Rosemary E. Jones

Predictors of 12-month outcome in bulimia nervosa and the influence of attitudes to shape and weight.

Seventy-five patients with bulimia nervosa were treated with 1 of 3 short-term psychological treatments and were then entered into a closed 1-year period of follow-up. Pretreatment predictors of 3 measures of outcome were sought. Only 2 variables were significantly associated with outcome: attitudes toward shape and weight, and self-esteem. The nature of the relation between attitudinal disturbance and outcome was complex and unexpected. The data set was also used to test the major prediction of the cognitive view of bulimia nervosa, namely that among patients who have responded to treatment, the residual level of attitudinal disturbance will predict subsequent outcome. This prediction was confirmed.

The Late Paleogene to Neogene Volcanic Arc in the Southern Central Andes (28°–37° S)

Evolution of arc magmatism along the Southern Central Andes (~28°–37° S) is strongly controlled by changes in the geometry of the downgoing slab (e.g., slab dip angle). This is particularly evident in the present-day Chilean-Pampean flat-slab and the late Miocene Payenia shallow subduction segments. Typical Andean-type volcanism was established from the late Oligocene to late Miocene in the high Andes (29°30″–30°30″S), with arc-related calc-alkaline volcanism having geochemical signatures that reflect changes in the residual mineral assemblages related to increased crustal thickness (>50 km). The increase in crustal thickness resulted from increased compression along the Southern Central Andean margin due to the subduction of the Juan Fernandez Ridge, and consequent shallowing of the downgoing slab during Mid to Late Miocene. Associated with the decrease in the slab dip angle, the volcanic front migrated to the east. Further south, magmas developed across the present-day Payenia back-arc region (35°–37° S) show an increase in slab-derived components in the middle Miocene to early Pliocene times, which also suggests a progressive shallowing of the subducting slab at these latitudes. However, trace element ratios indicate a low-to-intermediate pressure residual mineral assemblage and no significant increase in crustal thickness is apparent, unlike further north in the Chilean-Pampean flat-slab segment. Although flat-slab geometry still prevails in this latter segment, re-steepening of the slab during early Pliocene times (~5–3 Ma) promoted an increase of arc and back-arc magmatism at these more southerly latitudes of the Southern Central Andes. A dynamic link between slab geometry, geochemistry, and volcanic activity is therefore observed in the Southern Central Andes.

Paleogene Arc-Related Volcanism in the Southern Central Andes and North Patagonia (39°–41° S)

The influence of tectonic processes in evolution of magmatic suites evaluated through their geochemical signature has always been a subject of debate. Late Paleocene arc volcanism in the Southern Central Andes, particularly in North Patagonia, can be used to infer a direct relationship between magmatic episodes and tectonic changes along the Andean margin. Eocene arc-related volcanism (~44 Ma) in the North Patagonian Andes shows evidence for limited influence of the subducting slab on the composition of arc magmas and they exhibit an alkaline tendency. By Oligocene times (~29 Ma), arc volcanic sequences in the Auca Pan depocenter show predominantly arc-like geochemical signatures and have been derived from a calc-alkaline source. However, a comparison with younger arc sequences (<28 Ma) in the region suggests that the magmatic source turned more tholeiitic in composition with a remarkable increase in the influence of slab-derived fluids, as seen in volcanic rocks from Cura Mallin and Abanico retro and intra-arc basins. It is proposed that the marked geochemical variations between these magmatic periods are related to the tectonic changes associated with the breakup of the Farallon plate at ~28–26 Ma. The geochemical data from Eocene and Oligocene volcanic sequences provide further evidence for the strong link between tectonics and magmatism.