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P. W. Lipman

Publications and source records attributed to P. W. Lipman.

At least 19 recordsLinked to original sources
USGS2011

Evolution of silicic magma in the upper crust: the mid-Tertiary Latir volcanic field and its cogenetic granitic batholith, northern New Mexico, USA

Structural and topographic relief along the eastern margin of the Rio Grande rift, northern New Mexico, provides a remarkable cross-section through the 26-Ma Questa caldera and cogenetic volcanic and plutonic rocks of the Latir field. Exposed levels increase in depth from mid-Tertiary depositional surfaces in northern parts of the igneous complex to plutonic rocks originally at 3-5 km depths in the S. Erosional remnants of an ash-flow sheet of weakly peralkaline rhyolite (Amalia Tuff) and andesitic to dactitic precursor lavas, disrupted by rift-related faults, are preserved as far as 45 km beyond their sources at the Questa caldera. Broadly comagmatic 26 Ma batholithic granitic rocks, exposed over an area of 20 by 35 km, range from mesozonal granodiorite to epizonal porphyritic granite and aplite; shallower and more silicic phases are mostly within the caldera. Compositionally and texturally distinct granites defined resurgent intrusions within the caldera and discontinuous ring dikes along its margins: a batholithic mass of granodiorite extends 20 km S of the caldera and locally grades vertically to granite below its flat-lying roof. A negative Bouguer gravity anomaly (15-20 mgal), which encloses exposed granitic rocks and coincides with boundaries of the Questa caldera, defined boundaries of the shallow batholith, emplaced low in the volcanic sequence and in underlying Precambrian rocks. Paleomagnetic pole positions indicate that successively crystallised granitic plutons cooled through Curie temperatures during the time of caldera formation, initial regional extension, and rotational tilting of the volcanic rocks. Isotopic ages for most intrusions are indistinguishable from the volcanic rocks. These relations indicate that the batholithic complex broadly represents the source magma for the volcanic rocks, into which the Questa caldera collapsed, and that the magma was largely liquid during regional tectonic disruption. -from Author

Transactions of the Royal Society of Edinburgh, Ea↗
USGS2004

Emplacement mechanisms of the South Kona slide complex, Hawaii Island: Sampling and observations by remotely operated vehicle Kaiko

Emplacement of a giant submarine slide complex, offshore of South Kona, Hawaii Island, was investigated in 2001 by visual observation and in-situ sampling on the bench scarp and a megablock, during two dives utilizing the Remotely Operated Vehicle (ROV) Kaiko and its mother ship R/V Kairei. Topography of the bench scarp and megablocks were defined in 3-D perspective, using high-resolution digital bathymetric data acquired during the cruise. Compositions of 34 rock samples provide constraints on the landslide source regions and emplacement mechanisms. The bench scarp consists mainly of highly fractured, vesiculated, and oxidized a-a lavas that slumped from the subaerial flank of ancestral Mauna Loa. The megablock contains three units: block facies, matrix facies, and draped sediment. The block facies contains hyaloclastite interbedded with massive lava, which slid from the shallow submarine flank of ancestral Mauna Loa, as indicated by glassy groundmass of the hyaloclastite, low oxidation state, and low sulfur content. The matrix facies, which directly overlies the block facies and is similar to a lahar deposit, is thought to have been deposited from the water column immediately after the South Kona slide event. The draped sediment is a thin high-density turbidite layer that may be a distal facies of the Alika-2 debris-avalanche deposit; its composition overlaps with rocks from subaerial Mauna Loa. The deposits generated by the South Kona slide vary from debris avalanche deposit to turbidite. Spatial distribution of the deposits is consistent with deposits related to large landslides adjacent to other Hawaiian volcanoes and the Canary Islands. ?? Springer-Verlag 2004.

Bulletin of Volcanology↗
USGS2000

Voluminous lava-like precursor to a major ash-flow tuff: Low-column pyroclastic eruption of the Pagosa Peak Dacite, San Juan volcanic field, Colorado

The Pagosa Peak Dacite is an unusual pyroclastic deposit that immediately predated eruption of the enormous Fish Canyon Tuff (~5000 km3) from the La Garita caldera at 28 Ma. The Pagosa Peak Dacite is thick (to 1 km), voluminous (>200 km3), and has a high aspect ratio (1:50) similar to those of silicic lava flows. It contains a high proportion (40-60%) of juvenile clasts (to 3-4 m) emplaced as viscous magma that was less vesiculated than typical pumice. Accidental lithic fragments are absent above the basal 5-10% of the unit. Thick densely welded proximal deposits flowed rheomorphically due to gravitational spreading, despite the very high viscosity of the crystal-rich magma, resulting in a macroscopic appearance similar to flow-layered silicic lava. Although it is a separate depositional unit, the Pagosa Peak Dacite is indistinguishable from the overlying Fish Canyon Tuff in bulk-rock chemistry, phenocryst compositions, and 40Ar/39Ar age. The unusual characteristics of this deposit are interpreted as consequences of eruption by low-column pyroclastic fountaining and lateral transport as dense, poorly inflated pyroclastic flows. The inferred eruptive style may be in part related to synchronous disruption of the southern margin of the Fish Canyon magma chamber by block faulting. The Pagosa Peak eruptive sources are apparently buried in the southern La Garita caldera, where northerly extensions of observed syneruptive faults served as fissure vents. Cumulative vent cross-sections were large, leading to relatively low emission velocities for a given discharge rate. Many successive pyroclastic flows accumulated sufficiently rapidly to weld densely as a cooling unit up to 1000 m thick and to retain heat adequately to permit rheomorphic flow. Explosive potential of the magma may have been reduced by degassing during ascent through fissure conduits, leading to fracture-dominated magma fragmentation at low vesicularity. Subsequent collapse of the 75 x 35 km2 La Garita caldera and eruption of the Fish Canyon Tuff were probably triggered by destabilization of the chamber roof as magma was withdrawn during the Pagosa Peak eruption. (C) 2000 Elsevier Science B.V. All rights reserved.

Journal of Volcanology and Geothermal Research↗
USGS1996

Recurrent eruption and subsidence at the Platoro caldera complex, southeastern San Juan volcanic field, Colorado: New tales from old tuffs

Reinterpretation of a voluminous regional ash-flow sheet (Masonic Park Tuff) as two separate tuff sheets of similar phenocryst-rich dacite erupted from separate source calderas has important implications for evolution of the multicyclic Platoro caldera complex and for caldera-forming processes generally. Masonic Park Tuff in central parts of the San Juan field, including the type area, was erupted from a concealed source at 28.6 Ma, but widespread tuff previously mapped as Masonic Park Tuff in the southeastern San Juan Mountains is the product of the youngest large-volume eruption of the Platoro caldera complex at 28.4 Ma. This large unit, newly named the “Chiquito Peak Tuff,” is the last-erupted tuff of the Treasure Mountain Group, which consists of at least 20 separate ash-flow sheets of dacite to low-silica rhyolite erupted from the Platoro complex during a 1 m.y. interval (29.5−28.4 Ma). Two Treasure Mountain tuff sheets have volumes in excess of 1000 km 3 each, and five more have volumes of 50–150 km 3 . The total volume of ash-flow tuff exceeds 2500 km 3 , and caldera-related lavas of dominantly andesitic composition make up 250-500 km 3 more. A much greater volume of intermediate-composition magma must have solidified in subcaldera magma chambers. Most preserved features of the Platoro complex-including postcollapse asymmetrical trap-door resurgent uplift of the ponded intracaldera tuff and concurrent infilling by andesitic lava flows-postdate eruption of the Chiquito Peak Tuff. The numerous large-volume pre-Chiquito Peak ash-flow tuffs document multiple eruptions accompanied by recurrent subsidence; early-formed caldera walls nearly coincide with margins of the later Chiquito Peak collapse. Repeated syneruptive collapse at the Platoro complex requires cumulative subsidence of at least 10 km. The rapid regeneration of silicic magmas requires the sustained presence of an andesitic subcaldera magma reservoir, or its rapid replenishment, during the 1 m.y. life span of the Platoro complex. Either case implies large-scale stoping and assimilative recycling of the Tertiary section, including intracaldera tuffs.

Colorado↗
USGS1992

Jurassic ash-flow sheets, calderas, and related intrusions of the Cordilleran volcanic arc in southeastern Arizona: Implications for regional tectonics and ore deposits

Volcanologic, petrologic, and paleomagnetic studies of widespread Jurassic ash-flow sheets in the Huachuca-southern Dragoon Mountains area have led to identification of four large source calderas and associated comagmatic intracaldera intrusions. Stratigraphic, facies, and contact features of the caldera-related tuffs also provide constraints on the locations, lateral displacements, and very existence for some major northwest-trending faults and inferred regional thrusts in south-eastern Arizona. For example, the intricate Cochise thrust system, as mapped by others in the southern Dragoon Mountains, consists instead of primary depositional contacts within caldera-fill megabreccia, and the inferred regional thrusts do not exist, at least as previously interpreted. Silicic alkalic compositions of the Jurassic caldera-related, ash-flow tuffs; bimodal associated mafic magmatism; and interstratified coarse sedimentary deposits provide evidence for synvolcanic extension and rifting within the Cordilleran magmatic arc. Gold-copper mineralization is associated with subvolcanic intrusions at several of the Jurassic calderas.

Arizona↗
USGS1990

Volcanology and mineral deposits

Traditionally, volcanologists have focused on forecasting, observing, and interpreting events, processes, and products of eruptions at active volcanoes. Such work involves drama, beauty, fascination scientific problems, and the socially important aim of reducing risks to life and property. In contrast, old volcanic regions, which host many of the world's major hydrothermal-vein, porphyry, and massive-sulfide ore deposits, have been studied mainly by economic geologists, regional stratigraphers, and structural geologists who have limited familiarity with the complexities of volcanic processes. Such "dead" volcanoes, ranging in age from a few million million years (tertiary) to a few billion years (Precambrian), are commonly incompletely and discontinuously preserved due to rapid erosion of originally high-standing volcanic edifices. They can be difficult to date reliably, especially in terms of the time scales of individual volcanic events, and are variably hydrothermally altered-impeding high-resolution petrologic and geochemical studies. Many volcanologists, geochemists, and geophysicists who work on active volcanoes accordingly have been reluctant to become involved in studies of such less tractable rocks.

Earthquakes & Volcanoes (USGS)↗
USGS1989

Geochemistry of intrusive rocks associated with the Latir volcanic field, New Mexico, and contrasts between evolution of plutonic and volcanic rocks

Plutonic rocks associated with the Latir volcanic field comprise three groups: 1) ???25 Ma high-level resurgent plutons composed of monzogranite and silicic metaluminous and peralkaline granite, 2) 23-25 Ma syenogranite, and alkali-feldspar granite intrusions emplaced along the southern caldera margin, and 3) 19-23 Ma granodiorite and granite plutons emplaced south of the caldera. Major-element compositions of both extrusive and intrusive suites in the Latir field are broadly similar; both suites include high-SiO2 rocks with low Ba and Sr, and high Rb, Nb, Th, and U contents. Moreover, both intermediateto siliciccomposition volcanic and plutonic rocks contain abundant accessory sphene and apatite, rich in rare-earth elements (REE), as well as phases in which REE's are essential components. Strong depletion in Y and REE contents, with increasing SiO2 content, in the plutonic rocks indicate a major role for accessory mineral fractionation that is not observed in volcanic rocks of equivalent composition. Considerations of the rheology of granitic magma suggest that accessory-mineral fractionation may occur primarily by filter-pressing evolved magmas from crystal-rich melts. More limited accessory-mineral crystallization and fractionation during evolution of the volcanic magmas may have resulted from markedly lower diffusivities of essential trace elements than major elements. Accessory-mineral fractionation probably becomes most significant at high crystallinities. The contrast in crystallization environments postulated for the extrusive and intrusive rocks may be common to other magmatic systems; the effects are particularly pronounced in highly evolved rocks of the Latir field. High-SiO2 peralkaline porphyry emplaced during resurgence of the Questa caldera represents non-erupted portions of the magma that produced the Amalia Tuff during caldera-forming eruption. The peralkaline porphyry continues compositional and mineralogical trends found in the tuff. Amphibole, mica, and sphene compositions suggest that the peralkaline magma evolved from metaluminous magma. Extensive feldspar fractionation occurred during evolution of the peralkaline magmas, but additional alkali and iron enrichment was likely a result of high halogen fluxes from crystallizing plutons and basaltic magmas at depth. ?? 1989 Springer-Verlag.

Contributions to Mineralogy and Petrology↗
USGS1989

Geologic map of the Latir Volcanic Field and adjacent areas, northern New Mexico

This map was first published as a printed edition in 1989. The geologic data have now been captured digitally and are presented here along with images of the printed map sheet and component parts as PDF files. This map encompasses all or parts of ten 7.5 minute quadrangles in the Taos Range of the Sangre de Cristo Mountains in northern New Mexico. Geologic mapping was initiated in this area by the U.S. Geological Survey in response to its mandate under the Wilderness Act of 1964 to evaluate the mineral resource potential of the Latir and Wheeler Peak Wildernesses and the Columbine-Hondo Wilderness Study Area in the Carson National Forest. The mapping was later extended to adjacent areas in order to better understand the regional geology and geologic history of the range. The present map focuses on the early Tertiary (largely Oligocene) Latir Volcanic Field and plutonic rocks associated with it. The basement rocks in the map area are Paleoproterozic amphibolite-facies metasedimentary and metavolcanic rocks intruded by large bodies of quartz monzonite, granodiorite and gabbro dated at between 1,750 and 1,690 Ma. The basement rocks are locally overlain by Mississippian limestone or by Pennsylvanian and Permian redbeds. The basement rocks were thrust eastward across a thick section of similar late Paleozoic rocks along low-angle faults during the Laramide Orogeny. Post-Laramide erosion largely removed the sedimentary cover from the basement rocks and reduced the topography to a low-relief surface locally overlain by scattered lenses of Eocene to Oligocene shale, sandstone, and conglomerate. It was on this surface that the earliest rocks of the Latir Volcanic Field were deposited, beginning in the Oligocene, about 30 Ma. The early volcanic rocks comprise a thick sequence of andesite, dacite, and minor rhyolite, deposited as flows, breccia, and volcaniclastic sediments from numerous local volcanic centers; thin layers of rhyolite tuff are from distant eruptions, some probably in the San Juan Mountains. These volcanic rocks probably record early growth of an upper-crustal batholith. At 25 Ma enormous eruptions of peralkaline rhyolite ash-flow tuff were accompanied by collapse of the roof of the growing batholith to form the Questa Caldera, a volcanic depression at least 14 km across. The ash flows traveled for tens of kilometers from the caldera rims to form a widespread sheet of densely welded tuff; ash also fell back to fill the subsiding caldera depression. Concurrent extension along northwest-trending faults segmented the volcanic edifice and rotated the originally sub-horizontal layers, so that some are nearly vertical. Formation of the caldera was accompanied by further batholith growth, involving intrusion of large plutons of granite, granodiorite, and related rocks into both caldera fill and the adjacent rocks, including both the earlier volcanic rocks and the basement rocks. The large molybdenum deposit along the Red River east of Questa is related to the emplacement of one of these late granitic plutons. Intrusive activity continued into the Miocene. Development of the Rio Grande Rift beginning at about 15 Ma was accompanied by development of the north-south trending normal faults along the western foot of the Taos Range. The rift is filled with thousands of meters of clastic sediments interleaved with basalt flows, some as young as 3.6 Ma. The bounding faults of the rift cut the Questa Caldera so that the western part of the original structure is now deeply buried beneath the rift fill.

New Mexico↗
USGS1988

Origin of metaluminous and alkaline volcanic rocks of the Latir volcanic field, northern Rio Grande rift, New Mexico

Volcanic rocks of the Latir volcanic field evolved in an open system by crystal fractionation, magma mixing, and crustal assimilation. Early high-SiO2 rhyolites (28.5 Ma) fractionated from intermediate compositionmagmas that did not reach the surface. Most precaldera lavas have intermediate-compositions, from olivine basaltic-andesite (53% SiO2) to quartz latite (67% SiO2). The precaldera intermediate-composition lavas have anomalously high Ni and MgO contents and reversely zoned hornblende and augite phenocrysts, indicating mixing between primitive basalts and fractionated magmas. Isotopic data indicate that all of the intermediate-composition rocks studied contain large crustal components, although xenocrysts are found only in one unit. Inception of alkaline magmatism (alkalic dacite to high-SiO2 peralkaline rhyolite) correlates with, initiation of regional extension approximately 26 Ma ago. The Questa caldera formed 26.5 Ma ago upon eruption of the >500 km3 high-SiO2 peralkaline Amalia Tuff. Phenocryst compositions preserved in the cogenetic peralkaline granite suggest that the Amalia Tuff magma initially formed from a trace element-enriched, high-alkali metaluminous magma; isotopic data suggest that the parental magmas contain a large crustal component. Degassing of water- and halogen-rich alkali basalts may have provided sufficient volatile transport of alkalis and other elements into the overlying silicic magma chamber to drive the Amalia Tuff magma to peralkaline compositions. Trace element variations within the Amalia Tuff itself may be explained solely by 75% crystal fractionation of the observed phenocrysts. Crystal settling, however, is inconsistent with mineralogical variations in the tuff, and crystallization is thought to have occurred at a level below that tapped by the eruption. Spatially associated Miocene (15-11 Ma) lavas did not assimilate large amounts of crust or mix with primitive basaltic magmas. Both mixing and crustal assimilation processes appear to require development of relatively large magma chambers in the crust that are sustained by large basalt fluxes from the mantle. The lack of extensive crustal contamination and mixing in the Miocene lavas may be related to a decreased basalt flux or initiation of blockfaulting that prevented pooling of basaltic magma in the crust. ?? 1988 Springer-Verlag.

Contributions to Mineralogy and Petrology↗
USGS1987

Disruption of the Mauna Loa magma system by the 1868 Hawaiian earthquake: Geochemical evidence.

To test whether a catastrophic earthquake could affect an active magma system, mean abundances (adjusted for "olivine control") of titanium, potassium, phosphorus, strontium, zirconium, and niobium of historic lavas erupted from Mauna Loa Volcano, Hawaii, after 1868 were analyzed and were found to decrease sharply relative to lavas erupted before 1868. This abrupt change in lava chemistry, accompanied by a halved lava-production rate for Mauna Loa after 1877, is interpreted to reflect the disruptive effects of a magnitude 7.5 earthquake in 1868. This interpretation represents a documentable case of changes in magmatic chemical variations initiated or accelerated by a major tectonic event.

Hawaii↗
USGS1985

Degassing-induced crystallization of basaltic magma and effects on lava rheology

During the north-east rift eruption of Mauna Loa volcano, Hawaii, on 25 March-14 April 1984 (Fig. 1), microphenocryst contents of erupted lava increased from 0.5 to 30% without concurrent change in either bulk magma composition or eruption temperature (1,140 ?? 3 ??C). The crystallization of the microphenocrysts is interpreted here as being due to undercooling of the magma 20-30 ??C below its liquidas; the undercooling probably resulted from separation and release of volatiles as the magma migrated 12 km from the primary summit reservoir to the eruption site on the north-east rift zone. Such crystallization of magma during an eruption has not been documented previously. The undercooling and crystallization increased the effective viscosity of the magma, leading to decreased eruption rates and stagnation of the lava flow. ?? 1985 Nature Publishing Group.

Nature↗
USGS1985

Mesozoic ash-flow caldera fragments in southeastern Arizona and their relation to porphyry copper deposits

Jurassic and Upper Cretaceous volcanic and associated granitic rocks in southeast Arizona are remnants of large composite silicic volcanic fields, characterized by voluminous ash-flow tuffs and associated calderas. Presence of 10–15 large caldera fragments is inferred primarily from (1) ash-flow deposits more than 1 km thick, having features of intracaldera ponding; (2) “exotic-block” breccias within a tuff matrix, interpreted as caldera-collapse megabreccias; and (3) local granitic intrusions along arcuate structural boundaries of the thick volcanic sequences. Several porphyry copper deposits are associated with late granitic intrusions within the calderas or along their margins.

Geology↗