Flow direction and groundmass shear zones in dykes, Shimane Peninsula, Japan

Article Abstract:

A study was conducted comparing the usefulness of groundmass shear analysis and phenocryst orientation as indicators of magma flow direction in dikes at Sezaki in the Shimane Peninsula of southwest Japan. A new model of the formation of groundmass shear zones allows them to be used as reliable indicators of flow direction. However, phenocryst orientation in dikes may not be a reliable indicator of flow direction because it is strongly influenced by flattening resulting from magma pressure.

Dikes (Geology)

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The durations of Silurian graptolite zones

Article Abstract:

The duration of the Silurian epochs Llandovery, Wenlock, Ludlow and Pridoli, as revealed by radiometric and graphic studies, is around 13 Ma, 4 Ma, 5 Ma and 10 Ma, respectively, suggesting that duration of the Silurian period to be around 32 Ma. A coordination of data from these four divisions of the Silurian period helps formulate a bichronometric 'composite standard section' that provides a relationship between time-scale and biochrons.

Geology, Stratigraphic, Stratigraphy, Silurian period

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Timing of the cataclastic deformation along the Akaishi Tectonic line, central Japan

Article Abstract:

A study of the K-Ar ages of samples of cataclasites and fault gouges from the Akaishi Tectonic Line (ATL), central Japan, shows that ATL was active with the formation of strike-slip basin along its trace during middle Miocene. The results show that the hydrothermal alteration associated with the fault movement happened at nearly 15 Ma.

Analysis, Faults (Geology), Cataclastic rocks

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