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1.
There are two types of temporally and spatially associated intrusions within the Emeishan large igneous province (LIP); namely, small ultramafic subvolcanic sills that host magmatic Cu-Ni-Platinum Group Element (PGE)-bearing sulfide deposits and large mafic layered intrusions that host giant Ti-V magnetite deposits in the Panxi region. However, except for their coeval ages, the genetic relations between the ore-bearing intrusions and extrusive rocks are poorly understood. Phase equilibria analysis (Q-Pl-Ol-Opx-Cpx system) has been carried out to elucidate whether ore-bearing Panzhihua, Xinjie and Limahe intrusions are co-magmatic with the picrites and flood basalts (including high-Ti, low-Ti and alkali basalts), respectively. In this system, the parental magma can be classified as silica-undersaturated olivine basalt and silica-saturated tholeiite. The equivalents of the parental magma of the Xinjie and Limahe peridotites and picrites and low-Ti basalts are silica-undersaturated, whereas the Limahe gabbro-diorites and high-Ti basalts are silica-saturated. In contrast, the Panzhihua intrusion appears to be alkali character. Phase equilibria relations clearly show that the magmas that formed the Panzhihua intrusion and high-Ti basalts cannot be co-magmatic as there is no way to derive one liquid from another by fractional crystallization. On the other hand, the Panzhihua intrusion appears to be related to Permian alkali intrusions in the region, but does not appear to be related to the alkali basalts recognized in the Longzhoushan lava stratigraphy. Comparably, the Limahe intrusion appears to be a genetic relation to the picrites, whereas the Xinjie intrusion may be genetically related to be low-Ti basalts. Additionally, the gabbro-diorites and peridotites of the Limahe intrusion are not co-magmatic, and the former appears to be derived liquid from high-Ti basalts. 相似文献
2.
There are two types of temporally and spatially associated intrusions within the Emeishan large igneous province (LIP); namely, small uitramafic subvolcanic sills that host magmatic Cu-Ni-Platinum Group Element (PGE)-bearing sulfide deposits and large mafic layered intrusions that host giant Ti-V magnetite deposits in the Panxi region. However, except for their coeval ages, the genetic relations between the ore-bearing intrusions and extrusive rocks are poorly understood. Phase equilibria analysis (Q-PI-OI-Opx-Cpx system) has been carried out to elucidate whether ore-bearing Panzhihua, Xinjie and Limahe intrusions are co-magmatic with the picrites and flood basalts (including high-Ti, low-Ti and alkali basalts), respectively. In this system, the parental magma can be classified as silica-undersaturated olivine basalt and silica-saturated tholeiite. The equivalents of the parental magma of the Xinjie and Limahe peridotites and picrites and iow-Ti basalts are silica-undersaturated, whereas the Limahe gabbro-diorites and high-Ti basalts are silica-saturated. In contrast, the Panzhihua intrusion appears to be alkali character. Phase equilibria relations clearly show that the magmas that formed the Panzhihua intrusion and high-Ti basalts cannot be co-magmatic as there is no way to derive one liquid from another by fractional crystallization. On the other hand, the Panzhihua intrusion appears to be related to Permian alkali intrusions in the region, but does not appear to be related to the alkali basalts recognized in the Longzhoushan lava stratigraphy. Comparably, the Limabe intrusion appears to be a genetic relation to the picrites, whereas the Xinjie intrusion may be genetically related to be low-Ti basaits. Additionally, the gabbro-diorites and peridotites of the Limahe intrusion are not co-magmatic, and the former appears to be derived liquid from high-Ti basalts. 相似文献
3.
《International Geology Review》2012,54(3):270-289
The Hongshishan mafic–ultramafic intrusion (SIMS zircon U–Pb age 286.4 ± 2.8 Ma) consists of dunite, clinopyroxene peridotite, troctolite, and gabbro. Major elements display systematic correlations. Trace elements have identical distribution patterns, including flat rare-earth element (REE) patterns with positive Eu anomalies and enrichments in large ion lithophile elements (LILE) but depletions in Nb and Ta, indicating fractional crystallization as a key factor in magmatic evolution. Petrologic and geochemical variations in drill core samples demonstrate that minor assimilation and progressive magma injections were closely associated with Ni–Cu mineralization. Mass balance estimates and Sr–Nd isotopes reveal that the Hongshishan parental magmas were high-Mg and low-Ti tholeiitic basalts and were derived from a lithospheric mantle source that had been modified by subducted slab metasomatism before partial melting. Southward subduction of the Palaeo-Tianshan–Junggar Ocean is further constrained by a compilation of inferred, subduction-induced modifications of mantle sources in mafic–ultramafic intrusions distributed in the eastern Tianshan–Beishan area. Integrating the regional positive ?Nd(t) granites, high-Mg and low-Ti basaltic magmas (mafic–ultramafic intrusions), and slightly later high-Ti basalts in NW China suggests that their petrogenesis could be attributed to Permian mantle plume activities. 相似文献
4.
5.
秦岭早中生代壳幔岩浆混合作用——来自东江口花岗岩体闪长质包体的地球化学证据 总被引：3，自引：0，他引：3
东江口花岗岩及闪长质包体分别获得了218 Ma 和224 Ma 的形成年龄,闪长质包体中存在岩浆不平衡结构并发育与寄
主花岗岩相同的钾长石斑晶及淬冷形成的针状磷灰石,揭示了花岗岩形成过程中曾发生二元岩浆混合作用。这种混合作用
已造成寄主花岗岩和闪长质包体化学组成的趋同,同时使得它们的Sr-Nd-Pb 同位素组成发生强烈均一化。但暗色闪长质包
体锆石具有较宽的εHf（t ）值（-4.58~3.31）,保留了二端元岩浆源区的特征。秦岭早中生代同期闪长质包体锆石εHf（t ）＞
10 及寄主花岗岩锆石εHf（t ）＜ -10 的差异表明,它们分别来自相对亏损地幔源区和中元古代滞留于地壳的幔源基性物质,
而两个源区的岩浆,自224 Ma 以来发生强烈混合作用,形成大规模的壳幔混合花岗岩体。 相似文献
6.
The Potato River intrusion is a Keweenawan (1100 Ma) mafic plutonemplaced in Keweenawan volcanics and earlier Proterozoic metasedimentaryrocks along the southeastern flank of the Lake Superior syncline.It comprises the following lithostratigraphic zones: a thinto absent Border zone of altered olivine gabbro; a Lower zoneof olivine gabbro; a Picritic zone of picrite and troctolite;a Middle zone of olivine gabbro and leucogabbro; an Upper zoneof quartz leucogabbro and ferrogabbro; and a Roof zone of granophyricand granitic rocks. Fractional crystallization is evident fromcompositional changes in the rocks and cumulus minerals withstratigraphic height. Elements concentrated in the cumulus mineralsolivine and plagioclase (Mg, Fe2+, Al, Ca, Ni, Co, Cr, Sr) decreasewith height; elements concentrated in the trapped liquid (Na,K, La, Y, Zr, Nb, Rb, Ba) increase with height; and other elements(Ti, Fe3+, P, Ga, V, Sc, Cu, Zn) show complicated behavior relatedto the appearance of additional cumulus phases such as clinopyroxene,Fe-Ti oxides, and apatite. Lower zone rocks contain some sulfide,probably from sulfur derived from the country rock, and theUpper zone has sulfides probably precipitated from an immisciblesulfide liquid. The sulfide-bearing rocks have similaritiesto those of other intrusions, such as Bushveld, Stillwater,and Skaergaard. The picritic and troctolitic rocks of the Picritic zone indicatethat the intrusion was open to additional injections of maficmagma. Roof zone granophyric rocks are residual liquids intrudedalong the upper margin of the intrusion during regional tilting,but Roof zone granitic rocks are probably melted country rock.An attempt is made to estimate by reverse stratigraphic summationthe compositional path of the magma that solidified above thePicritic zone. The first compositions are highly aluminous,which suggests that the upper part of the intrusion has beenenriched in plagioclase by convection-aided crystal sorting.A complementary unit of mafic rocks is not exposed, but it couldbe present down dip. Some of the later compositions are similarto typical Keweenawan high-Al tholeiites. The magma did notundergo extreme iron enrichment, probably because of oxygenfugacity buffering. 相似文献
7.
Isotopic evidence for multiple contributions to felsic magma chambers: Gouldsboro Granite, Coastal Maine 总被引：1，自引：0，他引：1
The Gouldsboro Granite forms part of the Coastal Maine Magmatic Province, a region characterized by granitic plutons that are intimately linked temporally and petrogenetically with abundant co-existing mafic magmas. The pluton is complex and preserves a felsic magma chamber underlain by contemporaneous mafic magmas; the transition between the two now preserved as a zone of chilled mafic sheets and pillows in granite. Mafic components have highly variably isotopic compositions as a result of contamination either at depth or following injection into the magma chamber. Intermediate dikes with identical isotopic compositions to more mafic dikes suggest that closed system fractionation may be occurring in deeper level chambers prior to injection to shallower levels. The granitic portion of the pluton has the highest Nd isotopic composition (εNd = + 3.0) of plutons in the region whereas the mafic lithologies have Nd isotopic compositions (εNd = + 3.5) that are the lowest in the region and similar to the granite and suggestive of prolonged interactions and homogenization of the two components. Sr and Nd isotopic data for felsic enclaves are inconsistent with previously suggested models of diffusional exchange between the contemporaneous mafic magmas and the host granite to explain highly variable alkali contents. The felsic enclaves have relatively low Nd isotopic compositions (εNd = + 2 – + 1) indicative of the involvement of a third, lower εNd melt during granite petrogenesis, perhaps represented by pristine granitic dikes contemporaneous with the nearby Pleasant Bay Layered Intrusion. The dikes at Pleasant Bay and the felsic enclaves at Gouldsboro likely represent remnants of the silicic magmas that originally fed and replenished the overlying granitic magma chambers. The large isotopic (and chemical) contrasts between the enclaves and granitic dikes and granitic magmas may be in part a consequence of extended interactions between the granitic magmas and co-existing mafic magmas by mixing, mingling and diffusion. Alternatively, the granitic magmas may represent an additional crustal source. Using granitic rocks such as these with abundant evidence for interactions with mafic magmas complicate their use in constraining crustal sources and tectonic settings. Fine-grained dike rocks may provide more meaningful information, but must be used with caution as these may also have experienced compositional changes during mafic–felsic interactions. 相似文献
8.
The role of crustal fertility in the generation of large silicic magmatic systems triggered by intrusion of mantle magma in the deep crust 总被引：1，自引：0，他引：1
S. Sinigoi J. E. Quick G. Demarchi U. Klötzli 《Contributions to Mineralogy and Petrology》2011,162(4):691-707
The Sesia magmatic system of northwest Italy allows direct study of the links between silicic plutonism and volcanism in the
upper crust and the coeval interaction of mafic intrusions with the deep crust. In this paper, we focus on the chemical stratigraphy
of the pre-intrusion crust, which can be inferred from the compositions of crustal-contaminated mafic plutonic rocks, restitic
crustal material incorporated by the complex, and granitic rocks crystallized from anatectic melts. These data sources independently
indicate that the crust was compositionally stratified prior to the intrusion of an 8-km-thick gabbroic to dioritic body known
as the Mafic Complex, with mica and K-feldspar abundance decreasing with depth and increasing metamorphic grade. Reconsideration
of published zircon age data suggest that the igneous evolution initiated with sporadic pulses at around 295 Ma, when mafic
sills intruded deep granulites which provided a minor amount of depleted crustal contaminant, very poor in LIL elements. With
accelerated rates of the intrusion, between 292 and 286 m.y, mafic magmas invaded significantly more fertile, amphibolite-facies
paragneisses, resulting in increased contamination and generating hybrid rocks with distinct chemistry. At this point, increased
anatexis produced a large amount of silicic hybrid melts that fed the incremental growth of upper-crustal plutons and volcanic
activity, while the disaggregated restite was largely assimilated once ingested by the growing Mafic Complex. This “igneous
climax” was coincident with an increasing rate of intrusion, when the upper Mafic Complex began growing according to the “gabbro
glacier” model and, at about the same time, volcanic activity initiated. Cooling lasted millions of years. In the coupled
magmatic evolution of the deep and upper crust, the Mafic Complex should be considered more as a large reservoir of heat rather
than a source of upper-crustal magma, while the fertility of “under/intra-plated” crust plays a crucial role in governing
the generation of large volumes of continental silicic magmas. 相似文献
9.
冈底斯带西段那木如岩体始新世岩浆作用及构造意义 总被引：8，自引：4，他引：4
冈底斯带西段狮泉河南部那木如岩体岩性变化较大,其中产出大量基性岩透镜体及暗色微细粒包体,空间上与花岗岩类呈渐变过渡接触关系。本文在详细野外调研的基础上,对狮泉河-札达一带那木如花岗岩及其中基性岩石进行了系统的岩石学、地球化学和同位素年代学研究。结果表明,那木如岩体主体岩性为黑云母花岗岩,其SiO2为65%~76%,全碱含量较高,花岗岩中K2O+Na2O=5.50%~8.71%,基性岩石中则4.42%~6.7%。花岗岩类稀土元素最高含量为284.8×10-6,最低只有105.4×10-6;而基性岩类最高为120.4×10-6,最低72.48×10-6。两者稀土元素分配曲线均呈右倾平缓样式,花岗岩具有不明显Eu负异常,微量元素显示出花岗岩类和基性岩类具有相似的蛛网分布样式。两者均明显富K而亏损Nb、Ti等不活泼的HFS元素,显示出明显的岩浆混合作用趋势。4件花岗岩和基性岩样品所显示的LA-ICP-MS法锆石U-Pb年龄分别为46.11±0.78Ma、45.47±0.4Ma、46.7±2.9Ma和45.4±1.4Ma,变化在45.4~46.7Ma范围内,表明始新世早期(~46Ma)区域发生了岩浆混合作用。这一时限与冈底斯中、东部岩浆作用时代(40~52Ma)非常一致,表明始新世早期整个冈底斯发生了规模巨大的岩浆事件,暗示着印度-欧亚大陆碰撞作用在东西方向上所表现出的同时性。 相似文献
10.
新疆喀拉通克铜镍矿镁铁质岩体形成时代、成矿特征与深部找矿前景 总被引：1，自引：1，他引：0
喀拉通克镁铁质岩体群位于准噶尔地块东北缘,由13个小岩体组成。在以往的研究中,这些岩体多被视为同期形成。笔者新获得的锆石SHRIMP U-Pb年龄显示,镁铁质岩体群发育晚石炭世和早二叠世2个时期的岩体,其中Y3岩体闪长岩、苏长岩以及G21岩体淡色辉长岩的年龄分别为290 Ma、283 Ma和281 Ma,与Y1和Y9含矿岩体的年龄在误差范围内一致;Y5岩体辉长岩和闪长岩的年龄均为320 Ma,明显早于其他岩体。结合区域构造演化资料分析,晚石炭世Y5岩体是俯冲环境下岩浆作用的产物,这与以往研究较多的早二叠世后碰撞伸展环境下形成的岩体不同。在该矿区,具有工业价值的硫化物矿体主要赋存在Y1~Y3以及Y9岩体中,其中Y1和Y9岩体中富硫化物的矿体主要分布在岩体中部,而Y2和Y3岩体中矿体主要分布在底部的苏长岩中,在Y1-Y2以及Y2-Y3岩体结合部位均可见块状矿体。矿体空间分布及其与通道对应关系显示镁铁质含矿岩体可能形成于不同的岩浆通道系统或通道的不同部位。矿物学变化显示Y3、Y9和G21演化程度相对高于Y1和Y2岩体;同时,前者硫化物矿石多为中等稀疏浸染状和星点状,后者多为稠密浸染状和块状矿石,且前者浸染状矿石的Ni/Cu比值(0.15~2.00)总体小于后者(0.14~4.48)。上述特征表明含矿岩体的岩浆相对演化程度与矿化富集程度有一定的关系。综合分析地质、物探资料以及成矿特征,笔者认为Y1-Y3岩体深部仍具有寻找成矿岩体的潜力。G21岩体的演化程度较高,但具有与Y2、Y3岩体相似的重力异常和源区性质,推测该地段深部可能存在体积更大的岩体。 相似文献
11.
Peter J. Michael 《Contributions to Mineralogy and Petrology》1991,108(4):396-418
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. 相似文献
12.
Lars Peter Salmonsen Christian Tegner 《Contributions to Mineralogy and Petrology》2013,165(6):1155-1171
Although it is one of the best-studied layered mafic intrusions in the world, the crystallization sequence of the Skaergaard Intrusion, east Greenland, remains in debate. In particular, it has been argued that the crystallization sequence in the Upper Border Series, which crystallized downwards from the roof of the magma chamber, differs from that in the Layered Series formed at the floor. The proposed deviation would require chemical stratification of the magma, and a reexamination of the crystallization sequence therefore has important implications for understanding the dynamics of the system. Here, we examine a new sample set from the Upper Border Series, combining field observations, petrography and anorthite contents of plagioclase with bulk rock Ti, V, P, Cu and Mn concentrations. We demonstrate that the first phases on the liquidus were plagioclase and olivine followed by augite, then ilmenite and magnetite (simultaneously), sulfides, apatite and finally ferrobustamite (now inverted to hedenbergite). This crystallization sequence represents extreme differentiation along the tholeiitic trend, and it mirrors those at the floor (Layered Series) and walls (Marginal Border Series). We therefore propose a revised subdivision of the Upper Border Series into equivalents of the subzones in the Layered Series denoted by apostrophes (LZa′, LZb′, etc.). Moreover, the first appearance of each of the cumulus phases occurs at similar plagioclase core anorthite contents. The mirror images of the crystallization sequences and the anorthite contents of plagioclase cores in the three series imply that the Skaergaard magma chamber solidified by in situ crystallization along the floor, walls and roof from one, largely homogenous, convecting magma body. 相似文献
13.
The Paleoproterozoic Kauhajärvi gabbro is one of several Fe-, Ti-, and P-rich mafic intrusions associated with granitoids in the Fennoscandian shield in western Finland. The gabbro is cut by the late-orogenic Lauhanvuori granite (ca.1870?Ma), whereas the surrounding area is composed of synorogenic, collision-related granitoids and calc-alkaline volcanic rocks (ca. 1890?Ma) belonging to the Mid Finland Granitoid Complex. The mafic intrusions were probably emplaced into a Svecofennian rift zone. They are characterized by a high phosphorus content; the common occurrence of ilmenite as separate grains; and the coeval crystallization of apatite, Fe-Ti oxides, and Fe-Mg silicates. The Kauhajärvi gabbro is composed of two geochemically and structurally distinct zones. The basal zone is composed of poorly-layered, fine- to medium-grained gabbro, which represents an early intrusion of tholeiitic magma, and has rather high concentrations of chromium, magnesium and silica. Typically, the concentrations of iron, titanium and phosphorus are low, except for the top that is enriched in apatite and ilmenite. During most of the crystal-liquid fractionation of the basal zone magma, low f O2 limited the crystallization of Fe-Ti-oxides. Instead, titanium became enriched in the uppermost layer of the basal zone. The main zone represents a later injection of more evolved tholeiitic magma and makes up 80 to 90%of the total intrusion volume. Peridotite is common, along with gabbro and gabbronorite, in the lower and middle parts of the main zone, and anorthosite is common near the top of the main zone. The Mg:Fe ratio in mafic minerals and vanadium concentrations in magnetite decrease upwards. The variation within the main zone can be explained by crystal-liquid fractionation of a single batch of a parental magma under conditions of relatively high f O2. Titanium is not progressively enriched. The ratio of titanium to iron (TiO2/Fe2O3 = 0.16 to 0.20; Fe total as Fe2O3) is constant in the main zone and normal for mafic intrusions. Titanium is sited in separate ilmenite grains and in lamella within ilmenomagnetite (Ti-bearing magnetite). The high phosphorus content in the main zone is interpreted to result in crystallization of ilmenite and ilmenomagnetite instead of Ti-rich magnetite under relatively high f O2 conditions. High concentrations of titanium, iron and phosphorus in rocks of the main zone can be explained by pre-emplacement crystal-melt fractionation in a deep magma reservoir and/or contamination of mantle-derived mafic magmas by granitic magmas from partial melting of crustal rocks. A low-grade Fe-Ti-P resource at Kauhajärvi consists of layers with as much as 20 wt. % combined ilmenite (usually 8 to 11 wt. %), apatite (1 to 8 wt. %) and magnetite (1 to 9 wt. %). Mineralized layers are of variable thickness (2?m to 30?m) and occur in variable host rocks (peridotite or gabbro). The Fe-Ti oxides are most abundant in peridotite and pyroxene- or olivine-rich gabbronorite within the main zone. The contact between mineralized rocks (4%TiO2) and non- or slightly-mineralized rocks is gradual. The deposit as a whole consists of three to five mineralized layers with maximum combined thickness of 70?m. Apatite is most abundant in the oxide-rich layers, but is locally also concentrated in anorthosite with low Fe-Ti oxide contents. The weight ratio of ilmenite to magnetite is 3:2. The ratio of total Ti-Fe-oxides to apatite averages 4.0, with the range of 1.5 to >15. 相似文献
14.
Felsic alkalic rocks are a minor component of many ocean island volcanic suites, and include trachyte and phonolite as well as various types of alkaline and peralkaline rhyolite. However, there is considerable debate on the nature of their formation; for example, are they formed by partial melting of anomalous mantle or the final products of fractional crystallization of mafic magmas. The phonolites and foidal phonolites on Rarotonga were formed by low pressure crystal fractionation of two chemically distinct parental magmas. Low silica and high silica mafic magmas produced a basanite-foidal phonolite series and an alkali basalt-phonolite series, respectively. The foidal phonolite composition evolved from the low silica mafic magmas by approximately 60% fractionation of titanaugite + leucite + nepheline + magnetite + apatite. Fractionation continued with the crystallization of aegirine-augite + nepheline + kaersutite + magnetite + apatite. The phonolites formed from the alkali basalts by approximately 40% fractionation of kaersutite + titanaugite + Fe-Ti oxide + plagioclase + apatite and continued to evolve further by fractionation of anorthoclase + nepheline + aegerine-augite + Fe-Ti oxides. As the magmas fractionated in both suites, their overall viscosities (solid + liquid) increased until a point was reached whereby viscosity inhibited the eruption of magmas with compositions intermediate between the mafic rocks and the felsic rocks. However, the magmas continued to fractionate under static conditions with the residual fluid becoming foidal phonolitic in the low silica suite or phonolitic in the high silica suite. These phonolitic liquids, as a result of an increase in volatiles and enrichment of alkalis over aluminum, would actually have a lower viscosity than the intermediate liquids. This decrease in viscosity and the switch from a magma chamber being predominantly a liquid with suspended solids to a solid crystalline network with an interstitial liquid enabled phonolitic liquids to migrate, pool, and eventually erupt on the surface. 相似文献
15.
Cihai and Cinan are Permian magnetite deposits related to mafic-ultramafic intrusions in the Beishan region, Xinjiang, NW China. The Cihai mafic intrusion is dominantly composed of dolerite, gabbro and fine-grained massive magnetite ore, while gabbro, pyrrhotite + pyrite-bearing clinopyroxenite and magnetite ore comprise the major units in Cinan. Clinopyroxene occurs in both deposits as 0.1–2 mm in diameter subhedral to anhedral grains in dolerite, gabbro and clinopyroxenite. High FeO contents (11.7–28.9 wt%), low SiO2 (43.6–54.3 wt%) and Al2O3 contents (0.15–6.08 wt%), and low total REE and trace element contents of clinopyroxene in the Cinan clinopyroxenite imply crystallization early, at high pressure. This clinopyroxene is FeO-rich and Si and Ti-poor, consistent with the clinopyroxene component of large-scale Cu-Ni sulfide deposits in the Eastern Tianshan and Panxi ares, as well as Tarim mafic intrusion and basalt, implying the Cinan mafic intrusion and sulfide is related to tectonic activity in the Tarim LIP. The similar mineral chemistry of clinopyroxene, apatite and magnetite in the Cihai and Cinan gabbros (e.g., depleted LREE, negative Zr, Hf, Nb and Ta anomalies in clinopyroxene, lack of Eu anomaly in apatite and similarity of oxygen fugacity as indicated by V in magnetite), indicate similar parental magmatic characteristics. Mineral compositions suggest a crystallization sequence of clinopyroxenite/with a small amount of sulfide – gabbro – magnetite ore in the Cinan deposit, and magnetite ore – gabbro – dolerite in Cihai. The basaltic magma was emplaced at depth, with magnetite segregation (and formation of the Cinan magnetite ores) occurring in relatively low fO2 conditions, after clinopyroxenite and gabbro fractional crystallization. The evolved Fe-rich basaltic magma rapidly rose to intermediate or shallow depths, forming an immiscible Fe-Ti oxide magma as fO2 increased and leaving a Fe-poor residual magma in the chamber. The residual magmas was emplaced at different levels in the crust, forming the Cihai gabbro and dolerite, respectively. Finally, the immiscible Fe-Ti oxide magma was emplaced into the earlier formed dolerite because of late magma pulse uplift, resulting in a distinct boundary between the magnetite ores and dolerite. 相似文献
16.
Evolution of the Kap Edvard Holm Complex: a Mafic Intrusion at a Rifted Continental Margin 总被引：1，自引：0，他引：1
The Kap Edvard Holm Layered Series forms part of the East GreenlandTertiary Province, and was emplaced at shallow crustal level(at depths corresponding to a pressure of 1–2 kbar) duringcontinental break-up. It consists of two suites: a gabbro suitecomprising olivine and oxide gabbros, leucocratic olivine gabbrosand anorthosites, and a suite of wehrlites that formed fromthe intrusion of the gabbros during their solidification bya hydrous, high-MgO magma. Ion microprobe analyses of clinopyroxenereveal chemical contrasts between the parental melt of the wehrlitesuite and that of the gabbro suite. Thin sills (1–2 mthick) of the wehrlite suite, however, have clinopyroxene compositionssimilar to the gabbro suite, and were formed by interactionwith interstitial melts from the host layered gabbros. All evolvedmembers of the gabbro suite have elevated Nd, Zr and Sr concentrationsand Nd/Yb ratios, relative to the melt parental to the gabbrosuite. These characteristics are attributed to establishmentof a magma chamber at depths corresponding to a pressure of10 kbar, where melts evolved before injection into the low-pressuremagma chamber. Anorthosites of the gabbro suite are believedto have crystallized from such injections. The melts becamesupersaturated in plagioclase by the pressure release that followedtransportation to the low-pressure magma chamber after initialfractionation at 10 kbar. The most evolved gabbros formed bysubsequent fractionation within the low-pressure magma chamber.Our results indicate that high-pressure fractionation may beimportant in generating some of the lithological variationsin layered intrusions. KEY WORDS: fractionation; ion microprobe; layered intrusions; rift processes; trace elements
*Corresponding author. 相似文献
17.
含矿与无矿侵入体的区分是阐明岩浆型矿床成因的基础,也是深部找矿预测的依据。本文选择四川米易青皮村岩体为例,通过岩相学及矿物成分剖面和定量化结构分析,试图阐明无矿岩浆侵入体的固结过程,并与攀枝花含矿岩体对比,进一步揭示含矿与无矿侵入体形成过程的区别。岩相学分析表明,青皮村岩体中粒辉长岩的造岩矿物可以划分为四个世代：①粗粒斜长石→②中粒斜长石+单斜辉石→③黑云母+铁钛氧化物→④伟晶状斜长石,展示了封闭系统的固结过程。加上粗晶辉长岩脉的矿物组合钠长石+单斜辉石+角闪石+磷灰石,可以将青皮村岩体的组成矿物划分为5个世代,进而划分成四个晶体群：通道晶体群、岩浆房晶体群、基质晶体群和流体晶体群。晶体成分剖面分析表明,通道晶和岩浆房晶显示正环带,具有封闭系统降温结晶的特点,其中通道晶的生长伴随着减压作用;基质晶初始为正环带,末期显示反环带,反映了残余流体的聚集与逃逸;而流体晶体群的产出则反映了超临界流体的相分离和排气作用。定量化结构分析揭示了岩浆固结晚期的粗化过程,是封闭岩浆系统固结过程的重要证据,与岩相学和晶体成分剖面分析结果一致。此外,青皮村岩体中Fe Ti氧化物含量甚低,其体积分数仅为4%,暗示它们不可能聚集成矿。与攀枝花岩体相比,青皮村岩体固结过程中缺失先存晶体的溶蚀结构,后者被认为是高温含矿流体输入的结果。据此,本文提出,外来含矿流体(透岩浆流体)输入与否决定了镁铁质岩浆侵入体的产矿能力;进而认为,是流体输入导致了岩浆分异,而不是岩浆分异产生了含矿流体。 相似文献
18.
Erik H. Erikson Jr. 《Contributions to Mineralogy and Petrology》1977,60(2):183-207
The Mount Stuart batholith is a Late Cretaceous calc-alkaline pluton composed of rocks ranging in composition from two-pyroxene gabbro to granite. Quartz diorite is most abundant. This batholith may represent the plutonic counterpart of the high-alumina basalt association. A petrogenetic model is developed in which this intrusive series evolved from one batch of magnesian high-alumina basalt, represented by the oldest intrusive phase, by successive crystal fractionation of ascending residual magma. However, the possibility that this intrusive suite originated from an andésite (quartz diorite) parent by fractionation cannot be excluded.Computer modeling of this intrusive sequence provides a quantitative evaluation of the sequential change of magma composition. These calculations clearly indicate that the igneous suite is consanguineous, and that subtraction of early-formed crystals from the oldest rock is capable of reproducing the entire magma series with a remainder of 2–3% granitic liquid. This model requires that large amounts of gabbroic cumulate remain hidden at depth- an amount equal to approximately 8–10X the volume of the exposed batholith. Mass balances between the amounts of cumulate and residual liquid calculated compare favorably with the observed amounts of intermediate rocks exposed in the batholith, but not with the mafic rocks.Mafic magmas probably fractionated at depth by crystal settling, whereas younger quartz diorite and more granitic magmas underwent inward crystallization producing gradationally zoned plutons exposed at present erosional levels. 相似文献
19.
新疆北部幔源岩浆矿床的类型、时空分布及成矿谱系 总被引：6，自引：1，他引：5
新疆北部与幔源岩浆有关的矿床种类齐全,成矿环境复杂,时代和类型繁多,在中国乃至世界颇具特色。主要矿床类型包括铬铁矿矿床、钒钛磁铁矿矿床、铜镍硫化物矿床、铂族元素(PGE)矿床、铜镍-钒钛铁复合型矿床、含钴磁铁矿矿床、玄武岩自然铜矿床、热液型钴-多金属矿床,以及非金属矿床等。按照含矿地质体的类型,可分为6种类型:蛇绿岩型、层状杂岩型、小侵入体型、阿拉斯加型、浅成岩型和喷出岩型。这些幔源岩浆矿床可划分为3个成岩成矿系列:铜镍系列、钛铁系列和铬铁系列。钛铁系列以碱性层状岩体型钒钛磁铁矿、铁磷矿为代表,岩石具有明显的富Fe特征,属于碱性富铁质的高钛玄武岩系列;铜镍系列以小侵入体型铜镍矿、阿拉斯加型铜镍-PGE矿为代表,岩石属于铁质的拉斑玄武岩-钙碱性系列;铬铁系列主要为蛇绿岩型铬铁矿,岩石具富Mg贫Fe特征,属于镁质系列。3个系列的岩浆都具有亏损地幔源特征,可能都与地幔柱活动有关;岩浆源区富含相应的成矿元素,是形成3个系列矿床相应成矿地质体的主要条件。3个系列矿床的成矿机制可分为深部熔离/岩浆分异、就地分凝、矿浆贯入、岩浆热液等过程。根据各系列矿床之间存在的紧密联系,建立了与幔源岩浆作用有关的3个系列矿床综合模式: 亏损地幔部分熔融产生的幔源岩浆在上升过程中发生熔离/分异,分离为3个系列,由于外部物质加入在地壳深部发生分异和熔离,在不同深度富集形成铬铁矿、钒钛磁铁矿和铜镍硫化物矿床,临近地表时流体富集和分离成含矿流体,分别形成浅成岩型磁铁矿和喷出岩型自然铜矿。新疆北部各类幔源岩浆矿床从早到晚主要产于3期构造阶段/构造类型: 大陆裂解期、板块俯冲期、碰撞/后碰撞造山期(又分3个阶段: 碰撞后伸展阶段、幔柱叠加造山阶段、后碰撞结束阶段)。 相似文献
20.
寄主岩浆硫化物和氧化物矿床的镁铁质-超镁铁质岩体对比分析与成矿过程评述 总被引：4，自引：2，他引：2
镁铁质-超镁铁质岩体是世界上岩浆硫化物(Ni-Cu-PGE)和氧化物(Fe-Ti-V-P)矿床的主要载体.全球主要岩浆硫化物和氧化物矿床均可以产于大火成岩省、克拉通区的裂谷带或伸展环境、褶皱带内的后碰撞伸展环境.寄主岩浆硫化物矿床的岩体规模相差甚大(从6×104km2到＜0.1km2),既有超镁铁质岩石组合也有镁铁质岩石组合,但其原生岩浆主要为拉斑玄武质岩浆.含镍铜的铂族元素矿床主要赋存于规模很大的层状岩体中,而镍铜硫化物矿床主要赋存于小岩体中.寄主钒钛磁铁矿或磁铁矿矿床的岩体主要是以辉长岩为主的层状杂岩体.寄主钛铁矿-磷灰石矿床的岩体均为层状的斜长岩-纹长二长岩-紫苏花岗岩岩体.尽管其岩石组合相差很大,但其原生岩浆均属拉斑玄武质.寄主硫化物矿床的岩体相对富Si、Mg、Cr、Ni,而寄主氧化物矿床的岩体相对富Fe-Ti-P-V,造岩矿物晶体化学也反映了这种差异.对全球主要含矿岩体的对比分析表明,导致这种反差的主要控制因素应该是岩浆生成时的压力状态,源区性质和熔融程度的差异可能只在局部范围内起作用.对岩浆硫化物矿床成矿过程的认识集中体现在金川模式和岩浆通道模式上,对岩浆氧化物矿床成矿过程的认识体现在氧化物和磷灰石是堆晶相还是从不混溶的矿浆中结晶的.对比分析表明,成矿过程具有多样性,试图用一种模式概括所有同类矿床成矿过程的想法未必可取.毫无疑问,适宜的氧化还原环境是形成岩浆矿床的必要务件,伴随岩浆演化及成矿过程的氧速度变化及其诱因问题尚待进一步探索. 相似文献