Abstract-A series of experiments were designed to investigate the textural and compositional changes that take place during disequilibrium partial melting of chondritic material. Chips of the L6 chondrite, Leedey, were heated at 1200 "C and logf02 = IW-1 for durations of 1 h to 21 days. We observed a progression of kinetically-controlled textural changes in melt and restite minerals and changes in the liquidus mineralogy in response to factors such as volatile loss. During the course of the experiments, both olivine and orthopyroxene recrystallized at different times. Rare relic chondrules could still be identified after 2 1 days. The silicate melts that form are very heterogeneous, in terms of both major and trace element chemistry, reflecting heterogeneity of the localized mineral assemblage, particularly with respect to phosphates and clinopyroxene. Metal-sulfide melts formed in short-duration runs are also heterogeneous. The experimental data are relevant to aspects of the genesis of primitive achondrites such as the acapulcoites. The observed textures are consistent with a model for acapulcoite petrogenesis in which silicate melting was limited to only a few volume percent of the chondritic source rock. The experiments are also relevant to the behavior of chondritic material that has been partially melted in an impact environment.

Fine scale heterogeneities in strontium isotope ratios, 40Ar-39Ar ages, and chemical com~sition have been determined for individual mineral grains and enclaves in the rhyolites of San Vincenzo, Italy. The rhyolites are peraluminous with phenocrysts of alkali feldspar, piagioclase, biotite, and cordierite and have previously been divided into two groups on the basis of whole rock major element chemistry. Group B lavas are distinguished from Group A in having higher MgO and CaO contents as well as containing two pyroxenes and chilled latite enclaves. The Group B lavas show textural evidence for d~sequilib~um~ such as resorption and sieve zones in feldspars. Laser fusion 40Ar-39Ar dating of individual alkali feldspar crystals suggests that the eruption of these rhyolites took place 4.38 + 0.04 Ma, ~though small amounts of excess argon are present in subhedral and cloudy crystals. The groundmass in the Group A sample has a higher initial R7Sr/86Sr (0.725) than that of the Group B (0.7 13). The Sr isotope compositions of chemically and texturally characterized individual grains reveal marked disequilibrium between minerals and the host glass as well as within-grain zonation. The feldspars and coarse-grained biotites have initial 87Sr/8"Sr that are intermediate between those of the Group A and B glasses, with alkali feldspar generally having higher initial 87Sr/86Sr ratios than plagioclase. Chilled latite enclaves, which are present in only the Group B lavas, have relatively low initial 8'Sr/86Sr ratios in the range 0.7082-0.7088. The mineral chemistry and isotope data indicate that restite does not form a significant portion of the crystalline assemblage and, therefore, cannot be the source of the strontium isotope disequilibrium. Xenocrysts mixed into the rhyolite from a mafic magma were identified as clinopyroxene megacrysts, clinopyroxene-orthopyroxene clots, orthopyroxene-plagioclase clots, and plagioclase with extensive sieve textures. These grains all have relatively low initial 87Sr/86Sr ratios. Other grains that may be xenocrysts are cordierites with cores containing inclusions of biotite, spinel, and sillimanite, and alkali feldspars with excess 4"Ar. The strontium isotope di~quilib~um in phenocrysts of plagioclase, alkali feldspar, and biotite is attributed to a changing melt chemistry that was too rapid for strontium diffusive equilibration. A mode1 for the San Vincenzo magma chamber is proposed in which the Sr isotope evolution of the Group B rhyolites is due to magma mixing of a crustal melt with latite magma containing unradiogenic strontium. The variable initial strontium isotope compositions of Group A phenocrysts may be due to assimilation or crystallization along the interface between mingled Group A and B magmas.

Complete chemical analyses, including ferric and ferrous iron, H 2 O contents and dD values for 16 phlogopite and biotite and 2 hornblende separates are presented. Samples were obtained from volcanic rocks from four localities: (1) phlogopite phenocrysts from minette lavas from the western Mexico continental arc, (2) biotite and hornblende phenocrysts from andesite lavas from Mono Basin, California, (3) phlogopite and biotite from clinopyroxenite nodules entrained in potassic lavas from the East African Rift, Uganda, and (4) phlogopite phenocrysts from a wyomingite lava in the Leucite Hills, Wyoming. The Fe 2 O 3 contents in the micas range from 0.8 to 10.5 wt%, corresponding to 0.09 to 1.15 Fe 3ϩ per formula unit (pfu). Water contents vary from 1.6 to 3.0 wt%, corresponding to 1.58 to 3.04 OH pfu, significantly less than would be expected for a site fully occupied by hydroxyl. Cation-and anion-based normalization procedures provide accurate mineral formulae with respect to most cations and anions, but are unable to generate accurate estimates of Fe 3ϩ ͞Fe T , and overestimate OH at the expense of O on the hydroxyl site. These inaccuracies are present despite acceptable adjusted totals and stoichiometric calculated site occupancies. The phlogopite and biotite phenocrysts in arc-related lavas from western Mexico and eastern California have the highest Fe 3ϩ ͞Fe T ratios (56-87%), reflecting high magmatic oxygen fugacities (DNNO ϭ ϩ2 to ϩ5), in contrast to those from Uganda (25-40%) and the Leucite Hills (23%). There is no correlation between the OH content and the Fe 3ϩ ͞Fe T ratio in the micas. Values of K Mg͞Fe 2ϩ D (+ 2s errors) were calculated for three phlogopite-olivine pairs (0.12 + 0.12, 0.26 + 0.14, 0.09 + 0.12), two biotite-hornblende pairs (0.73 + 0.08 and 1.22 + 0.10) and a single phlogopite-augite pair (1.15 + 0.12). Values of K F͞OH D for two biotite and hornblende pairs could not be determined without significant error because of the extremely low F contents (Ͻ 0.2 wt%) of the four phases. The dD values obtained in this study encompass a large range (Ϫ137 to Ϫ43‰). The phlogopite and biotite separates from Uganda have dD values of Ϫ70 to Ϫ49‰, which overlap those believed to represent "primary" mantle. There is a larger range in dD values (Ϫ137 to Ϫ43‰) for phlogopite phenocrysts from western Mexico minette lavas, although their range in d 18 O values (5.2-6.2‰) is consistent with "normal" mantle. It is unlikely, therefore, that the variable dD values reflect heterogeneity in the mantle source region of the minette magmas. Nor can the extremely low dD values reflect degassing of H 2 or H 2 O since almost 100% loss of dissolved water in the magma is required, an unrealistic scenario given the stability of the hydrous phenocrysts. The very low dD values of the Mascota minette phlogopites require that the hydrogen be introduced from an external source (e.g., meteoric water). Whatever the process responsible for the observed hydrogen isotope composition, it had no effect on the d 18 O value, f O 2 , a H...

In this paper we examine the merit of bargaining theory, in its economic and ecological forms, as a model for understanding variation in the frequency of participation in cooperative fishing among men of Ifaluk atoll in Micronesia. Two determinants of bargaining power are considered: resource control and a bargainer's utility gain for his expected share of the negotiated resource. Several hypotheses which relte cultural and life-course parameters to bargaining power are tested against data on the frequency of cooperative sail-fishing participation. Consistent with predictions generated from bargaining theory, we show that (1) age is negatively correlated with cooperative fishing participation, (2) men of highranking clans and men with high levels of education fish less than men of low-ranking clans and less-educated men, (3) men with high expected utility gains from fishing returns fish more than men with low expected utility gains, (4) number of dependents is positively correlated with cooperative fishing participation, and (5) the number of young genetic offspring residing with a man is positively correlated with cooperative fishing participation, whereas the number of genetic offspring more than 13 years old who are residing with a man is negatively correlated with cooperative fishing participation.