From seamount to oceanic island, Porto Santo, central East-Atlantic

The uplifted and deeply eroded volcanic succession of Porto Santo (central East-Atlantic) is the product of a wide spectrum of dynamic processes that are active in shoaling to emergent seamounts. Two superimposed lapilli cones marking the base of the exposed section are interpreted as having formed from numerous submarine to subaerial phreatomagmatic explosions, pyroclastic fragmentation being subordinate. The lower basaltic and the upper mugearitic to trachytic sections are dominated by redeposited tephra and are called 'lapilli cone aprons'. Vertical growth due to accumulation of tephra, voluminous intrusions, and minor pillowed lava flows produced ephemeral islands which were subsequently leveled by wave erosion, as shown by conglomerate beds. Periods of volcanic quiescence are represented by abundant biocalcarenite lenses at several stratigraphic levels. The loose tephra piles became stabilized by widespread syn-volcanic intrusions such as dikes and trachytic to rhyolitic domes welding the volcanic and volcaniclastic ensemble into a solid edifice. Shattering of a submarine extrusive trachytic dome by pyroclastic and phreatomagmatic explosions, accentuated by quench fragmentation, resulted in pumice- and crystal-rich deposits emplaced in a prominent submarine erosional channel. The dome must have produced an island as indicated by a collapse breccia comprising surf-rounded boulders of dome material. Subaerial explosive activity is represented by scoria cones and tuff cones. Basaltic lava flows built a resistant cap that protected the island from wave erosion. Some lava flows entered the sea and formed two distinct types of lava delta: 1. closely-packed pillow lava and massive tabular lava flows along the southwestern coast of Porto Santo, and 2. a steeply inclined pillow-hyaloclastite breccia prism composed of foreset-bedded hydroclastic breccia, variably-shaped pillows, and thin sheet flows capped by subhorizontal submarine to subaerial lava flows along the eastern coast of Porto Santo.The facies architectures indicate emplacement: 1. on a gently sloping platform in southwestern Porto Santo, and 2. on steep offshore slopes along high energy shorelines in eastern Porto Santo.Growth of the pillow-hyaloclastite breccia prism is dominated by the formation of foreset beds but various types of syn-volcanic intrusions contributed significantly. Submarine flank eruptions occurred in very shallow water on the flanks of the hyaloclastite prism in eastern Porto Santo. The island became consolidated by intrusion of numerous dikes and by emplacement of prominent intrusions that penetrate the entire volcanic succession. Volcanic sedimentation ended with the emplacement of a debris avalanche that postdates the last subaerial volcanic activity.     

内蒙锡林浩特鸽子山火山地质研究

鸽子山火山位于内蒙古自治区锡林浩特市东南,处于大兴安岭-大同新生代火山喷发带中段,是锡林浩特-阿巴嘎火山群中保存最为完好的一座玄武质火山。火山喷发物的分布面积约55km²,主要为降落火山渣、溅落熔结火山碎屑岩和熔岩流,成分主要为碧玄岩,晚期有少量的橄榄拉斑玄武岩,碧玄岩中含有较多二辉橄榄岩包体和辉石及歪长石巨晶。火山由锥体、熔岩流和火山碎屑席组成,锥体由早期的降落锥和晚期溅落锥复合而成。火山口经历多次塌陷而成为破火口。锥体西侧及北东侧出露两个仍保留了原始形态的熔岩溢出口,熔岩流类型为结壳熔岩,由多个岩流单元组成,局部地区的熔岩流中发育较多保存完好的喷气锥、喷气碟或喷气塔。火山碎屑席主要分布在锥体的东侧,厚度由锥体向外逐渐减薄。火山活动可分为早、晚两个阶段,早期为爆破式喷发,形成火山渣锥和碎屑席,属亚布里尼型喷发,晚期主要为溢流式喷发,形成溅落锥和大规模熔岩流,其活动时代为晚更新世末-全新世。     

Evolution of Irruputuncu volcano,Central Andes,northern Chile

The Irruputuncu is an active volcano located in northern Chile within the Central Andean Volcanic Zone (CAVZ) and that has produced andesitic to trachy-andesitic magmas over the last ∼258 ± 49 ka. We report petrographical and geochemical data, new geochronological ages and for the first time a detailed geological map representing the eruptive products generated by the Irruputuncu volcano. The detailed study on the volcanic products allows us to establish a temporal evolution of the edifice. We propose that the Irruputuncu volcanic history can be divided in two stages, both dominated by effusive activity: Irruputuncu I and II. The oldest identified products that mark the beginning of Irruputuncu I are small-volume pyroclastic flow deposits generated during an explosive phase that may have been triggered by magma injection as suggested by mingling features in the clasts. This event was followed by generation of large lava flows and the edifice grew until destabilization of its SW flank through the generation of a debris avalanche, which ended Irruputuncu I. New effusive activity generated lavas flows to the NW at the beginning of Irruputuncu II. In the meantime, lava domes that grew in the summit were destabilized, as shown by two well-preserved block-and-ash flow deposits. The first phase of dome collapse, in particular, generated highly mobile pyroclastic flows that propagated up to ∼8 km from their source on gentle slopes as low as 11° in distal areas. The actual activity is characterized by deposition of sulfur and permanent gas emissions, producing a gas plume that reaches 200 m above the crater. The maximum volume of this volcanic system is of ∼4 km³, being one of the smallest active volcano of Central Andes.     

New observations on Rajahmundry Traps of the Krishna-Godavari Basin

The Rajahmundry Traps of the Krishna Godavari Basin (K-G Basin) consist of three distinct basalt flows interbedded with two intertrappean sedimentary horizons, which in turn are underlain by the late Cretaceous fossiliferous limestone bed (infratrappean) and overlain by the Cenozoic Rajahmundry Formation (conglomerate/sandstone). Among the three, the lower flow is characterized by the presence of the physical volcanological features such as rootless cones, tumuli and dyke like forms along with single to multitier columnar and radial jointing. The middle and upper flows are simple, massive and vesicular and exhibit spheroidal weathering. Physical volcanological features and lithological attributes indicate that the lower flow was formed by an explosive volcanic activity in hydrous environment, followed by sub aerial eruption to form the middle and upper flows. The fossiliferous limestone bed is a representative horizon for the K-T boundary mass extinction caused due to intense volcanism. Intertrappean sediments exhibit weathered soil profiles (palaeosols) with limestone beds denoting a distinct time gap during various phases of lava eruption. Evaluation of the palaeogeographic scenario of the Krishna and Godavari Rivers does not provide any evidence for the existence of Cretaceous palaeovalley which would have provided pathway for lava transportation from the Deccan volcanic province of western India to the K-G Basin situated along the east coast. The present study opens up an alternative approach to explain the origin of basalt flows at Rajahmundry. In all probability the lavas could be intrabasinal. NW-SE and NESW faults or their intersection zones are probable pathways for lava eruption in the K-G Basin.     

花岗岩混合问题:与玄武岩对比的启示——关于花岗岩研究的思考之一

最近,花岗岩混合成了花岗岩研究的热点,国内外许多学者探讨了花岗岩混合问题,并尝试用不同端元组分不同比例的混合来解释花岗岩的地球化学变化。本文从花岗岩与玄武岩的对比出发,探讨了花岗岩混合的可能性和局限性。作者认为,花岗岩混合的现象是普遍存在的,但是次要的和局部的。岩浆混合的能力或能干性(competence of mixing)主要取决于岩浆的黏性和温度,而黏性又与硅氧四面体有关。相对于玄武岩,花岗岩的SiO_2含量高,温度低,因此,花岗质岩浆的混合能干性很低。玄武质岩浆的混合是mixing(以化学混合为主),而花岗质岩浆的混合通常只是mingling(以机械混合为主),只有在少数情况下才能达到mixing的程度,例如,埃达克岩与地幔混合形成的高镁安山岩或高镁埃达克岩。许多人认为,花岗岩中的暗色微粒包体是花岗质岩浆混合作用最显著、最直接证据。研究表明,花岗岩中的暗色微粒包体大多是闪长质成分的,其初始成分大多是玄武质的。因此,暗色微粒包体不是花岗质岩浆混合作用最显著、最直接证据,而是玄武质岩浆混合能力强过花岗质岩浆的证据。与玄武质岩浆的起源比较,花岗质岩浆从一开始熔融就是不均一的,这源于源区的不均一及熔融过程的复杂性。花岗质岩浆原始均一性的假定是不可能的。花岗岩成分的变化以及在哈克图解中成分点的"连续谱系",主要是由源区不均一性引起的,混合和分异可能有一定的作用,但毕竟是次要的。花岗质岩浆从源区生成、迁移、直至在地表喷出或在浅部定位的全过程,是一个不断均一化和不均一化的过程。但是,由于花岗质岩浆的黏性大,上述过程及岩浆演化的程度和规模都受到限制,也限制了岩浆混合的程度和规模。许多人仅从花岗岩地球化学成分的变化来研究花岗岩的成因,而很少考虑花岗岩物理性质对岩浆演化的制约。对比玄武岩与花岗岩,我们认为,地球化学方法在花岗岩中应用的范围和程度可能远远不及玄武岩,我们应当重新考虑花岗岩的地球化学应用问题。     

松辽盆地改造残留的古火山机构与现代火山机构的类比分析

现代火山机构形态有盾状、锥状和穹状,可按喷发样式进一步划分为7种类型。据此分类,在松辽盆地周缘剖面及其北部徐家围子断陷区可识别出4类火山机构：盾状火山机构,由喷溢相熔岩组成,可夹有薄层爆发相火山碎屑岩;层火山机构,由互层的熔岩与火山碎屑岩组成,喷溢相与爆发相交替的序列明显;火山碎屑锥,几乎全部由火山碎屑（熔）岩组成,爆发相为主;熔岩穹丘由高粘度的流纹质、英安质熔岩堵塞火山口后缓慢挤出形成,喷溢相和侵出相发育,兼有火山通道相。盆地内埋藏火山机构最小坡度为3°,最大坡度为25°,底部直径为2～14 km,分布面积为4～50 km²,火山岩厚度为100～600 m;总体上呈现出数目多、个体规模小、受区域大断裂控制、具裂隙式-多中心喷发、彼此相互叠置的特征。火山岩岩性和岩相是控制松辽盆地古火山机构类型及形态的主要因素。     

Strange attractors in magmas: evidence from lava flows

Magma mixing structures from three different lava flows (Salina, Vulcano and Lesbos) are studied in order to assess the possible chaotic origin of magma mixing processes. Structures are analysed using a new technique based on image analysis procedures that extract time series that are representative of the relative change in composition through the structures. These time series are then used to reconstruct the attractors underlying the magma mixing process and to calculate the fractal dimension of the attractors. Results show that attractors exist and possess fractional dimensions. This evidence suggests that the mixing of magmas is a chaotic process governed by a low number of degrees of freedom. In addition, fractal dimension analyses allows us to discriminate between different regimes of mixing in the three lava flows. In particular our analyses suggest that the lava flow of Salina underwent more turbulent mixing than the lava flows of Lesbos and Vulcano.     

浙江新昌早白垩世复合岩流中的岩浆混合作用

浙江新昌拔茅地区早白垩世复合岩流中各种火山岩（Ｒｂ－Ｓｒ等时线年龄为９６．３Ｍａ）属高钾钙碱性岩系，在其中发现了中生代火山活动中岩浆混合作用的确凿证据，岩相学及地球化学研究表明，这种复合岩流中的安山质岩浆是由同时代橄榄拉斑玄武岩浆和流纹岩浆相互混合而形成的。     

Contrasting origin of two A-type rhyolite series from the Early Permian Nomgon bimodal volcanic association (Southern Mongolia)

A-type rhyolites of contrasting compositions and eruption characters were revealed among two volcanic series of the Early Permian bimodal association in the Nomgon graben. Rhyolites of the lower volcanic series formed extrusions, lava domes, and tuff horizons. They had low FeO_t, Zr, Hf, Nb, Ta, Y, and REE concentrations and also a moderately depleted Nd isotope composition (ε_Nd(Т) = 6.7–7.1). Their formation was related to anatexis of the juvenile continental crust, triggered by the thermal effect of mafic magmas. Rhyolites of the upper volcanic series formed extensive lava flows and dikes. Their composition was characterized by high FeO_t, Zr, Hf, Nb, Ta, Y, and REE concentrations, and also depleted Nd isotope characteristics (ε_Nd(Т) = 7.7–9.0). These rhyolite melts formed under long-term crystallizational differentiation of basaltoids in the intracrustal magmatic chambers, with limited participation of crustal contamination. The source of magmas for the upper volcanic series was the sublithospheric mantle.     

浙江新昌复合式火成杂岩的岩石学、地球化学及其地质意义

浙江新昌复合式火成杂岩包括复合火山岩流和复合侵入杂岩。复合火山岩流由玄武岩和流纹岩/流纹质熔结凝灰岩组成,有的含少量安山质-英安质岩流和岩石包体;复合侵入杂岩由辉绿岩和花岗岩复合而成,含闪长质-石英闪长质岩石包体。它们在空间上紧密伴生,同位素年龄为96~113 Ma;地球化学上,它们统属钙碱性岩系,具有轻稀土元素和大离子亲石元素富集、高场强元素亏损等特点,稀土元素、微量元素配分型式基本相同,Sr=0.7069~0.7079,εNd (t ) = -2.3~-5.3,指示它们的微量元素和同位素发生过充分的交换。这些特点与浙闽沿海其他复合岩流和复合侵入杂岩的特点基本一致。它们形成在伸展构造背景,由起源于受消减作用影响的岩石圈地幔部分熔融而产生的玄武岩岩浆底侵,并与深熔的壳源花岗岩浆发生不同程度的岩浆混合而形成。新昌复合式火成杂岩的研究,为更深入研究中国东南部沿海地区晚中生代地球动力学环境变化和构造-岩浆作用提供了一个典型实例。     

花岗质岩浆能够结晶分离和演化吗？

学术界普遍认为花岗岩能够分离和演化,实际上这是不对的,理由是没有野外和镜下观察的证据。岩浆演化的理论是对的,该理论是从研究玄武质岩浆得来的,只适合玄武质岩浆而不适合花岗质岩浆。本文指出,鲍温反应原理不适用于花岗质岩浆。文中呼吁要重视区分幔源岩浆和壳源岩浆,幔源岩浆可以演化,但是,幔源岩浆不可能演化为壳源岩浆,壳源岩浆不可能演化。     

Petrology, volcanology and metallogeny of Palaeogene collision-related volcanism of the Eastern Rhodopes (Bulgaria)

Tertiary collision-related volcanic rocks of the Eastern Rhodopes (37–25.5 Ma) display calc-alkaline and shoshonitic affinities, with (A) intermediate to basic and (B) acid compositions. (A) Latites, andesites, also shoshonites and basaltic andesites and scarce basalts, absarokites and ultrapotassic latites were emitted through different eruptive styles: lava flows often autobrecciated, domes, ash and scarce pumice falls and flows. Lahars are frequent. K₂O contents of intermediate volcanics decrease from North to South towards the collision suture. (B) Rhyolites, trachyrhyolites and trachydacites show explosivity progressively decreasing with time. Several eruptive types can be distinguished: pyroclastic flows (weakly and strongly welded ignimbrite deposits), ash and lapilli falls, domes and lava flows. The large (30×10 km) Borovitza caldera is the result of a paroxysmic explosive phase.
  All rocks are characterized by high contents of Rb, Th and Y. Conversely, negative Ba and Ta–Nb anomalies are typical of collision-related magmatism.
  Intense hydrothermal episodes, contemporaneous with the volcanic activity, have converted large amounts of explosive products into bentonite and zeolites deposits. Typical metallogeny is associated with this collision-related volcanism: large Pb, Zn with Cu and Ag deposits and small U or Au deposits are exposed.     

评花岗岩的哈克图解

哈克图解是研究岩浆岩地球化学必用的图件,许多结论就是根据哈克图解做出的。哈克图解只是一个逻辑推理的工具,它所推出的结论是否正确,不是由图解本身决定的,而是由实践决定的。岩浆演化的理论是对的,岩浆演化的理论是从研究层状侵入体得来的,它仅适用于玄武质岩浆,而不适用于花岗质岩浆。实践是检验真理的唯一标准,由哈克图解得出的结论没有经过实践的检验是不能成为真理的,这是最基本、最简单的道理。     

Main Mineralization Mechanism of Magmatic Sulphide Deposits in China

Before intruding, primary magmas have undergone liquation and partial crystallization atdepth; as a result the magmas are partitioned into barren magma, ore-bearing magma, ore-richmagma and ore magma, which then ascend and are injected into the present locations once ormultiple times, thus forming ore deposits. The above-mentioned mineralizing process is knownas deep-seated magmatic liquation-injection mineralization. The volume of the barren magma isgenerally much larger than those of the ore-bearing magma, ore-rich magma and ore magma. Inthe ascending process, most of the barren magma intrudes into different locations or outpoursonto the ground surface, forming intrusions or lava flows. The rest barren magma, ore-bearingmagma, ore-rich magma and ore magma may either multiple times inject into the same space inwhich rocks and ores are formed or separately inject into different spaces in which rocks and oresare formed. The intrusions containing such deep-seated magmatic liquation-injection depositshave a much smaller volume, greater ore potential and higher ore grade than that of in-situmagmatic liquation deposits. Consequently this mineralizing process results in the formation oflarge deposits in small intrusions.     

Concentric zoning in the Tunk Lake pluton,coastal Maine

The Tunk Lake pluton of coastal Maine, USA is a concentrically zoned granitic body that grades from an outer hypersolvus granite into subsolvus rapakivi granite, and then into subsolvus non-rapakivi granite, with gradational contacts between these zones. The pluton is partially surrounded by a zone of basaltic and gabbroic enclaves, interpreted as quenched magmatic droplets and mushes, respectively, as well as gabbroic xenoliths, all hosted by high-silica granite. The granite is zoned in terms of mineral assemblage, mineral composition, zircon crystallization temperature, and major and trace element concentration, from the present-day rim (interpreted as being closer to the base of the chamber) to the core (interpreted as being closer to the upper portions of the chamber). The ferromagnesian mineral assemblage systematically changes from augite and hornblende with augite cores in the outermost hypersolvus granite to hornblende, to hornblende and biotite, and finally, to biotite only in the subsolvus granite core of the pluton. Sparse fine-grained basaltic enclaves that are most common in the outermost zone of the pluton suggest that basaltic magma was present in the lower portions of the magma chamber at the same time that the upper portions of the magma chamber were occupied by a granitic crystal mush. However, the slight variations in initial Nd isotopic ratio in granites from different zones of the pluton suggest that contamination of the granitic melt by basaltic melt played little role in generating the compositional gradation of the pluton. The zone of basaltic and gabbroic chilled magmatic enclaves, and gabbroic xenoliths, hosted by high-silica granite, that partially surround the pluton is interpreted as mafic layers at the base of the pluton that were disrupted by invading late-stage high-silica magma. These mafic layers are likely to have consisted of basaltic lava layers and basalt that chilled against granitic magma to produce coarse-grained gabbroic mush. Basaltic and gabbroic magmatic enclaves and gabbroic xenoliths are hornblende-bearing, suggesting that their parent melts were relatively hydrous. The water-rich nature of the underplating mafic magmas may have prevented extensive invasion of the granitic magma by these magmas, owing to the much greater viscosity of the granitic magma than the mafic magmas in the temperature range over which magma interaction could have occurred.     

Review of post-collisional volcanism in the Central Anatolian Volcanic Province (Turkey), with special reference to the Tepekoy Volcanic Complex

Neogene-Quaternary post-collisional volcanism in Central Anatolian Volcanic Province (CAVP) is mainly characterized by calc-alkaline andesites-dacites, with subordinate tholeiitic-transitional-mildly alkaline basaltic volcanism of the monogenetic cones. Tepekoy Volcanic Complex (TVC) in Nigde area consists of base surge deposits, and medium to high-K andesitic-dacitic lava flows and basaltic andesitic flows associated with monogenetic cones. Tepekoy lava flows petrographically exhibit disequilibrium textures indicative of magma mixing/mingling and a geochemisty characterized by high LILE and low HFSE abundances, negative Nb–Ta, Ba, P and Ti anomalies in mantle-normalized patterns. In this respect, they are similar to the other calc-alkaline volcanics of the CAVP. However, TVC lava flows have higher and variable Ba/Ta, Ba/Nb, Nb/Zr, Ba/TiO₂ ratios, indicating a heterogeneous, variably fluid-rich source. All the geochemical features of the TVC are comparable to orogenic andesites elsewhere and point to a sub-continental lithospheric mantle source enriched in incompatible elements due to previous subduction processes. Basaltic monogenetic volcanoes of CAVP display similar patterns, and HFS anomalies on mantle-normalized diagrams, and have incompatible element ratios intermediate between orogenic andesites and within-plate basalts (e.g. OIB). Accordingly, the calc-alkaline and transitional-mildly alkaline basaltic magmas may have a common source region. Variable degrees of partial melting of a heterogeneous source, enriched in incompatible elements due to previous subduction processes followed by fractionation, crustal contamination, and magma mixing in shallow magma chambers produced the calc-alkaline volcanism in the CAVP. Magma generation in the TVC, and CAVP in general is via decompression melting facilitated by a transtensional tectonic regime. Acceleration of the extensional regime, and transcurrent fault systems extending deep into the lithosphere favoured asthenospheric upwelling at the base of the lithosphere, and as a consequence, an increase in temperature. This created fluid-present melting of a fluid-enriched upper lithospheric mantle or lower crustal source, but also mixing with asthenosphere-derived melts. These magmas with hybrid source characteristics produced the tholeiitic-transitional-mildly alkaline basalts depending on the residence times within the crust. Hybrid magmas transported to the surface rapidly, favored by extensional post-collision regime, and produced mildly alkaline monogenetic volcanoes. Hybrid magmas interacted with the calc-alkaline magma chambers during the ascent to the surface suffered slight fractionation and crustal contamination due to relatively longer residence time compared to rapidly rising magmas. In this way they produced the mildly alkaline, transitional, and tholeiitic basaltic magmas. This model can explain the coexistence of a complete spectrum of q-normative, ol-hy-normative, and ne-normative monogenetic basalts with both subduction and within-plate signatures in the CAVP.     

Erratum to: Review of post-collisional volcanism in the Central Anatolian Volcanic Province (Turkey), with special reference to the Tepekoy Volcanic Complex

Neogene-Quaternary post-collisional volcanism in Central Anatolian Volcanic Province (CAVP) is mainly characterized by calc-alkaline andesites-dacites, with subordinate tholeiitic-transitional-mildly alkaline basaltic volcanism of the monogenetic cones. Tepekoy Volcanic Complex (TVC) in Nigde area consists of base surge deposits, and medium to high-K andesitic-dacitic lava flows and basaltic andesitic flows associated with monogenetic cones. Tepekoy lava flows petrographically exhibit disequilibrium textures indicative of magma mixing/mingling and a geochemisty characterized by high LILE and low HFSE abundances, negative Nb–Ta, Ba, P and Ti anomalies in mantle-normalized patterns. In this respect, they are similar to the other calc-alkaline volcanics of the CAVP. However, TVC lava flows have higher and variable Ba/Ta, Ba/Nb, Nb/Zr, Ba/TiO₂ ratios, indicating a heterogeneous, variably fluid-rich source. All the geochemical features of the TVC are comparable to orogenic andesites elsewhere and point to a sub-continental lithospheric mantle source enriched in incompatible elements due to previous subduction processes. Basaltic monogenetic volcanoes of CAVP display similar patterns, and HFS anomalies on mantle-normalized diagrams, and have incompatible element ratios intermediate between orogenic andesites and within-plate basalts (e.g. OIB). Accordingly, the calc-alkaline and transitional-mildly alkaline basaltic magmas may have a common source region. Variable degrees of partial melting of a heterogeneous source, enriched in incompatible elements due to previous subduction processes followed by fractionation, crustal contamination, and magma mixing in shallow magma chambers produced the calc-alkaline volcanism in the CAVP. Magma generation in the TVC, and CAVP in general is via decompression melting facilitated by a transtensional tectonic regime. Acceleration of the extensional regime, and transcurrent fault systems extending deep into the lithosphere favoured asthenospheric upwelling at the base of the lithosphere, and as a consequence, an increase in temperature. This created fluid-present melting of a fluid-enriched upper lithospheric mantle or lower crustal source, but also mixing with asthenosphere-derived melts. These magmas with hybrid source characteristics produced the tholeiitic-transitional-mildly alkaline basalts depending on the residence times within the crust. Hybrid magmas transported to the surface rapidly, favored by extensional post-collision regime, and produced mildly alkaline monogenetic volcanoes. Hybrid magmas interacted with the calc-alkaline magma chambers during the ascent to the surface suffered slight fractionation and crustal contamination due to relatively longer residence time compared to rapidly rising magmas. In this way they produced the mildly alkaline, transitional, and tholeiitic basaltic magmas. This model can explain the coexistence of a complete spectrum of q-normative, ol-hy-normative, and ne-normative monogenetic basalts with both subduction and within-plate signatures in the CAVP.     

Intrusion of basaltic magma into a crystallizing granitic magma chamber: The Cordillera del Paine pluton in southern Chile

The Cordillera del Paine pluton in the southernmost Andes of Chile represents a deeply dissected magma chamber where mafic magma intruded into crystallizing granitic magma. Throughout much of the 10x15 km pluton, there is a sharp and continuous boundary at a remarkably constant elevation of 1,100 m that separates granitic rocks (Cordillera del Paine or CP granite: 69–77% SiO₂) which make up the upper levels of the pluton from mafic and comingled rocks (Paine Mafic Complex or PMC: 45–60% SiO₂) which dominate the lower exposures of the pluton. Chilled, crenulate, disrupted contacts of mafic rock against granite demonstrate that partly crystallized granite was intruded by mafic magma which solidified prior to complete crystallization of the granitic magma. The boundary at 1,100 m was a large and stable density contrast between the denser, hotter mafic magma and cooler granitic magma. The granitic magma was more solidified near the margins of the chamber when mafic intrusion occurred, and the PMC is less disrupted by granites there. Near the pluton margins, the PMC grades upward irregularly from cumulate gabbros to monzodiorites. Mafic magma differentiated largely by fractional crystallization as indicated by the presence of cumulate rocks and by the low levels of compatible elements in most PMC rocks. The compositional gap between the PMC and CP granite indicates that mixing (blending) of granitic magma into the mafic magma was less important, although it is apparent from mineral assemblages in mafic rocks. Granitic magma may have incorporated small amounts of mafic liquid that had evolved to >60% SiO₂ by crystallization. Mixing was inhibited by the extent of crystallization of the granite, and by the thermal contrast and the stable density contrast between the magmas. PMC gabbros display disequilibrium mineral assemblages including early formed zoned olivine (with orthopyroxene coronas), clinopyroxene, calcic plagioclase and paragasite and later-formed amphibole, sodic plagioclase, mica and quartz. The early formed gabbroic minerals (and their coronas) are very similar to phenocrysts in late basaltic dikes that cut the upper levels of the CP granite. The inferred parental magmas of both dikes and gabbros were very similar to subalkaline basalts of the Patagonian Plateau that erupted at about the same time, 35 km to the east. Mafic and silicic magmas at Cordillera del Paine are consanguineous, as demonstrated by alkalinity and trace-element ratios. However, the contemporaneity of mafic and silicic magmas precludes a parent-daughter relationship. The granitic magma most likely was derived by differentiation of mafic magmas that were similar to those that later intruded it. Or, the granitic magma may have been contaminated by mafic magmas similar to the PMC magmas before its shallow emplacement. Mixing would be favored at deeper levels when the cooling rate was lower and the granitic magma was less solidified.     

澳大利亚伊尔岗克拉通科马提岩型镍矿成矿作用及找矿方法

澳大利亚西部伊尔岗克拉通卡尔古利地体是世界上太古宙与科马提岩有关的硫化物镍矿床最为集中的地区。该区科马提岩型硫化镍矿床主要有两大类型：①由高品位的块状、海面陨铁状和网状矿石组成,赋存于科马提岩熔岩流（主要为火山橄榄岩）底部,以卡姆巴尔达矿床为代表;②以低品位的浸染状镍硫化物矿石为主,赋存于厚层纯橄榄岩的中部,以芒特基斯为代表。与镍成矿有关的科马提岩形成于晚太古代（2．70Ga）,具铝不亏损（Al2O3／TiO2=15～25）地球化学特征,一般形成于具含硫围岩的动态高岩浆流环境。伊尔岗克拉通科马提岩型镍硫化物矿床形成于经历岩浆作用（结晶、分异和浓集）和地壳硫混染作用的硫不饱和镁铁质-超镁铁质岩浆的熔岩通道或管道中。在矿床成因讨论的基础上,提出该类型矿床的找矿标志和勘查方法。     

新疆东天山白山钼矿深部岩体地球化学特征及成因意义

白山钼矿深部钻探表明矿体下部存在着矿化花岗斑岩体,所获岩芯显示其岩性主要为似斑状钾长花岗岩、黑云母斜长花岗岩和花岗斑岩.该岩体具有高Al、Na和Sr,低Mg、Y和Yb,以及高Sr/Y和La/Yb比值等特点,类似于埃达克质岩的地球化学特征,暗示来源于较深的含石榴子石的源区;岩石形成时代和地球化学构造判别图解表明,岩体形成于造山后的构造环境.因此,白山钼矿岩体可能为加厚下地壳熔融的产物.白山钼矿床的成矿作用可能与埃达克质岩浆活动有关,其成矿过程得益于高Mo丰度的地壳源区、成岩过程中提供流体和岩浆高氧逸度环境等.