Ofioliti最新文献

{"title":"Late Cretaceous arc and back-arc formation within the Southern Neotethys: whole-rock, trace element and Sr-Nd-Pb isotopic data from basaltic rocks of the Yüksekova Complex (Malatya- Elazığ, SE Turkey)","authors":"M. Ural, M. Arslan, M. C. Göncüoğlu, K. Tekin, S. Kürüm","doi":"10.4454/OFIOLITI.V40I1.435","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V40I1.435","url":null,"abstract":"The remnants of the Southern Neotethys are represented by ophiolitic bodies and subduction/accretion complexes along the Southeast Anatolian-Zagros suture belt in the Eastern Mediterranean. Around Malatya and Elazig areas (SE Turkey), they are found within imbricated slices of a melange complex, known as the Yuksekova Complex. The studied basaltic rocks are common members of this melange complex, and show distinctive features of sources with tholeiitic to tholeiitic-transitional character. Petrography, whole-rock trace element and isotopic data reveal two different compositional groups. Group I is transitional between island arc tholeiites and normal mid-ocean ridge basalt, and Group II includes back-arc (BABB), enriched mid-ocean ridge (E-MORB), and ocean island basalt type (OIB) compositions. According to the known Late Cretaceous stratigraphic ages, the studied basaltic rocks have (87Sr/86Sr)i = 0.703666- 0.706394, (143Nd/144Nd)i = 0.512734-0.512927, 208Pb/204Pb = 38.3216-39.3400, 207Pb/204Pb = 15.5018-15.6262 and 206Pb/204Pb = 18.5655-19.3209. In addition, eNdi values vary between +3.99 and +8.01 with two-stage TDM values ranging from 0.25 to 0.59 Ga. In the Sr versus Nd isotope correlation diagram, most samples plot along the mantle array line. In the correlation diagrams of 206Pb/204Pb versus 208Pb/206Pb and 207Pb/206Pb, the rock samples also plot nearly on the Northern Hemisphere Reference Line, similar to Atlantic and Pacific Ocean ridge basalts. As a whole, the isotopic data reveal that the studied rocks were derived from a depleted mantle source. When plotted in the conventional tectonic discrimination diagrams based on immobile trace elements, the samples can be related to an arc environment (Group I basalts), and back arc basin (Group II basalts) developed by generation and maturation of the rifted arc in later stages. This interpretation is supported by ages obtained from pillow lava-radiolarian chert associations indicating that the arc stage was realized during the late Cenomanian-early Turonian, followed by Coniacian-early Maastrichtian spreading in a back arc basin within the closing southern branch of Neotethys.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"40 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2015-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70970028","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The role of MORB and SSZ magma-types in the formation of Jurassic ultramafic cumulates in the Mirdita ophiolites (Albania) as deduced from chromian spinel and olivine chemistry","authors":"E. Saccani, R. Tassinari","doi":"10.4454/OFIOLITI.V40I1.434","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V40I1.434","url":null,"abstract":"Both the Western (WMO) and Eastern (EMO) Mirdita ophiolites include well-developed ultramafic cumulitic sequences. In the WMO, they mainly con- sist of dunites, plagioclase-dunites, plagioclase-wehrlites, and troctolites. In contrast, in the EMO they mainly consist of chromitiferous-dunites, dunites, lher- zolites and olivine-websterites, as well as minor plagioclase-bearing dunites and lherzolites, and troctolites. The main rock-forming minerals in ultramafic cu- mulates are cumulus olivine associated with various inter-cumulus minerals, as well as chromian spinel occurring as both cumulus and inter-cumulus phase. Mg#, FeO/MgO ratios and TiO 2 , Al 2 O 3 concentrations in parental melts were calculated from olivine and spinel compositions. The inferred parental melt compositions indicate that the dunite-troctolite layered series at the mantle tectonite-ultramafic cumulate transition zone in the WMO was derived from a nor- mal-type mid-ocean ridge basaltic (N-MORB) parental melt. In contrast, the dunite-troctolite layered series from the top of the WMO ultramafic cumulitic se- quence was derived from a medium-Ti basaltic (MTB) parental melt originated, in turn, in a nascent forearc setting. The inferred composition of parental melts indicate that chromitiferous dunites, dunites, and lherzolites from the EMO were originated from primary boninitic melts, whereas olivine-websterites were originated from slightly fractionated boninitic liquids. The inferred parental melt compositions plagioclase- bearing dunites and lherzolites, as well as troctolites from the EMO are compatible with an N-MORB type parentage, being the only exception one plagioclase- dunite, which may have derived from a low-Ti tholeiitic melt. Comparison of the ultramafic cumulates from the WMO and EMO indicates that both these units, though to a different extent, have experienced similar and coeval magmatic events. The investigated WMO ultramafic cumulates record N-MORB and MTB magmatic episodes. The investigated EMO ultramafic cumulates testify for boninitic, N-MORB, and very subordinate low-Ti tholeiitic magmatic events. It is therefore concluded that both WMO and EMO were generated in a protoforearc-forearc setting likely initiated nearby an active mid-ocean spreading ridge.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"07 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2015-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70969844","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Enviromental contamination of heavy metals and chrysotile asbestos in the Munzur and Pulumur streams (Tunceli, Turkey)","authors":"Okay Çimen, F. Köksal, A. Önal, Y. Ö. Tutay","doi":"10.4454/OFIOLITI.V40I1.433","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V40I1.433","url":null,"abstract":"The Munzur and Pulumur streams are essential water supplies of the Tunceli Province (Turkey). Chromite bearing ultramafic rocks and Zn-Cu mineral- ization products are possible causes of the toxic elements enrichment in the streams. Sediment and soil samples were collected along these streams to deter- mine the level of toxic element enrichment. Multi-element normalized patterns of the samples with respect to the upper crust display enrichments in Cr, Ni, Co, Cs, W, Pb, As, Sb, Au, Hg and Cr, Ni, Co, W, for the Munzur and Pulumur streams, respectively. Also, the calculated Igeo index values show the pres- ence of contaminations of Cr, Ni, As, Hg, Cd and Cr, Ni, As in the Munzur and Pulumur streams, respectively. Elemental grouping in the samples indicates two different effects related to the ultramafic host rocks and mineralization products in the study area. Additionally, mineralogical XRD analyses exhibit the presence of chrysotile, plagioclase, quartz and calcite. The fibrous chrysotile and heavy metal contaminations must be considered as a threat for public health.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"4 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2015-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70969792","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"THE CALC-ALKALINE MONTE CAPO STELLA DYKES IN THE OPHIOLITIC UNIT OF THE ELBA ISLAND (ITALY): GEOLOGICAL SETTING AND COMPOSITIONAL CHARACTERIZATION","authors":"E. Pandeli, A. P. Santo, M. Candido, C. Petrone, R. Giusti","doi":"10.4454/OFIOLITI.V39I2.431","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V39I2.431","url":null,"abstract":"In this paper we studied in detail magmatic dykes filling fractures in the pillow lavas of the Ophiolitic Unit cropping out in the Monte Capo Stella Promontory (southern part of the Elba Island in the Northern Tyrrhenian Sea). The Elba Island is well known for its Tertiary complex tectonic stack of nappes, Late Miocene intrusion of acidic magmatic bodies and Fe-mineralizations. The phaneritic sub-volcanic rock (Monte Capo Stella dykes, MCSD) shows a porphyritic texture with variable pheno- and xenocrysts content. The main phenocrysts consist of plagioclase, quartz, K-feldspar and biotite. The MSCD, displaying calc-alkaline affinity, have a High-Potassium dacitic composition. Moderate fractionation and negative Eu anomaly characterize the chondrite normalised REE patterns. The mantle-normalized trace element patterns exhibit relatively high content of the most incompatible elements with negative spikes of Ba, Ta, Nb, Sr, P, and Ti. The measured 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopic ratios are 0.708129 and 0.512209 respectively. In spite of the lack of radiometric data, the MCSD can be related to the acidic to intermediate magmatism that occurred in the interland of the Northern Apennines Chain during late Miocene-Quaternary times. In particular, the MSCD belong to the intermediate rocks of the Tuscan Magmatic Province and display petrological and geochemical characteristics closely resembling those of a mafic enclave collected in the 6.8 Ma Orano Porphyry (Elba Island) and of some 9-4 Ma High Potassium Calc-Alkaline (HKCA) Capraia Island rocks. Thus, in the context of the Elba Island, the studied dykes represent the magmatic bodies showing the most peculiar HKCA features. The intrusion age of the MCSD can be put in the time interval between the intrusion of the Orano Porphyry in Western Elba (6.8 Ma) and that of the Monte Castello dyke (5.8 Ma) in Eastern Elba, and possibly before the Central Elba Fault (CEF) activity. This study also refines the deformation history of the Ophiolitic Unit in the Elba Island defining three final brittle deformation stages.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"39 1","pages":"79-93"},"PeriodicalIF":1.3,"publicationDate":"2014-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70969652","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"GEOCHEMICAL EVALUATION OF THE LATE MAASTRICHTIAN SUBDUCTION-RELATED VOLCANISM IN THE SOUTHERN NEOTETHYS IN VAN AREA, AND A CORRELATION ACROSS THE TURKISH-IRANIAN BORDER","authors":"A. Çolakoğlu, K. Günay, M. C. Göncüoğlu, V. Oyan, Kemal Erdoğan","doi":"10.4454/OFIOLITI.V39I2.429","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V39I2.429","url":null,"abstract":"The Yuksekova melange to the NE of Van, close to the Turkish-Iranian border is part of the Berit-Elazig-Van ophiolitic belt. It structurally overlies the Bitlis-Puturge metamorphic complex and includes the remnants of the southern Neotethys. The melange complex comprises mantle rocks together with massive and pillowed lavas and dykes associated with late Maastrichtian micritic limestones and radiolarian cherts. The lavas are trachyandesite/basaltic, whereas the dykes are alkali basalt in composition. Both rock types were probably formed by low-degree partial melting of a mixed source including primitive mantle and depleted MOR mantle components, which were subsequently affected by subduction modification. The geochemical character constrains the formation of these basalts, yet the youngest ones dated in the Yuksekova melange to an intra-oceanic subduction zone within the Neotethys at the end of Cretaceous. The new ages and the tectonic setting of the volcanic rocks are correlated with other oceanic assemblages (e.g., Khoy and Inner Zagros ophiolites in Iran) across the Turkish-Iranian border.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"39 1","pages":"51-65"},"PeriodicalIF":1.3,"publicationDate":"2014-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70969567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The gabbro and serpentinized peridotite of Bonassola (Bracco-Levanto ophiolite, Italy) – An extremely low natural radiation area to improve in situ gamma spectrometry","authors":"R. Braga, G. Cinelli","doi":"10.4454/OFIOLITI.V39I2.428","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V39I2.428","url":null,"abstract":"Outcrops of dunite, serpentinized peridotite and clinopyroxene-rich coarse gabbro around Bonassola (Bracco-Levanto ophiolite, NW Italy) have been analyzed for natural radionuclides using γ-spectrometry. The very low activity concentrations of natural radionuclides in the dunite outcrop (< 9.0 Bq kg -1 226 Ra; < 3.5 Bq kg -1 228 Ac and < 25 Bq kg -1 40 K) indicate that this site is characterised by a very low natural radiation for both cosmic (being at sea level) and terrestrial contributions. Before starting a field radiometric survey it is important to assess the local background, i.e. the g radiation that does not originate from rock, in order to correct the measurements for the local background. Contrary to the general practice regarding the background radiation in γ-spectrometry measurements, the investigated mafic-ultramafic outcrops has been used to estimate the detection limits for in situ measurement of 238 U, 232 Th and 40 K using sodium iodine (NaI) scintillator detectors. These results have proved useful to quantify the minimum detectable amount of activity (MDA) of 238 U, 232 Th and  40 K for the NaI detector; the MDA points at sub ppm levels for 238 U and 232 Th and 0.01 wt% K 2 O. This study also permits to assess the radiological risk of dimension stones that are petrographically similar to the serpentinized ultramafics occurring in the Bracco-Levanto ofiolite. The comparison of the activity concentration index I, defined by the EU Basic Safety Standards Directive and depending on the activity concentrations of 226 Ra, 232 Th and 40 K, with other stones used as building material, indicates that the Bonassola mafic-ultramafic rocks provide a negligible contribution to the indoor gamma radiation dose.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"39 1","pages":"43-49"},"PeriodicalIF":1.3,"publicationDate":"2014-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70969940","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"GEODYNAMIC SIGNIFICANCE OF THE JANATABAD PERIDOTITES AND ASSOCIATED CHROMITITES (S IRAN): IMPLICATIONS FOR SUBDUCTION INITIATION","authors":"R. Monsef, I. Monsef, M. Rahgoshay","doi":"10.4454/OFIOLITI.V39I2.430","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V39I2.430","url":null,"abstract":"The Janatabad peridotites are exposed in the Hajiabad-Esfandagheh Melange Zone in the southern part of Iran. These peridotites are dominantly composed of harzburgites with small lenses and veins of chromitite ores surrounded by dunite sheaths. Harzburgites have accessory chromites characterized by moderate X Cr of 0.59-0.61, and X Mg of 0.52-0.58, resembling depleted mid-ocean ridge peridotites, supposed to have originated as the residue from a high degree of partial melting and MORB-like magma extraction at the inception of subduction. Dunites can be divided into two types: Type 1 dunite with moderate X Cr of 0.53-0.62 and X Mg of 0.48-0.53, and Type 2 dunite with high X Cr of 0.63-0.67 and low X Mg of 0.40-0.48. Two distinctive melts are required for the formation of these dunites: a MORB-like melt for the Type 1 dunite, and a transitional-like melt for the Type 2 dunite. These compositional variations from MORB to melts transitional between MORB and boninite are due to the hydrous fluids derived from the subducted oceanic slab into the overlying mantle wedge at the beginning of the down dip motion of the slab. Al-rich podiform chromitites, characterized by relatively low X Cr of 0.53-0.54 and relatively high X Mg of 0.60- 0.71, may have formed from MORB-like melts. In particular, the interaction between primitive MORB-like melts and depleted harzburgites produced Type 1 dunites and secondary silica-rich melts from which Al-rich chromitites crystallized. Type 2 dunites can be generated by the interaction between transitional-like melts and depleted harzburgites above a lithosphere in subsidence. Accordingly, it is inferred that the Janatabad peridotites formed by rifting of a Late Triassic to Early Jurassic embryonic ocean during subduction initiation of Neo-Tethyan lithosphere in an intra-oceanic environment.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"39 1","pages":"67-78"},"PeriodicalIF":1.3,"publicationDate":"2014-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70969608","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New record of middle jurassic radiolarians and evidence of neotethyan dynamics documented in a melange from the central dinaridic ophiolite belt (CDOB, NE Bosnia and Herzegovina)","authors":"B. Šegvić, Duje Kuko, Ivan Dragievi, Alan Vranjkovi, Vlatko Bri, Š. Gorian, Elvir Babaji, Hazim Hrvatovi","doi":"10.4454/OFIOLITI.V39I1.427","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V39I1.427","url":null,"abstract":"Within the ophiolitic melange of the Central Dinaridic Ophiolitic Belt (CDOB) that stretches throughout the Balkans region in SE Europe, a latest Bajocian-early Bathonian radiolarian assemblage was obtained from chert-rich shaly to silty matrix. The sampling locality in northern Bosnia and Herzegovina is characterized by a highly-diversified ophiolitic suite, consisting of basic and ultrabasic rocks of different geotectonic provenances. This makes the radiolarian dating a convenient complementary tool for studying the geodynamic history of CDOB within a broader regional context. The host sediments and the nature of their associated crystalline rocks suggest that radiolarian deposition occurred relatively close to the Adria shelf margins, predating or being contemporaneous to the rapid transitions in the Dinaridic Neotethys geotectonic setting, changing from active ridge magmatism to an intraoceanic subduction environment and island-arc volcanism. The minimum age of ophiolite melange formation is defined by the mineral equilibration ages in metamorphic sole (161±4 Ma), with the obduction tectonics that must have lasted at least until the Oxfordian time (i.e. termination of MOR activity in the Dinarides). This age correlates well with the ages of sediments reported elsewhere in the melange of the Dinaride-Hellenide orogenic system.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"39 1","pages":"33-43"},"PeriodicalIF":1.3,"publicationDate":"2014-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70969440","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Construction of a sheeted dyke complex: evidence from the northern margin of the troodos ophiolite and its southern margin adjacent to the arakapas fault zone","authors":"A. Cooke, Lee P. Masson, A. Robertson","doi":"10.4454/OFIOLITI.V39I1.426","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V39I1.426","url":null,"abstract":"The structure of a sheeted dyke complex in relation to intrusion is important for an understanding of sea-floor spreading. Here, we provide data for a previously undescribed ~ E-W cross-strike section along the northern margin of the Troodos massif. For comparison, we also provide new information for a ~NS section along the southern margin of the Troodos massif, adjacent to the Arakapas Fault Zone, an inferred oceanic transform fault. The N-Troodos margin section is divided into two main segments with opposing dip directions, corresponding to the Solea graben in the east and the Stravros graben in the west. High-temperature, hydrothermally altered dykes occur relatively early in a relative intrusive chronology of both grabens, followed by gabbroic bodies and ubiquitous grey sheeted dykes; plagiogranite dykes intruded at relatively later stages. Chemical analysis reveals a trend towards a boninite-type composition, both in the sheeted complex as a whole and in several specific sections for which crosscutting relations were documented in detail. The relatively steeply dipping, late-stage, boninitic-type dykes are interpreted as feeders to the Upper Pillow Lavas. To the N of the Arakapas Fault Zone, large plagiogranite bodies intruded relatively early and were in turn transected by grey dykes, small gabbroic intrusions and late-stage isolated brown dykes. Chemical analyses show that both early-stage grey dykes and the later-stage brown dykes were fed by chemically similar magma. Highly depleted boninite-type dykes occur close to the Arakapas Fault Zone. The relatively late-stage brown dykes show a swing in orientation towards ~ E-W near the transform zone, reflecting an inferred up to ~ 90° relatively clockwise, vertical-axis rotation. The earlier-stage grey dykes are indicative of lesser amounts of vertical-axis rotation but show complex rotations about low-angle axes. Small-scale faults are mainly of normal and left-lateral strike-slip type. Taking alternatives into account, we infer that the faulting in the dyke section took place near a left-offset spreading axis within an overall right-slipping, transtensional transform fault zone. In addition, depleted mantle harzburgites were exposed and eroded on the seafloor within an inferred southward extension of the transform zone (now within the Late Cretaceous Moni Melange), proving additional evidence of a transtensional setting near or within the Arakapas transform. The combined evidence suggests that the Troodos sheeted dyke complex as a whole developed in response to unstable, asymmetrical spreading above a subduction zone in which relatively late-stage amagmatic extension is likely to have played an important role. The spreading crust was bounded to the south (in present coordinates) by a relatively broad transtensional transform fault zone, along which mantle rocks were locally exposed and eroded on the seafloor.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"39 1","pages":"1-30"},"PeriodicalIF":1.3,"publicationDate":"2014-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70969541","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characterization of the accreted Ophiolite slices of Rutland island, Andaman sea: Evolution in a Suprasubduction zone setting","authors":"A. Bhattacharya, T. Pal, B. Ghosh","doi":"10.4454/OFIOLITI.V38I2.422","DOIUrl":"https://doi.org/10.4454/OFIOLITI.V38I2.422","url":null,"abstract":"Detailed mapping of a  rocks110 km 2 area of the Rutland Island has demarcated four dismembered thrust slices of Cretaceous ophiolite which are interleaved with Eocene sediments. The ophiolite sequence is represented by tectonite, chromitite pods, transitional peridotite, layered ultramafic-mafic, intrusives of plagiogranite-diorite suite and extrusives of basalt and boninite, capped by pelagic sediments. The layered ultramafics and the massive chromitites are characterized by high Mg-olivine (Fo 92-93 ), high Mg-orthopyroxene (En 88–90 ), low CaO (X Ca M2 = 0.01 to 0.03), low alumina (Al 2 O 3 = 0.66 to 1.20 wt %) and high Cr-chromites, which is typical of boninitic melts in suprasubduction zone (SSZ) environments. The estimated Al 2 O 3 contents of the parental melt (10.80 wt%) correspond to a boninitic parental melt. The Type-2 low-Ca boninite extrusives with SiO 2 < 58 wt%, MgO = 8.4 to 9.5 wt% is the extrusive equivalent of boninitic parental lava. As boninitic rocks show higher depletion of Zr and Y than the basaltic rocks, the source rock for boninite was more depleted than that of  basalts. Tectonites showing embayed clinopyroxene grains and irregular shaped Cr-spinel as residual phases preserve records of partial melting. The degree of partial melting of the mantle tectonite has been estimated as ~ 20%, based on Cr content of the spinel. Petrographic features of the transitional peridotites show dissolution of orthopyroxene and clinopyroxene grains and development of small fresh olivine grains along the embayed margins and fractures, displaying melt-rock interaction effects in the mantle rocks. The melt-rock interaction features as well as the bivariant relation of TiO 2 wt% vs. Al 2 O 3 wt% of the chromites reflect the evolution of the Rutland ophiolite in a SSZ setting.","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":"38 1","pages":"121-142"},"PeriodicalIF":1.3,"publicationDate":"2013-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70969280","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}