Abstract: New field and thermobarometric work in the Californian Salinian block clarifies current and pre- Tertiary relationships between the schist of Sierra de Salinas and Cretaceous arc-related granitic rocks. The contact is variably preserved as a brittle fault and high-temperature mylonite zone, the Salinas shear zone, which represents the contact between North America and sediments accreted above the Farallon slab between ~76 Ma and ~70 Ma.

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Geochemical analyses and geobarometric determinations have been combined to create a depth vs. radiogenic heat production database for the Jurassic-Cretaceous Sierra Nevada batholith, California. This database shows a wide range of heat production values at any given depth, but an overall pattern of relatively invariant heat production of ~2 ?W/m3 within the ~3-km-thick volcanic pile at the top of the batholith, below which heat production increases

Uranium-lead zircon (laser ablation multi-collector ICP-MS spot analysis) ages from La Caridad porphyry copper deposit in the Nacozari District, Northeastern Sonora, Mexico, suggest a short period of magmatism, between 55.5 and 52.6 Ma. Two U-Pb ages from the mineralized quartz monzonite unit, showing different textural characteristics, yielded indistinguishable crystallization ages (~54 Ma), and indicate that the intrusion responsible for the mineralization

Xenoliths of deep origin hosted by Miocene ultrapotassic rocks in the Southern Pamir bear important new information regarding the geological processes accompanying tectonism during the Indo?Eurasian collision. Four types have been studied: sanidine eclogites (omphacite, garnet, sanidine, quartz, biotite, kyanite), felsic granulites (garnet, quartz, sanidine and kyanite), basaltic eclogites (omphacite and garnet), and a glimmerite (biotite, clinopyroxene

We investigated calcite globules and veins in two spinel-garnet peridotite xenoliths from the sub-Sierra Nevada mantle. The studied xenoliths have been entrained in a Miocene (11 Ma) volcanic plug. These carbonates are spatially associated with silicate glass inclusions, suggesting that they are primary inclusions ? inclusions that formed at high temperature in the mantle and not at or close to the Earth?s surface. The host peridotites represent

Reinterpretation of onshore and offshore geologic mapping, examination of a key offshore well core, and revision of cross-fault ties jointly indicate net Neogene dextral strike slip of 154?2 km along the San Gregorio?Hosgri fault zone, a strand of the San Andreas transform system in coastal California. Slip rates over time are not well constrained, but were greater than at present during early phases of strike slip after fault initiation in late

New eclogite localities and new 40Ar/39Ar ages within the Western Gneiss Region of Norway define three discrete ultrahigh-pressure (UHP) domains that are separated by distinctly lower pressure, eclogite facies rocks. The sizes of the UHP domains range from c. 2500 to 100 km2; if the UHP culminations are part of a continuous sheet at depth, the Western Gneiss Region UHP terrane has minimum dimensions of c. 165 50 5 km. 40Ar/39Ar mica and K-feldspar

Seismic data provide unique images of crust-mantle interactions during ongoing removal of the dense batholithic root beneath the southern Sierra Nevada. The removal was initiated between 10 and 3 Ma with a Rayleigh?Taylor-type instability, but with a pronounced asymmetric flow into a mantle downwelling (drip) beneath the adjacent Great Valley. A nearly horizontal bottom-to-the-SW shear zone accommodated the detachment of the ultramafic root from

We provide data on the geochemical and isotopic consequences of non- modal partial melting of a thick Jurassic pelite unit at mid-crustal levels which produced a migmatite complex in conjunction with the intrusion of part of the southern Sierra Nevada Batholith at ca. 100 Ma. Field relations suggest that this pelitic migmatite formed and then abruptly solidified prior to substantial mobilization and escape of its melt products. Hence this area yields