The three dimensional spatial variations in the cooling pattern of the Toki granitic body, a zoned pluton in Central Japan, have been evaluated quantitatively by thermochronology using cooling age determination based on the different closure temperatures for target mineral species. The Toki granite has hornblende K-Ar ages of about 74.3±3.7 Ma (n = 2; closure temperature of 510±25 o C), biotite K-Ar ages of 78.5±3.9 to 59.7±1.5 Ma (n = 33; 300±50 o C), and zircon fission-track ages of 75.6 ±3.3 to 52.8±2.6 Ma (n = 44; 240±50 o C).The spatial variation in the biotite K-Ar age is similar to that in the zircon fission-track age in samples collected from 11 boreholes and seven outcrop sites in the Toki granite, indicating that cooling was effectively from the roof and also from the northwest margin. This cooling pattern shows a strong correlation with the Alumina Saturation Index (ASI) distribution of the body.Larger ASI values correspond to earlier and more rapid cooling after emplacement and smaller value to slower cooling. Toki granite was effectively cooled from the peraluminous regions where assimilation of country sedimentary rock was most extensive.

Abstract. Samples from the Late Cretaceous

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[1] In the flowing fluid electric conductivity (FEC) logging method, well bore fluid is replaced with deionized water, following which FEC profiles in the well bore are measured at a series of times while the well is pumped at a constant rate. Locations where fluid enters the well bore show peaks in the FEC logs, which are analyzed to infer inflow strengths and salinities of permeable features intersected by the borehole. In multirate flowing FEC logging, the flowing FEC logging method is repeated using two or more pumping rates. The results, coupled with those of a conventional well test over the entire borehole, enable the transmissivities and inherent pressure heads of permeable features to be determined. Multirate FEC logging is carried out on a deep borehole in fractured granitic rock using three different pumping rates. Results identify 19 hydraulically conducting fractures and indicate that transmissivity, pressure head, and salinity vary significantly among them. Using three pumping rates rather than the minimum number of two permits an internal consistency check on the analysis that provides a measure of the uncertainty of the results. Good comparisons against static FEC profiles and against independent chemical, geological, and hydrogeological data have further enhanced confidence in the results of the multirate flowing FEC logging method.

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