Changing trade patterns of the West Pacific

In the enormous expansion of world trade in the quarter century after 1950, the share generated by countries of the Western Pacific remained remarkably constant. This relationship primarily reflected the rise of Japan as a major force in the international economy. Whereas Japan's own trade grew more widely oriented and the Western Pacific margins relatively less important as trading partners than before WW II, to the states of the Western Pacific Japan's status both as a supplier of imports and as an export market greatly enlarged —only rarely is Japan not the leading trading partner. The Japanese strategy of export-led growth has been replicated by South Korea, Taiwan, Hong Kong, and Singapore. All of these countries, as well as Japan itself, depend overwhelmingly on imports for their raw materials and energy supplies. Elsewhere trade patterns have been greatly modified by a rising spirit of nationalism that has emphasized development of manufacturing industries in Australia and New Zealand no less than in the states of SE Asia.     

Amphibole pyroxenite xenoliths: Cumulate or replacement phenomena from the upper mantle,Nunivak Island,Alaska

Interstitial to poikilitic amphibole found in garnet pyroxenite xenoliths has been interpreted, in the past, to represent a critically silica undersaturated, residual intercumulus melt trapped by its cumulate assemblage of anhydrous phases. The textural features of such amphibole in pyroxenite xenoliths from Nunivak Island, Alaska, however, are more compatible with an origin by replacement of the anhydrous phases of the pyroxenite, following a period of cooling and sub-solidus recrystallization in the upper mantle. The reaction of amphibole and olivine to give orthopyroxene, observed in two specimens, requires that the associated fluid phase was not critically silica undersaturated. The amphibole is therefore thought to reflect the interaction of an alkali-bearing, migratory, aqueous fluid and an upper mantle consisting of spinel lherzolite cut by veins of spinel and garnet pyroxenite.     

On the calculation of cosmic-ray exposure ages of stone meteorites

Abundances of cosmic ray-produced noble gases and ²⁶Al, including some new measurements, have been compiled for some 23 stone meteorites with exposure ages of < 3 × 10⁶ yr. Concentrations of cosmogenic He, Ne, and Ar in these meteorites have been corrected for differences in target element abundances by normalization to L-chondrite chemistry. Combined noble gas measurements in depth samples of the Keyes and St. Séverin chondrites are utilized to derive equations for normalizing the production rates of cosmogenic ³He, ²¹Ne, and ³⁸Ar in chondrites to an adopted ‘average’ shielding: ${}^{22}\text{Ne}{}^{21}\text{Ne}\text{= 1.114.}$ The measured unsaturated ²⁶Al concentrations and the calculated equilibrium ²⁶Al for these meteorites are combined to estimate exposure ages. These exposure ages are statistically compared with chemistry- and shielding-corrected concentrations of cosmogenic He, Ne, and Ar to derive absolute production rates for these nuclides. For L-chondrites, at ‘average’ shielding, these production rates (in 10^?8 cm³/g 10⁶ yr) are: ³He = 2.45,²¹Ne = 0.47, and ³⁸Ar = 0.069, which are ~ 25% higher than production rates used in the past. From these production rates and relative chemical correction factors, production rates for other classes of stone meteorites are derived.     

Greatlakean Substage: A replacement for Valderan Substage in the Lake Michigan basin

New evidence from recent field and seismic investigations in the Lake Michigan basin and in the type areas of the Valders, Two Creeks and Two Rivers deposits necessitates revision of late-glacial ice-front positions, rock- and time-stratigraphic nomenclature and climatic interpretations and deglaciation patterns for the period ca. 14,000–7,000 radiocarbon years B.P. The previously reported and long accepted pattern of deglaciation for the Lake Michigan basin started with a regular retreat from the Lake Border Morainic System, with a minor oscillation marked by the Port Huron moraine(s) and then an extensive Twocreekan deglaciation followed by a major (320 km) post-Twocreekan advance (Valders). However, we now record a major retreat between the times of the Lake Border and Port Huron moraines, followed by a gradual retreat from the Port Huron limit and interrupted by a minor standstill (deposition of Manitowoc Till), a retreat (Twocreekan) and a readvance (Two Rivers Till). No Woodfordian or younger readvance was as extensive as had been the preceding one. This sequence argues for a normal, climatically controlled, progressive deglaciation rather than one interrupted by a major post-Twocreekan (formerly Valderan) surge. This revision appears finally to harmonize the geologic evidence and the palynological record for the Great Lakes region. Our investigations show that Valders Till from which the Valderan Substage was named is late-Woodfordian in age. We propose the term “Greatlakean” as a replacement for the now misleading time-stratigraphic term “Valderan”. The type section and the definition of the upper and lower boundaries of the Greatlakean Substage remain the same as those originally proposed for the Valderan Substage but the name is changed.     

The metamorphic history of LL-group ordinary chondrites

A study of feldspar grain size and microprobe analysis of coexisting orthopyroxene, olivine, diopside, and metal in twenty equilibrated LL-group chondrites and clasts defines the conditions of metamorphism, indicates the relative position of samples within the parent body, and suggests an accretionary-metamorphic history.

Variation of mineral chemistry indicates a range of equilibrium temperature and parallels textural variation, providing two continuous relative temperature scales, based on mean feldspar grain size and the calcium content of orthopyroxene coexisting with diopside. Maximum equilibrium temperatures range from less than 600° up to 950°C. The total Tschermak's component in orthopyroxene indicates that maximum pressure was less than 1 kbar, and a pressure gradient correlates directly with temperature. A reduction sequence, evident from systematic variation of iron in ferromagnesian silicates and metal, correlates inversely with temperature.

The maximum permissible sampling depth for the formation of surface breccias (2/10 r) also limits pressure to less than 1 kbar. The LL parent body had a minimum radius of 200 km, determined using the permissible sampling depth and published cooling rates.

The data are broadly consistent with simple reheating of colder material within a completely accreted body. This model may have problems with volatile depletion, a required lack of impact sampling during metamorphism, and the timing of the event. The data are more consistent with accretion of colder material on a hot but cooling surface. Both models apparently require a recycling process during accretion to account for the reduction sequence.     

The relationship of elasticity and crystal structure in andalusite and sillimanite

The nine elastic constants of andalusite and sillimanite have been determined, using the technique of Brillouin scattering. They are, in megabars, for andalusite: c ₁₁=2.334, c ₂₂=2.890, c ₃₃=3.801, c ₄₄=0.995, c ₅₅=0.878, c ₆₆=1.123, c ₂₃=0.977, c ₁₃=1.162, c ₁₂=0.814; for sillimanite: c ₁₁=2.873, c ₂₂=2.319, c ₃₃=3.884, c ₄₄=1.224, c ₅₅=0.807, c ₆₆=0.893, c ₂₃=1.586, c ₁₃=0.834, c ₁₂=0.947. Both structures are characterized by chains of edge-linked coordination octahedra extending parallel to the crystallographic c direction, cross-linked by polyhedra of lower coordination. In each structure the stiffness measured parallel to c is greater than that measured normal to c. The shear moduli can be directly correlated with the relative rigidity of the cross-linking structures.     

Episodic Cenozoic volcanism and tectonism in the Andes of Peru

Radiometric and geologic information indicate a complex history of Cenozoic volcanism and tectonism in the central Andes. K-Ar ages on silicic pyroclastic rocks demonstrate major volcanic activity in central and southern Peru, northern Chile, and adjacent areas during the Early and Middle Miocene, and provide additional evidence for volcanism during the Late Eocene. A provisional outline of tectonic and volcanic events in the Peruvian Andes during the Cenozoic includes: one or more pulses of igneous activity and intense deformation during the Paleocene and Eocene; a period of quiescence, lasting most of Oligocene time; reinception of tectonism and volcanism at the beginning of the Miocene; and a major pulse of deformation in the Middle Miocene accompanied and followed through the Pliocene by intense volcanism and plutonism. Reinception of igneous activity and tectonism at about the Oligocene-Miocene boundary, a feature recognized in other circum-Pacific regions, may reflect an increase in the rate of rotation of the Pacific plate relative to fixed or quasifixed mantle coordinates. Middle Miocene tectonism and latest Tertiary volcanism correlates with and probably is genetically related to the beginning of very rapid spreading at the East Pacific Rise.