The Longrono-Soria basin was formed between N60°E-striking, left-stepping, left-lateral strike-slip faults during the Late Jurassic-Early Cretaceous (Wealdian), when as much as 6 km (20,000 ft) of fluvio-deltaic strata accumulated in it. During basin development, the ends of the master faults propagated, increasing fault length and offset. Outside the basin, compressional deformation with superimposed folding was induced near the ends of the master faults. At the same time within the basin, normal faults and depocenters migrated in a direction opposite to that of the propagating master faults. The resulting extension allowed a N130°E-trending, 50-km (31-mi) wide, synsedimentary syncline to develop in the basin fill. This syncline was related to formation of a ha f graben in the basement. The high rate of subsidence and the high heat flow led to a sequential development within the sediments of water escape structures, hydroplastic-type compaction-related microfaulting, pseudocleavage, and metamorphism--420°C (788°F), 1-2 kb, 100-150°C/km (5.5-8.25°F/mi) gradient.

Our interpretation of the geometry, sedimentation, tectonics, and thermal evolution of the Longrono-Soria basin is based upon 2 mathematical models of strike-slip basins and one analogue model: (1) Rodger's calculations predicting vertical deformation, stress accumulation, and secondary faulting; (2) an unpublished finite element method by Liu that gives stress deviation and accumulation patterns; and (3) microtectonics, which provide a model for stress deviations at the tip of the microfaults and for the geometry of deformation during micro-rhombgraben development. The 3 models show comparable fault geometry and stress patterns, and fit our data from the Longrono-Soria basin.

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