[1] The South Portuguese Zone (SPZ) constitutes the southernmost segment of the Variscan Iberian Massif. It is bounded to the north by the Beja-Acebuches Ophiolitic Complex and related accretionary wedge. To the south lie the Iberian Pyrite Belt (IPB) and flysch deposits forming the southern extent of the zone. Structural analysis within the Spanish side of the SPZ supports continuous south propagating deformation, evolving from early synmetamorphic thrusting in the internal zone to thin-skinned tectonics in the southern external domain. The accretion of the SPZ to the Ossa Morena Zone is also witnessed by the presence of various mélanges, observed throughout the investigated area. Part of the mélanges observed in the IPB are related to the volcanics and mineralizations setting. A key point to understand the IPB mineralizations genesis is to constrain the volcanogenic model. One underestimated feature is the large amount of submarine calc-alkaline ignimbritic facies, implying the presence of caldera structures within the province. Such correlation between caldera environment and ore deposits strongly suggests that the IPB developed in a continental arc. Our geodynamic model proposes an early north directed subduction associated with the obduction of the oceanic crust toward the south. Southward, this episode is immediately followed by the development of the accretionary prism, while farther south, a second subduction zone responsible for the arc setting of the IPB initiates. Subsequent Visean continental collision is associated with the deposit of the south propagating flysch and the present geometry of the SPZ.

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The Jackass Lakes pluton (JLP), located in the central Sierra Nevada batholith, is a 98 Ma composite intrusion that preserves fi eld, structural, and petrologic evidence of how incrementally emplaced plutons grow and evolve both spatially and temporally. In contrast to many other Sierra Nevada batholith intrusions, the compositional and textural diversity found within the JLP allows individual increments to be easily discerned in the fi eld. Previous work has resulted in two different incremental emplacement models for the JLP. The fi rst states that the JLP was emplaced and assembled via vertical diking or sheeting, some downward return fl ow along the margins of the pluton, and local stoping. The second involves replenishment by mafi c sheets that may represent originally subhorizontal fl oors of an evolving magma chamber. We present new data and a model suggesting that the JLP (1) contains multiple, irregularly shaped intrusions of both felsic and mafi c material that do not represent dikes or paleofl oors; (2) magma increments were extensively mingled, both between and within intrusions; (3) records evidence of magma mixing locally and possibly at the intrusion scale; (4) has not been tilted; (5) has magmatic mineral fabrics that record superimposed regional strain, not emplacement-related strain; (6) preserves large metavolcanic pendants representing subhorizontal roof contacts; and (7) was emplaced by ductile deformation of its host rocks, return fl ow, and widespread stoping of older host rock and its internal increments. This model, based on fi eld, structural, strain, thermobarometric, and petrologic analyses, elucidates that the JLP construction is considerably more complex spatially and temporally than previous models suggest, and highlights processes involved during incremental emplacement of plutons. on June 18, 2010 geosphere.gsapubs.org Downloaded from JLP incremental construction Geosphere, April 2010 131 B C S Z 85 75 80 80 80 85 85 85 70 60 85 50 70 50 60 85 75 Jura-Cretaceous metavolcanic rocks 0 1 2 km 95-85 Ma plutons 98 Ma Jackass Lakes plutoñ 107-99 Ma plutons Magmatic foliation inclined; trace

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