Radioactive and trace element distribution in basaltic rocks of Lower Silesia

Summary The distribution of radioactive(Th, U, K) and selected trace(Rb, Sr, Ba, Y, Zr, V, Cr, Ni) elements in volcanic rocks from the Opole and Jawor regions of the Lower Silesia has been studied. The behaviour of these elements in the studied rocks indicates that the Lower Silesian volcanic rocks are characterized by less differentiated type than other volcanic rocks of the Bohemian Massif, the Opole rock types probably having a less differentiated character than the Jawor rock types.

---

¶rt;a an¶rt;u a¶rt;uamu(Th, U, K) u m ¶rt;u(Rb, Sr, Ba, Y, Zr, V, Cr, Ni) m auu n¶rt;a am n u u uuu. a n mam n¶rt;num, m aum u uuu n¶rt;mam ¶rt; aamuu n¶rt; u ¶rt;uuau, aum u ana¶rt; uu. au a n¶rt;num, m auu n¶rt; amu n ¶rt;uuau ma ua n¶rt; u amu .

     

The origin of the high-K latites from Camp Creek,Arizona: constraints from experiments with variable fO2 and a_{{\text{H}}_{\text{2}} {\text{O}}}

Near-liquidus melting experiments were performed on a high-K latite at fO₂'s ranging from iron-wustite-graphite (IWG) to nickel-nickel oxide (NNO) in the presence of a C-O-H fluid phase. Clinopyroxene is a liquidus phase under all conditions. At IWG , the liquidus at 10 kb is about 1,150° C but is depressed to 1,025° C at NNO and . Phlogopite and apatite are near-liquidus phases, with apatite crystallizing first at pressures below 10 kb. Phlogopite is a liquidus phase only at NNO and high . Under all conditions the high-K latites show a large crystallization interval with phlogopite becoming the dominant crystalline phase with decreasing temperature. Increasing fO₂ affects phlogopite crystallization but the liquidus temperature is essentially a function of . The chemical compositions of the near-liquidus phases support formation of the high-K latites under oxidizing conditions (NNO or higher) and high . It is concluded from the temperature of the H₂O-saturated liquidus at 10 kb, the groundmass: crystal ratio and presence of chilled latite margins around some xenoliths that the Camp Creek high-K latite magma passed thru the lower crust at temperatures of 1,000° C or more.     

Fault interaction and seismicity: Laboratory investigation and its seismotectonic interpretation

Systems of two parallel linear faults of the same length with the angle of inclination =45° were investigated under uniaxial linearly increasing load. Perspex plates were used as models. For each treated fault configuration the morphology of tensile cracks and the sequence of seismoacoustic events of shear and tensile origin were studied.It is shown that the seismic regime of a fault system is strongly influenced by the contact conditions on a fault plane; it is different in the faults with the aseismic contact, represented by open slits, and in the faults with the seismoactive contact, represented by filled slits, respectively.The experiments proved the dominating role of a fast shear displacement of the stick-slip type in the regime of seismic energy release of a fault system. The tensile crack generation seems to be only of little—if not negligible—importance. On the other hand, the existence of tensile cracks in a fault system can play an important role in the course of subsequent loading cycles because the stick-slip displacements can take place not only along the primary faults but also along the planes of tensile cracks.A comparison of some results of model experiments and the already published results of geological and seismological investigations indicated that the way of seismic energy relase on faults in nature and in the laboratory could be of the same character. Several analogies between the seismic regime of a fault model and of real seismic regions were found concerning the morphology of faults, off-fault fore- and aftershocks, and earthquake doublets, respectively.     

The effect of quartz on the magnetic anisotropy of quartzite

Summary The magnetic susceptibility of quartz single crystals is diamagnetic (–14×10 ^–6 in SI units) and exhibits only very small anisotropy (mostly less than 1%); thus the susceptibility of the quartz matrix in quartzite can be regarded as virtually isotropic. Owing to the influence of the negative and isotropic susceptibility of the quartz matrix, the degree of anisotropy of quartzite, as inferred from model calculations, is higher than that of the ferrimagnetic fraction. This influence is very strong if the mean susceptibility of quartzite is in the vicinity of zero.

---

uma aa m ¶rt;uaaumu (nuuum–14 × 10 ^–6 um ) u a aumnuu ( 1%). m aum, m nuuum a a auma m m numa namuu umn. amamu ¶rt;uau ¶rt;m, m n nuu uu muam u umn nuuumu a a mn aumnmu auma , mn aumnmu aum auu. m uu au m¶rt;a, ¶rt;a ¶rt;a nuuum ua .