Peter Lipman | United States Geological Survey (original) (raw)

Papers by Peter Lipman

Scientific Investigations Map, 2020

West topographic rim of Bonanza caldera, as viewed to northwest, up valley of Kerber Creek. In di... more West topographic rim of Bonanza caldera, as viewed to northwest, up valley of Kerber Creek. In distance, Antora Peak (center, 13,269') is capped by densely welded dacitic Bonanza Tuff (33.12 Ma), while Windy Point (left, 12,800') exposes thin layer of basal rhyolitic Bonanza Tuff that has undergone local rheomorphic flowage. Lower slopes of both high points are west-dipping sequence of interlayered andesitic lavas and volcaniclastic rocks that make up the erosionally modified inner wall of Bonanza caldera. Sheep Mountain (right distant skyline, 12,228') is pre-Bonanza dacitic lava dome (33.78 Ma) that partly fills the older Marshall caldera, source of the 33.9-Ma Thorn Ranch Tuff. On left side of Kerber Creek, timbered slope is lower portion of southwest caldera wall; on right side of creek is dip slope on flank of postcollapse resurgent dome. The valley of Kerber Creek coincides with the main ring fault, along which more than 3 km of subsidence was accommodated during eruption of the Bonanza Tuff and concurrent caldera collapse.

Frontiers in Earth Science, 2019

Large-volume silicic volcanism poses global hazards in the form of proximal pyroclastic density c... more Large-volume silicic volcanism poses global hazards in the form of proximal pyroclastic density currents, distal ash fall and short-term climate perturbations, which altogether warrant the study of how silicic magma bodies evolve and assemble. The southern rocky mountain volcanic field (SRMVF) is home to some of the largest super-eruptions in the geological record, and has been studied to help address the debate over how quickly eruptible magma batches can be assembled-whether in decades to centuries, or more slowly over 100's of kyr. The present study focuses on the San Luis caldera complex within the SRMVF, and discusses the paradigms of rapid magma generation vs. rapid magma assembly. The caldera complex consists of three overlapping calderas that overlie the sources of three large-volume mid-Cenozoic ignimbrites: first, the Rat Creek Tuff (RCT; zoned dacite-rhyolite, 150 km 3), followed by the Cebolla Creek Tuff (mafic dacite, 250 km 3) and finally, the Nelson Mountain Tuff (NMT; zoned daciterhyolite, 500 km 3), which are all indistinguishable in age by 40 Ar/ 39 Ar dating. We argue for a shared magmatic history for the three units on the basis of (1) similar mineral trace element compositions in the first and last eruptions (plagioclase, sanidine, biotite, pyroxene, amphibole, titanite, and zircon), (2) overlapping zircon U-Pb ages in all three units, and (3) similar thermal rejuvenation signatures visible in biotite (low-Mn, high-Ba) and zircon (low-Hf, low-U) geochemistry within the RCT and NMT. It is postulated that the NMT was sourced from a pre-existing magma reservoir to the northeast, which is corroborated by the formation of the nearby Cochetopa Caldera during the eruption of the NMT. The inferred lateral magma transport has two important implications: (1) it demonstrates long-distance transport of highly viscosity magmas at volumes (100's of km 3) not previously recorded, and (2) the sourcing of magma from a nearby pre-existing magma reservoir greatly reduces the rate of magma generation necessary to explain the close coincidence of three overlapping, large-volume magma systems. Additionally, the concept of magmatic "flux" (km 3 kyr −1) is discussed in this context, and it is argued that an area-normalized flux (km 3 kyr −1 km −2) provides a more useful number for measuring magma production rates: it is expected that magmatic volumes will scale with footprint of the thermal anomaly, and not taking this into account may lead to errant volumetric

Da~hed lines arc boundaries between volcanoes.

Radiocarbon, 1978

This list contains the results of some measurements made between 1966 and 1975, and includes some... more This list contains the results of some measurements made between 1966 and 1975, and includes some earlier unpublished dates. Samples are counted in the form of acetylene gas, as previously, and ages computed on the basis of the Libby half-life, 5568 ± 30 years. The dates have not been corrected for fractionation by making a 13C measurement. The error listed, always larger than the one-sigma statistical counting error commonly used, takes into account possible fractionation in the laboratory and in nature and variability experienced with replicate samples. We thank Linda Wilt for helping in the preparation of the manuscript and Charles Oman for his technical assistance.

AGUFM, Dec 1, 2007

ABSTRACT While the linkage between Cordilleran plutonism and volcanism remains debated, data for ... more ABSTRACT While the linkage between Cordilleran plutonism and volcanism remains debated, data for large silicic volcanic fields (LSVF) document informative space-time-composition parallels. The comparable dimensions and spacing of centers and similar petrological and geochemical characteristics support the view that, like Cordilleran batholiths, LSVF are composed of multiple periodically constructed magmatic systems. The spatiotemporal record of volcanism at two well-studied LSVF that are geometrically, compositionally, and temporally comparable, the 10 to 1 Ma Altiplano-Puna Volcanic Complex (APVC) of the Central Andes and the 37 to 26 Ma Southern Rocky Mountain volcanic field (SRMVF) of Colorado, provide windows into the construction of the uppermost parts of Cordilleran batholiths. Both the APVC and SRMVF involved eruption of numerous dacite to rhyolite ignimbrites with volumes >100 km3; several with volumes >1000 km3. Some calderas in both regions were polycyclic, with the largest caldera sources 60 km or more across. Area covered in both regions is on the order of 70,000 to 100,000 km2, during eruptive activity of ~10 m.y. Cumulative magmatic volume of ignimbrites is about 10,000 km3 for the APVC and 15,000 km3 for the SRMVF, and estimated peak magma- production rates are as high as 12,000 to 8,000 km3/m.y respectively. Calderas in both areas are associated with pre-and post-caldera andesitic to dacitic lava eruptions. The calderas and other magmatic centers of both areas lie within regional gravity lows that suggest the subvolcanic growth of upper-crustal composite batholiths associated with the silicic volcanism. Both the APVC and the SRMVF lie along the east margins of broad long-lived Cordilleran magmato-tectonic zones, involving plate convergence and low-angle subduction. The APVC is associated with a regional seismic anomaly interpreted as indicating the presence of partial melt in the middle crust; no comparable feature(s) are present beneath the SRMVF, plausibly because of its greater age. The spatiotemporal records from these fields suggest that the combined volcano-plutonic system records a magmatic flare-up that was at least an order of magnitude more intense than the steady-state rates that characterize the long-term evolution of destructive plate margins. The flare-up initiated suddenly, at rates slightly above steady state, escalated to a climactic stage, and declined rapidly. This pattern, and the organization of activity into distinct pulses of increasing intensity and spatial definition with time at LSVF should produce a plutonic record. While Cordilleran batholiths such as the Sierra Nevada Batholith in California contain evidence of comparable flare-ups, resolution of the plutonic record does not distinguish individual pulses. Issues in need of future study include refining the volume-time and spatiotemporal patterns, determining the trigger for magmatic flare-ups and controls on episodic magmatism--both volcanic and plutonic , and resolving the disparate records in the two realms.

Open-File Report, 1987

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey e... more This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards. Any use of trade names is for descriptive purposes only and does not imply endorsement by the USGS. The GLORIA surveying responsibilities are split between IOS and USGS personnel. The IOS participants are responsible for all operations involving GLORIA, as well as for all deck operations and maintenance of the airgun seismic-reflection system and the 3.5-and 10-kHz profiling systems. The USGS personnel are responsible for all aspects of the gravimeter and gradiometer operations and for wachstanding duties for everything except GLORIA and the navigation system. The co-chief scientists from the USGS and IOS are jointly responsible for general survey planning and construction of two sets of field mosaics of the GLORIA data.