Alkalic Lavas Research Articles

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.

The tholeiite to alkalic basalt transition at Haleakala Volcano, Maui, Hawaii

Previous studies of alkalic lavas erupted during the waning growth stages (<0.9 Ma to present) of Haleakala volcano identified systematic temporal changes in isotopic and incompatible element abundance ratios. These geochemical trends reflect a mantle mixing process with a systematic change in the proportions of mixing components. We studied lavas from a 250-m-thick stratigraphic sequence in Honomanu Gulch that includes the oldest (∼1.1 Ma) subaerial basalts exposed at Haleakaka. The lower 200 m of section is intercalated tholeiitic and alkalic basalt with similar isotopic (Sr, Nd, Pb) and incompatible element abundance ratios (e.g., Nb/La, La/Ce, La/Sr, Hf/Sm, Ti/Eu). These lava compositions are consistent with derivation of alkalic and tholeiitic basalt by partial melting of a compositionally homogeneous, clinopyroxene-rich, garnet lherzolite source. The intercalated tholeiitic and alkalic Honomanu lavas may reflect a process which tapped melts generated in different portions of a rising plume, and we infer that the tholeiitic lavas reflect a melting range of ∼10% to 15%, while the intercalated alkalic lavas reflect a range of ∼6.5% to 8% melting. However, within the uppermost 50 m of section. 87Sr/86Sr decreases from 0.70371 to 0.70328 as eruption age decreased from ∼0.97 Ma to 0.78 Ma. We infer that as lava compositions changed from intercalated tholeiitic and alkalic lavas to only alkalic lavas at ∼0.93 Ma, the mixing proportions of source components changed with a MORB-related mantle component becoming increasingly important as eruption age decreased.

New evidence for crustal accretion in the outer Mariana fore arc: Cretaceous radiolarian cherts and mid-ocean ridge basalt-like lavas

New age determinations on radiolarian cherts, foraminifers, and volcanic rocks document the presence of allochthonous fragments of Cretaceous oceanic plate, suggesting accreted terrane, in the outer Mariana fore arc, more than 50 km from the trench. Three dredges, from 3km 2 area along a steep scarp, recovered a diverse assemblage of rocks representing an ophiolite suite (chert, mafic and intermediate lavas and intrusive rocks). Trace element patterns of the lavas suggest at least three tectonic associations (island arc, ocean island, and oceanic plate). The cherts contain two deep-water assemblages of radiolaria of middle to late Valan-ginian (131-138 Ma) and Albian (97-112 Ma) age. Foraminifers recovered with the chert are Aptian to Albian in age. The lavas record a wide range of K-Ar ages, 85 Ma for a metabasalt with trace-element signatures of mid-ocean ridge basalt, 71 Ma for a highly metamorphosed alkalic basalt, and 39 Ma for a fresh glassy boninite. These ages imply multiple volcanic events and at least two tectonic settings for magma genesis. The cherts and metabasalts are too old to have formed in situ or to be part of trapped West Philippine Basin crust. The mix of old oceanic plate with younger are rocks requires complex tectonic relations. We suggest that one or more fragments of Cretaceous oceanic plate (chert, mid-ocean ridge basalt, and alkalic lavas) were accreted to the Mariana fore arc and have been extensively faulted and probably intruded by arc lava (island-arc tholeiite and boninite).

Chemical constraints on the petrogenesis of mildly alkaline lavas from Vestmannaeyjar, Iceland: the Eldfell (1973) and Surtsey (1963?1967) eruptions

The Vestmannaeyjar archipelago is composed of alkalic lavas erupted at the southern end of the active, southward propagating, Eastern Volcanic Zone. Recent eruptions include the most primitive (Surtsey) and most evolved (Eldfell) compositions found in this area. We studied time-stratigraphic sample suites from both eruptions to characterize the magmatic environment of Vestmannacyjar. All samples are nearly homogeneous in radiogenic isotopic ratios (87Sr/86Sr 0.70304 to 0.70327;143Nd/144Nd 0.51301 to 0.50307;206Pb/204Pb 18.96 to 19.18;207Pb/204Pb 15.50 to 15.53;208Pb/204Pb 38.47 to 38.76; KH Park and A Zindler, in preparation). Compositional trends of lavas from the two eruptions are not consistent with fractionation in a near-surface environment, but indicate rather moderate pressure evolution of small magma batches. At Eldfell, mugearite lavas can be modeled by 30% closed-system fractional crystallization of olivine+plagioclase+clinopyroxene+Fe−Ti oxides from parental hawaiite. The phase proportions are consistent with an experimentally determined moderate pressure (8 kbar) cotectic in mildly alkaline systems (Mahood and Baker 1986). Compositional variations of Surtsey lavas can be modeled by crystallization of clinopyroxene+olivine+plagioclase+minor Fe−Ti oxides. The presence of sodic plagioclase megacrysts and clinopyroxene with ∼8 wt% Al2O3 in xenoliths from Surtsey lavas are consistent with a moderate pressure fractionation event. Based on major-element and REE data the most primitive Surtsey lavas formed by small degrees of melting of a lherzolite source. The alkaline nature of Vestmannaeyjar lavas is not the result of assimilation of lower crustal melts (cf. Oskarsson et al. 1985; Steinthorsson et al. 1985).

High and low pressure phase equilibria of a mildly alkalic lava from the 1965 Surtsey eruption: Experimental results

Melting experiments have been performed on a primitive, mildly alkalic glassy lava (10 wt.% MgO) from the 1965 eruption of the Surtsey volcano located at the tip of the south-eastern propagating rift zone of Iceland. At atmospheric pressure, approximately on the FMQ oxygen buffer, olivine (Fo 81) crystallizes from 1240°C, followed by plagioclase (An 70) from 1180°C and augite from 1140°C. The experimental glasses coexisting with olivine, plagioclase and augite are ferrobasaltic enriched in FeO (13.6–14.2 wt.%) and TiO 2 (4.0–4.4 wt.%). In high pressure, piston-cylinder, graphite-controlled runs, olivine occurs as the liquidus phase until 14 kbar, above which augite is the liquidus phase. Low-Ca pyroxene is not a liquidus phase at any pressure. The high pressure liquids are, relative to the one atmosphere liquids, significantly enriched in Al 2O 3 and Na 2O and depleted in CaO as a result of changes in the crystallizing assemblages. Furthermore, liquidus augite is dominantly subcalcic and shows significant enrichment in Al and depletion in Ti. Subliquidus plagioclase is enriched in sodium relative to low pressure phase compositions. Evaluated in normative projections, contrasting liquid lines of descent are revealed as a function of pressure. At one atmosphere, the multisaturated liquids are located close to the thermal divide defined by the plane olivine-plagioclase-augite, but appear, with advanced degrees of crystallization, to be moving away from the thermal divide toward normative quartz. The augites crystallizing in the one atmosphere experiments are calcic and slightly nepheline normative. In the 10 and 12.5 kbar experiments, the augites become subcalcic and dominantly hypersthene normative. Because of this shift in augite compositions, transitional basaltic liquids may at high pressure evolve from the tholeiitic side of the olivine-plagioclase-diopside normative divide onto the alkalic side. With increasing pressure above 15 kbar, the liquidus augite compositions move back toward the olivine-plagioclase-diopside normative divide.

High and low pressure phase equilibria of a mildly alkalic lava from the 1965 Surtsey eruption: Implications for the evolution of mildly alkalic and transitional basalts in the south-eastern propagating rift zone of Iceland.

The south-eastern propagating rift zone of Iceland shows a progression from tholeiitic, to transitional, and mildly alkalic basalts going toward the front of the propagator. A petrogenetic model has been formulated based on low and high pressure melting experiments. The evolution of the magmas behind the front of the propagating rift is dominated by near surface processes (e.g., Katla and Hekla volcanic systems). Compared with the one atmosphere liquid line of descent, the Vestmannaeyjar lavas, erupted at the front of the propagating rift, have systematically higher Al 2O 3 and Na 2O contents consistent with the experimentally determined effects of high pressure, Labradoritic plagioclase megacrysts, which occur in the early phase of the Surtsey eruption at the front of the propagator, are consistent with the predicted effect of high pressure on plagioclase composition. On the other hand, augites similar to those of the high pressure experiments are unknown among the phenocryst and xenolith assemblages of the Vestmannaeyjar lavas (and other Icelandic lavas). Petrographic evidence points toward a high water content in the evolved lavas of the Vestmannaeyjar. A relatively high water activity and high pressure in the magma chambers at the front of the propagator could have caused a significant suppression of the liquids temperature, in particular for plagioclase. Seismic and magnetotelluric evidence suggest that magma chambers behind the propagating front occur at the depth equivalent to 2–3 kbar of pressure. At the front, magma chambers have been located by geophysical evidence at significantly greater depths equivalent to 3–8 kbar. The lavas erupted at the front of the propagator are located to the alkalic side of the thermal divide and, therefore, can be expected to evolve toward nepheline saturation under slightly hydrous conditions. The most evolved of these lavas are of ferrobasaltic compositions and may be saturated with augite. The lavas erupted behind the front are located to the transitional side of the divide and evolve toward quartz saturation under essentially anhydrous conditions. In contrast to the Vestmannaeyjar lavas, the lavas behind the propagator often contain augite as a phenocryst. It is concluded that the chemical variation observed along the south-eastern propagating rift of Iceland is an effect of primary chemical features and that water plays a significant role on the liquid lines of descent at the front of the propagator.

Isotopic characteristics of Hannuoba basalts, eastern China: Implications for their petrogenesis and the composition of subcontinental mantle

Alkalic and tholeiitic basalts from the Hannuoba region of eastern China have 87 Sr 86 Sr and 143 Nd 144 Nd ranging from the prevalent mantle (PREMA) field to inferred bulk Earth ratios. Ratios of 206 Pb 204 Pb range from 17.10 to 17.94 and all samples have 207 Pb 204 Pb and 208 Pb 204 Pb ratios significantly above the Northern Hemisphere reference line (NHRL). Although the oldest Hannuoba lavas are alkalic basalts, alkalic and tholeiitic lavas are intercalated, and they are isotopically distinct. Relative to the alkalic lavas, tholeiitic lavas have higher 87Sr 86 Sr , lower 143 Nd 144 Nd and less radiogenic Pb isotope ratios. The isotopic ratios and incompatible-element trends defined by all Hannuoba lavas are consistent with mixing of isotopically and compositionally distinct components. We infer that the alkalic basalts were generated by small degrees of melting of an asthenospheric source, similar to that required for some oceanic basalts. However, the tholeiitic basalts contain an enriched mantle component, similar to EMI in the oceanic mantle, which may have resided in the upwelling asthenosphere or subcontinental lithospheric mantle. Mixing between these mantle components may have occurred during the rifting event that caused extension in northeast China ∼ 40 Ma ago. Specifically, we propose that melting within the upwelling asthenospheric created the Hannuoba alkalic lavas whereas the dominantly younger tholeiitic lavas resulted from partial melting of continental lithosphere that was heated by the ascending asthenosphere. Similar models have been proposed for continental basalts erupted in the western U.S.A. and British Tertiary Province.

Evolution of Mauna Kea Volcano, Hawaii: Petrologic and geochemical constraints on postshield volcanism

All subaerial lavas at Mauna Kea Volcano, Hawaii, belong to the postshield stage of volcano construction. This stage formed as the magma supply rate from the mantle decreased. It can be divided into two substages: basaltic (∼240–70 ka) and hawaiitic (∼66–4 ka). The basaltic substage (Hamakua Volcanics) contains a diverse array of lava types including picrites, ankaramites, alkalic and tholeiitic basalt, and high Fe‐Ti basalt. In contrast, the hawaiitic substage (Laupahoehoe Volcanics) contains only evolved alkalic lavas, hawaiite, and mugearite; basalts are absent. Sr and Nd isotopic ratios for lavas from the two substages are similar, but there is a distinct compositional gap between the substages. Lavas of the hawaiitic substage can not be related to the older basalts by shallow pressure fractionation, but they may be related to these basalts by fractionation at moderate pressures of a clinopyroxene‐dominated assemblage. We conclude that the petrogenetic processes forming the postshield lavas at Mauna Kea and other Hawaiian volcanoes reflect movement of the volcano away from the hotspot. Specifically, we postulate the following sequence of events for postshield volcanism at Mauna Kea: (1) As the magma supply rate from the mantle decreased, major changes in volcanic plumbing occurred. The shallow magma chamber present during shield construction cooled and crystallized, and the fractures enabling magma ascent to the magma chamber closed. (2) Therefore subsequent basaltic magma ascending from the mantle stagnated within the lower crust, or perhaps at the crust‐mantle boundary. Eruptions of basaltic magma ceased. (3) Continued volcanism was inhibited until basaltic magma in the lower crust cooled sufficiently to create relatively low‐density, residual hawaiitic melts. Minor assimilation of MORB‐related wall rocks, reflected by a trend toward lower 206Pb/204Pb in evolved postshield lavas, may have occurred at this time. A compositional gap developed because magma ascent was not possible until a low‐density hawaiitic melt could escape from a largely crystalline mush. Eruption of this melt created aphyric hawaiite and mugearite lavas which incorporated cumulate gabbro, wherlite, and dunite xenoliths during ascent.

Evolution of alkalic lavas at Haleakala Volcano, east Maui, Hawaii

The postshield and posterosional stages of Haleakala Volcano contain intercalated alkalic basalt and evolved alkalic lavas. Isotopic and incompatible element abundance ratios in the Haleakala postshield basalts changed systematically with time, providing evidence for significant temporal changes in the mantle components contributing to the magmatic sources. Specifically, a depleted, i.e. low87Sr/86Sr and high143Nd/144Nd, mantle component is more abundant in younger lavas. However, as magma-production rates decreased during the postshield and posterosional stages, basaltic melts in magma reservoirs cooled and fractionated, leading to evolved residual melts such as hawaiite. Because primary basalt compositions changed with time, the evolved Haleakala lavas formed from a range of parental compositions. However, basalts and evolved lavas of similar age and isotopic ratios (Sr and Nd) have major and trace element contents that are consistent with a crystal-fractionation model. Although alkalic basalt and hawaiite are the dominant lavas of the postshield stages of both Haleakala and Mauna Kea volcanoes, there are important differences between their lavas. For example, compositional differences between the hawaiite suites at Haleakala and Mauna Kea indicate that, on average, the evolved lavas at Haleakala formed at lower pressures. Also, at Haleakala basalts are intercalated with hawaiites, whereas at Mauna Kea basalts and hawaiites are separated by a sharp boundary. These differences probably reflect a higher magma supply rate to the Haleakala volcano.

Mahukona: The missing Hawaiian volcano

Research Article| November 01, 1990 Mahukona: The missing Hawaiian volcano Michael O. Garcia; Michael O. Garcia 1Department of Geology and Geophysics, University of Hawaii, Honolulu, Hawaii 96822 Search for other works by this author on: GSW Google Scholar Mark D. Kurz; Mark D. Kurz 2Chemistry Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar David W. Muenow David W. Muenow 3Chemistry Department and Hawaii Institute of Geophysics, University of Hawaii, Honolulu, Hawaii 96822 Search for other works by this author on: GSW Google Scholar Author and Article Information Michael O. Garcia 1Department of Geology and Geophysics, University of Hawaii, Honolulu, Hawaii 96822 Mark D. Kurz 2Chemistry Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 David W. Muenow 3Chemistry Department and Hawaii Institute of Geophysics, University of Hawaii, Honolulu, Hawaii 96822 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1990) 18 (11): 1111–1114. https://doi.org/10.1130/0091-7613(1990)018<1111:MTMHV>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Michael O. Garcia, Mark D. Kurz, David W. Muenow; Mahukona: The missing Hawaiian volcano. Geology 1990;; 18 (11): 1111–1114. doi: https://doi.org/10.1130/0091-7613(1990)018<1111:MTMHV>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract New bathymetric and geochemical data indicate that a seamount west of the island of Hawaii, Mahukona, is a Hawaiian shield volcano. Mahukona has weakly alkalic lavas that are geochemically distinct. They have high 3He/4He ratios (12-21 times atmosphere), and high H2O and Cl contents, which are indicative of the early stage of development of Hawaiian volcanoes. The He and Sr isotopic values for Mahukona lavas are intermediate between those for lavas from Loihi and Mauna Loa volcanoes and may be indicative of a temporal evolution of Hawaiian magmas. Mahukona volcano became extinct at about 500 ka, perhaps before reaching sea level. It fdls the previously assumed gap in the parallel chains of volcanoes forming the southern segment of the Hawaiian hotspot chain. The paired sequence of volcanoes was probably caused by the bifurcation of the Hawaiian mantle plume during its ascent, creating two primary areas of melting 30 to 40 km apart that have persisted for at least the past 4 m.y. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geological and petrologic evolution of seamounts near the EPR based on submersible and camera study

Observations from 17 ALVIN dives and 14 ANGUS runs plus laboratory study of basalt samples collected with ALVIN help to constrain the morphologic, volcanic and petrologic evolution of four seamounts near the East Pacific Rise (EPR). Comparison among the four volcanoes provides evidence for a general pattern of near-EPR seamount evolution and shows the importance of sedimentation, mass wasting, hydrothermal activity and other geologic processes that occur on submerged oceanic volcanoes. Seamount 5, closest to the EPR (1.0 Ma) is the youngest seamount and may still be active. Its summit is covered by fresh lavas, recent faults and hydrothermal deposits. Seamount D is on crust 1.55 Ma and is inactive; like seamount 5, it has a breached caldera and is composed exclusively of N-MORB. Seamounts 5 and D represent the last stages of growth of typical N-MORB-only seamounts near the EPR axis. Seamounts 6 and 7 have bumpy, flattish summits composed of transitional and alkalic lavas. These lavas probably represent caldera fillings and caps overlying an edifice composed of N-MORB. Evolution from N-MORB-only cratered edifices to the alkalic stage does not occur on all near-EPR seamounts and may be favored by location on structures with relative-motion-parallel orientation.

Petrology and age of alkalic lava from the Ratak Chain of the Marshall Islands

Volcanic rock dredged from the flanks of four volcanic edifices in the Ratak chain of the Marshall Islands consist of alkalic lava that erupted above sea level or in shallow water. Compositions of recovered samples are predominantly differentiated alkalic basalt and hawaiite but include strongly alkalic melilitite. Whole rock 40Ar/39Ar total fusion and incremental heating ages of 87.3±0.6 Ma and 82.2±1.6 Ma determined for samples from Erikub Seamount and Ratak Guyot, respectively, are within the range predicted by plate rotation models but show no age progression consistent with a simple hot spot model. Whole rock major element, and mineral chemistry are similar to those of alkalic lavas from other oceanic islands, but isotopic and certain trace element ratios reveal distinctive mantle source characteristics. Zr/Nb ratios of ∼3.0±0.2 for Bikar and Ratak Guyot, compared to 5.2±0.3 for Majuro Atoll and Erikub Seamount, at comparable degree of differentiation, suggest a more alkalic trend for the northern sites. The 143Nd/144Nd isotopic ratios range from 0.51283 to 0.51289 and 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios range from 20.55 to 21.11, 15.71 to 15.77, and 39.93 to 40.75, for samples from Erikub and Ratak. Variations in isotopic and some incompatible element ratios suggest interisland heterogeneity. Similar highly radiogenic lead isotopes, coupled with distinct incompatible element ratios, especially with low Ba/Nb ratios (∼6), are observed for St. Helena in the South Atlantic and for Tubuai and Mangaia in the South Pacific. The similar mantle signature shown by lavas from Tubuai and Mangaia in the Austral‐Cook chain, which are located at approximately the position where the Ratak edifices formed during the Late Cretaceous, indicates that this mantle anomaly is not of recent origin but has erupted distinctive lava compositions for at least 87 m.y.

Origin of Sr, Nd and Pb isotopic systematics in high-Sr basalts from central Arizona

Alkalic and tholeiitic basalts were erupted in the central Arizona Transition Zone during Miocene-Pliocene time before and after regional faulting. The alkalic lava types differ from the subalkaline lavas in Sr, Nd and Pb isotopic ratios and trace element ratios and, despite close temporal and spatial relationships, the two types appear to be from discrete mantle sources. Pre-faulting lava types include: potassic trachybasalts (87Sr/86Sr = 0.7052 to 0.7055, ɛNd= −9.2 to −10.7); alkali olivine basalts (87Sr/ 86Sr = 0.7049 to 0.7054, ɛNd= −2 to 0.2); basanite and hawaiites (87Sr/86Sr = 0.7049 to 0.7053, ɛNd= −3.5 to −7.8); and quartz tholeiites (87Sr/86Sr = 0.7047, ɛNd= −1.4 to −2.6). Post-faulting lavas have lower 87Sr/86Sr (<0.7045) and ɛNd from −3.2 to 2.3. Pb isotopic data for both preand post-faulting lavas form coherent clusters by magma type with values higher than those associated with MORB but within the range of values found for crustal rocks and sulfide ores in Arizona and New Mexico. Pb isotopic systematics appear to be dominated by crustal contamination. Effects of assimilation and fractional crystallization are inadequate to produce the Sr isotopic variations unless very large amounts of assimilation occurred relative to fractionation. It is impossible to produce the Nd isotopic variations unless ancient very unradiogenic material exists beneath the region. Moreover the assumption that the alkalic lavas are cogenetic requires high degrees of fractionation inconsistent with major- and trace-element data. Metasomatism of the subcontinental lithosphere above a subduction zone by a slab-derived fluid enriched in Sr, Ba, P and K could have produced the isotopic and elemental patterns. The degree of metasomatism apparently decreased upward, with the alkalic lavas sampling more modified regions of the mantle than the tholeiitic lavas. Such metasomatism may have been a regional event associated with crustal formation at about 1.6 Ga. Disruption and weakening of the subcontinental lithosphere in the Transition Zone of the Colorado Plateau by volcanism probably made deformation possible.

South Arch volcanic field—Newly identified young lava flows on the sea floor south of the Hawaiian Ridge

Research Article| July 01, 1989 South Arch volcanic field—Newly identified young lava flows on the sea floor south of the Hawaiian Ridge Peter W. Lipman; Peter W. Lipman 1U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar David A. Clague; David A. Clague 2U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar James G. Moore; James G. Moore 2U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Robin T. Holcomb Robin T. Holcomb 3U.S. Geological Survey, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar Geology (1989) 17 (7): 611–614. https://doi.org/10.1130/0091-7613(1989)017<0611:SAVFNI>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Peter W. Lipman, David A. Clague, James G. Moore, Robin T. Holcomb; South Arch volcanic field—Newly identified young lava flows on the sea floor south of the Hawaiian Ridge. Geology 1989;; 17 (7): 611–614. doi: https://doi.org/10.1130/0091-7613(1989)017<0611:SAVFNI>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Several young lava fields were imaged by GLORIA sidescan sonar along the Hawaiian Arch south of Hawaii. The largest, 35 by 50 km across, includes a central area characterized by high sonar backscatter and composed of several flow lobes radiating from a vent area. Reflection profiling and sea-floor photography indicate that the central lobes are flat sheet flowsbounded by pillowed margins; thin surface sediment and thin palagonite rinds on lava surfaces suggest ages of 1-10 ka. Vents are localized along the arch crest near bases of Cretaceous seamounts. Two dredged flows are basanite and alkalic basalt, broadly similar to rejuvenated-stage and some pre-shield alkalic lavas on the Hawaiian Ridge. Arch volcanism representsperipheral leakage of melt from the Hawaiian hot spot over much larger areas than previously recognized. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Nature and cause of compositional variation among the alkalic cap lavas of Mauna Kea Volcano, Hawaii

Most Hawaiian basaltic shield volcanoes are capped by moderately to strongly evolved alkalic lavas (MgO<4.5 wt.%). On Mauna Kea Volcano the cap is dominantly composed of hawaiite with minor mugearite. Although these lavas contain dunite and gabbroic xenoliths, they are nearly aphyric with rare olivine and plagioclase phenocrysts and xenocrysts. The hawaiites are nearly homogeneous in radiogenic isotope ratios (Sr, Nd, Pb) and they define coherent major and trace element abundance trends. These compositional trends are consistent with segregation of a plagioclase-rich cumulate containing significant clinopyroxene and Fe-Ti oxides plus minor olivine. Elements which are usually highly incompatible, e.g., Rb, Ba, Nb, are only moderately incompatible within the hawaiite suite because these elements are incorporated into feldspar (Rb, Ba) and oxides (Nb). However, in the most evolved lavas abundances of the most incompatible elements (P, La, Ce, Th) exceed (by ∼5–10%) the maximum enrichments expected from models based on major elements. Apparently, the crystal fractionation process was more complex than simple, closed system fractionation. The large amounts of clinopyroxene in the fractionating assemblage and the presence of dense dunite xenoliths with CO2 inclusions formed at minimum pressures of 2 kb are consistent with fractionation occurring at moderate depths. Crystal segregation along conduit or magma chamber walls is a possible mechanism for explaining compositional variations within these alkalic cap lavas.

Isotopically depleted, alkalic lavas from Bowie Seamount, northeast Pacific Ocean

Bowie Seamount, located 200 km west of the Queen Charlotte Islands, British Columbia, is one of the southernmost of the Pratt–Welker Seamounts in the Gulf of Alaska. Eight dredge hauls recovered hawaiite and mugearite, with major-and trace-element compositions similar to those of Hawaiian alkali basalts. All samples are enriched in light incompatible elements but are isotopically MORB-like: 87Sr/86Sr = 0.70269–0.70285; 143Nd/144Nd = 0.51307–0.51315; and 206Pb/204Pb = 18.26–19.18. Sr- and Pb-isotope ratios correlate positively, whereas Sr and Nd correlate negatively, and lie on a mixing trend between DMM and HIMU mantle components. Juan de Fuca MORB have similar ratios and define similar mixing trends.The combined geochemical data require that the mantle source of Bowie (and Pratt–Welker) magmas has only recently been enriched in incompatible elements. The enrichment process could involve (i) metasomatism of the underlying lithosphere by CO2-rich fluids from a depleted source or (ii) mixing of silicate melts from a HIMU source with small-degree partial melts from depleted mantle. Alternatively, the magmas may be partial melts of subducted, 1.2 Ga oceanic crust that was variably enriched in U and Sr(?) during sea-floor alteration.

Loihi Seamount, Hawaii: a mid-plate volcano with a distinctive hydrothermal system

The initial discovery of deep-sea hydrothermal vents at the Galapagos Rift1,2 has resulted in a decade of exploration and experimentation. Subsequent discoveries in the Pacific3–8 and Atlantic9 ocean basins have established the importance of these features as sources of mantle-derived gases and solutes10–2, and as loci for heat dissipation13,14, polymetallic sulphide mineral deposition15,16 and geochemical exchange17–19. The presence of dense communities of bacteria and specialized macrofauna20–22 has called into question the absolute role of sunlight as the principal energy source for marine organisms. Until recently, these deep-sea vents were known only at, or near, plate boundaries, but recent dredging23,24, near-bottom-water sampling25–27 and sea-floor camera survey28 programmes have indicated that hydrothermal vents are present at the summit of Loihi Seamount, a mid-plate, hotspot submarine volcano at the southern end of the Hawaiian island chain29. Here we report results obtained from sampling two active vent fields. The fluid chemistry (especially high CO2 and Fe), presence of alkalic lavas and iron-depositing bacteria, and absence of macrofauna suggest that mid-plate vents may differ from the hydrothermal vents found at mid-ocean ridges.

Comment on “Ra-Th disequilibria systematics: Timescale of carbonatite magma formation at Oldoinyo Lengai volcano, Tanzania”

This paper discusses potential flaws in study by Williams, Gill, and bruland (1986) dealing with the extreme disequilibria between uranium and thorium series nuclides in alkalic carbonatite lava specimens. It discusses the apparent discrepencies between chemical compositions of lava which were reported from the same eruption. Clarification is made on the actual timing of eruptions in this volcanic region and the effects this would have on the petrogenesis interpretation of these rocks.

Late Miocene volcanic stratigraphy of central Banks Peninsula, Canterbury, New Zealand

Abstract Banks Peninsula consists of Late Miocene alkalic to transitional volcanic rocks erupted from two major composite volcanoes (Lyttelton and Akaroa) and a host of minor monogenetic vents. Four volcanic groups are defined in this paper: Lyttelton (11-9.7 Ma), Mt Herbert (9.7-8.0 Ma), Akaroa (9.0-8.0 Ma), and Diamond Harbour (7.0-5.8 Ma). Three further formations, which are petrographically distinct and volumetrically minor, were erupted between 8.1 and 7.3 Ma, marking the transition from Akaroa to Diamond Harbour volcanism. Eruption of 350 km3 of mildly alkalic to transitional hawaiite to trachyte lavas of the Lyttelton Volcanic Group constructed a major composite volcano which forms the northwestern half of the peninsula. Late in the history of activity, the Lyttelton crater was breached in the southeast. The Mt Herbert Volcanic Group, comprising 100 km3 of mildly alkalic lavas and pyroclastic rocks, was then erupted from two main vents on the southeastern segment of Lyttelton Volcano. It consists o...

Petrology and geochronology of volcanic rocks from seamounts along and near the Hawaiian Ridge: Implications for propagation rate of the ridge

Lavas from three seamounts along and three seamounts near the Hawaiian Ridge are petrographically and geochernically similar to lavas from the Hawaiian Islands. Rock types recovered include tholeftic and alkalic lavas. The composition of these lavas is virtually identical to that of lavas from the Hawaiian Islands. This indicates that the source composition and petrogenesis of lavas along the Hawaiian chain are very consistent. The three along-ridge seamounts are in areas where there were gaps in the radiometric age data base. New ages further document the linear age progression along the chain and define a new propagation rate of 9.6±0.4 cm/yr (which is identical to the present-day plate motion of the island of Hawaii). The near-ridge seamounts are Cretaceous in age (74–77 Ma) and are part of NNW-trending linear chains that predate and are unrelated to the NW- and N-trending Hawaiian and Emperor chains.