the preshield stage is about 17 to 40 ka, which is similar to the tholeiitc to alkalic transition during the postshield stage of Hawaiian volcanism. The total duration of the preshield stage of Hawaiian volcanism is estimated to be at least 250,000 years, which is more than twice previous estimates. The overall length of magmatic activity, for a typical Hawaiian volcano is now estimated to be ~ 1.4 Ma.

Volatiles in Alkalic Basalts form the North Arch Volcanic Field, Hawaii: Extensive Degassing of Deep Submarine-erupted Alkalic Series Lavas

The North Arch volcanic field is a submarine suite of alkali basaltic to nephelinitic lavas of the seafloor north of Oahu at water depths of 3900–4380 m. Glasses from these lavas were analyzed for H2O, CO2, Cl, S, Fe3+/∑Fe, and noble gases to investigate the role of volatiles in the generation, evolution, and degassing of these alkalic series lavas. In contrast to the systemic negative correlation between concentrations of SiO2 and nonvolatile incompatible elements (e.g. P2O5), the behavior of the volatile components is much more irregular. Concentrations of H2O in glasses vary by a factor of two ( 0.69–1.42 wt %) and show a poor correlation with melt composition, whereas concentrations of dissolved CO2 in glasses (260–800 p.p.m) increase with increasing alkalinity of the glasses. The H2O2 concentrations in the glasses are in equilibrium with an H2O–CO2 vapor at the depth of eruption (400 bar pressure). Samples collected directly from vent structures are highly vesicular, suggesting that these samples were gas rich upon eruption. Estimated bulk volatile contents of the two most vesicular vent samples are high (1.9±0.1 wt % H2O and 5.4±0.4 CO2) and are interpreted to have formed by closed system degassing. Estimated bulk volatile contents in four other vesicular vent samples are lower 1.3±0.2 wt % H2O and 2.0±0.4 wt % CO2), and these samples are interpreted to have lost some gas during eruption. Glass samples from inflated, flat lava flows are nonvesicular and interpreted to have lost essentially all exsolved gas during eruption and flow. Forward degassing models can predict the observed range in dissolved H2O and CO2 contents, calculated vapor compositions, and vesicularity as a function of SiO2. The models involve open to closed system degassing of an H2O–CO2 vapor phase from melts initially having H2O/P2O5=3 and CO2H2O=1–4 mass. Cl concentrations (400–1360 p.p.m) in glasses correlate with concentrations of nonvolatile, incompatible elements. Concentrations of noble gases measured on bulk glass samples are low compared with mid-oceanic ridge basalt (MORB). The low concentrations result mainly from extensive vapor exsolution from the magma. The helium isotopic ratios for gases released from vesicles are similar to MORB values [6.8–8.5 times the air ratio (RA)], whereas those released from glasses are lower than MORB values as a result of in situ decay of U and Th. The S contents (0.11–0.22 wt %) of most of the alkali olivine basaltic and basanitic glasses are sufficient to saturate the silicate melt with immiscible Fe–S–O liquid at the T and P of eruption and quenching. However, two vesicular samples appear to hae lost some dissolved S owing to eruptive degassing. Magmatic oxygen fugacitites estimated from Fe3+/∑Fe range from ΔFMQ=-0.8 to +0.7, with the nephelinitic glasses being more oxidizing than the less alkalic glasses. We infer that the mantle source region for the North Arch magmas was homogeneous with respect to Fe3+/∑Fe and that melting occurred in the absence of graphite or CH4- rich fluid. The effect of variable partial melting on magmatic oxygen fugacity may be a common feature of Hawaiian volcanism. These complex data pint to a simple result, namely that parental magma compositions can be derived by variable extents of melting of a homogeneous source followed by olivine crystallization and degassing at 400 bar. If the parental liquids are produced by 1.6–9.0% partial melting (±20% relative), then mantle volatile contents are estimated to be 525±75 p.p.m. H2O, 1300±800 p.p.m. CO2 and 30± p.p.m. Cl.

Oxygen isotope constraints on the sources of Hawaiian volcanism

We have measured oxygen isotope ratios in 99 separates of olivine and 14 separates of plagioclase or glass from Hawaiian lavas. These data confirm that the source(s) of some Hawaiian basalts are lower in δ18O than peridotite xenoliths and the source region for mid-ocean ridge basalts (MORB). Our data document correlations between oxygen and radiogenic isotope ratios and consistent differences in δ18O between volcanoes. Low values of δ18O are associated with a ‘depleted’ component that is relatively high in 206Pb/204Pb, low in 3He/4He, and anomalously low in 207Pb/204Pb relative to 206Pb/204Pb. This component is preferentially sampled in lavas from the so-called Kea trend volcanoes (Kilauea, Mauna Kea, Kohala and Haleakala).Low δ18O values in the ‘Kea’ component suggest that it is hydrothermally altered oceanic crust. The similarity of the Kea end member to Pacific MORB in terms of Sr, Nd, and Pb isotope ratios further suggests that this component is assimilated from the local Pacific plate in subcrustal magma chambers. Anomalous 206Pb/204Pb-207Pb/204Pb relationships indicate recent enrichment in U/Pb in this component and further support the hypothesis that this component is young ( < 108 yr) Pacific crust. The isotopic distinctions between Loa and Kea trend volcanoes implies a systematic difference in the magma supply and plumbing systems of volcanoes on these two trends.Samples from Lanai and Koolau have ‘enriched’ radiogenic isotope compositions (radiogenic Sr and non-radiogenic Nd and Pb) and higher δ18O than typical upper mantle values, suggesting the incorporation of recycled sediment and/or oceanic crust in their sources. Other isotopic end members to Hawaiian lavas (e.g., high 3He/4He and post-erosional lavas) have δ18O values within the range typical of the upper mantle.

Isotopic tracing of volcanic source regions from Hawaii: decoupling of gaseous from lithophile magma components

The well established geology and geochemistry of Hawaiian volcanism allows a detailed evaluation of the relationships between geochemically distinct tracers, such as the noble gases and the lithophile elements Sr, Nd and Pb. Four volcanic evolutionary stages show characteristic Sr-Nd-Pb isotopic progressions: early and late stages include depleted melts, whereas the intermediate shields tend to be less depleted, including source components similar to bulk earth values. In contrast, 3He/ 4He ratios gradually decrease from high values during the early stage to MORB-like values for the late stage. This lack of correlation between the lithophile and noble gas records may be accounted for by: (1) a unique ‘Loihi-like’ mantle component for Hawaii, or (2) a systematic offset between the two records. Whereas many studies have preferred the first scenario, we opt for the latter, and suggest that both systems are coupled in the deep mantle, but become decoupled when a gas-rich melt phase separates from the plume. We suggest that incipient CO 2-dominated melts, carrying the noble gases, could separate in the plume flexure, and may buoyantly migrate ahead of the plume, carrying the bulk of its lithophile inventory. These melts permeate the lithosphere, which, upon sufficient heating by the plume, could generate the initial stage alkali basalts and tholeiites. The subsequent formation of the shield stage tholeiites occurs when the main plume, carrying the less depleted lithophile signature, has risen to shallower levels, and commences to melt on a large scale. The melts of this stage show lower 3He/ 4He ratios owing to asthenospheric entrainment by the plume, which has previously lost a major part of its volatile inventory, allowing for dilution of the isotopic signature by MORB-type noble gases. If this model is correct, the less depleted (Sr, Nd and Pb) and less degassed (noble gases) components are from one and the same source, and may provide the best estimate for the isotopic composition of the deep mantle.

The correlation between geomagnetic field reversals, Hawaiian volcanism, and the motion of the Pacific plate

The correlation between geomagnetic field reversals and volcanism is investigated, according to the speculated consequence on volcanoes of the transient electric currents in the geodynamo, through Joule's heating, before and after every reversal event. We evaluate the temporal variation during the last ~ 70 Ma both of the magma emplacement rate Q(t) from the Hawaii hot spot, and of the speed v(t) of the Pacific plate, by means of the observed volumes of islands and seamounts along the Hawaii/Emperor Seamounts chain, and their respective radiometric datings. Results confirm expectations. A justification of the volcanic crises that lead to the generation of the large igneous provinces during the last ~ 250 Ma also emerged. We describe in detail the complex pattern of the timings of the different effects. Joule's power is generally responsible for ~ 75-80% of magmatism, and friction power only for ~ 20-25%; but, on some occasions almost ~ 100% is fuelled by friction alone. The visco-elastic coupling between lithosphere and asthenosphere results ~ 96% viscous, and ~ 4% elastic.

Geochemical and Isotopic Evolution of Loihi Volcano, Hawaii

A 680m thick section from the deeply dissected east flank of Loihi Volcano was sampled using the Pisces V submersible to evaluate the volcano's geochemical evolution. Three types of lavas were recovered: tholeiitic, weakly alkalic and strongly alkalic. The ratio of alkalic to tholeiitic lavas varies systematically with depth, from predominantly alkalic at the base of the section to tholeiitic at the top. Glasses from these rocks have similar ratios of highly incompatible elements and Pb, Sr and Nd isotopes, but distinct ratios of highly to moderately incompatible elements. Partial melting modeling indicates that these tholeiitic and alkalic lavas could be derived by variable degrees of partial melting of a slightly heterogeneous source. Many distinct parental magmas were generated for each rock type during the 100–150 k.y. that the east flank section was formed. Crystal fractionation and olivine accumulation were the dominant processes controlling compositional variation among lavas of the same rock type. Magma mixing features were observed in only a few of the lavas collected. Loihi typifies the preshield stage of Hawaiian volcanism when the volcano drifts closer to the focus of the hotspot. The compositional variation in Loihi's east flank section, which may represent 40% of the volcano's extrusive history, is consistent with the predicted increase in partial melting during this drift. The transition from dominantly alkalic to tholeiitic volcanism on Loihi was fitful but relatively rapid and is now nearly complete. This transition is the opposite of that which occurs during the post-shield stage of Hawaiian volcanism as the volcano migrates away from the hotspot focus. Loihi's tholeiitic lavas overlap in ratios of incompatible trace elements and Pb, Sr and Nd isotopes with lavas from its more active neighbor, Kilauea. The small differences in major element contents between lavas from these adjacent volcanoes can be explained by high-pressure orthopyroxene fractionation of Loihi magmas, which may be a consequence of a low magma-supply rate, or by slightly shallower depths of melt segregation for Kilauea magmas.

Extreme 176Hf/ 177Hf in the sub-oceanic mantle

The results of Hf isotopic analysis of peridotites are presented. Development of a hot-SIMS technique for Hf isotope analysis has made this possible at concentration levels that were previously prohibitively low. 176Hf/ 177Hf ratios in abyssal peridotites and in two xenoliths from the subcontinental lithosphere fall within the range observed for present-day oceanic basalts. 176Hf/ 177Hf ratios in anhydrous spinel lherzolites from Salt Lake Crater, Hawaii, however, range to extremely radiogenic values, although 143Nd/ 144Nd is within the range of present-day MORBs. These high 176Hf/ 177Hf ratios (ε Hf up to 76) are well outside the range of oceanic volcanics and indicate that peridotites such as these cannot have contributed significantly to Hawaiian volcanism. The high 176Hf/ 177Hf, combined with the enriched trace element characteristics of the Salt Lake Crater peridotites may be explained by either metasomatism of a depleted peridotite by a melt which underwent extensive re-equilibration with material similar to the suboceanic lithosphere beneath Hawaii, or by ancient melt depletion (> 1 Ga) and recent enrichment of material stored in the sublithospheric mantle. The good correlation between Hf and Nd isotopes in OIBs indicates that the OIB source is not influenced by the high 176Hf/ 177Hf type mantle identified in the Salt Lake Crater xenoliths. In contrast, the lack of correlation between Hf and Nd isotopes in MORB can be explained by pollution of the MORB reservoir with small amounts of this high-field-strength-element-depleted, high 176Hf/ 177Hf, lherzolitic material.

The open-system geochemical evolution of alkalic cap lavas from Haleakala Crater, Hawaii, USA

Lavas ranging from alkalic basalt to mugearite are exposed in a continuous stratigraphic section in Haleakala Crater on the island of Maui. These lavas define a series of discrete magma batches separated by sharp compositional breaks characterized by upsection increases in incompatible element (e.g., K 2O, Nb, REE, Th, Ba, Rb) contents, Al 2O 3/CaO ratios, and La/Sm ratios and complementary decreases in compatible element (e.g., MgO, Ni, Cr, V, Sc) contents. Within magma batches, there are systematic upsection decreases in incompatible element contents, Al 2O 3/CaO ratios, and La/Sm ratios and systematic increases in compatible element contents. The observed compositional cyclicity can be explained as the result of alternating periods of low and high magma chamber recharge rates. The upsection interbatch compositional breaks represent periods of low or negligible magma chamber recharge, during which eruption is suppressed and the geochemical effects of crystal fractionation dominate those imposed by magma mixing. At the initiation of recharge, the influx of mafic magma into the magma chamber produces an eruption, resulting in partial evacuation of the magma chamber. Following eruption, recharge magma mixes with magma remaining in the magma chamber. Continued recharge and mixing during these eruptive periods cause the compositions of lavas to become more mafic with time. Thus, during a recharge period, the bulk composition of the magma chamber approaches that of the recharge magmas. The most mafic lavas (i.e., the youngest lavas within each magma batch) typically are relatively evolved (Mg# < 48, MgO < 7 wt%) and, therefore, cannot represent primary magmas. Evidence for polybaric fractionation suggests that these lavas represent recharge magmas that have undergone crystal fractionation in a deeper-level reservoir prior to injection into the shallow-level Haleakala magma chamber. The observed fine-scale geochemical cyclicity is superimposed over the larger-scale, systematic changes in isotope ratios and highly incompatible trace element ratios that are attributed to time-dependent changes in the proportions of distinct mantle components in the source of these lavas. These contrasting scales of temporal geochemical variability illustrate how shallow-level magma chamber processes have imposed short time period (≈ 2000 years) compositional controls on magmas whose compositions were also changing over relatively long time periods (≈ 800,000 years) due to source-related effects. The decrease in magma supply rates during the alkalic cap phase of Hawaiian volcanism probably results in increased magma chamber residence times, thus creating the greater magmatic diversity observed. The specifics of the petrologic and geochemical evolution of individual Hawaiian volcanoes during this period differ at least in part because of differences in magma supply rates.

Posterosional volcanism in the Cretaceous part of the Hawaiian Hotspot Trail

Multibeam bathymetry and seismic reflection profiling shows the Cretaceous products of the Hawaiian hotspot to be a ridge of coalesced guyots that prolong the N‐NW trend of the more isolated Paleocene Emperor Seamounts, a 10,000 km2 plateau (Detroit Plateau), where the trail changes strike to NW, and the Obruchev Rise hotspot ridge, which extends to the Kamchatka Trench. The northernmost guyots were submerged and tilted southeast by the load of new shield volcanoes added to the end of the chain, then secondary volcanism built small cones on their summit platforms and in a gap between two guyots. Dredged rock samples and the distribution of the cones indicates that on one guyot these submarine eruptions were in the alkalic postshield stage of Hawaiian volcanism, and at another were probably in the alkalic rejuvenated stage. Seamount‐building eruptions at Detroit Plateau produced lavas (nepheline melilitites) that belong geochemically to the alkalic rejuvenated stage, and are very similar to Pleistocene lavas in the Hawaiian Islands. However, these eruptions postdated passage off the hotspot plume by a much longer time than the 0.5–2.5 m.y. observed in the Hawaiian Islands, and were probably initiated by different tectonic processes.

Evolution of Hawaiian basalts: a hotspot melting model

Melt generation and extraction along the Hawaiian volcanic chain should be largely controlled by the thermal structure of the Hawaiian swell and the heat source underneath it. We simulate numerically the time- and space-dependent evolution of Hawaiian volcanism in the framework of thermal evolution of the Hawaiian swell, constrained by residual topography, geoid anomalies, and anomalous heat flow along the Hawaiian volcanic chain. The transient heat transfer problem with melting relationships and variable boundary conditions is solved in cylindrical coordinates using a finite difference method. The model requires the lithosphere to be thinned mechanically by mantle plume flow. Melting starts quickly near the base of the plate when the hotspot is encountered. Thermal perturbation and partial melting are largely concentrated in the region where the original lithosphere is thinned and replaced by the mantle flow. The pre-shield Loihi alkalic and tholeiitic basalts are from similar sources, which are a mixture of at least three mantle components: the mantle plume, asthenosphere, and the lower lithosphere. The degree of partial melting averages 10–20%, with a peak value of 30% near the plume center. As a result of continuous compaction, melts are extracted from an active partial melting zone of about 10–20 km thickness, which moves upwards and laterally as the heating and compaction proceed. The rate of melt extraction from the swell increases rapidly to a maximum value of ∼ 1 × 10 5 km 3/m.y. over the center of the heat source, corresponding to eruption of large amounts of tholeiitic lavas during the shield-building stage. This volume rate is adequate to account for the observed thickness of the Hawaiian volcanic ridge. Melts from direct partial melting of the mantle plume at depth may be important or even dominant at this stage, although the amount is uncertain. At the waning stage, mixing of melts from the mantle flow pattern with those from low-degree partial melting of the lithosphere may produce postshield alkalic basalts. After the plate moves off the heat source, continuous conductive heating can cause very low degree partial melting (less than 1%) of the lithosphere at shallow depths for about one million years. This process may be responsible for producing post-erosional alkalic basalts. The extraction time for removing such small amount of melts is about 0.4–2 m.y., similar to the time gap between the eruption of post-erosional alkalic lavas and the shield-building stage. Our results show that multi-stage Hawaiian volcanism and the general geochemical characteristics of Hawaiian basalts can be explained by a model of plume-plate interaction.

Melt Generation by Plumes: A Study of Hawaiian Volcanism

Melt Generation by Plumes: A Study of Hawaiian Volcanism

Paleomagnetic evidence for Cretaceous age of two volcanoes on the south flank of the Island of Hawaii

Apuupuu and Dana seamounts are located on the south flank of the island of Hawaii, near the active submarine volcano, Loihi Though previous work suggests that they are older, inactive volcanoes, their ages and relationship to Hawaiian volcanism are uncertain. We make age estimates for these two seamounts by comparing paleomagnetic poles, derived using a magnetic inversion technique, to the Pacific apparent polar wander path. The paleopoles of Apuupuu and Dana seamounts are located at 65.8°N, 9.2°E and 66.7°N, 358.7°E, respectively. Both poles are insignificantly different and located on the Late Cretaceous part of the polar wander path, between the 82 and 72 Ma mean poles, suggesting that the seamounts formed contemporaneously long before their part of the Pacific plate drifted over the Hawaiian hot spot.

Cumulate Xenolith in Oahu, Hawaii: Implications for Deep Magma Chambers and Hawaiian Volcanism

The maximum depth at which large (>1000 km(3)) terrestrial mafic magma chambers can form has generally been thought to be the Moho, which occurs at a mean depth of about 35 kilometers beneath the continents and 8 kilometers beneath ocean basins. However, the presence of layers of cumulus magnesium-rich spinel and olivine and intercumulus garnet in an unusual mantle xenolith from Oahu, Hawaii, suggests that this rock is a fragment of a large magma chamber that formed at a depth of about 90 kilometers; Hawaiian shield-building magmas may pond and fractionate in such magma chambers before continuing their ascent. This depth is at or near the base of the 90-million-year-old lithosphere beneath Oahu; thus, rejuvenated stage alkalic magmas containing mantle xenoliths evidently also originate below the lithosphere.

Book Review

Book Review Get access Observations and Interpretation of Hawaiian Volcanism and Seismicity, 1779–1955: An Annotated Bibliography and Subject Index by T. L. Wright and T. J. Takahashi. University of Hawaii Press, Honolulu. 1989. $30.00, cloth. L. Wilson L. Wilson Search for other works by this author on: Oxford Academic Google Scholar Journal of Petrology, Volume 31, Issue 3, June 1990, Page 779, https://doi.org/10.1093/petrology/31.3.779 Published: 01 June 1990

Observations and Interpretation of Hawaiian Volcanism and Seismicity 1779–1955

Active volcanos and their associated earthquakes are by far the most dramatic elements of Hawaii's natural history heritage. Indeed, the islands owe their very existence to these forces of nature, so it is not surprising that a host of scientists, journalists, and an even wider variety of citizen observers have, over the years, created a rich and diverse written record of their findings. This volume is the result of an exhaustive effort to gather and distill information from all available references on volcanism and seismicity for the period 1779–1955, a task of enormous proportions.