R. M. Gates

Bio: R. M. Gates is an academic researcher from University of Wisconsin-Madison. The author has contributed to research in topics: Becke line test & Devonian. The author has an hindex of 4, co-authored 6 publications receiving 52 citations.

The Use of Becke line colors in refractive index determination

Abstract: The dispersion of immersion liquids is generally much greater than that of most minerals of the same refractive index. Colors appear in the Becke line when the liquid and mineral dispersion curves intersect. The colors produced oder a guide to the wave length for which the liquid and mineral have the same refractive index. Frcm the Becke line colors the refractive index of the mineral for the D (589 mμ) line can be estimated with accuracy better than ±.002.

Late Paleoproterozoic climate, tectonics, and metamorphism in the southern Lake Superior region and Proto-North America: Evidence from Baraboo interval quartzites

Abstract: Red, supermature quartzites of the Baraboo interval of the Lake Superior region contain detrital zircon that ranges in age from 1782 to 1712 Ma. Deposition clearly occurred after the geon 18 Penokean orogeny. These late Paleoproterozoic sedimentary rocks consist largely of quartz, kaolinite or pyrophyllite, and hematite; detrital feldspar and muscovite are rare or absent. Their Chemical Index of Alteration ranges from 96.8 to 98.6, among the most chemically mature clastic sediments in the geological record. The quartzites are underlain by mature, feldspar‐free paleosols, accounting for the absence of feldspar in the overlying sediments and indicating the presence of first‐cycle quartzose detritus. Such physical and chemical characteristics imply that late Paleoproterozoic deposition in the Lake Superior region occurred in a stable tectonic setting with subdued topographic relief in a warm, humid climate. Folding and low‐grade metamorphism of the quartzites is thought to reflect ∼1630 Ma foreland ...

Determination of Fe^(3+) and Fe^(2+) Concentrations in Feldspar by Optical Absorption and EPR Spectroscopy

Abstract: Ferrous and ferric iron concentrations in feldspars with low total iron content (<0.32 wt% total Fe) were determined from optical and electron paramagnetic resonance (EPR) spectra to better than ±15 percent of the amount present. Optical spectra indicate that Fe^(2+) occupies two distorted M-sites in plagioclases of intermediate structural state. The linear dependence of the Fe^(2+)/Fe total ratio on An content demonstrates that Fe^(2+) substitutes for Ca (not Na) so that the number of Ca-sites is a principal factor in iron partitioning in plagioclase. EPR powder spectra show that the number of sites for Fe^(3+) depends on structural state rather than on plagioclase chemistry. The observed linear correspondence of EPR double-integrated intensities with optical peak areas shows that all Fe^(3+) is tetrahedrally coordinated in both plagioclase and disordered potassium feldspar. Microcline perthites show, in addition to tetrahedral Fe^(3+), a signal due to axially coordinated ferric iron, which we associate with formation of hematite inclusions.

The powder patterns and lattice parameters of plagioclase felspars. I. The soda-rich plagioclases

Abstract: Geiger-counter powder records of soda-rich plagioclases have been carefully measured and indexed The lattice parameters of the synthetic specimens are almost independent of the lime content, the largest variation (that in β*) amounting to only 0·2° After strong heating the powder patterns of the natural specimens closely approached those of the synthetic specimens Eight out of the nine natural plagioclases gave lattice parameters which fall within experimental error on a continuous line There is a fairly large variation in lattice parameters, especially for γ*, which changes by 2° As the lime content increases the lattice parameters of the natural plagioclases approach those for the high-temperature synthetic and heated natural specimens until at An50 the separation is only one-fifth of that at An0 The ninth specimen (from a dacite) gives parameters midway between the curves, thus exhibiting a state of partial inversion The partially heated natural plagioclases and the plagioclase from the dacite give parameters indistinguishable within experimental error from the parameters of unheated plagioclases with a higher lime content There is, therefore, no reliable powder X-ray method for the determination of composition in the region An0-An50 If the composition is known the powder method may be used for the determination of the thermal state If the plagioclase can be judged to be in the low-temperature state from geological evidence the powder method can be used to estimate the composition with an accuracy of 2 % An