Allen Glazner - Academia.edu (original) (raw)

Papers by Allen Glazner

Advances in Volcanology, 2015

One way to frame the debate about the relationships between volcanic and plutonic rocks is this: ... more One way to frame the debate about the relationships between volcanic and plutonic rocks is this: are plutons samples of magma that passed through the crust, or residues left behind by extraction of erupted liquids? In the former case plutons are compositionally equivalent to cogenetic volcanic rocks, barring biases introduced by passing through the crustal filter; in the latter they are cumulates, having lost liquid to eruption. These hypotheses make specific predictions about trace-element variations, which we test using global geochemical databases for circum-Pacific convergent margins and western North America. Volcanic rocks are far more abundant in these datasets than plutonic rocks and are biased to more mafic compositions. After subsampling the volcanic dataset to match the plutonic dataset, we find little evidence for significant loss of liquid from plutons. Rather, plutonic and volcanic trace-element patterns are generally indistinguishable. Where distinctions do occur, they are backwards; for example, a higher proportion of plutonic rocks has low Eu, Zr, and Ba, features of fractionated liquids, than volcanic rocks. These observations support the hypothesis that liquids fractionated from crystal-rich magmas are of small volume and are relatively immobile (e.g., aplites). These conclusions, derived from bulk-rock geochemistry, are supported by U-Pb zircon geochronology and field and textural observation. These data support the view that plutonic rocks are texturally modified samples of the same magmas that erupt. Partial melting provides an alternative to crystal fractionation for the origin of high-silica volcanic rocks.

GSA Today, 2019

I learned very early the difference between knowing the name of something and knowing something.-... more I learned very early the difference between knowing the name of something and knowing something.-Richard Feynman

Cenozoic volcanism in the Mojave Desert region of southern California comprises two main groups: ... more Cenozoic volcanism in the Mojave Desert region of southern California comprises two main groups: early Miocene ([approx]24--18 Ma) synextensional magmatism ranging from basalt to rhyolite, and postkinematic middle Miocene to Quaternary volcanism that is almost exclusively basaltic. Flat-lying basalts of the latter group, herein termed the Mojave Neovolcanic Belt (MNB), are distributed across the central and eastern Mojave Desert, and were erupted in three main pulses: (1) during the middle Miocene ([approx]17--15 Ma), in a belt from near Tiefort Mtn. to the El Paso Mts.; (2) during the late Miocene ([approx]9--4 Ma); and (3) in a Plio-Quaternary pulse ([approx]3--0 Ma) that includes the southern Cima field and all the cones scattered along the axis of the Barstow-Bristol trough. Several temporal and geographic trends are evident in the MNB. In general, younger basalts are higher in [var epsilon][sub Nd], lower in [sup 87]Sr/[sup 86]Sr, more alkalic, less crustally contaminated, and more likely to contain mantle xenoliths than older basalts. Mantle xenoliths are restricted to the eastern and southern Mojave block. Basalts of all three groups become dramatically richer in K[sub 2]O to the east, ranging from subalkaline basalts in the west to alkali basalts and trachybasalts in the east. Isotopic provincialitymore » is apparent, but mantle differences are difficult to distinguish from the effects of crustal contamination. Lavas with mantle xenoliths consistently have [var epsilon][sub Nd] > 5 and [sup 87]Sr/[sup 86]Sr < 0.7042. Eruptive centers of the MNB show no consistent relationship to regional tectonic features. Although alkali basalts are generally associated with rifting, several MNB volcanoes were erupted through active fold and thrust belts.« less

Special Paper 397: Geoinformatics: Data to Knowledge, 2006

... including both graphical and map-plotting analysis tools Walker, JD, Bowers, TD, Black, RA, G... more ... including both graphical and map-plotting analysis tools Walker, JD, Bowers, TD, Black, RA, Glazner, AF, Farmer, GL, and Carlson, RW, 2006 ... and isotopic data for eastern Califor-nia shows clear space-time-composition patterns in magma-tism (Glazner et al., 1999; Manley et al ...

Eos, Transactions American Geophysical Union, 2009

The Western North American Volcanic and Intrusive Rock Database (NAVDAT) is a free, Web-accessibl... more The Western North American Volcanic and Intrusive Rock Database (NAVDAT) is a free, Web-accessible, and searchable repository of age, chemical, and isotopic data for Late Cretaceous and younger (~85 million years ago to present) igneous rocks from western North America, principally from the western conterminous United States and northern Mexico. The database (http://navdat.org) provides the Earth science community and the

The compositionally zoned Late Cretaceous Lamarck granodiorite, west of Bishop, hosts numerous ma... more The compositionally zoned Late Cretaceous Lamarck granodiorite, west of Bishop, hosts numerous mafic intrusions ranging from hornblende gabbro to mafic granodiorite. Frost and Mahood (1987) suggested from field relations that the Lamarck and the associated mafic plutons were co-intrusive. Contact relations between the Lamarck host and the mafic intrusions are variable (sharp to diffuse) and in places suggest commingling. In

Science, 1992

relation between terrestrial C and atmospheric C02. Assessment of modern terrestrial inventories ... more relation between terrestrial C and atmospheric C02. Assessment of modern terrestrial inventories alone will not provide sufficient information to predict potential future sinks and sources for atmospheric CO,. One must also base such predictions on time-series data and process studies to determine the effects of landscape alterations, including those caused by human activities (2)

A critical question regarding volcano-pluton links is whether plutons are samples of magma that p... more A critical question regarding volcano-pluton links is whether plutons are samples of magma that passed through on its way to eruption, or residues left behind after volcanic rocks were extracted. A persistent theme of recent work on granites sensu lato is that many are sedimentary accumulations of crystals that lost significant volumes of magmatic liquid. This view is based on observations of structures that clearly seem to reflect deposition on a magma chamber floor (e.g., flows of chilled mafic magma into silicic magma) and on the inference that many other structures, such as modal layering, truncated layering, and crystal accumulations, reflect crystal sedimentation on such chamber floors. There are significant physical and geochemical reasons to question this view, based on observations in the Sierra Nevada of California and similar results from other batholiths. First, few granites show the enrichments in Ba, Sr, and relative Eu that feldspar accumulation should produce. Second...

Journal of Geophysical Research: Solid Earth, 1991

Quatemary alkali basalts from Pisgah Crater and Amboy Crater in southem Califomia exhibit unusual... more Quatemary alkali basalts from Pisgah Crater and Amboy Crater in southem Califomia exhibit unusual chemical and isotopic variations which probably result from assimilation of mafic crust. Although lavas from both volcanoes are alkali basalts and hawaiites with isotopic and chemical characteristics that are similar to ocean island basalts (OIB) (e.g., era=2.6-5.9, 87Sr/•6Sr=-0.7038-0.7049, Hf/Ba=0.014-0.017), they display highly correlated and unusual variations in their chemical and isotopic compositions. At each volcano, MgO decreased during the eruptive sequence from =8.5 wt % to •4.5 wt %. Incompatible elements are positively correlated with MgO and therefore also decreased during the eruptive sequence. Nd, Sr, and Pb isotope ratios correlate strongly with MgO. Compositional and isotopic data cannot be explained by any combination of closed-system fractionafion, partial melting of the mantle, or silicic contamination. These data indicate that the basalts represent mixing between a high-MgO, high-%d component, common to both Pisgah and Amboy craters, with lower-MgO and-e•d components that are unique to each center. The high-MgO component most likely-is a primitive mantle-derived magma, based in part on its similarity to nearby xenolith-bearing Quatemary basalts. The low-MgO components are interpreted to be partial melts of mafic crust. If our model is correct, then both volcanoes evolved from eruption of nearly pure mantle melts early in their history to empfion of nearly pure remelted mafic crust late in their history. The crustal source could not have been underplated Mesozoic or younger oceanic crust, but its age is otherwise unconstrained; nearby Mesozoic gabbros and Proterozoic diabases have appropriate isotopic compositions. The basalt data provide no evidence that ancient enriched lithospheric mantle currently underlies the Mojave Desert. If such mantle was present at any time beneath this region, it must have been removed during one or more of the many tectonic events that affected the Mojave Desert during the Phanerozoic. Regional variability of isotope ratios in basalts is commonly interpreted to reflect variability of the underlying mantle. Data from this study raise the possibility that some of this variability may result from cryptic contamination of OIB-like basalts by mafic crust. Petermah et al., 1970] indicate significant variations in 87Sr/86Sr within and between the volcanoes. Our study was designed to gather data which could be used to further define these geochemical and isotopic variations and to test whether they arose in the mantle source regions or through subsequent evolution and interaction with the crust.

Geology, 1994

Three types of sedimentary basins may develop in large-magnitude detachment-type extensional syst... more Three types of sedimentary basins may develop in large-magnitude detachment-type extensional systems. Possible early Miocene examples of these basin types have been identified in association with northeast-directed extension on the central Mojave metamorphic core complex, southern California. From west to east the basins are (1) the Tropico basin, a flexural basin formed on the unextended footwall behind, and bounded by, the detachment breakaway zone; (2) the Pickhandle basin, a supradetachment half graben bounded to the southwest by the detachment breakaway and to the northeast by the hanging wall; and (3) the Clews basin, an intra-hanging-wall basin that formed on the upper plate of the detachment system. Different basin types may be recognized by the nature and geometry of their strata. The footwall flexural basin should be shallow and areally extensive, with basin fill dominated by fine-grained, low-energy deposits. The supradetachment basin typically will be elongate normal to the extension direction and characterized by a thick sequence of volcanic and coarse-grained deposits that reflect its fault-controlled margins. Intrahanging-wall basins may be of half-or full-graben geometry and will vary in dimension depending on the spacing of the transfer elements. Recognition of these basin types is potentially useful in delineating features of the extensional system that are important to its reconstruction, including the detachment breakaway zone and the boundaries of the extensional system parallel and normal to the extension direction.

Geology, 1991

... Dokka (1989) interpreted these data to record postextensional vertical-axis rotation of a roo... more ... Dokka (1989) interpreted these data to record postextensional vertical-axis rotation of a rooted crostai block containing the entire Mojave extensional belt ... Heizer, LA, Tatum, TL, Frost, EG, and Okaya, DA, 1990, Interpretation of CALCRUST and industry seismic data in the Old ...

Geology, 1996

Page 1. Geology doi: 10.1130/0091-7613(1996)024&amp;lt;0335:MGGITM&amp;gt;2.3.CO;... more Page 1. Geology doi: 10.1130/0091-7613(1996)024&amp;lt;0335:MGGITM&amp;gt;2.3.CO;2 1996;24;335-338 Geology Jonathan S. Miller, Allen F. Glazner and Douglas E. Crowe the Cretaceous arc Muscovite-garnet granites in the Mojave Desert: Relation to crustal structure of ...

Geological Society of …, 2005

... BARTLEY, John M. 1 , COLEMAN, Drew S. 2 , and GLAZNER, Allen F. 2 , (1) Geology and Geophysic... more ... BARTLEY, John M. 1 , COLEMAN, Drew S. 2 , and GLAZNER, Allen F. 2 , (1) Geology and Geophysics, Univ of Utah, 135 S 1460 E, 717 WBB, Salt Lake ... Within the JFZ, erosion localized by the faults accounts for most, if not all, cols and passes (eg, Forester, Junction, Shepherd ...