攀西小关河地区核桃树富铂岩浆硫化物矿床岩石地球化学特征及成矿机制研究     

朱飞霖  白梅  陶琰 《岩石学报》2017,33(7):2225-2240

核桃树富铂岩浆硫化物矿床位于四川会理县小关河地区,是峨眉山大火成岩省中含较高铂族元素含量的岩浆硫化物矿床之一。本文通过对核桃树岩体及部分硫化物矿石主量元素、微量元素及铂族元素的系统分析,讨论了该岩体的岩浆源区及母岩浆性质、地幔部分熔融程度,并探讨了其成因机制。研究认为,核桃树含矿岩体属拉斑玄武岩成因系列,具有与峨眉山玄武岩相似的微量元素组成特征,是峨眉山大火成岩省构造-岩浆活动的产物;铂族元素的原始地幔标准化配分型式与金宝山铂钯矿相似,没有PGE相对于Ni和Cu的明显亏损,Pt和Pd相对Os、Ir、Ru和Rh富集,为PPGE富集的左倾型式,Pd/Ir=1.5~13.1,低于一般大陆拉斑玄武岩,与原始地幔接近。通过岩石地球化学及模拟分析表明,成矿母岩浆MgO约为11.93%、SiO_2约为49.88%、FeOT约为13.71%、TiO_2约为2.61%,为高Mg拉斑玄武质岩浆,是由类似于洋岛玄武岩岩浆源区成分的地幔经过较高程度(约20.17%)的部分熔融形成的苦橄质岩浆演化而来。与小关河地区主要的几类岩浆硫化物矿床的镍铜铂族元素组成及硫化物熔离模式对比分析发现,核桃树高的PGE含量和低的Cu/Pd比值说明了该矿床的硫化物是从PGE不亏损的玄武质岩浆中熔离出来的,类似金宝山矿床。成岩成矿机制分析认为,部分熔融形成的苦橄质岩浆在上升的过程中,发生了以橄榄石(约12.7%)为代表的镁铁质矿物堆积,并形成残余髙镁玄武质岩浆;部分残余髙镁玄武质岩浆向浅部运移过程中,由于温度降低、混染等因素的影响,导致岩浆S饱和,触发硫化物熔离作用的发生(R值为2000~50000),熔离出硫化物熔体与岩浆通道内晶出的橄榄石构成含矿"晶粥",在构造挤压作用下,在浅部岩浆房中由于重力影响发生堆积作用形成具有较富PGE的含矿岩体,R值较大变化正好与PGE含量较大变化相对应。  相似文献   

Ophiolites of the Central Asian Orogenic Belt:Geochemical and petrological characterization and tectonic settings     

Harald Furnes  Inna Safonova 《地学前缘(英文版)》2019,10(4):1255-1284

We present a compilation of published data(field,petrography,ages and geochemistry)from 73 ophiolitic complexes of the Central Asian Orogenic Belt.The ophiolitic complexes,ranging in age from Neoproterozoic to Triassic.have been geochemically classified as subduction-related and subductionunrelated categories applying recent,well-established discrimination diagrams.The subductionunrelated category is further subdivided into Mid-Ocean Ridge type(MOR),a common rift-drift stage and Plume type,and the subduction-related category is subdivided into Backarc(BA),Forearc(FA).Backarc to Forearc(BA-FA)and Volcanic Arc(VA)types.The four subduction-related types define highly different geochemical features,with the BA and FA types defining end members showing subduction influence of 10%-100%and 90%-100%subduction influence,respectively,and the two other types(BAFA and VA)define values between the two end members.The subduction-related category comprises79%of the examined ophiolites,of which the BA type ophiolites is by far the dominant group,followed by the BA-FA type,and with FA and VA types as subordinate groups.The Neoproterozoic and Ordovician complexes exhibit the highest,whereas those of Silurian age exhibit the lowest subduction-influence.Of the remaining 21%subduction-unrelated ophiolites,the MOR type dominates.Both the subductionrelated and subduction-unrelated types,in particular the latter,are commonly associated with alkaline basalts taken to represent ocean island magmatism.Harzburgite,dunite,gabbro and basalt are the common lithologies in all ophiolite types,whereas the BA-FA,FA and VA types generally contain intermediate to felsic rocks,and in the FA type boninites occur.The subduction-related ophiolites types generally show low metamorphic grade,whereas greenschist.amphibolite and blueschist grades occur in the subduction-unrelated and BA types.The highly different subduction contribution(from 0 to 100%in the MOR and FA,respectively),attest to variable dips of the subducting slab,as well as variable flux of subduction-related elements into the mantle above subducting slabs,from where the ophiolite magmas got their geochemical fingerprints.As most MOR ophiolites get subducted to the deep mantle,the subduction-related ophiolites have become a dominant ophiolitic type on Earth’s surface through all times supporting the idea about the early start of Plate Tectonics.  相似文献   

Sulfur and chlorine degassing from primitive arc magmas: temporal changes during the 1982–1983 eruptions of Galunggung (West Java, Indonesia)     

J. C. M. de Hoog  G. W. Koetsier  S. Bronto  T. Sriwana  M. J. van Bergen   《Journal of Volcanology and Geothermal Research》2001,108(1-4)

The 1982–1983 eruptions of Galunggung represent a nine-month period of intermittent volcanic activity with significant changes in explosivity and emission of volatiles. Eruptions started with Vulcanian explosions but changed gradually to Strombolian activity. Compositions of juvenile material changed from basaltic andesite to high-Mg basalt, which are among the most primitive rock types known in the Indonesian arc system. Although bulk compositions suggest a single evolution trend, we infer from the compositions of melt inclusions in olivine phenocrysts that the magmas represent derivatives of a complex spectrum of primary melts. Primitive inclusions in olivine phenocrysts from magma erupted during the Strombolian phase contain up to 2000 ppm sulfur, but concentrations decrease rapidly with increasing SiO₂ down to matrix glass values (50–100 ppm). ‘Vulcanian’ inclusions appear to be degassed before eruption (200 ppm S). Chlorine concentrations increase from 750 to 2200 ppm in Strombolian, and from 800 to 1500 in Vulcanian magmas, whereas matrix glass contains about 1000 ppm in both cases. Ash leachates show two cycles of decreasing S/Cl ratios: from 9.7 to 5.6 at the start of the activity, and from 12.2 to 2.0 after four months. As the second cycle follows upon increased seismic activity at shallow depth, it probably reflects degassing of fresh sulfur-rich magma arriving in the shallow Galunggung reservoir. In contrast to the degassed state of Vulcanian magma, the significant amounts of adsorbed sulfur on the ashes point to an excess source of sulfur, which was most likely derived from intruding Strombolian magma. Hence, the observed sulfur flux of 2 Mt is not in accordance with a petrologic estimate of 0.09 Mt. Using a published value of 550 Mt of erupted material about 0.34 km³ fresh undegassed magma is needed to account for the observed sulfur flux. This is close to the erupted volume of Vulcanian magma (0.26 km³), which presumably was replaced completely by Strombolian magma during the eruption. Using the petrologic method, we calculate a total release of 0.3 Mt chlorine, which agrees well with an output of 0.47 Mt estimated independently from S/Cl ratios of the ash leachates and TOMS sulfur yields. Ash leachates show that about 35% of the sulfur and 30% of the chlorine was scavenged from the eruption plumes. Our results suggest that sulfur and chlorine were largely decoupled during degassing, which resulted in considerable variations in S/Cl ratios during the Galunggung eruptions. We infer that sulfur degassing reflects the arrival of fresh magma at shallow depth, whereas chlorine is largely derived from simultaneously erupted material. As a consequence, the petrologic estimates are more consistent with observed emissions for chlorine than for sulfur.  相似文献   

南岭中西段若干复式花岗岩体的成因模式研究   总被引：6，自引：1，他引：6  

汪传胜汪相  姚晓娟 《岩石矿物学杂志》2004,23(3):203-213

岩石学、岩石地球化学、黑云母矿物化学和副矿物特征等研究表明，南岭中西段3个复式花岗岩体的演化规律表现为两种方式：一种是以花山复式花岗岩体为代表的不同母岩浆演化方式，其补体美华花岗岩可能经历了与花山主体岩浆相似的分离结晶作用；另一种是以金鸡岭复式花岗岩体和大东山复式花岗岩体为代表的相同母岩浆演化方式，它们的补体螃蟹木花岗岩和猪蹄石花岗岩分别为金鸡岭主体和大东山主体花岗质母岩浆经过分离结晶作用形成。两种不同产出方式的补体花岗岩可能表明它们与主体岩浆的形成机制不同。  相似文献   

Commingling and mixing of S-type peraluminous, ultrapotassic and basaltic magmas in the Cayconi volcanic field, Cordillera de Carabaya, SE Peru     

Hamish A Sandeman  Alan H Clark 《Lithos》2004,73(3-4):187-213

The Cayconi district of the Cordillera de Carabaya, SE Peru, exposes a remnant of an upper Oligocene–Lower Miocene (22.2–24.4 Ma) volcanic field, comprising a diverse assemblage of S-type silicic and calc-alkaline basaltic to andesitic flows, members of the Picotani Group of the Central Andean Inner Arc. Basaltic flows containing olivine, plagioclase, clinopyroxene, ilmenite and glass, and glassy rhyolitic agglutinates with phenocrystic quartz, cordierite, plagioclase, sanidine, ilmenite and apatite, respectively exhibit mineralogical and geochemical features characteristic of medium-K mafic and Lachlan S-type silicic lavas. Cordierite-bearing dacitic agglomerates and lavas, however, are characterized by dispersed, melanocratic micro-enclaves and phenocrysts set in a fine-grained quartzo-feldspathic matrix. They contain a bimodal mica population, comprising phlogopite and biotite, as well as complexly zoned, sieve-textured plagioclase grains, sector-zoned cordierite, sanidine, quartz, irregular patches of replaced olivine, clinopyroxene and orthopyroxene and accessory phases including zircon, monazite, ilmenite and chromite. The coexistence of minerals not in mutual equilibrium and the growth/dissolution textures exhibited by plagioclase are features indicative of magmatic commingling and mixing. Trachytic-textured andesite flows interlayered with olivine+plagioclase–glomerophyric, calc-alkaline basalts have a phenocrystic assemblage of resorbed orthopyroxene and plagioclase and exhibit melanocratic groundmass patches of microphenocrystic phlogopite, Ca-rich sanidine, ilmenite and aluminous spinel. The mineralogical and mineral chemical relationships in both the dacites and the trachytic-textured andesites imply subvolcanic mixing between distinct ultrapotassic mafic melts, not represented by exposed rock types, and both the S-type silicic and calc-alkaline mafic magmas. Such mixing relationships are commonly observed in the Oligo-Miocene rocks of the Cordillera de Carabaya, suggesting that the S-type rocks in this area and, by extension, elsewhere derive their unusually high K₂O, Ba, Sr, Cr and Ni concentrations from commingling and mixing with diverse, mantle-derived potassic mafic magmas.  相似文献   

Evidence for Early LREE-enriched Mantle Source Regions: Diverse Magmas from the c. 3{middle dot}0 Ga Mallina Basin, Pilbara Craton, NW Australia     

SMITHIES  R. H.; CHAMPION  D. C.; SUN  S-.S. 《Journal of Petrology》2004,45(8):1515-1537

The c. 2·97–2·95 Ga magmatic history ofthe Mallina Basin, in the Pilbara Craton of NW Australia, includeswhat is perhaps the most lithologically diverse magmatism ofany similar-sized Archaean terrain, and is unusual for similar-sizedterrains of any age. The magmatism includes light rare earthelement (LREE)-rich basaltic rocks, LREE-rich gabbros and rockswith boninite-like compositions (collectively the ‘Mallinamafic suite’), and high-Mg diorites (sanukitoids). TheMallina mafic suite is characterized by high primitive mantlenormalized (La/Nb)_PM (>3) and (La/Yb)_PM (>2), and non-radiogenicNd-isotopic compositions (  相似文献   

The Bjerkreim-Sokndal Layered Intrusion, Rogaland, SW Norway: Evidence from marginal rocks for a jotunite parent magma     

B. Robins  O. Tumyr  M. Tysseland  L. B. Garmann 《Lithos》1997,39(3-4):121-133

The Late-Proterozoic Bjerkreim-Sokndal Layered Intrusion (BKSK) consists of andesine anorthosite, leuconorite, troctolite, norite, gabbronorite, jotunite, mangerite, quartz mangerite and charnockite. The sequence of appearance of cumulus minerals and their compositions suggest a parent magma that was evolved, had plagioclase (±olivine) on the liquidus, was sufficiently TiO₂-rich for hemo-ilmenite to crystallise early, and low in CaO and CaO/Al₂O₃compared to basalts as reflected by the sodic plagioclases and the delayed appearance of cumulus augite. Fine- to medium-grained jotunites found along the northern contact of the BKSK consist of plagioclase (An_45–53), inverted pigeonite (Mg# = 55-50), sparse augite (Mg# = 69-59), Fe-Ti oxides, K-feldspar, quartz and apatite. They are basic to intermediate rocks with relatively high FeO^total, high TiO₂, low MgO/MgO + FeO, moderate Al₂O₃ and low CaO and normative diopside. The jotunites have compositions that are consistent with the parental magma for the lower part of the BKSK Layered Series, and are interpreted as being marginal chills. Similar, but slightly more differentiated, jotunite magmas were subsequently emplaced into the BKSK and the surrounding region as broad dykes and small plutons. Jotunite is a minor rock type in most massif-type anorthosite provinces but may have an important petrological significance.  相似文献   

浙江东南沿海地区中生代火山作用与铅-锌-银的成矿关系          下载免费PDF全文

陈克荣  陈武  魏元柏 《地质找矿论丛》1989,(2):18-27

浙江东南沿海发育的中生代酸-中酸性火山岩,属钙碱性和富钾弱碱性岩系,为同源同熔岩浆结晶分异产物;与火山岩系有关的Pb-Zn-Ag矿床产于流纹质火山-侵入杂岩体中,受火山基底断裂和火山构造的双重控制;矿床中硫主要来源于岩浆,Pb、Zn、Ag主要来源于火山基底岩石,部分来源于岩浆,火山热液形成于次火山期后,成矿早期热液具岩浆水与大气降水混合性质,晚期以大气降水为主.  相似文献   

The central Kenya peralkaline province: Insights into the evolution of peralkaline salic magmas   总被引：1，自引：0，他引：1  

R. Macdonald  B. Scaillet 《Lithos》2006,91(1-4):59-73

The central Kenya peralkaline province comprises five young (< 1 Ma) volcanic complexes dominated by peralkaline trachytes and rhyolites. The geological and geochemical evolution of each complex is described and issues related to the development of peralkalinity in salic magmas are highlighted. The peralkaline trachytes may have formed by fractionation of basaltic magma via metaluminous trachyte and in turn generated pantellerite by the same mechanism. Comenditic rhyolites are thought to have formed by volatile-induced crustal anatexis and may themselves have been parental to pantelleritic melts by crystal fractionation. The rhyolites record very low temperatures of equilibration (≤ 700 °C) at low fO₂ (≤ FMQ). The development of compositional zonation within the magma reservoirs has been ubiquitous, involving up to tens of cubic km of magma at timescales of 10³–10⁴ years. Magma mixing has also been commonplace, sometimes between adjacent centres. Isotopic evidence relating to rates and timescales of pre-eruptive residence times and crystal fractionation processes is summarized.  相似文献   

Trace element characteristics of partial melts produced by melting of metabasalts at high pressures: Constraints on the formation condition of adakitic melts   总被引：13，自引：0，他引：13  

J. Adam    T.H. Green 《中国科学D辑(英文版)》2006,49(9):915-925

Modern adakite, Archean tonalite-trondhjemite- granodiorite (TTG) and adakitic rocks derived from lower continental crust are high Na and Al felsic rocks and are characterized by strong heavy REE and Y de- pletion and high Sr/Y and La/Yb ratios, which sug…  相似文献