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USGS2009

Along-Arc and Back-Arc Attenuation, Site Response, and Source Spectrum for the Intermediate-Depth 8 January 2006 M 6.7 Kythera, Greece, Earthquake

An M 6.7 intermediate-depth (66 km), in-slab earthquake occurring near the island of Kythera in Greece on 8 January 2006 was well recorded on networks of stations equipped with acceleration sensors and with broadband velocity sensors. All data were recorded digitally using recording instruments with resolutions ranging from almost 11 to 24 bits. We use data from these networks to study the distance dependence of the horizontal-component Fourier acceleration spectra (FAS) and horizontal-component pseudoabsolute response spectral acceleration (PSA). For purposes of simulating motions in the future, we parameterize the distance decay using several forms of the geometrical-spreading function, for each of which we derive Q as a function of frequency. By extrapolating the distance decay back to 1 km, we obtain a reference spectrum that can be used in future simulations. This spectrum requires a more complicated spectral shape than the classic single-corner-frequency model; in particular, there appears to be an enhancement of motion around 0.2-0.3 Hz that may be due to the radiation of a 3-5 sec pulse from the source. We infer a ?? 0 value of about 0.055 sec for rock stations and a stress parameter in the range of 400-600 bars. We also find distinctive differences in the site response of stations on soft soil and soil; both the FAS and the 5% damped PSA amplifications have similar peak amplitudes (about 2 and 4 for soil and soft-soil sites, respectively, relative to the rock sites) at similar frequencies (between about 0.4 and 2.0 Hz, with the soft-soil amplifications peaking at somewhat lower frequencies than the soil amplifications). One of the most distinctive features of the data is the clear difference in the motions for along-arc and back-arc stations, with the former being significantly higher than the latter over a broad range of frequencies at distances beyond about 250 km. The motions from the Kythera earthquake are roughly comparable to those from intermediate-depth earthquakes elsewhere, but they appear to be significantly higher than those from recordings of shallow earthquakes in Greece of comparable magnitude and hypocentral distance.

Bulletin of the Seismological Society of America↗

USGS2022

Detrital zircon ages from upper Paleozoic–Triassic clastic strata on St. Lawrence Island, Alaska: An enigmatic component of the Arctic Alaska–Chukotka microplate

New lithologic and detrital zircon (DZ) U-Pb data from Devonian–Triassic strata on St. Lawrence Island in the Bering Sea and from the western Brooks Range of Alaska suggest affinities between these two areas. The Brooks Range constitutes part of the Arctic Alaska–Chukotka microplate, but the tectonic and paleogeographic affinities of St. Lawrence Island are unknown or at best speculative. Strata on St. Lawrence Island form a Devonian–Triassic carbonate succession and a Mississippian(?)–Triassic clastic succession that are subdivided according to three distinctive DZ age distributions. The Devonian–Triassic carbonate succession has Mississippian-age quartz arenite beds with Silurian, Cambrian, Neoproterozoic, and Mesoproterozoic DZ age modes, and it exhibits similar age distributions and lithologic and biostratigraphic characteristics as Mississippian-age Utukok Formation strata in the Kelly River allochthon of the western Brooks Range. Consistent late Neoproterozoic, Cambrian, and Silurian ages in each of the Mississippian-age units suggest efficient mixing of the DZ prior to deposition, and derivation from strata exposed by the pre-Mississippian unconformity and/or Endicott Group strata that postdate the unconformity. The Mississippian(?)–Triassic clastic succession is subdivided into feldspathic and graywacke subunits. The feldspathic subunit has a unimodal DZ age mode at 2.06 Ga, identical to Nuka Formation strata in the Nuka Ridge allochthon of the western Brooks Range, and it records a distinctive depositional episode related to late Paleozoic juxtaposition of a Paleoproterozoic terrane along the most distal parts of the Arctic Alaska–Chukotka microplate. The graywacke subunit has Triassic maximum depositional ages and abundant late Paleozoic grains, likely sourced from fringing arcs and/or continent-scale paleorivers draining Eurasia, and it has similar age distributions to Triassic strata from the Lisburne Peninsula (northwestern Alaska), Chukotka and Wrangel Island (eastern Russia), and the northern Sverdrup Basin (Canadian Arctic), but, unlike the Devonian–Triassic carbonate succession and feldspathic subunit of the Mississippian(?)–Triassic clastic succession, it has no obvious analogue in the western Brooks Range allochthon stack. These correlations establish St. Lawrence Island as conclusively belonging to the Arctic Alaska–Chukotka microplate, thus enhancing our understanding of the circum-Arctic region in late Paleozoic–Triassic time.

Alaska↗

USGS1971

Quaternary faulting in the eastern Alaska Range

Quaternary faulting is well displayed along the Denali fault system and the recently recognized and related Totschunda fault system in the eastern Alaska Range. The principal movement on both fault systems is right-lateral strike-slip. Offset glacial features of Wisconsin age indicate minimum Holocene slip rates of 1.1 to 3.5 cm per year along parts of the Denali fault system, and 0.9 to 3.3 cm per year along the Totschunda fault system. Strike-slip movement along the Denali fault system may be no older than early Pliocene and, southeast of the Totschunda fault system junction, may have terminated by the middle Pleistocene. The strike-slip Totschunda fault system, a much younger feature probably no older than middle Pleistocene, exhibits 9 to 10 km of right-lateral offset and 1,500 m of relative vertical movement. The Totschunda fault system is aligned with, and has the same sense of slip as, the Fairweather fault in the Gulf of Alaska. The Denali fault system and the Queen Charlotte Islands fault are part of a major transform fault system separating the North American and Pacific plates. Continental southern Alaska between the Aleutian arc and the Denali fault system is now largely coupled to the Pacific plate. The Totschunda-Fairweather alignment probably represents the beginning of a new transform fault by-passing the southeast part of the Denali fault system.

Alaska↗

USGS2007

Geochemistry of Selected Coal Samples from Sumatra, Kalimantan, Sulawesi, and Papua, Indonesia

Introduction Indonesia is an archipelago of more than 17,000 islands that stretches astride the equator for about 5,200 km in southeast Asia (figure 1) and includes major Cenozoic volcano-plutonic arcs, active volcanoes, and various related onshore and offshore basins. These magmatic arcs have extensive Cu and Au mineralization that has generated much exploration and mining in the last 50 years. Although Au and Ag have been mined in Indonesia for over 1000 years (van Leeuwen, 1994), it was not until the middle of the nineteenth century that the Dutch explored and developed major Sn and minor Au, Ag, Ni, bauxite, and coal resources. The metallogeny of Indonesia includes Au-rich porphyry Cu, porphyry Mo, skarn Cu-Au, sedimentary-rock hosted Au, epithermal Au, laterite Ni, and diamond deposits. For example, the Grasberg deposit in Papua has the world's largest gold reserves and the third-largest copper reserves (Sillitoe, 1994). Coal mining in Indonesia also has had a long history beginning with the initial production in 1849 in the Mahakam coal field near Pengaron, East Kalimantan; in 1891 in the Ombilin area, Sumatra, (van Leeuwen, 1994); and in South Sumatra in 1919 at the Bukit Asam mine (Soehandojo, 1989). Total production from deposits in Sumatra and Kalimantan, from the 19thth century to World War II, amounted to 40 million metric tons (Mt). After World War II, production declined due to various factors including politics and a boom in the world-wide oil economy. Active exploration and increased mining began again in the 1980's mainly through a change in Indonesian government policy of collaboration with foreign companies and the global oil crises (Prijono, 1989). This recent coal revival (van Leeuwen, 1994) has lead Indonesia to become the largest exporter of thermal (steam) coal and the second largest combined thermal and metallurgical (coking) coal exporter in the world market (Fairhead and others, 2006). The exported coal is desirable as it is low sulfur and ash (generally <1 and < 10 wt.%, respectively). Coal mining for both local use and for export has a very strong future in Indonesia although, at present, there are concerns about the strong need for a major revision in mining laws and foreign investment policies (Wahju, 2004; United States Embassy Jakarta, 2004). The World Coal Quality Inventory (WoCQI) program of the U.S. Geological Survey (Tewalt and others, 2005) is a cooperative project with about 50 countries (out of 70 coal-producing countries world-wide). The WoCQI initiative has collected and published extensive coal quality data from the world's largest coal producers and consumers. The important aspects of the WoCQI program are; (1) samples from active mines are collected, (2) the data have a high degree of internal consistency with a broad array of coal quality parameters, and (3) the data are linked to GIS and available through the world-wide-web. The coal quality parameters include proximate and ultimate analysis, sulfur forms, major-, minor-, and trace-element concentrations and various technological tests. This report contains geochemical data from a selected group of Indonesian coal samples from a range of coal types, localities, and ages collected for the WoCQI program.

Open-File Report↗

USGS2012

Geology of the Prince William Sound and Kenai Peninsula region, Alaska: Including the Kenai, Seldovia, Blying Sound, Cordova, and Middleton Island 1:250,000-scale quadrangles

The Prince William Sound and Kenai Peninsula region includes a significant part of one of the world’s largest accretionary complexes and a small part of the classic magmatic arc geology of the Alaska Peninsula. Physiographically, the map area ranges from the high glaciated mountains of the Alaska and Aleutian Ranges and the Chugach Mountains to the coastal lowlands of Cook Inlet and the Copper River delta. Structurally, the map area is cut by a number of major faults and postulated faults, the most important of which are the Border Ranges, Contact, and Bruin Bay Fault systems. The rocks of the map area belong to the Southern Margin composite terrane, a Tertiary and Cretaceous or older subduction-related accretionary complex, and the Alaska Peninsula terrane. Mesozoic rocks between these two terranes have been variously assigned to the Peninsular or the Hidden terranes. The oldest rocks in the map area are blocks of Paleozoic age within the mélange of the McHugh Complex; however, the protolith age of the greenschist and blueschist within the Border Ranges Fault zone is not known. Extensive glacial deposits mantle the Kenai Peninsula and the lowlands on the west side of Cook Inlet and are locally found elsewhere in the map area. This map was compiled from existing mapping, without generalization, and new or revised data was added where available.

Alaska↗

USGS2009

Evidence for an Alleghanian (Early Carboniferous to Late Permian) tectonothermal event in the New Jersey Coastal Plain basement from 40 Ar/ 39 Ar biotite data, geochemistry and gravity modeling

40 Ar/ 39 Ar dating of biotite from felsic orthogneiss recovered from the -3890-foot level of the Island Beach State Park (IBSP) well beneath the outer New Jersey Coastal Plain was accomplished using CO 2 laser incremental-heating techniques. Over 75% of the Ar released from the incremental-heating experiment form a well-behaved plateau with a calculated age of 243.98 ?? 0.10 Ma. The new 244 Ma biotite age reported here is a cooling age younger than the metamorphic event that crystallized or reheated the biotite. We consider reheating of older biotite to be unlikely because the concordant 40 Ar/ 39 Ar spectrum upon repeated incremental laser heating showed a well-developed plateau. Thus, biotites from the IBSP gneiss are interpreted as having crystallized during a single thermal event, followed by cooling to below 300 ??C. The IBSP well falls on a structural and geophysical anomaly trend that is along strike with rocks of the Bronson Hill anticlinorium to the north of the IBSP gneiss. Locally graphitic metasedimentary schists and gneisses recovered from New Jersey wells inboard of the IBSP well gneiss correlate to similar lithologies of the Connecticut Valley synclinorium west of the Hartford basin. Our reinterpretation of the IBSP gneiss as metamorphosed dacite or dacitic tuff is consistent with a correlation to some rocks of the Bronson Hill magmatic arc east of the Hartford basin. If correct, this would imply a Late Ordovician age for the protolith of the IBSP gneiss. Reported 40 Ar/ 39 Ar biotite ages of 235-253 Ma from southwestern Rhode Island, and of 238-247 Ma from southeastern Connecticut, are interpreted as cooling ages following a tectonothermal event associated with the Alleghanian orogeny (Early Carboniferous to Late Permian). Cooling ages of Alleghanian age (Early Carboniferous to Late Permian) are not recognized west of the Bronson Hill volcanic arc in either central Connecticut or in Massachusetts. Therefore, the 244 Ma cooling age presented here, and the geochemical affinity of the IBSP gneiss to some orthogneisses of the Bronson Hill arc, support an interpretation of the IBSP well as representing the southern continuation of the Bronson Hill arc into New Jersey. Moreover, it documents the presence of rocks beneath the outer New Jersey Coastal Plain that experienced a Permian Alleghanian metamorphism. ?? 2009 Elsevier Ltd. All rights reserved.

Journal of Geodynamics↗

USGS1990

Trace-element and Sr, Nd, Pb, and O isotopic composition of Pliocene and Quaternary alkali basalts of the Patagonian Plateau lavas of southernmost South America

The Pliocene and Quaternary Patagonian alkali basalts of southernmost South America can be divided into two groups. The "cratonic" basalts erupted in areas of Cenozoic plateau volcanism and continental sedimentation and show considerable variation in 87Sr/86Sr (0.70316 to 0.70512), 143Nd/144Nd (e{open}Nd) and 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios (18.26 to 19.38, 15.53 to 15.68, and 38.30 to 39.23, respectively). These isotopic values are within the range of oceanic island basalts, as are the Ba/La, Ba/Nb, La/Nb, K/Rb, and Cs/Rb ratios of the "cratonic" basalts. In contrast, the "transitional" basalts, erupted along the western edge of the outcrop belt of the Pliocene and Quaternary plateau lavas in areas that were the locus of earlier Cenozoic Andean orogenic arc colcanism, have a much more restricted range of isotopic composition which can be approximated by 87Sr/86Sr=0.7039??0.0004, e{open}Nd, 206Pb/204Pb=18.60??0.08, 207Pb/204Pb=15.60??0.01, and 208Pb/204Pb=38.50??0.10. These isotopic values are similar to those of Andean orogenic are basalts and, compared to the "cratonic" basalts, are displaced to higher 87Sr/86Sr at a given 143Nd/144Nd and to higher 207Pb/204Pb at a given 208Pb/204Pb. The "transitional" basalts also have Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios higher than the "cratonic" and oceanic island basalts, although not as high as Andean orogenic are basalts. In contrast to the radiogenic isotopes, ??18O values for both groups of the Patagonian alkali basalts are indistinguishable and are more restricted than the range reported for Andean orogenic are basalts. Whole rock ??18O values calculated from mineral separates for both groups range from 5.3 to 6.5, while measured whole rock ??18O values range from 5.1 to 7.8. The trace element and isotopic data suggest that decreasing degrees of partial melting in association with lessened significance of subducted slabderived components are fundamental factors in the west to east transition from arc to back-arc volcanism in southern South America. The "cratonic" basalts do not contain the slab-derived components that impart the higher Ba/La, Ba/Nb, La/Nb, Cs/Rb, 87Sr/86Sr at a given 143Nd/144Nd, 207Pb/204Pb at a given 208Pb/204Pb, and ??18O to Andean orogenic arc basalts. Instead, these basalts are formed by relatively low degrees of partial melting of heterogeneous lower continental lithosphere and/or asthenosphere, probably due to thermal and mechanical pertubation of the mantle in response to subduction of oceanic lithosphere below the western margin of the continent. The "transitional" basalts do contain components added to their source region by either (1) active input of slab-derived components in amounts smaller than the contribution to the mantle below the arc and/or with lower Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios than below the arc due to progressive downdip dehydration of the subducted slab; or (2) subarc source region contamination processes which affected the mantle source of the "transitional" basalts earlier in the Cenozoic. ?? 1990 Springer-Verlag.

Contributions to Mineralogy and Petrology↗

USGS2003

The 1997 eruption of Okmok Volcano, Alaska: A synthesis of remotely sensed imagery

Okmok Volcano, in the eastern Aleutian Islands, erupted in February and March of 1997 producing a 6-km-long lava flow and low-level ash plumes. This caldera is one of the most active in the Aleutian Arc, and is now the focus of international multidisciplinary studies. A synthesis of remotely sensed data (AirSAR, derived DEMs, Landsat MSS and ETM+ data, AVHRR, ERS, JERS, Radarsat) has given a sequence of events for the virtually unobserved 1997 eruption. Elevation data from the AirSAR sensor acquired in October 2000 over Okmok were used to create a 5-m resolution DEM mosaic of Okmok Volcano. AVHRR nighttime imagery has been analyzed between February 13 and April 11, 1997. Landsat imagery and SAR data recorded prior to and after the eruption allowed us to accurately determine the extent of the new flow. The flow was first observed on February 13 without precursory thermal anomalies. At this time, the flow was a large single lobe flowing north. According to AVHRR Band 3 and 4 radiance data and ground observations, the first lobe continued growing until mid to late March, while a second, smaller lobe began to form sometime between March 11 and 12. This is based on a jump in the thermal and volumetric flux determined from the imagery, and the physical size of the thermal anomalies. Total radiance values waned after March 26, indicating lava effusion had ended and a cooling crust was growing. The total area (8.9 km 2 ), thickness (up to 50 m) and volume (1.54×10 8 m 3 ) of the new lava flow were determined by combining observations from SAR, Landsat ETM+, and AirSAR DEM data. While the first lobe of the flow ponded in a pre-eruption depression, our data suggest the second lobe was volume-limited. Remote sensing has become an integral part of the Alaska Volcano Observatory’s monitoring and hazard mitigation efforts. Studies like this allow access to remote volcanoes, and provide methods to monitor potentially dangerous ones.

Journal of Volcanology and Geothermal Research↗

USGS2012

Sea-floor geology of Long Island Sound north of Duck Pond Point, New York

The U.S. Geological Survey, the National Oceanic and Atmospheric Administration (NOAA), and the Connecticut Department of Environmental Protection are mapping the sea floor in coastal areas of the northeastern United States. As part of the project, more than 100 square kilometers of multibeam-echosounder data, 23 sediment samples, bottom video, and 86 still photographs were obtained from an area in Long Island Sound north of Duck Pond Point, New York, in the study area of NOAA survey H11999. This report delineates the sediment types and sea-floor features found within this area in order to better understand the sea-floor processes occurring in this part of Long Island Sound. The sea floor in the study area is dominated by ubiquitous sand-wave fields and three northeast-southwest trending bathymetric depressions. Barchanoid and transverse sand waves, including sinusoidal, bifurcating, arced, and straight-crested morphologies, are variably present. Asymmetrical sand-wave profiles indicate a westward to southwestward direction of sediment transport in most of the study area; current ripples and megaripples on the stoss slopes of the sand waves indicate transport is ongoing. The majority of the sediment on the sea floor is sand, although bouldery, gravelly, and muddy sediments are also present. Gray, cohesive mud crops out on the walls of some of the scour depressions associated with the troughs of large sand waves. Clasts of the muddy sediment scattered on the sea floor around the depressions demonstrate the intensity of the scour and suggest erosion of the underlying distal deltaic sediments.

New York↗

USGS1991

Jurassic normal and strike-slip faults at Crater Island, northwestern Utah

At Crater Island, northern Silver Island Mountains, northwestern Utah, an unbroken Tertiary fault block within the Basin and Range province exhibits Jurassic or older structures that are virtually unmodified by subsequent tectonism, providing an opportunity to examine the tectonics of the Jurassic back arc of the Cordillera. Widespread high-angle faults, mainly striking north and northeast, offset the moderately west-dipping strata down to the west, thereby extending the strata parallel to bedding by 10% to 20%. These faults apparently belong to a single kinematic event of west-northwest oriented extension subparallel to bedding. The normal faults merge with a north-northwest dextral strike-slip fault system. The two fault systems are kinematically compatible, suggesting that they may have been contemporaneous. A low-angle (thrust?) fault nearly parallel to bedding within Ordovician strata is cut by the high-angle faults. Intrusive relations with about 160 Ma granitoid rocks show that all of these faults are Late Jurassic or older, with a reasonable lower age limit of Early Jurassic established on the basis of paleogeographic reconstructions using sedimentary deposits in the region. Jurassic dikes indicate a minimum horizontal compression direction that is parallel to the extension direction indicated by the normal faults, thus supporting the inference that normal and strike-slip faulting took place during the late Middle or early Late Jurassic. We interpret these data to indicate that minor thrusting, probably during the Jurassic, was followed by extensional faulting within a strike-slip fault system, probably close in time to intrusion. These relations are similar to those reported previously in the nearby Newfoundland Mountains. Other mountains of northern Utah and adjacent Nevada also have examples of Jurassic normal faults that contrast with the more generally observed thrust faults and tectonite fabrics. These data point to a possible regional extensional tectonic event affecting the crust far inland of the Jurassic magmatic arc, an event probably associated with back-arc magmatism.

Utah↗

USGS2013

Porphyry copper assessment of Southeast Asia and Melanesia: Chapter D in Global mineral resource assessment

The U.S. Geological Survey collaborated with member countries of the Coordinating Committee for Geoscience Programmes in East and Southeast Asia (CCOP) on an assessment of the porphyry copper resources of Southeast Asia and Melanesia as part of a global mineral resource assessment. The region hosts world-class porphyry copper deposits and underexplored areas that are likely to contain undiscovered deposits. Examples of known porphyry copper deposits include Batu Hijau and Grasberg in Indonesia; Panguna, Frieda River, and Ok Tedi in Papua New Guinea; and Namosi in Fiji. This assessment covers the countries of Cambodia, Indonesia, Lao People’s Democratic Republic, Malaysia, Myanmar, Papua New Guinea, Singapore, Thailand, and parts of southeastern China, India, the Solomon Islands, Vanuatu, and Fiji. Twenty-two geographic areas were delineated as tracts that are permissive for porphyry copper deposits in Southeast Asia. Permissive tracts are grouped into four broadly defined geographic/geologic areas, as follows: (1) the Indochina Peninsula area, (2) Indonesian and Malaysian Islands, (3) New Guinea Island and Papuan New Guinea islands, and (4) Melanesia. Individual tracts range from less than 1,000 to more than 350,000 square kilometers in area. Permissive tracts are based on mapped and inferred subsurface (<1 kilometer depth) distributions of igneous rocks of specific age ranges that define magmatic arcs and magmatic belts that are likely to contain porphyry copper deposits. Most of these magmatic arcs are subduction-related, although some have porphyry-style deposits occurring in postcollisional and (or) poorly understood tectonic settings. Although maps at a variety of different scales were used in the compilation, the final tract boundaries are intended for use at a scale of 1:1,000,000. Global grade and tonnage models for porphyry copper deposits were evaluated. Most of the known deposits are best described as fitting the copper-gold (Cu-Au) subtype of porphyry copper deposit. For some permissive tracts, a general porphyry copper-gold-molybdenum (Cu-Au-Mo) model was used. Assessment participants estimated numbers of undiscovered deposits at different levels of confidence for most of the permissive tracts. These estimates were combined with grade and tonnage models using a Monte Carlo simulation to estimate undiscovered resources. Additional resources in extensions of deposits with identified resources were not evaluated. Assessment results, presented in tables and graphs, show mean amounts of metal and mineralized rock in undiscovered deposits at different quantile levels, as well as the arithmetic mean for each tract. This assessment estimated a mean of 89 undiscovered porphyry copper deposits for the assessed permissive tracts in Southeast Asia and Melanesia. About 288 million metric tons (Mt) of copper and 18,000 metric tons (t) of gold, as well as byproduct molybdenum and silver, could be associated with undiscovered deposits. This represents about four times the number of deposits with identified resources (23) already discovered in Southeast Asia; reliable reported identified resources for those 23 deposits total 84 Mt of copper and 6,000 t of gold. Eleven permissive tracts have no known porphyry copper deposits with reported resources. Three of those 11 tracts lacked sufficient information for a probabilistic assessment and are discussed in qualitative terms. On a regional basis, both the Indochina Peninsula area and the Indonesian-Malaysian Islands area are estimated to contain about 10 times as much in place copper in undiscovered porphyry copper deposits as has been identified to date. For the New Guinea Island areas, the ratio of undiscovered to identified copper resources is about 2. Some parts of the region have a long history of porphyry exploration cycles and mine development, interrupted at times by political and social unrest, environmental concerns, and natural disasters. Changes in mining laws within the region and the recent high price of gold on the world market have prompted renewed interest in porphyry copper deposits in Southeast Asia and Melanesia. However, predicted undiscovered deposits may not be found, and if found, may not be developed. This assessment includes an overview of the assessment results with summary tables. Detailed descriptions of each tract are included in appendixes, with estimates of numbers of undiscovered deposits, and probabilistic estimates of amounts of copper, molybdenum, gold, and silver that could be contained in undiscovered deposits for each permissive tract. A geographic information system (GIS) that accompanies the report includes tract boundaries and a database of known porphyry copper deposits and significant prospects.

Scientific Investigations Report↗

USGS2011

Geologic map of the Suquamish 7.5' quadrangle and part of the Seattle North 7.5' x 15' quadrangle, Kitsap County, Washington

The Suquamish 7.5' quadrangle is in the center of the Puget Lowland, Washington. The quadrangle contains the northern two-thirds of Bainbridge Island and adjacent parts of the Kitsap Peninsula. Puget Sound and contiguous waterways form 35 percent of the map area. Maximum elevation is 137 m in the northwest corner of the quadrangle, west of Suquamish; the modal elevation is 44 m. The center of the quadrangle is 20 km west-northwest of downtown Seattle. Winslow, in the southeast corner of the quadrangle, is a 35-minute ferry ride from Seattle. The Suquamish quadrangle lies within the Salish Lowland physiographic province (Haugerud, 2004), a broad region in the forearc of the Cascade Volcanic Arc that extends from south of Olympia, Washington, to north of Campbell River, British Columbia, and includes both the Puget Lowland of western Washington and the Georgia Depression of northwestern Washington and southwestern British Columbia. To the east are the Cascade Range and Coast Mountains; to the west is the outer-arc high of the Coast Ranges. The Salish Lowland is the locus of late Cenozoic subsidence: Jones (1996) indicates as much as 1 km of unconsolidated fill beneath some areas. The Lowland is crossed by east-west topographic highs formed by bedrock uplifts. A northern San Juan high divides the Lowland into Georgia Depression and Puget Lowland subprovinces. A southern high, which lies athwart the south end of Bainbridge Island immediately south of the map area, coincides with the Seattle Fault Zone along which uplift has brought Eocene rocks to elevations of 800-1,200 m, 8-10 km higher than equivalent strata in the floor of the Seattle structural basin that underlies central and northern Bainbridge Island and areas to the east (Brocher and others, 2001; Blakely and others, 2002). Deformation along the Seattle Fault appears to be driven by north-south shortening of the Cascade forearc (Wells and others, 1998). Pleistocene glacial deposits underlie most of the map area. Most extensive are the various members of the Vashon Drift, deposited in the Vashon stade of the Fraser Glaciation of Armstrong and others (1965) between about about 17,000 years ago. This study was undertaken in response to (1) awareness of the hazard posed by future earthquakes in the Seattle Fault Zone, at the south edge of the quadrangle, and the need to marshal geologic evidence for the rate and style of deformation; (2) increasing population on Bainbridge Island and consequent pressure on groundwater resources; (3) concern about landslide hazards; and (4) awareness of the role that the nearshore zone plays in supporting marine resources.

Washington↗

USGS1990

Age determinations and growth rates of Pacific ferromanganese deposits using strontium isotopes

87Sr 86Sr ratios, trace element and REE compositions, and textural characteristics were determined for three hydrogenetic Fe-Mn crusts, one hydrothermal deposit, and two mixed hydrothermalhydrogenetic crusts from the Pacific. The Sr isotope data are compared to the Sr seawater curve for the Cenozoic to determine the ages and growth rates of the crusts. The 87Sr 86Sr in the crusts does not increase monotonically with depth as expected if the Sr were solely derived from seawater and perfectly preserved since deposition. This indicates post-depositional exchange of Sr or heterogeneous sources for the Sr originally contained in the crusts. Textures of hydrogenetic crusts generally correlate with Sr isotopic variations. The highest porosity intervals commonly exhibit the highest 87Sr 86Sr ratios, indicating exchange with younger seawater. Intervals with the lowest porosity commonly have lower 87Sr 86Sr and may preserve the original Sr isotopic ratios. Minimum ages of crust growth inception were calculated from dense, low porosity intervals. Growth of the hydrogenetic crusts began at or after 23 Ma, although their substrates are Cretaceous. Estimated average growth rates of the three hydrogenetic crusts vary between 0.9 and 2.7 mm/Ma, consistent with published rates determined by other techniques. Within the Marshall Islands crust, growth rates for individual layers varied greatly between 1.0 and 5.4 mm/Ma. For one crust, very low 87Sr 86Sr ratios occurred in detrital-rich intervals. Hydrothermal Fe-Mn oxide from the active Lau Basin back-arc spreading axis (Valu Fa Ridge) has an 87Sr 86Sr ratio with a predominantly seawater signature ( 87Sr 86Sr 0.709196), indicating a maximum age of 0.9 Ma. One crust from an off-axis seamount west of Gorda Ridge may have begun precipitating hydrogenetically at 0.5 Ma (0.709211), and had increasing hydrothermal or volcanic input in the top half of the crust, indicated by a significantly lower 87Sr 86Sr ratio (0.709052). ?? 1990.

Geochimica et Cosmochimica Acta↗

USGS1990

Age determinations and growth rates of Pacific ferromanganese deposits using strontium isotopes

87 Sr 86 Sr ratios, trace element and REE compositions, and textural characteristics were determined for three hydrogenetic Fe-Mn crusts, one hydrothermal deposit, and two mixed hydrothermalhydrogenetic crusts from the Pacific. The Sr isotope data are compared to the Sr seawater curve for the Cenozoic to determine the ages and growth rates of the crusts. The 87 Sr 86 Sr in the crusts does not increase monotonically with depth as expected if the Sr were solely derived from seawater and perfectly preserved since deposition. This indicates post-depositional exchange of Sr or heterogeneous sources for the Sr originally contained in the crusts. Textures of hydrogenetic crusts generally correlate with Sr isotopic variations. The highest porosity intervals commonly exhibit the highest 87 Sr 86 Sr ratios, indicating exchange with younger seawater. Intervals with the lowest porosity commonly have lower 87 Sr 86 Sr and may preserve the original Sr isotopic ratios. Minimum ages of crust growth inception were calculated from dense, low porosity intervals. Growth of the hydrogenetic crusts began at or after 23 Ma, although their substrates are Cretaceous. Estimated average growth rates of the three hydrogenetic crusts vary between 0.9 and 2.7 mm/Ma, consistent with published rates determined by other techniques. Within the Marshall Islands crust, growth rates for individual layers varied greatly between 1.0 and 5.4 mm/Ma. For one crust, very low 87 Sr 86 Sr ratios occurred in detrital-rich intervals. Hydrothermal Fe-Mn oxide from the active Lau Basin back-arc spreading axis (Valu Fa Ridge) has an 87 Sr 86 Sr ratio with a predominantly seawater signature ( 87 Sr 86 Sr 87 Sr 86 Sr 0.709196 "> 0.709196 ), indicating a maximum age of 0.9 Ma. One crust from an off-axis seamount west of Gorda Ridge may have begun precipitating hydrogenetically at 0.5 Ma (0.709211), and had increasing hydrothermal or volcanic input in the top half of the crust, indicated by a significantly lower 87 Sr 86 Sr ratio (0.709052).

Geochimica et Cosmochimica Acta↗

USGS1981

Gravity anomaly and interpretation map of the Chignik and Sutwik Island quadrangles, Alaska

The gravity field of the Chignik and Sutwik Island quadrangles near the center of the Alaska Peninsula represents a complex series of transitions between probable continental crust on the north, probable oceanic crust on the south, sedimentary basins on each side of the peninsula, and a central structural high and volcanic arc. The resulting gravity field may be generalized as a central southwest- to northeast-trending gravity high bordered on both sides by flanking gravity lows over sedimentary basins underlying the lowlands and continental shelf. All three gravitational features show discontinuities and magnitude variations that reflect the complex geologic setting. Data concerning this complex gravity field have accumulated slowly and intermittently since an initial measurement was made at Port Heiden more than 25 years go (Thiel and others, 1958, 1959). A few reconnaissance measurements by R. V. Allen and an offshore traverse conducted by the U.S. Coast and Geodetic Survey R/V Surveyor were made in the early 1960's (Barnes and others, 1966; Barnes, 1967). At about the same time, Gulf Oil Corp. contracted for a relatively detailed survey of the lowlands on the north shore of the peninsula; the map prepared from this survey is now available (Gulf Oil Corp., Port Moller Development Contract Report, available at U.S. Geological Survey, Anchorage, Alaska). In the early 1970's, a few new land measurements were made by P. L. Dobey, of the Alaska Division of Geological and Geophysical Surveys, and an offshore traverse was completed by the R/V C. Greene on contract to the U.S. Geological Survey (Fisher, 1979, and M. A. Fisher, written commun., 1977). The most recent measurements, the basis for this map, were made by M. E. Yount, D. L. Detra, D. R. Jefferis, and J. E. Case during the mineral assessment of the two quadrangles. D. F. Barnes, R. L. Morin, D. R. Jefferis, and R. F. Sikora have shared in the data compilation. Geologic background for the text was provided by R. L. Detterman, T. P. Miller, E. Young, and F. H. Wilson (1979, 1981).

Alaska↗

USGS2003

Descriptions of mineral occurrences and interpretation of mineralized rock geochemical data in the Stikine geophysical survey area, Southeastern Alaska

Detailed descriptions of some of the more significant mineral occurrences in the Stikine Airborne Geophysical Survey Project Area are presented based upon site-specific examinations by the U.S. Geological Survey in May of 1998. Reconnaissance geochemical data on unmineralized igneous and sedimentary host rocks, and mineralized rocks are also presented and are accompanied by a brief analysis of geochemical signatures typical of each occurrence. Consistent with the stated goal of the geophysical survey; to stimulate exploration for polymetallic massive sulfides similar to the Greens Creek deposit, the majority of the described occurrences are possible members of a belt of Late Triassic mineral deposits that are distributed along the eastern edge of the Alexander terrane in southeastern Alaska. Many of the described occurrences in the Duncan Canal-Zarembo Island area share similarities to the Greens Creek deposit. When considered as a whole, the geology, mineralogy, and geochemistry of these occurrences help to define a transitional portion of the Late Triassic mineral belt where changes in shallow to deeper water stratigraphy and arc-like to rift-related igneous rocks are accompanied by concomitant changes in the size, morphology, and metal endowments of the mineral occurrences. As a result, Late Triassic mineral occurrences in the area appear as: 1) small, discontinuous, structurally controlled stockwork veins in mafic volcanic rocks, 2) small, irregular replacements and stratabound horizons of diagenetic semi-massive sulfides in dolostones and calcareous shales, and as 3) larger, recognizably stratiform accumulations of baritic, semi-massive to massive sulfides at and near the contact between mafic volcanic rocks and overlying sedimentary rocks. Empirical exploration guidelines for Greens Creek-like polymetallic massive sulfide deposits in southeastern Alaska include: 1) a Late Triassic volcano-sedimentary host sequence exhibiting evidence of succession from tectonic activity to quiescence (such as conglomeratic and/or mafic volcaniclastics or flows overlain by platform carbonate or shale sequences), 2) presence and proximity to Late Triassic mafic-ultramafic intrusions, 3) presence of quartz-carbonate-fuchsite altered ultramafic bodies, 4) pyritic, graphitic shales, 5) presence of barite and/or iron-manganese-rich carbonates, 6) low-iron sphalerite and antimony-rich sulfosalt minerals, 7) a geochemical signature including Fe-Zn-Pb-Cu-Ag-Au-Sb-Hg-As-Cd-Ba-Mn-Mo-Tl and the ultramafic-related suite of elements Ni-Cr-Co, and 8) a geophysical signature characterized by the coincidence of a sharp resistivity contrast with evidence for buried intrusive rocks. Critical factors for the development of larger, economic orebodies are significant thickness of pyritic, graphitic shale indicating that a locally reducing sedimentary setting was established and that accumulation of an insulating shale blank occurred, and proximity to Late Triassic aged hypabyssal mafic-ultramafic intrusive rocks.

Open-File Report↗

USGS1996

Porphyry deposits of the Canadian Cordillera

Porphyry deposits are intrusion-related, large tonnage low grade mineral deposits with metal assemblages that may include all or some of copper, molybdenum, gold and silver. The genesis of these deposits is related to the emplacement of intermediate to felsic, hypabyssal, generally porphyritic intrusions that are commonly formed at convergent plate margins. Porphyry deposits of the Canadian Cordillera occur in association with two distinctive intrusive suites: calc-alkalic and alkalic. In the Canadian Cordillera, these deposits formed during two separate time periods: Late Triassic to Middle Jurassic (early Mesozoic), and Late Cretaceous to Eocene (Mesozoic-Cenozoic). Deposits of the early Mesozoic period occur in at least three different arc terranes (Wrangellia, Stikinia and Quesnellia) with a single deposit occurring in the oceanic assemblage of the Cache Creek terrane. These terranes were located outboard from continental North America during formation of most of their contained early Mesozoic porphyry deposits. Some of the deposits of this early period may have been emplaced during terrane collisions. Metal assemblages in deposits of the calc-alkalic suite include Mo-Cu (Brenda), Cu-Mo (Highland Valley, Gibraltar), Cu-Mo-Au-Ag (Island Copper, Schaft Creek) and Cu-Au (Kemess, Kerr).The alkalic suite deposits are characterized by a Cu-Au assemblage (Copper Mountain, Afton-Ajax, Mt. Milligan, Mount Polley, Galore Creek). Although silver is recovered from calc-alkalic and alkalic porphyry copper mining operations, silver data are seldom included in the published reserve figures. Those available are in the range of 1-2 grams per tonne (g??t-1). Alkalic suite deposits are restricted to the early Mesozoic and display distinctive petrology, alteration and mineralization that suggest a similar tectonic setting for both Quesnellia and Stikinia in Early Jurassic time. The younger deposits, late Mesozoic to Cenozoic in age, formed in an intracontinental setting, after the outboard host arc and related terranes accreted to the western margin of North America. These deposits are interpreted to occur in continental arc settings, and individual deposits are hosted by a variety of older country rocks. These younger deposits also show a spectrum of metal associations: Cu-Mo (Huckleberry, Berg), Cu-Au (-Mo) (Bell, Granisle, Fish Lake, Casino), Mo (Endako, Boss Mountain, Kit-sault, Quartz Hill), Mo-W (Logtung), Au-W (Dublin Gulch) and Au (Ft. Knox). There may be a continuum between Mo, Mo-W, Au-Mo-W and Au deposits. The distribution and timing of these post-accretion deposits likely reflect major crustal structures and subduction geometry. Cordilleran porphyry metallic deposits show the full range of morphological and depth relationships found in porphyry deposits worldwide. In addition, the Cordillera contains numerous alkalic suite deposits, which are rare worldwide: the unusual, possibly syntectonic Gibraltar deposit; and end-member gold-rich granite-hosted deposits, such as Ft. Knox (Alaska).

Geoscience Canada↗

USGS2014

Geochemical and Nd-Sr-Pb isotopic evolution of metabasites from rifting of continental lithosphere, Seward Peninsula, Alaska, and implications for paleogeographic reconstruction

The chemical character of mafic rocks from the Arctic Alaska–Chukotka terrane records rifting of continental crust during the early Paleozoic, possibly during the Ordovician. The mafic rocks are part of a metamorphosed Neoproterozoic to Devonian continental margin sequence preserved in a Mesozoic metamorphic terrane, the Nome Complex, of Seward Peninsula, Alaska. Protoliths of the mafic rocks include basalt and mafic clastic rocks, which were interlayered with calcareous, pelitic, and feldspathic sediments, and gabbro and diabase, likely feeder dikes and sills to the basalt. Major-element, trace-element, and rare-earth element (REE) analyses of these mafic rocks, together with analyses of Nd, Pb, and Sr isotopes, form two compositional groups. The two groups differ in Nb/Y (one plots as basalt, the other as alkali to subalkali basalt), TiO 2 , P 2 O 5 , and Nb (and other elements). The high-Ti group is characterized by enrichment of light REE; the low-Ti group lacks such enrichment. The trace-element and isotopic characteristics of the two groups resemble typical non-arc magmas derived from the mantle: the low-Ti group has compositions between normal mid-ocean ridge basalt (N-MORB) and enriched mid-ocean ridge basalt (E-MORB), while those of the high-Ti group are between E-MORB and ocean-island basalt (OIB). The two groups have overlapping positive values of ε Nd (+0.34 to +7.40). TiO 2 /Yb ratios suggest the high-Ti group formed from melts generated under normal thickness of continental crust, while the low-Ti group formed from melts generated at shallower conditions, presumably after rift-related crustal thinning had progressed. Geologic, paleontologic, and geochronologic characteristics of the Nome Complex support an origin along the NE margin of Baltica. The rift-related magmatism in the Nome Complex likely occurred during the opening of the Uralian ocean along that margin; by implication, related parts of the Arctic Alaska–Chukotka terrane may have experienced a similar origin.

Alaska↗