{"created":"2021-03-01T06:09:07.337766+00:00","id":5274,"links":{},"metadata":{"_buckets":{"deposit":"8d1f3648-5b46-468a-8f00-97f65c21d207"},"_deposit":{"id":"5274","owners":[],"pid":{"revision_id":0,"type":"depid","value":"5274"},"status":"published"},"_oai":{"id":"oai:niigata-u.repo.nii.ac.jp:00005274","sets":["453:455","468:563:564"]},"item_6_alternative_title_1":{"attribute_name":"その他のタイトル","attribute_value_mlt":[{"subitem_alternative_title":"インド洋中央海嶺玄武岩の岩石学および南西インド洋海嶺東部に沿ったMORB広域的組成変化の要因"}]},"item_6_biblio_info_6":{"attribute_name":"書誌情報","attribute_value_mlt":[{"bibliographicIssueDates":{"bibliographicIssueDate":"2011-03-23","bibliographicIssueDateType":"Issued"},"bibliographicPageEnd":"94","bibliographicPageStart":"1","bibliographic_titles":[{}]}]},"item_6_date_granted_51":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2011-03-23"}]},"item_6_degree_grantor_49":{"attribute_name":"学位授与機関","attribute_value_mlt":[{"subitem_degreegrantor":[{"subitem_degreegrantor_name":"新潟大学"}]}]},"item_6_degree_name_48":{"attribute_name":"学位名","attribute_value_mlt":[{"subitem_degreename":"博士（理学）"}]},"item_6_description_4":{"attribute_name":"抄録","attribute_value_mlt":[{"subitem_description":"中央海嶺で生成される中央海嶺玄武岩(MORB)は部分溶融程度、結晶分化の程度、またはソースマントルの不均一性などの要因により様々な組成を示す。超低速拡大海嶺である南西インド洋海嶺(SWIR)は海嶺軸に沿った玄武岩組成の不均質が指摘されている一方で、中速であるインド洋中央海嶺(CIR)のロドリゲス三重会合点(RTJ)近傍での研究はほとんどない。本研究ではCIR、SWIRから得られた試料を元に海嶺軸に沿ったMORBの組成変化をセグメントスケール、さらに広域な範囲で検討を行った。YKO5-16Leg.1航海ではCIRセグメント2(CIR-S2)とセグメント3(CIR-S3)において海嶺軸の横断方向にしんかい6500によるサンプリングを行った。CIR-S2は海嶺軸内に円錐形の小海丘(コニカルコーン)が見られるが、CIR-S3は海嶺軸谷と平行な地形的高まりが存在する。CIR-S2のneo-volcanic zone(NVZ)ではコニカルコーンの斜面で枕状溶岩が観察され、頂上はシートフローで覆われていた。CIR-S2の断層崖(AVW)の下部はドレライト、上部は枕状溶岩で構成されている。また、シート状岩脈群がこの下部で発見されている。コニカルコーンで採取された玄武岩はほとんどが無斑晶質玄武岩だが、AVWの玄武岩・ドレライトはすべて斜長石の斑晶を持つ。CIR-S3はNVZ、old-volcanic zone(OVZ)、AVWのそれぞれのサンプリングが行われ玄武岩が採取された。OVZから採取された玄武岩のみ1-1.4%の斜長石斑晶を持つ。またAVWから得られた玄武岩は1-3.4%の発泡孔を持つ。このように得られたサンプルはそれぞれのセグメントの内部でも採取場所により異なった記載岩石学的特徴を持つ。CIR-S2、CIR-S3から得られた玄武岩・ドレライトの全岩化学組成はCIR-S2のコニカルコーン、AVWとCIR-S3でそれぞれ異なる特徴を示す。コニカルコーンから得られた玄武岩は非常に均質な組成を示し、またマントルかんらん岩のかんらん石と平衡なMg#を示す。一方でCIR-S3のAVWとCIR-S3から得られた玄武岩・ドレライトの組成はコニカルコーンよりは分化した値を示し、それぞれの結晶分化トレンドを示す。また高いK_2Oや揮発性成分やインコンパチブル元素含有量からCIR-S3の玄武岩はT-MORBの特徴を示す。コニカルコーンの玄武岩組成を未分化メルトと仮定し、低圧(1kbar)と高圧(5kbar)で結晶分別をする計算を行った結果、CIR-S2 AVWの玄武岩は高圧の、CIR-S3の玄武岩は低圧の結晶分別を被っていることが明らかになった。このような違いは海嶺下でのマグマシステムの違いによると推測される。CIR-S2の海嶺下ではマントルの伝導的冷却が効果的に起こり、メルトはマントル内(高圧)での結晶分別を被り、貫入岩としてマントル内で固結するため、生成される地殻は薄くなる(CIR-S2 AVW)。また、そのような高圧の結晶分別を被ることなく噴出した未分化な玄武岩も存在する(コニカルコーン)。一方CIR-S3ではマントルポテンシャル温度が高かった、またはT-MORB成分のためマントルがより深くから溶け始めたと考えられる。従って形成される地殻は厚く、噴出する玄武岩は分化する。このように隣り合ったセグメント同士でも異なるマグマシステムを持つことが明らかになった。次に、SWIRに沿った玄武岩組成変化を検討した。","subitem_description_type":"Abstract"},{"subitem_description":"先行研究を元に、本研究ではロドリゲス三重会合点(70°E)からGallieni FZ(52°20′E)の間を東から西に向かってArea IからArea IVの4地域に分け、これらの組成の関係を検討した。玄武岩の主要元素・微量元素組成でArea I、III、IVは一連の結晶分化トレンドを示すのに対して、Area IIの玄武岩組成はAl_2O_3、Na_2Oが高く、TiO_2、FeO*、CaOが低く、他の3地域とは違う傾きのトレンドを持つ。またArea IIのREEパターンはHREEではArea I同じ組成範囲示すが、LREEはArea Iよりも高い特徴を示す。同じマントルを仮定してメルティングと結晶分別の計算を行うとArea IIIとIVの玄武岩はArea Iよりも低い部分溶融程度のメルトからの結晶分別で説明することができる。またArea III玄武岩のインコンパチブル元素含有量がわずかにArea IVよりも高いことからArea IIIの玄武岩のほうがより低い部分溶融程度のメルトが起源であることが示唆される。このようにArea I、III、IVの玄武岩組成の違いは同一のソースからの異なる部分熔融度の違いで説明できたのに対し、Area IIの玄武岩組成を説明することはできない。従って、Area IIの玄武岩組成は異なるソースに由来していることが推測される。このように本研究ではセグメントスケールからより広い範囲で玄武岩組成が異なることが明らかになった。それはソースマントルの部分溶融程度の違いや結晶分化作用の程度、あるいは海嶺下のマグマシステムの違いで説明することができる。またSWIRにはマントル組成の不均質があることが明らかになった。","subitem_description_type":"Abstract"},{"subitem_description":"Compositions of mid-ocean ridge basalts vary depending on the degree of partial melting, extent of fractional crystallization and source mantle etc. Near the Rodriguez triple junction RTJ (70°E), the regional variations of MORB compositions along the SWIR, ultra-slow spreading ridge, have been reported and shown a heterogeneity of the MORB compositions, but few studies have been done along the CIR, intermediate spreading ridge. In this study, using basaltic samples from the CIR and the SWIR, compositional variations of the MORB along ridges are investigated. During YK-05-16 Leg.1, 2 dives have been done at the segment center of the segment 2 of the CIR (CIR-S2) and the segment 3 (CIR-S3). A number of conical cones (CC) are observed in a neo-volcanic zone (NVZ) within the CIR-S2. Pillow lavas appear at the slope, while the top of the CC are covered by a sheet flow. The dike swarm occurs at the foot of the axial valley wall (AVZ). Several small-scale ridges parallel to the rift valley are present within CIR-S3. Basalts from the CC are mainly aphyric basalts with a glassy rim. Dolerites are recovered from the lower part, and basalts are obtained from the upper part of the AVW. Within CIR-S3, basalts from the NVZ and the AVW are aphyric, and only basalts from the AVW are vesicular. Basalts from the old volcanic zone (OVZ) have plagioclase phenocrysts. Basalts from the CC show primitive and quite homogeneous composition and those from the AVW are more evolved. Basalt compositions from CIR-S3 show also more evolved features, but they are distinct from the crystallization trend of the AVW in CIR-S2. Trace element concentrations of basalts from CIR-S2 show N-MORB signatures and those from CIR-S3 have T-MORB signatures. Different crystallization trends between the AVW of CIR-S2 and CIR-S3 can be accounted by different fractionation pressures. Under the CIR-S2, efficient conductive cooling causes crystallization of melts in the mantle, therefore, basalts have undergone high pressure crystallization. In addition, primitive melts which have not undergone crystallization are also erupted (CC).","subitem_description_type":"Abstract"},{"subitem_description":"In contrast, high mantle potential temperature or the T-MORB component in the CIR-S3 result in melting at deeper depth, and basalts which undergone low pressure fractionation are erupted within CIR-S3. It is clear that there are different magma processes between adjacent segments. The SWIR are divided into 4 areas from RTJ to Gallieni FZ, Area I to Area IV (east to west). Basalt compositions of Area I, Area III, and Area IV are interpreted by differences in melting degrees from a same source. Basalts from Area III and IV are formed from the melts of lower melting degree than those from Area I. Moreover, incompatible element concentrations of Area III basalts are slightly higher than those of Area IV basalts, thus, Area III basalts are derived from melts with lower melting degree than those of Area IV basalts. On the contrary, Area II basalts show high Na_2O and Al_2O_3, and low TiO_2, FeO* and CaO. Furthermore, REE patterns of Area II basalts show similar concentrations of HREE, but higher LREE than those of Area I. These compositional features of Area II can not be explained by different melting degrees. It suggests that basalts from Area II are derived from abnormal mantle source. Using incompatible elements, and major element compositions of basalts from the CIR to the SWIR, including CIR-S1 and the RTJ area, these basalts (expect Area II basalts) can be produced by different melting degrees, extent of crystallization or pressures of fractional crystallization. Basalts from CIR-S2 and Area I are derived from higher melting degrees than other areas. Basalts from Area I (most primitive in SWIR) are more evolved than CC of CIR-S2 and those from RTJ are further more evolved. Basalts of Area III and Area IV are produced from lower degree of melting, and formed basalts which have wide range from primitive to evolved. MORB compositions along the CIR and the SWIR near the RTJ show various features caused by differences degree of partial melting, extent of crystallization and magma system beneath the ridge. And it is clear that there is heterogeneity of mantle composition under the SWIR.","subitem_description_type":"Abstract"}]},"item_6_description_5":{"attribute_name":"内容記述","attribute_value_mlt":[{"subitem_description":"新潟大学大学院自然科学研究科","subitem_description_type":"Other"},{"subitem_description":"平成23年3月23日","subitem_description_type":"Other"},{"subitem_description":"新大院博（理）甲第324号","subitem_description_type":"Other"}]},"item_6_description_53":{"attribute_name":"学位記番号","attribute_value_mlt":[{"subitem_description":"新大院博（理）甲第324号","subitem_description_type":"Other"}]},"item_6_dissertation_number_52":{"attribute_name":"学位授与番号","attribute_value_mlt":[{"subitem_dissertationnumber":"13101甲第3498号"}]},"item_6_full_name_3":{"attribute_name":"著者別名","attribute_value_mlt":[{"nameIdentifiers":[{"nameIdentifier":"50015","nameIdentifierScheme":"WEKO"}],"names":[{"name":"根尾, 夏紀"}]}]},"item_6_publisher_7":{"attribute_name":"出版者","attribute_value_mlt":[{"subitem_publisher":"新潟大学大学院自然科学研究科"}]},"item_6_select_19":{"attribute_name":"著者版フラグ","attribute_value_mlt":[{"subitem_select_item":"author"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"Neo, Natsuki"}],"nameIdentifiers":[{"nameIdentifier":"50014","nameIdentifierScheme":"WEKO"}]}]},"item_files":{"attribute_name":"ファイル情報","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2019-08-05"}],"displaytype":"detail","filename":"D_S_NN.pdf","filesize":[{"value":"26.5 MB"}],"format":"application/pdf","licensetype":"license_note","mimetype":"application/pdf","url":{"label":"本文","url":"https://niigata-u.repo.nii.ac.jp/record/5274/files/D_S_NN.pdf"},"version_id":"890dac7c-6758-4dcf-80ff-d5c8f34a519c"}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"eng"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"thesis","resourceuri":"http://purl.org/coar/resource_type/c_46ec"}]},"item_title":"Petrology of the basalts of the Central Indian Ridge and regional variations of MORBs along the eastern part of the Southwest Indian Ridge","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Petrology of the basalts of the Central Indian Ridge and regional variations of MORBs along the eastern part of the Southwest Indian Ridge"},{"subitem_title":"Petrology of the basalts of the Central Indian Ridge and regional variations of MORBs along the eastern part of the Southwest Indian Ridge","subitem_title_language":"en"}]},"item_type_id":"6","owner":"1","path":["455","564"],"pubdate":{"attribute_name":"公開日","attribute_value":"2012-06-05"},"publish_date":"2012-06-05","publish_status":"0","recid":"5274","relation_version_is_last":true,"title":["Petrology of the basalts of the Central Indian Ridge and regional variations of MORBs along the eastern part of the Southwest Indian Ridge"],"weko_creator_id":"1","weko_shared_id":2},"updated":"2022-12-15T03:38:16.146470+00:00"}