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61.
Evolution and Genesis of Magmas from Vico Volcano, Central Italy: Multiple Differentiation Pathways and Variable Parental Magmas 总被引:4,自引:0,他引:4
PERINI GIULIA; FRANCALANCI LORELLA; DAVIDSON JON P.; CONTICELLI SANDRO 《Journal of Petrology》2004,45(1):139-182
Vico volcano has erupted potassic and ultrapotassic magmas,ranging from silica-saturated to silica-undersaturated types,in three distinct volcanic periods over the past 0·5Myr. During Period I magma compositions changed from latiteto trachyte and rhyolite, with minor phono-tephrite; duringPeriods II and III the erupted magmas were primarly phono-tephriteto tephri-phonolite and phonolite; however, magmatic episodesinvolving leucite-free eruptives with latitic, trachytic andolivine latitic compositions also occurred. In Period II, leucite-bearingmagmas (87Sr/86Srinitial = 0·710370·71115)were derived from a primitive tephrite parental magma. Modellingof phonolites with different modal plagioclase and Sr contentsindicates that low-Sr phonolitic lavas differentiated from tephri-phonoliteby fractional crystallization of 7% olivine + 27% clinopyroxene+ 54% plagioclase + 10% FeTi oxides + 4% apatite at lowpressure, whereas high-Sr phonolitic lavas were generated byfractional crystallization at higher pressure. More differentiatedphonolites were generated from the parental magma of the high-Srphonolitic tephra by fractional crystallization of 1029%clinopyroxene + 1215% plagioclase + 4467% sanidine+ 24% phlogopite + 13% apatite + 710% FeTioxides. In contrast, leucite-bearing rocks of Period III (87Sr/86Srinitial= 0·708120·70948) were derived from a potassictrachybasalt by assimilationfractional crystallizationwith 2040% of solid removed and r = 0·40·5(where r is assimilation rate/crystallization rate) at differentpressures. Silica-saturated magmas of Period II (87Sr/86Srinitial= 0·710440·71052) appear to have been generatedfrom an olivine latite similar to some of the youngest eruptedproducts. A primitive tephrite, a potassic trachybasalt andan olivine latite are inferred to be the parental magmas atVico. These magmas were generated by partial melting of a veinedlithospheric mantle sources with different veinperidotite/wall-rockproportions, amount of residual apatite and distinct isolationtimes for the veins. KEY WORDS: isotope and trace element geochemistry; polybaric differentiation; veined mantle; potassic and ultrapotassic rocks; Vico volcano; central Italy 相似文献
62.
Petrogenesis of Tholeiitic Lavas from the Submarine Hana Ridge, Haleakala Volcano, Hawaii 总被引:3,自引:1,他引:3
REN ZHONG-YUAN; TAKAHASHI EIICHI; ORIHASHI YUJI; JOHNSON KEVIN T. M. 《Journal of Petrology》2004,45(10):2067-2099
Hana Ridge, the longest submarine rift zone in the Hawaiianisland chain, extending from Maui 140 km to the ESE, has a complexmorphology compared with other Hawaiian rift zones. A totalof 108 rock specimens have been collected from the submarineHana Ridge by six submersible dives. All of the rocks (76 bulkrocks analyzed) are tholeiitic basalts or picrites. Their majorelement compositions, together with distinctively low Zr/Nb,Sr/Nb, and Ba/Nb, overlap those of Kilauea lavas. In contrast,the lavas forming the subaerial Honomanu shield are intermediatein composition between those of Kilauea and Mauna Loa. The compositionalcharacteristics of the lavas imply that clinopyroxene and garnetwere important residual phases during partial melting. The compositionsof olivine and glass (formerly melt) inclusions imply that regardlessof textural type (euhedral, subhedralundeformed, deformed)olivine crystallized from host magmas. Using the most forsteriticolivine (Fo90·6) and partition coefficients 相似文献
63.
Abstract We review the carbon‐isotope data for finely disseminated carbonates from bioaltered, glassy pillow rims of basaltic lava flows from in situ slow‐ and intermediate‐spreading oceanic crust of the central Atlantic Ocean (CAO) and the Costa Rica Rift (CRR). The δ13C values of the bioaltered glassy samples from the CAO show a large range, between ?17 and +3‰ (Vienna Peedee belemnite standard), whereas those from the CRR define a much narrower range, between ?17‰ and ?7‰. This variation can be interpreted as the product of different microbial metabolisms during microbial alteration of the glass. In the present study, the generally low δ13C values (less than ?7‰) are attributed to carbonate precipitated from microbially produced CO2 during oxidation of organic matter. Positive δ13C values >0‰ likely result from lithotrophic utilization of CO2 by methanogenic Archaea that produce CH4 from H2 and CO2. High production of H2 at the slow‐spreading CAO crust may be a consequence of fault‐bounded, high‐level serpentinized peridotites near or on the sea floor, in contrast to the CRR crust, which exhibits a layer‐cake pseudostratigraphy with much less faulting and supposedly less H2 production. A comparison of the δ13C data from glassy pillow margins in two ophiolites interpreted to have formed at different spreading rates supports this interpretation. The Jurassic Mirdita ophiolite complex in Albania shows a structural architecture similar to that of the slow‐spreading CAO crust, with a similar range in δ13C values of biogenic carbonates. The Late Ordvician Solund–Stavfjord ophiolite complex in western Norway exhibits structural and geochemical evidence for evolution at an intermediate‐spreading mid‐ocean ridge and displays δ13C signatures in biogenic carbonates similar to those of the CRR. Based on the results of this comparative study, it is tentatively concluded that the spreading rate‐dependent tectonic evolution of oceanic lithosphere has a significant control on the evolution of microbial life and hence on the δ13C biosignatures preserved in disseminated biogenic carbonates in glassy, bioaltered lavas. 相似文献
64.
《地学前缘(英文版)》2023,14(1):101497
Young zircons from crystal-poor volcanic rocks provide the best samples for the investigations of pre-eruption magmatic processes and for testing a possible relationship between zircon Eu anomalies and crustal thickness. We report trace element chemistry and Hf-O isotope compositions of young zircons from 3 Holocene volcanoes in the Tengchong volcanic field, SE Tibet, in order to provide insights into magma evolution processes and conditions for high-K calc-alkaline volcanic rocks in a post-collisional setting. As decreasing zircon Ti content and falling temperature, zircon Hf content and Yb/Sm increase whereas zircon Eu anomaly and Th/U decrease, indicating fractional crystallization of plagioclase and zircon during magma cooling. More importantly, zircon Hf isotope ratio (εHf values) increases with decreasing zircon Ti content and falling temperature (T), suggesting gradually increasing incorporation of relatively high εHf juvenile materials in the crystallizing zircons during magma evolution. Negative correlations between zircon εHf and zircon δ18O also support open-system magma evolution. Our data suggest fractional crystallization of a magma with simultaneous contamination by high εHf and low δ 18O juvenile (immature) crustal materials during monotonic cooling after zircon saturation. The low-T, high-εHf and low- δ 18O zircons may indicate the involvement of the early Cretaceous juvenile granitic country rocks during shallow magma evolution. Average Eu anomalies in zircons from young Tengchong lavas yield crustal thickness of 40.7 ± 6.8 km, consistent with present crustal thickness (42.5 km) determined by geophysical methods. 相似文献
65.
中国东北中生代岩浆活动广泛发育,产于延边的新屯高镁闪长岩(128 Ma)是其中特殊的一类岩石,对于约束构造背景具有重要意义。新屯闪长岩高Mg#,富含LILEs、亏损HFSEs,εHf的范围为3.2~8.9,指示岩浆主要来自同位素亏损的地幔源区。较高的La/Sm和Th/Yb比值,较低的Ba/La比值,暗示俯冲沉积物参与了岩浆的形成。岩石学特征显示普通角闪石、磁铁矿等矿物结晶较早,表明初始岩浆为富水高氧逸度的体系。水饱和条件下斜长石结晶受到抑制、角闪石等矿物发生分离结晶可能是导致演化的岩浆具备高Sr/Y比值的重要原因。在130~110 Ma期间,东北地区在古太平洋板块俯冲后撤影响下发生弧后伸展,软流圈物质上涌改变了地幔楔热状态,导致俯冲沉积物发生部分熔融,交代上覆地幔楔形成了早白垩世高镁闪长岩。 相似文献
66.
内蒙古梅劳特乌拉SSZ型蛇绿岩中,新发现了早二叠世巴嘎哈尔高镁闪长岩。该闪长岩位于贺根山缝合带内。锆石LA-ICP-MS U-Pb测年表明,巴嘎哈尔闪长岩的侵位年龄为(282±2)Ma,其形成时代为早二叠世。该岩石高镁,MgO含量5.00%~10.94%,Mg#值54~74;SiO_2含量53.52%~58.64%,Al_2O_3含量13.48%~14.98%,Na_2O含量1.36%~3.59%;贫钾,K_2O含量0.48%~1.61%;贫TiO_2(0.28%~0.76%)和P_2O_5(0.080%~0.160%);富Cr(75.00×10~(-6)~555.90×10~(-6))和Ni(26.20×10~(-6)~228.40×10~(-6));富集K、Rb和Sr等大离子亲石元素,亏损Nb、Ta、Zr、Ti和P等高场强元素;稀土元素总量较低(25.16×10~(-6)~83.57×10~(-6)),稀土曲线为略右倾的平坦型。该岩石具有高镁闪长岩的地球化学特征,与赞岐岩相类似,属于俯冲带岛弧型岩浆岩。结合其与梅劳特乌拉SSZ型蛇绿岩中玻安岩和埃达克岩的岩石组合时空分布特征,表明古亚洲洋贺根山洋盆在早二叠世可能仍然处于大洋俯冲消减状态。该高镁闪长岩可能为俯冲洋壳+俯冲深积物来源的硅质熔体交代上覆地幔楔使其部分熔融的产物。 相似文献
67.
对羌塘地块东北缘甘孜-理塘缝合带南侧日啊日曲石英闪长岩进行了系统的锆石U-Pb年龄、主量-微量元素及Sr-Nd同位素分析, 以探讨其岩石成因及地球动力学意义.LA-ICP-MS锆石U-Pb定年结果表明, 石英闪长岩侵位年龄为218±1 Ma, 为晚三叠世岩浆活动的产物.岩石SiO2含量介于53.02%~62.06%之间, 富Al2O3(15.84%~17.00%)和CaO(6.71%~8.94%), 贫TiO2(0.49%~1.01%)和P2O5(0.04%~0.12%), 具有较高的MgO(3.31%~5.66%)和Mg#(50~62), 属准铝质钙碱性系列; 岩体稀土元素总量较低(38.05×10-6~61.58×10-6), 轻重稀土分馏不明显, LILE富集, HFSE亏损, 具有含量较高的Cr(33.45×10-6~176.64×10-6)和Ni(13.34×10-6~43.62×10-6).全岩(87Sr/86Sr)i比值较为一致(0.706 8~0.707 9), εNd(t)变化于-5.5~-1.6.主微量元素及同位素结果表明日啊日曲石英闪长岩具有高镁闪长岩的特征, 与赞岐岩地球化学特征类似, 为俯冲沉积物来源的熔体交代岩石圈地幔形成的尖晶石相金云母二辉橄榄岩低度(10%~15%)部分熔融的产物, 岩浆演化过程中经历了辉石、角闪石等矿物的分离结晶.微量元素构造判别图解表明岩石为俯冲环境下的弧岩浆岩, 结合区内蛇绿岩、研究区南部陆缘弧火山岩和义敦岛弧埃达克岩的发现, 认为古特提斯洋在晚三叠世时期可能仍处于消减状态, 日啊日曲高镁石英闪长岩形成于甘孜-理塘洋南西向俯冲过程中. 相似文献
68.
Ladislav A. Palinkaš Vladimir Bermanec Sibila Borojević Šoštarić Tea Kolar-Jurkovšek Sabina Strmić Palinkaš Ferenc Molnar Goran Kniewald 《Journal of Volcanology and Geothermal Research》2008
The Hruškovec quarry of basaltoid rocks is situated on the northwestern slopes of Mt. Kalnik, within the Zagorje–Mid-Transdanubian zone, a part of the North-western Dinarides. The basaltoids are inter-bedded with radiolarites of the Middle and Upper Triassic age (Langobardian, Carnian–Norian). Spilites, altered diabases and meta-basalts form part of Triassic volcanic-sedimentary sequence, made of sandstones, shales, micritic limestone, altered vitric tuffs and radiolarian cherts, incorporated tectonically into the Jurassic–Cretaceous mélange. 相似文献
69.
70.
Large amounts of fluid, bound up in the hydrated upper layers of the ocean crust, are consumed at convergent margins and released in subduction zones through devolatilization. The liberated fluids may play an integral role in subduction zone processes, including the generation of arc-magmas. However, exhumed subduction zone rocks often record little evidence of large-scale fluid flow, especially at deeper levels within the subduction zone. Basaltic pillows from the high-pressure Corsican and Zermatt-Saas ophiolites show a range of δ18 O values that overall reflect seafloor alteration prior to subduction. However, comparison between the δ18 O values of the cores and rims of the pillows suggests that the δ18 O values of the pillow rims at least have been modified during subduction and high-pressure metamorphism. Pillows that have not undergone high-pressure metamorphism generally have rims with higher δ18 O values than their cores, whereas the converse is the case in pillows that have undergone high-pressure metamorphism. This reversal in the core to rim oxygen isotope relationship between unmetamorphosed and metamorphosed pillows is strong evidence for fluid–rock interaction occurring during subduction and high-pressure metamorphism. However, the preservation of different δ18 O values in the cores and rims of individual pillows and within and between different pillows suggests that fluid flow within the subduction zone was strongly channelled. Resetting of the δ18 O values in the pillow rims was probably due to fluid-hosted diffusion that occurred over relatively short time-scales (<1 Myr). 相似文献