Geochemical
Journal,Vol. 33, pp. 59 to 66, 1999
NOTE
FissiontrackandK-Ardatingon some graniticrocksof
theHidaMountain
Range,CentralJapan
2
RYUJIYAMADA1*
and SATORUHARAYAMA
1Divisionof Earthand PlanetarySciences,GraduateSchoolof Science,KyotoUniversity
,
Kyoto606-8502,Japan
Matsumoto
390-0802,Japan
Facultyof Science,ShinshuUniversity,
2GeologyDepartment,
(Received
August18, 1997; AcceptedAugust11, 1998)
for two
Fissiontrack(FT)zirconagesfor eightsamples,and K-Aragesusing biotiteand hornblende
on four graniticrock bodiesand a dyke in the HidaMountainRange,Central
samplesweredetermined
<3 Mafor six samples,and >40 Ma for two samples
. K-Ar ages
Japan. FT zirconages weredetermined
were alwaysolderthan the FT ages, reflectingthe differencein closuretemperature
. Fora sampleof the
thermaloverprinting
wasfoundaccordingto the statistical
Okukurobe
Granite,the evidenceof secondary
The
FT
and
FT
distribution
test for singlegrain
aspect
.
apparentFT age of 44 ± 5 Ma (2d
ages
length
level) shouldnot correspond
to any geologicalevents
. On the basis of the radiometric
age data, the
Tonaliteintruded
as follows
: TheKitamatadani
orderof therockbodiescouldbe reconstructed
emplacement
Granite at -60-70 Ma, the OkukurobeGraniteprior to -60 Ma, the Kurobegawa
at-90 Ma,theTsurugidake
Granite(KG) priorto -7 Ma,anda dykeintrudedintoKGat -.1 Ma. Becausea simplecoolingprocessis
the cooling
not applicableto the rockbodiesin this region, it is necessaryto analyzesystematically
-tectonichistoryanalysis
historiesof relativelysmallparts of eachrockbodypriorto the thermo
.