目次のタイトル"Paleoniagnetism of Pliocene to Pleistocene Rocks in Southwest JapanThe directions of natural remanent magnetization of about 300 volcanic rock specimens collected from Southwest Japan of which ages range from Pliocene to Pleistocene were measured. The mean pole positions calculated from the results agree with the present geographic north pole within an oval of 95% confidence. This fact suggests that there were no considerable movement of paleomagnetic pole position during Pliocene and Pleistocene in Southwest Japan, and that Southwest Japan did not change its geographical situation since Pliocene epoch. Furthermore, the volcanic rocks of remote localities used in the study can be correlated much more exactly with one another by the aid of comprehensive knowledges, such as their stratigraphy, absolute age determined by isotope method and the paleomagnetic polarity change of their remanent magnetization

Nishida, Junichi

Sasajima, Sadao

Shimada, Masahiko

Kyoto University Research Information Repository

Title Paleoniagnetism Study of Pliocene to Pleistocene VolcanicRocks in Southwest JapanAuthor(s)Nishida, Junichi; Shimada, Masahiko; Sasajima, SadaoCitationMemoirs of the Faculty of Science, Kyoto University. Series ofgeology and mineralogy (1967), 34(1): 1-8Issue Date1967-12-16URL http://hdl.handle.net/2433/186543RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversityMEMolRs oF THE FAcvLTy oF SclENcE, KyoTo UNIvERslTy, SERIEs oF GEoL. & MrNERAL.                      Vol. XXX, IV, No. 1, pp. 1-8.Paleomagnetic Study on           Volcanic RocksSome Pliocene and Pleistocenein Southwest JapanByJunichi NisHiDA, Masahiko SHIMADA* and Sadao SAsAJIMA(Received Sept. 8, 1967)                                Abstract   The directions of natural remanent magnetization of about 300 volcanic rock specimenscollected from Sovthwest,Japan of which ages range from Plioccne to Pleistocenc werc measured•The mean pole positions calculated from the results agree with the present geographic northpole within an oval of 9591o confidence. This fact suggests that there were no considerable move-ment of paleomagnetic pole position during Pliocene and Pleistocene in Sourhwest Japan, andthat Southwest Japan did not change its geographical situation since Pliocene epoch.   Furthetmore. the volcanic rocks ofrembte localities used in the study can be correlated muchmore exactly with one anQther by the aid ofcomprehensive knowledges, such as their stratigraphy,absolute age determined by isotope method and the paleomagnetic polarity change of their re-manent magnetization.Introduction    It is a well known fact that volcanic rocks acquire the thermoremanent mag-netization in parallel with the direction of the ambient geomagnetic field whÅënthey are cooled down through their Curie temperature. Basing on the fact, manyinvestigators have tried to elucidate the nature of the past geomagnetic field byrneasuring directions of the magnetization of rocks.    Many studies on post-Pliocene rocks, particularly, have been reported all overthe world. Recently, Cox et al. (1966, 1967) reported the reverse-normal chronolo-gy of past geomagnetic field combining paleomagnetic results with the data ofK--A age determination on Pliocene and Pleistocene rocks.    In Japan, many investigators such as AsAMi (1954), NAGATA et al. (1959),KAwAi et al. (1961), ITo (1963) and MoMosF. (1963) reported the results on Neogenevolcanic rocks. The present authors have intended to estimate from SouthwestJapan the movement pf paleomagnetic pole position ranging from Paleozoic toRecent. As a part of the study, more tlian 300 volcanic rock specimens which * DePartment ofEarth Scjence, College ofGeneral Education, Osaka University2 Junichi NtsHmA, Masahiko SHiMADA and Sadao SAsAJiMArange from Pliocene toSouthwest Japan. Inrocks are reported and Pleistocene inthis paper, thetheir geologicalage were collected from various parts ofpaleomagnetic results obtained from theseapplication is also discussed.              Sampling sites and geological descriptions    About 300 rock specimens were collected from several ]ocalities inJapan. The index map ofsampling localities is shown in Fig. 1,Southwestatip     t40.Es3oeE4OON35'NE e,D eG 2ci3i'NieAg{l'                  Fig. 1. The index map ofsampling localities.                     A Kuju, Central part of, Kyushu.                     B Yobuko and Karatgu, Northern part of Kyushu.                     C Genbudo, Northern part ofHyogo. '                     D Kurayoshi, Northern part ofTQttori.                     E Wakurayama, Northern part of Shimane.    Geological and petrological srudies of these rocks were performed inmany investigators, and those reviews are briefly described as follows.detail byPaleomagnetic Study on Some Pliocene and Pleistocene Volcanic Rocks in Southwest,Japan 3    a) Kuj'u, Centratpart ofKpashu    Kuju district is one of the typical Cenozoic volcanic regions in Japan. Geo-logical study of this region has been performed by ONo (1963). According to hisstudy, the volcanic rocks of this region can be classified into four groups regardingtheir eruption times, i.e. Upper Miocene to Lower Pliocene, Lower Pliocene toUpper Pliocene, Upper Pliocene to Lower Pleistocene and Recent. 30 series ofIava flows are found in this region, of which 15 flows were collected.    b) Yobuko andKaratsu, Northernpart ofKlushu    In the northern part of Kyushu, basic rocks generally called Matsuura basalticrocks are widely developed. Geological and petrological studies on these rockswere extensively worked by MATsuMoTo (1961) and KoBAyAsHi et al. (1955, l956).According to them, these lava flows are considered to have erupted in Pleisto-cene epoch. Successive rock samples were collected from several sites.   'c) Cenbudo, NorthernPart ofHyogo    In the northern part of Hyogo Prefecture, there is some distribution of basiclava flows summarized as Genbudo basalt]. Geological and petrological studieson these basalts were performed by KoKAwA (1956), MATsuMoTo and WADATsuMi(1958, 1959), who3e estimates oferuption times were in early Pleistocene.    d) Kurayoshi, Northern Part of Tottori    In the northern part of Tottori Prefecture, there are several lava flows whosegeological studies were made by MuRAyAMA et al. (1963). According to theseinvestigators, the lava flows collected in the present study are presumed to bePliocene ones.    e) Mtlakura2ama, 2Vorthern part ofShiman.o    Wakurayama andesite is found around Mt. Wakurayama of Matsue city,Shimane Prefecture. HiRooKA and KAwAi (1967) determined the age of this an-desite to be 6.34Å}O.19m.y. by K-A method.Result and consideration    The directions of magnetization of the specimens were measured with anastatic magnetometer. The stability of the remanent magnetization was examinedby a.c.- and thermal demagnetization. Prior to the paleomagnetic use, the direc-t,ion ofn.r.m. has to be considered from the following criteria:    1) The number ofspecimens in each site is at leagt more than 4 and a radius of the circle of 950/. confidence obtained from each site does nbt exceed 200.    2) The data are adopted when the direction of n.r.m. is proved to be stable4 Junichi NisHmA, Masahiko SHiMADA and Sadao SAsAJiMAby the stability tests and gives better precision after the removal ofsoft component.    3) There is no evidence ofpossible self-reversed magnetization.    The directions of n.r.m. of PIiocene and Pleistocene rocks with the circle of959/6 confidence (a), the precision parameter (k), and their corresponding virtualpole positions are shown in Table 1 and Table 2 respectively. The mean directionsofn.r.m.s and their corresponding pole positions for Pliocene and Pleistocene epochsare given in Table 3. In Fig. 2, these results are also shown together with theCretaceous paleomagnetic pole position estimated from Southwest Japan (SAsAJiMAarpd SHiMADA, 1966).    As shown in this figure, the pole positions for Pliocene and PIeistocene epochsobtained from the present study show a good agreement with the present northpole within an oval of 959/. confidence, whereas the pole position for Cretaceousperiod is significantly deviated from the present pole. The latter fact was alreadydiscussed in detail by SAsAJiMA and SHiMADA (1966). However, the former resultsuggests that the directions of the geomagnetic field in Pliocene and Pleistocenemay be almost the same as that of the present day.    There are many investigators such as BLuNDELL (1961), Cox and DoELLTable 1. The direction of n.r.m. of Piiocene rocks in SouthwestJapan.ReferenceNumber201202203204205206207208209210211212213214215216Rock unit studiedLocation Name (Age)Kyushu Kuju H4H2HlYRwRlP,(R)P,(N)I3TpSan'inKurayoshiKurayoshibasalt V- 1  V-2  V-3  V-4  X/'-5San'ifi' ' WakurayamaWakttrayama andesite           (6.34 m.y.)N10101010101010699745488 Direction ofMagnetizationDm358.6 6.9348.7357.6177.5184.!154.5 19.1345.9 5.4125.3190.6248.0354.2165.0I. 65.5 45.3 32.6 46.0-59.6-41.0-40.3 55.8 37.0 55.7-42.5-66.6-14.1  8.0- 1.5l82.3     -39.6k72751730322397691458 90253 251286  97a95 6.0 5.8,12.1 9.0 8.710.4 4.9 8.114.1 6.s6.45.815.62.619.722.4V.P.P9N77N81N70N87S 84S78S 65N74N71N85S 43S75S 22N58S 54S 67aW134W 88W 14W 10W 69Wl17W159W145WlW155W133E 72E 52W 34E 1616p8.04.87.77.5   +9.77.63.68.39.66.64.87.88.11.39.9E 73     15.96m9.8 7.213.611.413.312.65.911.716.4 9.47.99.715.92.619.727.1Paleomagnetic Study on Some Pliocene and Pleistocene Volcanic RoÅëks in SouthwestJapan 5Table 2. The direction of n.r.m. of PIeistocene rocks in SouthwestJapan.ReferenceNumberIOI102103104105106107108109110111ll2-113114115116117118Rock unit studiedLocation Name (Age)Kuju -t lt pp -t It )t tl t)San'initst    A    Kp    Dh    D,    D2    K7    K6    K,    K2  Genbudobasalt (1.6 my)  Yakuno   basaltKannabeyama   basaltKyushuYobuko  Yobukobasalt B7    B6    B,    B3    B2    B,N149766710448676713111010'Direction ofMagnetization'Dm355.4338.3241.7355.2355.2323.7350.43tro.1 19.6228A15J4.3O.3312.4 13.6355.1169.9318.9Im 48.2 32.8-51.2 43.8 26.8 34.4 51.6 29.1 56.3-48.552.261.7 57.7 48.2 54.5 54.9-40.4 59.0k3528140585338 1676144a95 6.710.35.39.l9.310.112.310.6 7.71813880343 38 33 27 26 6014.55.76.94.210.0 7.69.29.86.3V.P.P9N83N65S39N80N69N54N83N64N74S 49N77N83N88N50N78N87S 76N57a6pW8      5.7E 11     6.6E 30     4.9W 23     7.1W 32     5.5E 29     6.7E 34    11.3E3      6.4W145      7.7E 39WI27E l54E 140E 50W143W 48E 177E 6712.45.48.34.58.57.69.1Zl7.16m8.715.6 7.111.510.011.516.911.711.019.36.1IO.46.213.010.813.11L29.3 tt t.+Table 3. The mean directions of n.r.m.s calculated from the data, and theircorresponding mean pole positions.AgePleistocenePliaceneMean directionD351.7358.0I48.149.3a957.77.5k2534Pole positionPN 82.0N 85.5x"E 2.0W35.06p6,66.6y. .. ..6m10.08.6(1960) and KAwAi et al. (1961), who tried to apply paleomagnetic results to solvesome geological problems. Considering from knowledges so far obtained about thenature and direction of Pliocene and Pleistocene geomagnetic field, it might be saidthat the geornagnetic field changed its polarity periodically during the epochs (Cox,DoELL and DALRyMpLE; 1966, 1967). Supposing the above mentioned feature of6 Junichi NisHiDA, Masahiko SHiMADA and Sadao SAsAJiMAOeE6oot.--.,Nt " sle vR>-t sy*."L,PteistocenePlioceneA(1. trv,C>gW6oo        .tEt2oo E)'Og. ms tx/ eC r, eta eousts ..-7 W12oe                                  18oe         Fig. 2. •Mean virtual geomagnetic pole obtained from SouthwestJapan.the past geomagnetic field, the volcanic rock series of far different localities can bebetter correlated with one another by the aid of combined knowledges, such astheir stratigraphy, absolute age determinations on some ro:ks and the paleomagneticpolarity changes of the remanence.    In fact, so far as Upper Pliocene to PIeistocene time concerns, it is safer toadopt as a standard, the normal-reverse polarity time scale proposed by Cox et al.(1967).    There is a series oflava flows in Kurayoshi, most ofwhich are reversely magne-tized, and these lava flows are considered to be Middle Pliocene in age. Some ofKuju lava flows in Middle Pliocene are also reversely magnetized. These reversalsmay possibly be correlated with each other.    On the basis of the above mentioned method, the present results on somePliocene and Pleistocene volcanic rocks with different localities in SouthwestJapancould be well ranked on the geological chronology. Thus obtained result issummarized in Fig. 3.Pateomagnetic Study on Some Pliocene and Pleistocene Volcanic Rocks in SouthwestJapan 7KUJU YOBUKOSAN'1NDoetl,Coxand1966l967KajuVoicariRocks101d833lO,gl8,6I08H3ll41l5l16m•v•Brunhesepoch)JaramilloE.i.SzE.a.looFs,cl!t.t.lJa.o-event117'lllt12--t--:-.J.T.'(110)--.+.-..Matuyamaepochtolduvaievenftit6y.')Gauss'.oepochH 20120220320411lttd!lllVotcaniRocks!'vvvvSh6naiVolcor)iRocks'(2l1)(212)213-Mammothevent6ilbertepoch,o,o.ot.s.lz1.i.1oo-Jatzo(2O207214(215)(216).3•y•2082092106.07,O( ) Reverse Fig. 3.polarity [] Nernial time EZZZ2 Reversal timeCorrelation of volcanic rocks of southwestJapan.Conclusion    From our present study, following conclusions may be led in final.    1) The pole positions of Pliocene and Plcistocene epochs agree well with thepresent north pole, and it strongly suggests that there were no movement of South-westJapan during and after those epochs.    2) The volcanic rock series of remote localities can be better correlated8 Junichi NisHTDA, Masahiko SHiMADA and Sadao SAsAJiMAby comprehensive knowledges of their stratigraphy and paleomagnetic polaritychanges of their remanence, together with some data of absolute age determina-tion among them.Acknowledgement    The authors wish to express their thanks to Professor Z. HATuDA ofKyotoUniversity for his continuous encouragement through the study. Their thanks arealso expressed to Dr. K. WADATsuMi ofHimeji Technological College for his valuableg. eological suggestions.ReferencesAsAMi, E. (1954): Proc. JraPan Acad., 30, pp. 102-105.BLuNDELL, DJ. (1961): Geol. Mag., 98, pp. 301-312.Cox, A. and R.R. DoELL (1960) : Geol. Soc. Ani. Bull. 71, pp. 645-768.Cox, A., R.R. DoELL and G.B. DALRyMpLE (1967): Earth Ptanet. Sei. Letters, 2, pp. 162-173.DoELL, R.R., G.B. DALRyMpLE and A. Cox (1966): Jfour. GeoPhLJ,s. Res., 71, pp. 531-541.HiRooKA, K. and N. KAwAi (1967): Jrour. Geot. Soc. .tapan, 73, p. 68.ITo, H. (1963): .Iour. Geo,ttag. Geoelec., 15, pp. 37-212.KAwAr, N., H. ITo and S. KuME (1961): GeoPh"s. .Iour., 6, pp. 124130.KoBAyAsHi, I., I. IMAi and K. MATsui (1955): Explanatory Text of the Geological Map of   Japan, `Yobuko' 1 :50,OOO, Geol. Surv. Japan.KoBAyAsHi, I., I. IMAi and K. MATsui (1956): Explanatory Text ofthe Geological Map ofJapan,   `Karatsu' 1 :50,OOO, Geol. Surv. Japan.KoKAwA, S. (1956) : Geescience Magazine, 9, pp. 35-54.MATsuMoTo, T. and K. WADATsuMi (1958): .lour. Geol. Soc. .JaPan, 64, pp. 625-637.MA'rsuMoTo, T. and K. NVADATsuMi (1959): Jrour. Geol. Soc. Jrapan, 65, pp. 117-127.MATsuMoTo, Y. (1961): Sci. ReP. Seisan Ka.gaku Inst., Kyushu Univ., 30, pp. 1-99.MoMosE, K. (1963) : Bull. Far!hg. Res. Inst., 41, pp. 487-.534.MuRAyAMA, M., N IssHiKi and T. SAKAMoTo (1963): Explanatory Text of the Geological   Map ofJapan, `Tottori-hokubu and Tottori-nanbu' 1:50,OOO, Geol. Surv.Japan.NAGATA, T., S. AKiMoTo, Y. SHiMizu, K. KoBAyAsHi and H. KrJNo (1959): Proc. JraPan Acad.,   35, pp. 378-383.ONo, K. (1963) : Explanatory Text ofthe Gcological Map of Japan, `Kuju' 1 :50,OOO, Geol. Surv.   Japan.SAsAJiMA, S. and M. SHiMADA (1966): Jour. Geol. Soc. .JaPan, 72, pp. 503-514.SAsAJiMA, S. and M. SHiMADA (19. 67): Trans. Am. GeoPhs. Union, 48, p. 84.

Paleoniagnetism Study of Pliocene to Pleistocene Volcanic Rocks in Southwest Japan

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Paleoniagnetism Study of Pliocene to Pleistocene Volcanic Rocks in Southwest Japan

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