Geochemistry and Intrusive History of the Ashland Pluton, Klamath Mountains, California and Oregon

The Ashland pluton is a calc-alkaline plutonic complex thatintruded the western Paleozoic and Triassic belt of the KlamathMountains in late Middle Jurassic time. The pluton comprisesa series of compositionally distinct magma pulses. The oldestrocks are hornblende gabbro and two-pyroxene quartz gabbro withinitial ⁸⁷Sr/⁸⁶Sr = 0{dot}7044, ¹⁸O = 8{dot}7%, and REE patternswith chondrite normalized La/Lu = 7. These units were followedby a suite of tonalitic rocks (La_N/Lu_N = 7) and then by a suiteof K₂O- and P₂O₅ rocks of quartz monzodioritic affinity (La_N/Lu_N= 13–21; La_N/Sm_N = 2{dot}4–3{dot}) The quartz monzodioriticrocks were then intruded by biotite granodiorite and granitewith lower REE abundances but more fractionated LREE(La_N/Lu_N= 13–19; La_N/Sm_N = 4{dot}3–6 and they, in turn,were host to dikes and bosses of hornblende diorite. The latestintrusive activity consisted of aplitic and granitic dikes.Combined phase equilibria and mineral composition data, indicateemplacement conditions of approximately P_total = 2{dot}3kb,P_H2O between 1{dot}5 and 2{dot}2 kb, and f_O2 between the nickel-nickeloxide and hematite-magnetite buffers. Successive pulses of magma display increasing SiO₂ togetherwith increasing ¹⁸O and decreasing initial ⁸⁷Sr/⁸⁶Sr. The isotopicdata are consistent with either (1) combined fractional crystallizationof andesitic magma and concurrent assimilation of crustal materialcharacterized by low Sr₁ and high (¹⁸O or, more probably, (2)a series of partial melting events in which sources were successivelyless radiogenic but richer in ¹⁸O Each intrusive stage displaysevidence for some degree of crystal accumulation and/or fractionalcrystallization but neither process adequately accounts fortheir compositional differences. Consequently, each stage appearsto represent a distinct partial melting or assimilation event. The P₂O₅-rich nature of the quartz monzodiorite suite suggestsaccumulation of apatite. However, the suite contains abundantmafic microgranitoid enclaves and most apatite in the suiteis acicular. These observations suggest that magma mixing affectedthe compositional variation of the quartz monzodiorite suite.Mass balance calculations are consistent with a simple mixingprocess in which P₂O₅-rich alkalic basalt magma (representedby the mafic microgranitoid enclaves) was combined with a crystal-poorfelsic magma (represented by the tonalite suite), yielding aquartz monzodioritic magma that then underwent differentiationby crystal fractionation and accumulation.     

High-resolution spectroscopy of gamma-ray bursts

We report on results from the Goddard germanium Gamma-Ray Burst Spectrometer flown on the ISEE-3 spacecraft. Spectral and temporal studies of two events on 4 and 19 November, 1978 are presented. The power law spectral indices were found to be respectively –1.82 and –1.31, the latter being the hardest event thus far detected. Evidence for two lines in the 4 November event is presented — a broad feature at 420 keV and a narrower one at 740 keV. These are consistent with a common redshift if the parent lines are assumed to be the positron annihilation line (511 keV) and the first excited state of iron (847 keV). If this interpretation is correct, it is shown that additional lines from higher levels of iron and possibly other nuclei are expected and that they may represent a significant contribution to the total spectrum above 1 MeV.Paper presented at the Symposium on Cosmic-Ray Bursts, held at Toulouse, France, 26–29 November, 1979.     

Hypersensitization of Kodak infrared plates: Results of some chemical methods and pre-exposure

Tests have been carried out on Kodak Spectroscopic Plates Type I-N, in order to find a treatment which could be easily applied to the infrared plates to be used with the Loiano 152 cm,f/8, Ritchey-Chrétien telescope. Different techniques have been tested, not only with the aim of achieving the higher speed gain, but also to obtain the better uniformity and reproducibility. Our results suggest that the advantages of preexposure techniques are underestimated in this respect. Furthermore, we find that blue and infrared preexposures (at 0.8 s) give different results, suggesting a different degree of dispersity in the latent image produced by pre-exposure in the two cases.Baths including both ammonia and Ag-compounds provide the higher speed gains, but the increment of the fog is often non-uniform and/or very high. The best results have been obtained with baths including AgNO₃ and AgCl. The rejuvenation process found by Sanduleak and the results obtained by Jenkins and Farnell on the reversibility of the gains due to silver-nitrate baths have been confirmed.     

Compton scattering of relativistic electrons in compact X-ray sources

The problem of single Compton scattering is considered and the resulting spectrum, angular distribution and polarization of scattered photons in a general case are obtained. The inverse Compton scattering (ICS) for arbitrary energies of electronsE and photons ₀ is investigated in detail. In the case of isotropically-distributed initial photons and relativistic electrons, a strong rise of the scattered spectrum near the upper edge takes place, starting from the values of the characteristic parameterb4E ₀10 (in units of mc²=1). The energy-loss rate of relativistic electrons due to ICS is calculated. It is shown that the relativistic electrons of the energiesE100 MeV, when scattering on the X-rays with ₀~10KeV, transmit the dominant part of their energy to the photons which fall after scattering into the energy range of the electrons (100 MeV).The radiation spectrum of ICS, as well as the energy-losses of relativistic electrons distributed by power-lawE ^–, are calculated. The radiation spectrum reveals the power-law behaviour with the different indices in two limits: the dependence ^–(1)/2 at ₀1 gradually changes to ^–(+1) ln (₀) law for ₀1.     

The spectra and light curves of two gamma-ray bursts

During the last half of 1977 the UCSD/MIT Hard X-Ray and Low Energy Gamma-Ray Experiment of HEAO-1 observed two of the three gamma-ray bursts detected by at least three satellites. The first of these bursts (20 October, 1977) had a fluence of (3.1±0.5)×10^–5 erg cm^–2 integrated over the energy range 0.135–2.05 MeV and over its duration of 38.7 s, placing it among the largest bursts observed. The second (10 November, 1977) had a fluence of (2.1±0.8)×10^–5 erg cm^–2 integrated over the energy range 0.125–3 MeV and over its duration of 2.8 s. The light curves of both bursts exhibit time fluctuations down to the limiting time resolution of the detectors (0.1 s). The spectrum of the 20 October, 1977 burst can be fitted with a power law (index –1.93±0.16), which is harder than other reported gamma-ray burst spectral fits. This burst was detected up to 2.05 MeV, and approximately half of its energy was emitted at photon energies above 0.5 MeV. The spectrum of the 10 November, 1977 burst is softer (index –2.4±0.7) and is similar to the spectrum of the 27 April, 1972 burst.Paper presented at the Symposium on Cosmic Gamma-Ray Bursts held at Toulouse, France, 26–29 November, 1979.     

Near-infrared spectrophotometry of the satellites and rings of Uranus

New spectrophotometry from 1.5 to 2.5 μm is reported for the Uranian satellites Titania, Oberon, and Umbriel. A spectrum of the rings of Uranus from 2.0 to 2.4 μm is also reported. No evidence is found for frost covering the surface of the ring material, consistent with the low albedo of the rings (P_K = 0.03) previously reported by Nicholson and Jones (1980). The surfaces of the satellites are found to be covered by dirty water frost. Assuming albedos of the frost and gray components covering the Uranian satellites to be the same as the light and dark faces of Iapetus, radii are derived that are roughly twice those inferred from the assumption of a visual albedo of 0.5.     

OSO-8 observations of CaII H and K,MgII h and k,Lα and Lβ above a sunspot

Observations with the French (L.P.S.P.) experiment on board OSO-8 of a sunspot and nearby plage region are described. The behaviour of the emission cores of the Ca II H and K and Mg II h and k resonance lines is very similar and the correspondence in intensity between the four lines persists in all observed features. In contrast, the Lyman lines show little correlation with the other lines. Their emission regions appear broader in the spectroheliograms than the underlying sunspot structure and must not necessarily possess a counterpart in lower layers. From the central intensity of L above the umbra an electron density of 4.3 × 10¹⁰ cm^-3 n _e ^* 2.3 × 10¹¹ cm^-3 at 20 000 K is estimated.Mitteilungen aus dem Kiepenheuer-Institut Nr. 186.Stockholm Observatorium, S-13300 Saltsjöbaden, Sweden.Laboratoire de Physique Stellaire et Planétaire, CNRS, P.O. Box 10, F-91370 Verrières-le-Buisson, France.     

On the temporal variation of the solar continuous brightness fluctuations

From a sequence of white-light photographs of solar granulation at the centre of the disk, obtained by Spectro-Stratoscope on May 17, 1975, two-dimensional spatial power spectra of photospheric intensity fluctuations were deduced. These show periodicities of 1000 s, 250–450 s (5-min oscillation), and shorter ones in the range 30–120 s. The reality of the shorter periods, however, seems to be questionable.The weighted mean wavenumber of the spatial power spectra and rms of the intensity fluctuation (I _rms) are also computed, showing the same periodicities as the power.Mitteilungen aus dem Kiepenheuer-Institut Nr. 188.On leave of absence from the Institute of Geophysics, University of Tehran.     

The distribution of infrared sources in the galactic plane

A study of the galactic structure has been made by deriving the brightness distribution of the galactic plane at 2.2 m and 4.2 m near infrared region using infrared objects detected by ground-based sky surveys. The infrared brightness distribution shows distinct peaks at every 8–12° galactic longitude and indicates a periodic structure. The one-to-one positional correlation observed between the periodic structure in 2.2 m infrared brightness and the 2.6 mm CO emission line suggests that the near-infrared sources are strongly associated with dense clouds of molecular hydrogen distributed in the galactic plane.     

Vertical motions in an intense magnetic flux tube

The recent discovery of localised intense magnetic fields in the solar photosphere is one of the major surprises of the past few years. Here we consider the theoretical nature of small amplitude motions in such an intense magnetic flux tube, within which the field strength may reach 2 kG. We give a systematic derivation of the governing expansion equations for a vertical, slender tube, taking into account the dependence upon height of the buoyancy, compressibility and magnetic forces. Several special cases (e.g., the isothermal atmosphere) are considered as well as a more realistic, non-isothermal, solar atmosphere. The expansion procedure is shown to give good results in the special case of a uniform basic-state (in which gravity is negligible) and for which a more exact treatment is possible.The form of both pressure and velocity perturbations within the tube is discussed. The nature of pressure perturbations depends upon a critical transition frequency, _p , which in turn is dependent upon depth, field strength, pressure and density in the basic (unperturbed) state of the tube. At a given depth in the tube pressure oscillations are possible only for frequencies greater than _p for frequencies below _p exponentially decaying (evanescent) pressure modes occur. In a similar fashion the nature of motions within the flux tube depends upon a transition frequency, _v . At a given depth within the tube vertically propagating waves are possible only for frequencies greater than _v ; for frequencies below _v exponentially decaying (evanscent) motions occur.The dependence of both _v and _p on depth is determined for each of the special cases, and for a realistic solar atmosphere. It is found that the use of an isothermal atmosphere, instead of a more realistic temperature profile, may well give misleading results.For the solar atmosphere it is found that _v is zero at about 12 km above optical depth ₅₀₀₀= 1, thereafter rising to a maximum of 0.04 s^–1 at some 600 km above ₅₀₀₀ = 1. Below ₅₀₀₀ = 1, in the convection zone, _v has a maximum of 0.013 s^–1. The transition frequency, _p , for the pressure perturbations, is peaked at 0.1 s^–1 just below ₅₀₀₀ = 1, falling to a minimum of 0.02 s^–1 at about one scale-height deeper in the tube