Lithospheric Origin of Oligocene-Miocene Magmatism in Central Chile: U-Pb Ages and Sr-Pb-Hf Isotope Composition of Minerals     

Montecinos  P.; Scharer  U.; Vergara  M.; Aguirre  L. 《Journal of Petrology》2008,49(3):555-580

Establishing the petrogenesis of volcanic and plutonic rocksis a key issue in unraveling the evolution of distinct subduction-relatedtectonic phases occurring along the South American margin. Thisis particularly true for Cenozoic times when large volumes ofmagma were produced in the Andean belt. In this study we havefocused on Oligo-Miocene magmatism in central Chile at 33°S.Our data include field and petrographic observations, whole-rockmajor and trace element analyses, U–Pb zircon dating,and Pb, Sr, and Hf isotope analyses of plagioclase, clinopyroxene,and zircon mineral separates. Combined with earlier dating resultsthe new zircon ages define a 28·8–5·2 Maperiod of plutonic and volcanic activity that ceased as a consequenceof flattening subduction of the Nazca–Farallon plate.Rare earth elements patterns are variable, with up to 92 timeschondrite concentrations for light rare earth elements yielding(La/Yb)_N between 3·6 and 7·0, and an absence ofEu anomalies. Initial Pb isotope signatures are in the rangeof 18·358–19·023 for ²⁰⁶Pb/ ²⁰⁴Pb, 15·567–15·700for ²⁰⁷Pb/ ²⁰⁴Pb and 38·249–39·084 for ²⁰⁸Pb/²⁰⁴Pb. Initial ⁸⁷Sr/ ⁸⁶Sr are mostly in the range of 0·70369–0·70505,with two more radiogenic values at 0·7066. Initial Hfisotopic compositions of zircons yield exclusively positiveHf_i ranging between + 6·9 and + 9·6. The newlydetermined initial isotope characteristics of the Oligo-Miocenemagmas suggest that the mantle source lithologies are differentfrom both those of Pacific mid-ocean ridge basalt and oceanisland basalt, plotting in the field of reference values forsubcontinental lithospheric mantle, characterized by moderatelarge ion lithophile element–high field strengh elementdepletion and high ²³⁸U/ ²⁰⁴Pb. A Hf model age of 2 Ga is estimatedfor the formation of the subcontinental mantle–continentalcrust assemblage in the region, suggesting that the initialSr and Pb isotope ratios inferred for the source of the Oligo-Mioceneparental magmas are the result of later Rb and U enrichmentcaused by mantle metasomatism. A time-integrated model Rb/Srof 0·039 and µ 16 are estimated for the sourceof the parental magmas, consistent with ratios measured in peridotitexenoliths from continental areas. Evolution from predominant(>90%) basaltic–gabbroic to andesitic–dioriticmagmas seems to involve a combination of (1) original traceelement differences in the metasomatized subcontinental mantle,(2) different degrees of partial melting and (3) fractionalcrystallization in the garnet- and spinel-peridotite stabilityfields. The genesis of more differentiated magmas reaching rhyolitic–graniticcompositions most probably also includes additional crystalfractionation at both shallow mantle depths and within the crust,possibly leading to some very minor assimilation of crustalmaterial. KEY WORDS: calc-alkaline magmatism; Oligo-Miocene; U–Pb dating; Sr–Pb–Hf isotopes; central Chile  相似文献   

The Role of Fractional Crystallization and Assimilationin the Evolution of the Zoned Mukhattata Pluton, Eastern Desert, Egypt     

Said A. El-Nisr  Mohamed M. El-Sayed 《Chemie der Erde / Geochemistry》2002,62(3):216-236

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Volcanological and petrological evolution of Marsili Seamount (southern Tyrrhenian Sea)     

Teresa Trua  Giancarlo Serri  Michael Marani  Alberto Renzulli  Fabiano Gamberi 《Journal of Volcanology and Geothermal Research》2002,114(3-4)

A swath bathymetric survey was conducted on Marsili Volcano, the biggest seamount in the Tyrrhenian Sea. It stands 3000 m above the surrounding oceanic crust of the 3500 m-deep Marsili back-arc basin and is axially located within the basin. The seamount has an elongated shape and presents distinctive morphology, with narrow (<1000 m) ridges, made up of several elongated cones, on the summit zone and extensive cone fields on its lower flanks. A dredging campaign carried out at water depths varying between 3400 and 600 m indicates that most of Marsili Seamount is composed of medium-K calc-alkaline basalts. Evolved high-K andesites were only recovered from the small cones on the summit axis zone. Petrological and geochemical characteristics of the least differentiated basalts reveal that at least two varieties of magmas have been erupted on the Marsili Volcano. Group 1 basalts have plagioclase and olivine as dominant phases and show lower Al, Ca, K, Ba, Rb and Sr, and higher Fe, Na, Ti and Zr with respect to a second type of basaltic magma. Group 2 basalts reveal the presence of clinopyroxene as an additional phenocryst phase. In addition, the two basaltic magmas have different original pre-eruptive H₂O content (group 1, H₂O-poor and group 2, H₂O-rich). Moreover, comparison of the compositional trends and mineralogical compositions obtained from MELTS [Ghiorso, M.S., Sack, R.O., Contrib. Mineral. Petrol. 119 (1995) 197–212] fractional crystallization calculations reveal that the evolved andesites can only exclusively be derived from a low-pressure (0.3 kbar) fractionation of magmas compositionally similar to the least evolved group 2 basalts. Finally, we suggest that the high vesicularity of the basalts sampled at relatively great depths (>2400 m) on the edifice is governed by H₂O and, probably, CO₂ exsolution and is not a feature indicative of shallow water depth eruption.  相似文献   

铜陵中生代中酸性侵入岩特征及成因   总被引：38，自引：4，他引：38       下载免费PDF全文

吴才来  陈松永  史仁灯  郝美英 《地球学报》2003,24(1):41-48

铜陵地区中酸性侵入岩可以划分为橄榄安粗岩系列和高钾钙碱性系列 ,橄榄安粗岩系列的岩石组合为辉石二长闪长岩 +二长闪长岩 +石英二长岩 ,这些岩石的里特曼指数大于 4(变化于 4.2～ 5 .8之间 ) ,岩石的稀土总量 ((REE)变化于2 11× 10 -6～ 2 6 4× 10 -6之间 ,且与金矿床关系较密切。高钾钙碱性系列侵入岩岩石组合为闪长岩 +石英二长闪长岩 +花岗闪长岩 ,岩石的里特曼指数小于 4(1.8～ 3 .2 ) ,ΣREE为 130× 10 -6～ 188× 10 -6,与铜矿床关系较为密切。结合包体岩石学研究得出 ,橄榄安粗岩系列岩浆为幔源碱性基性岩浆分异的产物 ,高钾钙碱性系列岩浆是分异的幔源岩浆和壳源酸性岩浆混合的产物。  相似文献   

辽西北票—义县地区义县旋回火山岩的岩石化学特征   总被引：3，自引：1，他引：3       下载免费PDF全文

彭艳东  张立东  张长捷郭胜哲邢德和  贾斌  陈树旺  丁秋红 《中国地质》2004,31(4):356-364

辽西地区是中国中生代火山岩主要分布区之一。义县组分为4个岩性段。义县火山旋回可分为4个亚旋回。第一亚旋回分为4个小旋回。从早期至晚期，义县旋回火山岩逐渐由基性向中基性、中性和酸性演化，火山岩岩石组合为基性岩-中性岩-酸性岩组合，从北票-义县，火山活动显示了由老到新的迁移性。主要氧化物关系表明岩石的SiO2与K2O呈正相关，SiO2与MgO、CaO、FeO Fe2O3呈负相关。TAS图解反映了火山岩较高碱度的总体特征，硅-碱关系图和AFM图解反映了火山岩属于亚碱性系列中的钙碱性系列岩石，在SiO2-K2O关系图上，绝大部分样品落于高钾钙碱性系列区内，少量落于钾玄岩系列区，因此义县旋回火山岩以高钾钙碱性系列岩石为主，部分为钾玄岩系列，表明岩石富钾。义县旋回火山岩具有大陆板内火山岩的基本特征。  相似文献   

新疆东天山泥盆纪火山岩岩石学特征及其形成的大地构造环境   总被引：1，自引：0，他引：1  

肖渊甫  茅燕石 《矿物岩石》1992,12(2):34-42

新疆东天山地区泥盆纪火山活动频繁,火山岩广泛发育。火山岩系由钙碱系列(占75％)石英安山岩、英安岩、玄武岩、碱长流纹岩以及大量的火山碎屑岩,和拉斑玄武系列(约占25％)的石英拉斑玄武岩,少量橄榄拉斑玄武岩组成。岩石普遍富含Na_2O,SiO_2,而贫MgO,K_2O,以CaO,属钠质型和普通型。稀有元素配分型式具“三隆起”特征,过渡族元素呈明显的“W”形态,稀土元素为铕平坦或略具亏损的轻稀土富集型。据研究,火山岩由南至北具明显的钾元素地球化学极性。反映其板块构造环境为一俯冲带倾向北的陆壳型岛弧。  相似文献   

Anhydrous and water-saturated melting experiments of an olivine andesite from Mt Yakushi-Yama, northeastern Shikoku, Japan     

Toshisuke  Kawasaki Koji  Okusako Toshihiro  Nishiyama 《Island Arc》1993,2(4):228-237

Abstract Melting experiments have been carried out on an olivine andesite of Mt Yakushi-Yama from the Miocene Setouchi volcanic belt in northeastern Shikoku, Japan. This andesite has been characterized by a low ratio of FeO*/Mg° (= 0.78). Phase relations have been determined within the pressure range of 2.8 to 19.3 kbar at 1000-1300°C under anhydrous and water-saturated conditions. At pressures less than 8.8 kbar, olivine is a liquidus phase. Orthopyroxene appears on the liquidus at 9.3 kbar under the anhydrous conditions. The multiple saturation point rises up to 17.5 kbar for water-saturated experiments. The andesite melt coexists with olivine and orthopyroxene just below the liquidus at 8.8–9.3 kbar and 1230°C for dry conditions, and at 17.5 kbar and 1060°C under water-saturated conditions. These experimental results indicate that the Yakushi-Yama olivine andesite magma could coexist with a harzburgitic mantle at depths between about 30 and 60 km, and at temperatures between 1060 and 1230°C. Experimental data also suggest a possibility that a high magnesian andesite magma would be generated by a direct partial melting of the uppermost harzburgitic mantle under anhydrous conditions.  相似文献   

Geochemical approach to magmatic evolution of Mt. Erciyes stratovolcano Central Anatolia, Turkey   总被引：1，自引：0，他引：1  

Biltan Kürküoglu  Erdal Sen  Erkan Aydar  Alain Gourgaud  Niyazi Gündogdu 《Journal of Volcanology and Geothermal Research》1998,85(1-4)

Erciyes stratovolcano, culminating at 3917 m, is located in the Cappadocian region of central Anatolia. During its evolution, this Quaternary volcano produced pyroclastic deposits and lava flows. The great majority of these products are calc-alkaline in character and they constitute Kocdag and Erciyes sequences by repeated activities. Alkaline activity is mainly observed in the first stages of Kocdag and approximately first-middle stages of Erciyes sequences. Generally, Kocdag and Erciyes stages terminate by pyroclastic activities. The composition of lavas ranges from basalt to rhyolite (48.4–70.5 wt.% SiO₂). Calc-alkaline rocks are represented mostly by andesites and dacites. Some compositional differences between alkaline basaltic, basaltic and andesitic rocks were found; while the composition of dacites remain unchanged. All these volcanics are generally enriched in LIL and HFS elements relative to the orogenic values except Rb, Ba, Nb depleted alkaline basalt. ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd isotopic composition of the volcanics range between 0.703344–0.703964, 0.512920–0.512780 for alkaline basalts and change between 0.704322–0.705088, 0.512731–0.512630 for alkaline basaltic rocks whereas calc-alkaline rocks have relatively high Sr and Nd isotopic ratios (0.703434–0.705468, 0.512942–0.512600). Low Rb, Ba, Nb content with high Zr/Nb, low Ba/Nb, La/Yb ratio and low Sr isotopic composition suggest an depleted source component, while high Ba, Rb, Nb content with high La/Yb, Ba/Nb, low Zr/Nb and low ⁸⁷Sr/⁸⁶Sr ratios indicate an OIB-like mantle source for the generation of Erciyes alkaline magma. These elemental and ratio variations also indicate that the different mantle sources have undergone different degree of partial melting episodes. The depletion in Ba, Rb, Nb content may be explained by the removal of these elements from the source by slab-derived fluids which were released from pre-collisional subduction, modified the asthenospheric mantle. The chemically different mantle sources interacted with crustal materials to produce calc-alkaline magma. The Ba/Nb increase of calc-alkaline samples indicates the increasing input of crustal components to Erciyes volcanics. Sr and Nd isotopic compositions and elevated LIL and HFS element content imply that calc-alkaline magma may be derived from mixing of an OIB-like mantle melts with a subduction-modified asthenospheric mantle and involvement of crustal materials in intraplate environments.  相似文献   

腾冲马鞍山、打鹰山、黑空山火山岩浆来源与演化   总被引：10，自引：6，他引：4  

赵勇伟  樊祺诚 《岩石学报》2010,26(4):1133-1140

本文对马鞍山、打鹰山、黑空山火山岩主微量和Sr、Nd、Pd同位素地球化学研究认为,腾冲火山岩浆源区具有MORB与富集地幔混合之特征,推测为新特提斯俯冲洋壳重新熔融,导致腾冲地区的高钾钙碱性岩浆的火山活动,解释了腾冲在新生代大陆板内构造环境背景下出现岛弧或活动大陆边缘火山岩地球化学特征的现象。马鞍山、打鹰山和黑空山火山高钾钙碱性岩浆经历了岩浆房阶段辉石、钛铁矿的结晶分离作用和岩浆上升过程中斜长石的结晶分离作用,导致岩浆成分从中基性向中酸性演化,火山岩从玄武质粗安岩→粗安岩→粗面质英安岩演化。  相似文献   

估算钙碱性长英质侵入岩结晶压力的地质压力计评述     

徐鸿雪  汪洋 《地质论评》2023,69(4):2023040029-2023040029

本文对四种常见的矿物压力计（角闪石全铝压力计、黑云母压力计、榍石压力计和“石英”压力计）的适用性进行了经验性检验。基于国内外典型钙碱性长英质岩体的矿物化学和全岩化学成分数据,采用不同压力计估算岩体侵位压力,并与角闪石全铝压力计结果对比。结果表明：角闪石六次配位Al压力计与广泛使用的角闪石全铝压力计的估算值存在系统相关性;榍石压力计计算的压力与角闪石全铝压力计的估计结果相关性较为显著;基于Qtz—Ab—Or简并花岗岩体系的“石英”压力计可以用于估计准铝质—弱过铝质钙碱性（狭义）花岗岩的结晶压力。但是,经验性的黑云母压力计和基于实验数据的黑云母压力压计均不能很好地复现角闪石全铝压力计的结果。黑云母压力计不适用于估算钙碱性侵入岩的结晶压力。  相似文献