On New Occurrence of Aegirine Augite-Amphibole-Quartz-Schists in the Sambagawa Crystalline Schists of the Besshi-Shirataki District, with Special Reference to the Preferred Orientation of Aegirine Augite and Amphibole

KOJIMA George

HIDE Kei

Journal of science of the Hiroshima University. Ser. C, Geology

The present authors have collected in the Besshi-Shirataki district, Shikoku, three samples of aegirine augite-bearing quartz-schists, which have not been known from the Sambagawa metamorphic zone proper. Geological setting and petrographical properties of these rocks are described. They have been found in the spotted terrain characterized by the forming of porphyroblastic albite petrographically, and by the presence of recumbent type of folding and syntectonic intrusion of ultramafic rocks tectonically. The quartz-schists consist of aegirine augite, alkalic amphibole (especially of glaucophane-crossite series), garnet, muscovite, quartz, albite, and accessory minerals such as apatite, hematite, pyrite, sphale-rite, and titanite. Petrofabric analyses have been carried out on aegirine augite, amphibole, muscovite, and quartz. Prisms of amphibole are oriented with the plane (100) parallel to the bedding-schistosity plane (ab), and with the crystallographic axis: c parallel to the b-lineation. In the quartz-schist at Shira-taki the axis: c is parallel both to the tectonic axis: b and to a. Grains of aegirine augite are oriented with the plaine (010) parallel to the bedding-schistosity plane (ab), and with the crystallographic axis: c parallel to the tectonic axis : b. Quartz diagrams show the common pattern, which is not distinguishable from that of the other quartz-schists in the district. These petrofabric characteristics suggest that the quartz-schists in question have experienced the same history of deformation and crystallization as the normal quartz-schists in the district, and that the possible effect of metasomatism from serpentinites locally in-truded late- or post-tectonically may be excluded.

eng

HIROSHIMA UNIVERSITY

[ISSN] 0075-4374

[NCID] AA10647954