Petrogenesis of the Kinsman Intrusive Suite: Peraluminous Granitoids of Western New Hampshire

The Kinsman Intrusive Suite occurs in six major plutons of westernNew Hampshire, covering a total area of 2240 km². It is an Acadian-agesyntectonic gneissic S-type peraluminous granitoid, rangingin composition from quartz diorite to granite. Much of the Kinsmanis characterized by very large (up to 120 mm in maximum dimension)megacrysts of alkali feldspar, but the bulk chemistry of therocks indicates that these cannot be phenocrysts crystallizedfrom initially homogeneous melts. Locally, there is abundant(20 per cent) almandine-rich garnet, and graphite is a commonaccessory.In contrast to the unannealed orthoclase in surroundingmetapelites, the alkali feldspar of the Kinsman has, for themost part, inverted to maximum microcline. The garnets havecore temperatures in the range of 800 to 900 ?C, and are pseudomorphedby, or show reaction rims to, biotite. Plagioclase commonlyshows zoning, some of it oscillatory. These features are magmaticin nature, and argue against the conclusions of previous investigatorsthat the mineralogy and textures of the rock are due to regionalmetamorphism of a previously-crystallized two-mica granitoidwhich has undergone prograde reactions such as:muse + bio +3 qtz 2 Kfs + gar + 2H₂O.The intrusives have also producedrecognizable contact-metamorphic features in the wallrocks andare probably coeval with the dominant M2 Acadian metamorphism.Majorelement analytical data for the Kinsman suite has been examinedby least squares mixing-model and extended Q-mode factor analysis.These calculations, supported by consideration of REE data,suggest that the most likely origin for the Kinsman magmas isby deep-crustal anatexis of slightly calcareous metapelites,and involves a reaction such as:bio + Al₂SiO₅ + qtz + feldspars gar + cord + Kfs + plag + melt.In non-calcareous pelites thisreaction produces a water-undersaturated peraluminous melt attemperatures above 700 ?C, and allows for the early crystallizationor recrystallization of K-feldspar, plagioclase, and garnetin a crystal-liquid mush or migma. Geochemically, garnet + plagioclaseare treated as restite, and a minimum-melt granite as the magmain the Q-mode and mixing-model calculations. The variabilityin chemistry of the Kinsman Intrusive Suite is best explainedon the basis of mixing of leucogranitic anatectic melts withgarnet-plagioclase restitic material and a quartz-feldspar-sillimanite-biotiterock, but only very slightly affected by crystal settling.     

Short polarity intervals within the Matuyama: transitional field records from hydraulic piston cored sediments from the North Atlantic

Detailed sampling of two short magnetozones within the Matuyama Chronozone recorded at DSDP Site 609 (49.86°N, 335.77°E) confirms that one, the Cobb Mountain Subchronozone (1.12 Ma), is a very short, full normal polarity interval and that the other, the older interval, is a record of a geomagnetic excursion which occurred at approximately 1.55 Ma. The Cobb Mountain Subchron lasted approximately 25,000 years, one third the duration of the Jaramillo Subchron. The normal polarity interval is bounded by two transition zones which document an antisymmetry in the sequence of directions in the reverse to normal and normal to reverse polarity transitions. We interpret the antisymmetry as reflecting a dependence upon the sense of the reversal, without significant changes in the relative contributions of non-dipole terms. The polarity interval recorded at 1.55 Ma lasted only 8,800 years with what may be regarded as full polarity directions observed across only 3 cm of stratigraphic section. This feature is interpreted as an excursion of the geomagnetic field and appears to be correlative with the Gilsa Subchron. Similarities between the transition bounding these two magnetozones suggest that these features occur as the result of the same process or triggering mechanisms in the earth's outer core.     

Evolution of Pangea: paleomagnetic constraints from the Southern Alps, Italy

A new early Late Triassic paleopole for Adria has been obtained from the Val Sabbia Sandstone in the Southern Alps. As Early Permian and Jurassic-Cretaceous paleomagnetic data from para-autochthonous regions of Adria such as the Southern Alps are consistent with ‘African’ APWPs[1–2], paleomagnetic data from this region can be used to bolster the West Gondwana APWP in the poorly known Late Permian-Triassic time interval. The Southern Alpine paleopoles are integrated with the West Gondwana and Laurussia APWPs of Van der Voo [1] and used to generate a tectonic model for the evolution of Pangea. The Early Permian overall mean paleopole for West Gondwana and Adria, in conjunction with the coeval Laurussia paleopole, support Pangea B of Morel and Irving [3]. The Late Permian/Early Triassic and the Middle/Late Triassic paleopoles from Adria and Laurussia support Pangea A-2 of Van der Voo and French [4]. The phase of transcurrent motion between Laurasia and Gondwana[5] that caused the Pangea B to A-2 transition occurred essentially in the Permian (at the end of Variscan orogeny) with an average relative velocity of approximately 10 cm/yr. Finally, the Late Triassic/Early Jurassic paleopoles from West Gondwana and Laurussia agree with Pangea A-1 of Bullard et al. [6], the widely accepted Pangea configuration at the time of the Jurassic breakup.     

A tertiary lamprophyre dike with high pressure xenoliths and megacrysts from Wiedemanns Fjord,East Greenland

Lamprophyric dikes, mainly of camptonite/monchiquite affinities occur in the Wiedemanns Fjord area. One example contains a complex assemblage of olivine-orthopyroxene-chrome spinel nodules, megacrysts of kaersutite, diopside, strongly reverse-zoned green salite and various spinel phases. Microprobe analyses are presented for all these phases and for the lilac-coloured titansalites and strongly-coloured kaersutites of the groundmass. It is concluded that these minerals record evolution under various P, T and oxidation regimes during the formation of a lamprophyric parent magma. The nodules provide evidence for deep fractures in this area supposedly associated with early rifting in the North Atlantic.     

Details of magnetic polarity transitions recorded in a high deposition rate deep-sea core

Concentrations of the (n, γ)-produced radionuclide⁶⁰Co were measured in lunar samples at various depths from the surface down to 360 g/cm². By comparing the data obtained to calculated production rates (based on the work of Lingenfelter et al. [8]) we determined the present day lunar neutron production rate, which was found to be (12 ± 3)neutrons/cm²sec (E < 10MeV).     

The lack of inorganic removal of dissolved silica during river-ocean mixing

The significance of the inorganic removal of dissolved silica from estuarine zones was investigated at three river mouths: the Orinoco, the Savannah and the Mississippi. Particular attention was given to the Mississippi river plume, where extensive inorganic silica uptake had been reported. Mixing curves and laboratory dilution experiments provided little evidence that the phenomenon was widespread. Because of an uncertain fresh water tie point, some inorganic uptake could not be completely ruled out for the Orinoco, but, in the plumes of the Savannah and Mississippi rivers, no inorganic silica removal was indicated. In contrast to published experiments on river sediments, laboratory dilution studies on suspended matter from the Mississippi river showed release of dissolved silica instead of uptake.     

Viscous damping of nonlinear magneto-acoustic waves

The motivation for the present work is discussed, and in Section 2 the nonlinear Burger's equation is derived for wave propagation in a compressible unstratified viscous fluid permeated by a magnetic field (initially constant), using the reductive perturbation method of Taniuti and Wei (1968). An analytic solution of the equation is given (after Sakai, 1972) and the angular behaviour is shown for certain parameters describing the nonlinearity and damping of the system, for both fast- and slow-mode disturbances.