The Ichinohe Basin, defined by the exposed extent of the Early and Middle Miocene Yotsuyaku and Keiseitoge formations, is tectonically characterized by N-S trending normal-faults at the eastern margin of the basin and by E-W trending normal-faults at the northern part of the basin. Such contradicting tectonic structures reflected a change in the stress regime during the Neogene time. The N-S oriented normal-faults with the longitudinal basin-filling of the Yotsuyaku Formation indicate the crustal extensional tectonism during the Early and Middle Miocene time. Talus sheets with steeply inclined basin walls also suggest that the basin was formed as a rifting basin within the Kitakami Massif. However, the E-W extensional regime must have changed into the E-W compressional stress regime after forming the Middle and Late Miocene Kadonosawa Basin, located farther north to the Ichinohe Basin. The newly exposed E-W trending normal-fault proves the change of stress regime during the Late Neogene time.

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Precambrian lower crustal rocks of Sri Lanka have undergone brittle faulting and fracturing. Here we studied the structures and fault rocks associated with the Randenigala fault, one of the major faults found in the basement of Sri Lanka. Field studies, petrography, SEM analysis and X-ray power diffraction of the cataclastic rocks associated with the fault indicate that the rocks have been formed at shallow depth, probably within 1–4 km of the crust, suggesting that the related brittle deformation is a younger event. We relate this brittle deformation to the tectonics in the Indian Ocean. Brittle faults in the basement have probably been formed at various stages since the break-up of Gondwana around Sri Lanka at about 130 Ma. Reactivation of early faults and formation of new ones could have occurred during subsequent events. The motion across the Indian Ocean related to the boundary between the Indian and Australian plates may have a significant effect on brittle tectonics in Sri Lanka. Apart from reactivation of existing faults, some faults could have been originated in the basement by the tectonics related to this motion, especially at 7.5–8 Ma. We speculate that the E-W trending Randenigala fault and other similar faults in Sri Lanka may be related to the onset of the E-W faulting and folding, which occurred at 7.5–8 Ma, in the central Indian Ocean. It is suggested that the current nearly N-S compression in the Indo-Sri Lankan lithosphere is responsible for recurrent seismicity and crustal movements in and around Sri Lanka.

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Cathodoluminesence (CL) microscopy of high-temperature skarn minerals from Fuka, Okayama, Japan, helped to distinguish minerals having similar optical properties and their internal textures. Spurrite and tilleyite, having similar optical properties, were easily distinguished using CL microscopy. Furthermore, growth patterns could be identified in single crystals of wollastonite using CL images. Although the chemical variations corresponding to the CL variations cannot be distinguished using electron microprobe analyses, they are considered to reflect minor variations in trace element and REE contents. Thus, cathodoluminescence microscopy is a useful tool to distinguish minerals and helps us in selecting suitable sub-samples for detail studies on trace and rare earth element geochemistry.

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