Download or read book Geochemical Expression of Volcanism in an On axis and Intraplate Hotspot written by Dana Lee Desonie and published by . This book was released on 1990 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Pacific Ocean basin is home to a set of hotspots diverse in their eruption rate, duration of volcanism, and basalt chemistry. Pacific hotspots are found in a spectrum of distinct plate tectonic settings, from near a spreading ridge to intraplate. Cobb hotspot, which resulted in formation of the Cobb-Eickelberg seamount (CES) chain, is currently located beneath Axial seamount, on the Juan de Fuca ridge. The Marquesas hotspot, which formed the Marquesas archipelago and, perhaps, older seamounts to the west, is a member of the cluster of hotspots found within French Polynesia, located well away from the nearest spreading ridge. Geochemical and geochronological studies of volcanism at these two hotspots contribute to an understanding of the effect of plate tectonic environment on hotspot volcanism. Cobb hotspot has the temporal but not the isotopic characteristics usually attributed to a mantle plume. The earlier volcanic products of the hotspot show a westward age progression away from the hotspot and a westward increase in the age difference between the seamounts and the crust on which they formed. These results are consistent with movement of the Pacific plate over a fixed Cobb hotspot and encroachment by the westwardly migrating Juan de Fuca ridge. CES lavas are slightly enriched in alkali and incompatible elements relative to those of the Juan de Fuca ridge but they have Sr, Nd, and Pb isotopic compositions virtually identical to those found along the ridge. Cobb hotspot is a stationary upper mantle melting anomaly whose volcanic products have strong mid-ocean ridge basalt affinity. Basaltic lavas from dredge hauls in the Marquesas archipelago decrease in age from northwest to southeast, with the youngest volcanism at a group of seamounts southeast of the island of Fatu Hiva. Tholeiitic and transitional basalts compose the shield of a typical Marquesan volcano; alkalic lavas form a later phase. Tholeiitic and transitional basalts result from variable degrees of melting of a relatively depleted mantle source with pods of incorporated radiogenic-Pb enriched material. Alkalic lavas represent smaller degrees of melting of a radiogenic Sr and Pb enriched mantle source. Volcanism at both hotspots can be explained by variable amounts of entrainment of a heterogeneous upper mantle into a mantle plume of isotopically depleted (Cobb) or enriched (Marquesas) composition.
Download or read book Curricula in the Atmospheric Oceanic Hydrologic and Related Sciences written by and published by . This book was released on 1992 with total page 750 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Secular and Recent Trends in the Geochemistry of the R union Hotspot and Other Global Hotspots written by Bradley Peters and published by . This book was released on 2016 with total page 486 pages. Available in PDF, EPUB and Kindle. Book excerpt: The origins of volcanic activity at intraplate "hotspot" localities cannot be easily explained by fundamental principles of plate tectonics. Decades of geochemical and geophysical research have produced controversial hypotheses that attempt to explain the physical mechanism of magma generation and the origin of the magmas in the deep Earth. The mantle plume hypothesis conjectures that hotspot volcanism results from upwelling of buoyant mantle material from the deep Earth, which may carry recycled crust and lithosphere that resided on Earth's surface billions of years ago. One requirement of the xviii plume hypothesis is that initial, intense stages of hotspot volcanism, which exist only in the geologic record, are genetically linked to later, waning stages of volcanism observed on Earth today. Physiographic evidence exists in several global localities, including the Réunion hotspot, that appears to link large igneous province volcanism to oceanic volcanism, however geochemical evidence linking the two is tenuous. Here, I demonstrate that certain trace element signatures of global hotspots are unlikely to reflect their mantle source in the same way as isotope systems. Next, I show that igneous rocks on Réunion possess a unique geochemical and isotopic signature that make them distinct from igneous rocks from other global hotspots. Finally, I interrogate the composition of the Deccan Traps mantle source in two ways. First, I use early-formed mineral phases to evaluate the presence of recycled material in the Deccan Traps mantle source. Second, I use lava compositions to re-construct a lithospheric and crustal assimilation history for Deccan Traps parental magmas and attempt to relate the composition of this parental magma to that of Réunion. Considering all chapters together, I show that these two volcanic provinces likely share a mantle source with a common composition, and that this source contains a small amount of recycled material. In addition, I provide new evidence that the Réunion mantle source was formed early in Earth's history and remained isolated from other mantle domains for long periods of geologic time.
Download or read book Open file Report written by and published by . This book was released on 1998 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Geochemical Studies of Hotspot Volcanism in the Southern Pacific and Its Implications for Mantle Structure and Dynamics written by Qun Charles Cheng and published by . This book was released on 1989 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dissertation Abstracts International written by and published by . This book was released on 1991 with total page 734 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Bulletin Division of Geology and Earth Resources written by Washington (State). Division of Geology and Earth Resources and published by . This book was released on 1994 with total page 736 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Oceanic Hotspots written by Roger Hekinian and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ocean Hotspots provides a comprehensive overview of recent and ongoing research on intraplate volcanism in the ocean basins with special emphasis on the Pacific Ocean. The geology of the seamounts and their associated seamount chains is described, along with detailed geophysical, geochemical and hydrothermal observations made by a multi-disciplinary group of marine geoscientists. These observations lead to a deeper understanding of how the ascending mantle melts, represented by hotspots, are able to penetrate the lithosphere, build seamounts, and enhance hydrothermal circulation. The "fixed" hotspot-generated seamount chains also provide key constraints on plate tectonic reconstructions on the Earth's crust.
Download or read book Toward an Improved Understanding of Intraplate Uplift and Volcanism Geochronology and Geochemistry of Intraplate Volcanic Rocks and Lower Crustal Xenoliths written by Leonard D. Ancuta and published by . This book was released on 2017 with total page 207 pages. Available in PDF, EPUB and Kindle. Book excerpt: The origin of diffuse intraplate volcanism and 4000 m high topography of the Hangay Mountains in central Mongolia is enigmatic, as it is not explained by or predicted by traditional plate tectonic models. Chapter One presents new whole-rock 40Ar/39Ar ages that range from Holocene to 30 Ma for the Cenozoic volcanic rocks in central Mongolia. The total volume of the Cenozoic volcanic rocks is approximately 1540 km3, but prior to erosion, the volume may have been as high as 2900 km3. Volcanism began to increase gradually in the early Miocene and peaked in the middle Miocene, with a gradual decrease in volume through the Holocene. The low total volumes and the lack of an age progressive hot-spot track rule out the presence of a mantle plume. The long-term gradual increase and subsequent decrease in volcanic output may also rule out delamination. Chapter Two presents the results of a geochemical study to understand the source of the volcanic rocks. Isotopic compositions of the volcanic rocks fall between prevalent mantle (PREMA) and enriched mantle (EM1) and are similar to other Cenozoic basalts from east Asia, though markedly different from the depleted MORB mantle (DMM) isotopic signature of the lithospheric mantle in Mongolia, suggesting the volcanic rocks must be derived from a sub-lithospheric source. A mantle upwelling beneath the region is likely, though the specific cause can not be identified by geochemistry and geochronology alone. In Chapter Three, two-pyroxene granulite lower crustal xenoliths brought to the surface by the Cenozoic volcanism were studied using U-Pb geochronology and geochemistry. U-Pb geochronology indicates the lower crust in central Mongolia began to form by at latest the Permo-Triassic, likely during the formation of the Central Asian Orogenic Belt (CAOB), which is consistent with arc-like geochemical signatures. Recent seismology studies indicate that the high elevations of the Hangay region could be isostatically supported by a thick crust. My new data suggests the lower crust, and by inference the high topography of the Hangay, formed in the Late Paleozoic to Early Mesozoic during the formation of the CAOB, which is significantly older than any other previous estimates.
Download or read book Washington Geologic Newsletter written by Washington (State). Division of Geology and Earth Resources and published by . This book was released on 1990 with total page 326 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Bulletin written by Washington (State). Division of Geology and Earth Resources and published by . This book was released on 1996 with total page 482 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book American Doctoral Dissertations written by and published by . This book was released on 1990 with total page 768 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Bibliography and Index of the Geology and Mineral Resources of Washington written by and published by . This book was released on 1996 with total page 494 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Bibliography and Index of the Geology and Mineral Resources of Washington 1986 1990 written by and published by . This book was released on 1996 with total page 480 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book New Insights Into Mantle Dynamics from Helium Isotopes and Argon Geochronology written by Kevin Konrad and published by . This book was released on 2017 with total page 278 pages. Available in PDF, EPUB and Kindle. Book excerpt: Earth’s mantle extends to nearly 3000 km depth, comprises >80 % of Earth’s total volume, and has the largest influence on the primordial and radiogenic heat budget. Despite its importance, the structure and composition of the mantle is still debated. There are three primary models for Earth’s mantle structure that contain some degree of overlap. First, the Burke model invokes both small scale convection in the upper mantle coupled with larger scale, whole mantle convection. This model implies that long lived intraplate volcanic island chains are derived from upwelling plumes that originate near the edges of thermochemical piles in the lower mantle, while smaller and more ephemeral volcanic provinces originate from melting in the upper mantle. Second, the Courtillot model is similar to the Burke model, except multiple plume types exist, some originating from the core-mantle boundary and some separating from massive lower mantle upwellings that stall near the mantle transition zone at 400-660 km. Third, the Anderson model invokes upper and lower mantle isolation throughout Earth’s history, with volcanism originating through melting of a chemically heterogeneous upper mantle. The origin and evolution of intraplate volcanism are therefore central to understanding the dynamics and evolution of the mantle. In this dissertation, I present new constraints on Earth’s mantle using geochemical, geochronological and geodynamical investigations of intraplate volcanism in both continental and oceanic settings. The first study focuses on the origin of the enigmatic intraplate volcanic fields (harrats) of Saudi Arabia. Helium isotope compositions and trace element concentrations were determined for mantle xenoliths and lava flows from Harrat Hutaymah, plus 3He/4He in several xenoliths from Harrat Al Birk, Al Kishb, and Ithnayn. Harrat Hutaymah is the most northeastern Arabian volcanic field, found off of the main axis of Arabian volcanism, referred to as the Makkah-Medinah-Nafud (MMN) line. Hutaymah has uniform 3He/4He of 7.5 R[subscript A] (where R[subscript A] is the atmospheric ratio) in nearly all xenolith types. The uniformity is explained by volatile equilibration between the xenoliths and the host magma through the trapping of fluids/gases along grain defects during magma ascent, followed by re-annealing at lower pressure. Anhydrous spinel lherzolites from Hutaymah, Ithnanyn and Al Birk are notably different, having lower 3He/4He of 6.8 R[subscript A] and distinctly depleted light rare earth element signatures. The widespread presence of this 6.8 R[subscript A] signature in the lherzolites appears to be representative of the Arabian Proterozoic lithosphere prior to any metasomatic overprinting associated with later volcanic/tectonic activity. The origin of volcanism associated with the harrats located off the MMN line appears to involve mixing of delaminated, ancient enriched lithosphere with shallow depleted asthenosphere. Elevated 3He/4He signatures associated with a deep mantle plume origin are absent in the peripheral harrats, although they appear to be weakly present in some volcanic formations along the MMN line. The second study investigated intraplate volcanism in the Marquesas Islands, French Polynesia. This archipelago represents the surface expression of a low buoyancy flux mantle plume in a region of oceanic lithosphere marked by deep seated fracture zones. The Marquesas plume appears to contain an intrinsically large isotopic and chemical heterogeneity, both geographically and through time. The study uses 3He/4He results, major and trace element compositions of whole rocks, 40Ar/39Ar age determinations, and chemical analyses of olivine-hosted melt inclusions (OHMIs). The new results indicate that magmas feeding Marquesas volcanism are chemically diverse and are derived by melting of small-scale heterogeneities in the source regions. Variation in Cl/K among the OHMIs suggests that both the melting of recycled altered crust and interaction of magmas with brine at shallow levels potentially affects the lavas erupted in this region. Lavas at Hiva Oa show an increase in 3He/4He from shield (8.3 R[subscript A]; 2.6 Ma) to late-shield stage (10.4-14.5 R[subscript A]; 2.2 Ma), followed by a slight decrease (9.0-11.4 R[subscript A]) during the post-shield phase (1.8 Ma). Elevated 3He/4He ratios (10 R[subscript A]) are restricted to the central islands of Nuku Hiva and Hiva Oa in the Marquesas chain, suggesting a concentrically zoned mantle plume that has primitive and hot material concentrated near its central axis. The third study provides a refined history of the Rurutu hotspot, a long-lived mantle plume situated beneath the Pacific plate. Provided are new 40Ar/39Ar age determinations for seamounts from the Tuvalu Islands region of the west Pacific. These islands and seamounts range in age from 64 to 47 Ma and are isotopically similar to some young volcanoes in the Cook-Austral region. Using age constrained seamounts from the Rurutu chain (0-10 Ma; 47-72 Ma) in combination with the Pacific Louisville hotspot (0-79 Ma) and Hawaiian hotspot (0-78 Ma), the relative motions of these hotspots were computed. These motions confirm that Hawaii is unique, having an abrupt, southward plume drift from 60-47 Ma, while both Louisville and Rurutu show similar, eastward trending motions. Using geodynamic models of plume motions based primarily on seismic tomography and mantle viscosity models, the conditions required to account for the observed motions were tested. The relative motions are best reproduced when the plumes are both rooted near the core-mantle boundary and have roots that are able to move by mantle flow. However, none of the model parameters can properly reproduce the rapid motions of the Hawaiian hotspot, indicating additional processes may be responsible. The relative hotspot motions cannot be reproduced when the plumes are sourced at the upper/lower mantle boundary and thus indicate a deeper origin for long-lived plumes. The studies presented herein generally support the Burke model for mantle structure. The results from age-progressive Pacific intraplate volcanism support a plume source that is derived from dense thermochemical piles in the lower mantle. These source regions have somewhat mobile edges and contain a component of primitive material. Geochemical results for the Arabian volcanic fields indicate that secondary convection in the upper mantle may generate melts near the lithosphere-asthenosphere boundary, and therefore also be a cause of intraplate volcanism.
Download or read book The Petrology Geochemistry and Geochronology of Hotspot Seamounts in the North Pacific and Arc backarc Volcanism on the Northern Antarctic Peninsula written by Randall Arthur Keller and published by . This book was released on 1996 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt: Volcanic rocks from hotspots and island arcs/backarcs typically have enriched trace element and isotopic compositions that contain a contribution from subducted oceanic crust. Isotopic and trace element data suggest that the enriched components in hotspot volcanism are ancient subducted sediment and crust, and the enriched components in arc/backarc volcanism are hydrous fluids and melts from the subducting slab. This thesis examines the origins of these enriched components, and how they change in time and space. The Hawaiian-Emperor seamount chain records over 81 million years of volcanism from the Hawaiian hotspot. Seamounts at the old (northern) end of the chain have isotopic compositions more depleted then anything previously reported from the Hawaiian hotspot. Detroit seamount (81 Ma) has the most depleted composition, and was created while an active spreading ridge was close to the hotspot. Proximity to a spreading ridge must have caused the hotspot to entrain and melt more of the depleted upper mantle. The Patton-Murray seamount platform, at the old end of the Cobb hotspot track in the Gulf of Alaska, was volcanically active at 33 Ma, 27 Ma, and 17 Ma. The 33 Ma tholeiitic phase and 27 Ma alkalic phase are related to passage over the hotspot. The 17 Ma phase erupted too late to be directly related to the hotspot, but may have been caused by minor extension along a zone of weakness originally created by passage over the hotspot. On the northern Antarctic Peninsula, volcanism occurred above a subducting slab up to 360 km from the South Shetland Trench. Volcanism on the South Shetland Arc has enriched trace element and isotopic compositions that can be modeled by mixing of subducted sediments and depleted mantle. Backarc basin volcanism in Bransfield Strait contains less of the subducted component, and the most depleted samples are distinguishable from MORB only by their slightly elevated Cs and Pb concentrations. Extreme-backarc volcanism on James Ross Island (360 km from the trench) shows no evidence for the subducted component in its trace element compositions, but its Pb isotopic ratios are affected by Pb from subducted sediment.
Download or read book Proceedings of the Ocean Drilling Program written by Ocean Drilling Program and published by . This book was released on 1988 with total page 1032 pages. Available in PDF, EPUB and Kindle. Book excerpt:
