Geology and geochemistry of early arc-volcanic rocks from Guam

Reagan, Mark K.; Meijer, Arend

doi:10.1130/0016-7606(1984)95<701:gagoea>2.0.co;2

Cited by 131 publications

(81 citation statements)

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“…Tracey and others (1964) first described Guam's geology in detail. Subsequently, Reagan and Meijer (1984) reclassified some of the volcanic rock units, and Siegrist and Randall (1992) reinterpreted some of the limestone units. Siegrist and Reagan (2007) accordingly updated the original map (Tracey and others, 1964) (fig.…”

Section: Geologymentioning

confidence: 99%

“…The basement beneath the NGLA is the Late Eocene to Early Oligocene Alutom Formation (Tracey and others, 1964). The Alutom Formation constitutes the second-oldest exposed volcanic rock unit on Guam, overlying the Late Middle Eocene Facpi Formation (Reagan and Meijer, 1984), which forms the island's basement. Age determinations of Guam geologic units are based mainly on fossil remains and correlations with other islands in the Pacific.…”

Section: Geologymentioning

confidence: 99%

“…The Alutom Formation is estimated to be 1,850-2,000 ft thick (Reagan and Meijer, 1984;Siegrist and Reagan, 2007). Basement rocks occupy less than 1 percent of Guam's northern surface.…”

Section: Geologymentioning

confidence: 99%

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The effects of withdrawals and drought on groundwater availability in the Northern Guam Lens Aquifer, Guam

Gingerich¹

2013

Scientific Investigations Report

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For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS.For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprodTo order this and other USGS information products, visit http://store.usgs.gov Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.Suggested citation: Gingerich, S.B., 2013, The effects of withdrawals and drought on groundwater availability in the Northern Guam Lens Aquifer, Guam: U.S. Geological Survey Scientific Investigations Report 2013-5216, 76 p., http://dx.doi.org/10.3133/ sir20135216. ISSN 2328-0328 (online) iii Executive SummaryMost of the public water supply on Guam is pumped from a freshwater lens in the Northern Guam Lens Aquifer, a limestone aquifer. Because of population growth and a potential military realignment involving the U.S. Marine Corps (USMC), groundwater withdrawals from wells are expected to increase. Currently (2013), the salinity of water pumped from some wells in the area is higher than acceptable for drinking water. The expected increase in demand for water has led to concern over the long-term sustainability of withdrawals from existing and proposed wells. In 2010, to aid in management of groundwater resources and to plan for sustainable growth on the island, the United States Marine Corps, Headquarters entered into a cooperative agreement with the U.S. Geological Survey (USGS) to study groundwater availability in northern Guam. The objective of this 3.5-year study was to estimate the effects of several hypothetical withdrawal scenarios on water levels, the transition zone between freshwater and saltwater, and salinity of pumped wells.On Guam, freshwater-lens systems are found in limestone and volcanic rocks, but the most important groundwater sources are from the freshwater parts of these systems in the high-hydraulic-conductivity limestone rocks of northern Guam. The most intensely developed groundwater system in this area comprises a lens-shaped freshwater body, an intermediate brackish-water transition zone, and underlying saltwater. For management purposes, the Guam Environmental Protection Agency (GEPA) delineated the Northern Guam Lens Aquifer (NGLA) into six hydrologically connected aquifer basins: Agafo Gumas, Andersen, Finegayan, Hagåtña, Mangilao, and Yigo-Tumon. Hydrologic DataKnowledge of the NGLA hydrology comes from compilation and analysis of data on water levels, salinity profiles in deep monitoring wells, production well pumping rates and salinities, and geologic information gleaned from decades of well drilling and hydrologic monitoring. The NGLA...

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Section: Geologymentioning

confidence: 99%

Section: Geologymentioning

confidence: 99%

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The effects of withdrawals and drought on groundwater availability in the Northern Guam Lens Aquifer, Guam

Gingerich¹

2013

Scientific Investigations Report

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“…With the exception of dredges from inner trench walls and large fault scarps (Bloomer and Hawkins, 1983;Bloomer and Fisher, 1987), our direct knowledge of intraoceanic forearc basement prior to ODP Legs 125 and 126 is based primarily on data from three island chains and two Deep Sea Drilling Project (DSDP) sites: the Mariana and Tonga frontal-arc islands (GuamSaipan and 'Eua) and the Bonin Islands, which expose Eocene island-arc tholeiites and boninites (Reagan and Meijer, 1984;Ewart et al, 1977;Shiraki et al, 1980); and DSDP Leg 60 Sites 458 and 459, which sampled Eocene arc tholeiites and lower Oligocene boninites and arc tholeiites, respectively, from the Mariana outer-arc high. Prior to Leg 126, basement beneath the thickly sedimented upper-slope basin between the frontal-arc and outer-arc high had never been sampled, nor had the deep forearc basement beneath the carapace of interbedded arc pillow lavas, flows, and sills been sampled.…”

Section: Arc/forearc Developments Background To Sites 787 792 and 793mentioning

confidence: 99%

Introduction

Taylor¹

1990

Proceedings of the Ocean Drilling Program

102

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“…On the other hand, LSB crystallization sequence is controlled by olivine and clinopyroxene fractionation (Kostopoulos and Murton, 1992;Natland, 1982). LSB 30 differentiation series is typified by suites from northern Zambales, Holes U1439 and U1442 of Expedition 352 and Hole 458, ODP Leg 60 (Meijer, 1982;Sharaskin, 1982 (Reagan & Meijer, 1984), Tonga Trench (Falloon et al, 2007;Falloon and Crawford, 1991), Troodos ophiolite (Cameron, 1985;König et al, 2008;Osozawa et al, 2012;Pearce & Robinson, 2010) and Oman ophiolite (Ishikawa et al, 2002;Kusano et al, 2017;Kusano et al, 2014;Nagaishi, 2008).…”

Section: Low-pressure Fractionation and Magma Mixingmentioning

confidence: 99%

Boninite and boninite-series volcanics in northern Zambales ophiolite: Doubly-vergent subduction initiation along Philippine Sea Plate margins

Perez¹,

Umino²,

Yumul³

et al. 2018

Preprint

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Abstract.A key component of subduction initiation rock suites is boninite, a high-magnesium andesite that is uniquely predominant in Western Pacific forearc terranes and in select Tethyan ophiolites such as Oman and Troodos. We report the discovery of low-calcium, high-silica boninite in the middle Eocene Zambales ophiolite (Luzon island, Philippines). Olivine-15 orthopyroxene microphyric high-silica boninite, olivine-clinopyroxene-phyric low-silica boninite and boninitic basalt occur Paleolatitudes derived from tilt-corrected sites in the Acoje Block place the juvenile arc of northern Zambales ophiolite in 25 the western margin of the Philippine Sea Plate. In this scenario, the origin of Philippine Sea Plate boninites (IBM and Zambales) would be in a doubly-vergent subduction initiation setting.

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Geology and geochemistry of early arc-volcanic rocks from Guam

Cited by 131 publications

References 0 publications

The effects of withdrawals and drought on groundwater availability in the Northern Guam Lens Aquifer, Guam

The effects of withdrawals and drought on groundwater availability in the Northern Guam Lens Aquifer, Guam

Introduction

Boninite and boninite-series volcanics in northern Zambales ophiolite: Doubly-vergent subduction initiation along Philippine Sea Plate margins

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