Magnetic and microwave structure in solar active regions

The structure of six active regions observed at 2.8 cm with the Stanford interferometer is compared with the configuration of the underlying photospheric magnetic fields, as given by the Kitt Peak magnetograph.The similar resolution and accuracy on the measured positions of both instruments allowed us to establish a more detailed spatial correspondence between radio and magnetic features than previously reached.The radio features which correspond to the cores of the active sources are always found to overlay regions of enhanced magnetic fields. Different spatial associations have been found depending on the brightness temperature of the sources. The possibility that this effect might be due to the development of the active region is also considered.     

New insights on diapirism in the Adriatic Sea: the Tremiti salt structure (Apulia offshore,southeastern Italy)

The reinterpretation of public seismic profiles in the Adriatic offshore of Gargano (Apulia, southern Italy) allowed the detection of a kilometre‐scale salt‐anticline, the Tremiti diapir, within the larger Tremiti Structure. This anticline was generated by diapirism of Upper Triassic anhydrites within a thick Mesozoic to Quaternary sedimentary succession. Both internal stratal patterns and shapes of Plio‐Quaternary units, and the occurrence of an angular unconformity between early Tortonian and Pliocene rocks on the Tremiti Islands, suggest that halokinesis began during the late Miocene and is still active today. An ancient extensional SE‐dipping fault, cutting an older Mesozoic low‐amplitude anhydritic ridge, played an important role during salt mobilization, which was promoted by NW‐SE shortening. The diapir grew in the footwall of this fault, causing its upward propagation. In some places, the ancient fault served as a preferential channel for the upward migration of the anhydrites.     

Geochemistry of metabasites from NE Sardinia, Italy: nature of the protoliths, magmatic trend, and geotectonic setting

Summary The metabasites of Montiggiu Nieddu occur as a lenticular body in the Hercynian migmatite complex of NE Sardinia and consist of two major lithological associations: ultramafic amphibolites and plagioclase-banded amphibolites, which are genetically related by processes of cumulate differentiation of an original tholeiitic magma. The ultramafic amphibolites consist of relics of igneous phases (anorthite, olivine, orthopyroxene, and clinopyroxene) and metamorphic minerals (orthopyroxene, clinopyroxene, plagioclase, garnet, chlorite, and amphibole) in variable proportions. Based on the distribution of the relics of igneous minerals three main compositional layers (A, B, C) have been identified in the ultramafic amphibolites. The plagioclase-banded amphibolites consist of dark-green and white bands made up of plagioclase, amphibole, garnet, and rare pyroxene in variable proportions. No relics of magmatic minerals were observed. The trace element patterns of the Montiggiu Nieddu metabasites are characterised by selective enrichment of incompatible elements of low ionic potential, such as Sr, Rb, Ba, and Th, and low abundance of K, Cr, Ni, and elements of high ionic potential (from Ta to Yb), which define a relatively flat trend similar to MORB composition. Ti, Y, and heavy rare earth elements are all positively correlated with Zr. This correlation suggests that no significant transport of these elements took place during metamorphism. The metabasites of Montiggiu Nieddu are characterised by low Ti, Ti/V, and Ti/Zr content, low rare earth and high-field strength element concentrations, and moderate selective enrichment in large-ion lithophile elements. They also show geochemical features similar to those of supra subduction zone tholeiites. The CaO-MgO diagram displays a segmented trend, which provides powerful evidence in favour of crystal-liquid separation during magmatic evolution. Received December 4, 2000; revised version accepted January 29, 2001