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湖北省地矿局鄂东北地质大队在大洪山地区进行金刚石地质找矿工作中,首次发现原生金刚石新源岩——钾镁煌斑岩.现已基本查明:新发现的钾镁煌斑岩体地处扬于准地台北部边缘,北部襄樊—广济深断裂,深断裂北部为秦岭地槽褶皱系,其地质环境与澳大利亚西部钾镁煌斑岩所处地质环境相似.岩体大都单独产出,仅个别呈复合体,其形态以脉状、似层状为主,可见分枝分叉现象.岩体一般长几十米至几百米,最长可达一千五百米,宽几米至几十米,最宽为一百五十米.钾 相似文献
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何松 《吉林大学学报(地球科学版)》1988,(4)
湖北省地矿局鄂东北地质大队在大洪山区进行金刚石地质找矿工作中,首次发现寻找金刚石新源岩——钾镁煌斑岩。 新发现的钾镁煌斑岩体地处扬子准地台北部边缘,北邻襄樊——广济深断裂,深断裂北部为秦岭地槽褶皱系,是老活动带,其地质环境与澳大利亚西部钾镁煌斑岩所处地质环境相似。岩体大都单独产出,仅个别呈复合体,其形态以脉状、似层状为主,可见分枝分叉现象。岩体一般长几十米至几百米,最长可达1500m。宽几米至几十米,最宽为150m。钾镁煌斑岩呈灰绿色,深灰色或黄灰色,风化后呈黄褐色,细粒斑状结构,块状构造、角砾状构造。岩石斑晶主要由橄榄石(假象)、辉石、黑云母、金云母、白榴石(假象)等矿物组成。基质及副矿物由透辉石、蚀变橄榄石、蚀变白榴石、镁 相似文献
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宋新宇 《矿物岩石地球化学通报》1993,(3)
老王寨金矿发现于80年代初,探明储量已达特大型金矿床规模。 1.矿床地质特征矿床位于哀牢山西部的浅变质地层中,构造上属唐古拉—兰坪—思茅褶皱系的墨红—绿春褶皱带。矿区靠近九甲—墨江断裂。矿区地层划分为泥盆系、石炭系和二叠系,为一套低绿片岩相变质的火山-沉积岩系,包括绢云板岩、变质石英杂砂岩、泥质灰岩和硅质岩。区内岩浆岩特别发育,主要有辉橄岩、玄武岩、辉长岩。煌斑岩脉非常多,且多为容矿岩石。其它脉岩还有花岗斑岩和石英斑岩。 相似文献
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云南普朗斑岩型铜矿田构造岩相成矿规律与控矿特征 总被引：2，自引：0，他引：2
云南西北部格咱岛弧是西南“三江”古特提斯阶段形成的重要地质构造单元,位于扬子西缘义敦岛弧带的南端。近年来新发现了包括普朗超大型斑岩型铜矿,红山-红牛、雪鸡坪大型和10余个中小型斑岩夕卡岩型铜矿床,成为斑岩型铜矿田和铜资源勘查开发基地。研究发现,矿田中矿床的形成与大地构造演化密切对应,不同阶段发育不同的矿床;对应于构造演化产生的区域北西向主干断裂控制岩带的展布,次级断裂及褶皱联合控制了岩体的形态和产状,斑岩型矿床主要产于背斜核部,其含矿斑岩侵位较浅,夕卡岩型铜矿主要产于向斜核部,含矿斑岩侵位相对较深;含矿斑岩多为复式岩体,顶部往往有火山岩岩盖,表明火山岩浆活动具有继承性的特征,普朗铜矿产于北西、北东东向两组断裂的交汇部位,形成岩体内斑岩铜(钼)矿、接触带夕卡岩铜矿和围岩中的大脉状铜矿“三位一体”的斑岩成矿系统,并在外带发育铅锌矿和浅成低温热液金(银)矿床。 相似文献
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新疆土屋斑岩铜矿床火山-侵入杂岩体、 成矿岩石及其蚀变 总被引：3，自引：1，他引：2
土屋斑岩铜矿床位于新疆东天山晚古生代大南湖-头苏泉岛弧中.矿区出露地层为石炭系企鹅山群火山-沉积岩.文章提出矿区出露的火山-沉积岩以及浅成侵入岩为一火山-侵入杂岩体,发育2个旋回4个岩相:第一旋回包括溢流相玄武岩和安山岩、爆发相集块角砾熔岩和爆发-沉积相凝灰岩;第二旋回包括次火山相闪长玢岩和玄武玢岩.斜长花岗斑岩侵入到火山机构断裂系中.矿体赋存于斜长花岗斑岩和闪长玢岩中.斜长花岗斑岩为成矿斑岩,次火山岩相闪长玢岩为容矿岩石,火山岩为围岩.土屋斑岩铜矿床可分为前成矿期和主成矿期.前成矿期形成于火山活动的晚期,发育青磐岩化;主成矿期形成于斜长花岗斑岩侵位时期,发育钾硅酸盐蚀变、绿泥石-绢云母蚀变和黄铁绢英岩化蚀变及与之有关的矿化,形成了土屋斑岩型矿化的主体.矿化阶段包括钾硅酸盐阶段、绿泥石-绢云母阶段和黄铁绢英岩化阶段等. 相似文献
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《中国煤炭地质》2020,(6)
以大同煤田中塔山井田、马道头井田和小峪井田的新鲜火成岩样品为研究对象,结合区域地质背景和前人研究成果,借助显微岩相学方法,分析了火成岩产出的构造条件、岩相学特征和岩石成因。结果表明,研究区的火成岩类型主要包括云煌岩、橄榄辉绿岩、玄武岩、气孔玄武岩、碳酸盐化气孔玄武岩等;以云煌岩为代表的煌斑岩类产于印支期,其位置与断裂密切相关,多以岩床形式侵入石炭-二叠纪煤系地层,对煤层具有明显的破坏作用;辉绿岩和玄武岩产于燕山期,多以岩墙形式产出,对煤层的影响相对较小;各岩石中碱性长石、橄榄石和黑云母矿物斑晶大多发生程度不等的碳酸盐化蚀变,其中以黑云母斑晶的蚀变最为明显。最后,结合不同井田煌斑岩分布情况的差异性,总结了煌斑岩侵入体对煤层、煤质及煤层瓦斯等3方面的影响。 相似文献
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The paper discusses the results of mineralogical and petrographic studies of spinel lherzolite xenoliths and clinopyroxene megacrysts in basalt from the Jixia region related to the central zone of Cenozoic basaltic magmatism of southeastern China. Spinel lherzolite is predominantly composed of olivine (Fo89.6–90.4), orthopyroxene (Mg# = 90.6–92.7), clinopyroxene (Mg# = 90.3–91.9), and chrome spinel (Cr# = 6.59–14.0). According to the geochemical characteristics, basalt of the Jixia region is similar to OIB with asthenospheric material as a source. The following equilibrium temperatures and pressures were obtained for spinel peridotite: 890–1269°C and 10.4–14.8 kbar. Mg# of olivine and Cr# of chrome spinel are close to the values in rocks of the enriched mantle. It is evident from analysis of the textural peculiarities of spinel lherzolite that basaltic melt interacted with mantle rocks at the xenolith capture stage. Based on an analysis of the P–T conditions of the formation of spinel peridotite and clinopyroxene megacrysts, we show that mantle xenoliths were captured in the course of basaltic magma intrusion at a significantly lower depth than the area of partial melting. However, capture of mantle xenoliths was preceded by low-degree partial melting at an earlier stage. 相似文献
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我国华北北部新近纪喷发的汉诺坝玄武岩,岩层出露比较完整,普遍含有超镁铁岩包体和各种高压巨晶。大麻坪代黄沟剖面出露较好,主要岩性为玄武岩,从上到下可分为上三、二、一层和底层。岩相学观察显示这些玄武岩含有1%~5%的捕虏晶且斑晶数量很少。橄榄岩包体为尖晶石二辉橄榄岩,轻稀土略微亏损,轻重稀土无分馏,显示这是只经过少量部分熔融后的原始地幔包体。通过对代黄沟碱性玄武岩中橄榄石、辉石和斜长石等斑晶或捕虏晶的矿物学分析,得出它们的成分变化是玄武岩混合了分解的地幔橄榄岩快速上升造成的。玄武岩的主量元素与二辉橄榄岩相平衡的原生熔体相比,Mg#(52.0~62.7)以及CaO(7.3%~8.5%)、Ni((82~192)×10-6)和Cr((65~192)×10-6)含量都较低。玄武岩的稀土分配模式为轻稀土富集的右倾型,δEu=1.01~1.05,δCe=0.95~1.02,富集高场强元素Nb、Ta、Zr及大离子亲石元素Ba、Sr。玄武岩痕量元素Ba/Rb和Rb/Sr的比值显示源区可能遭受过流体的交代作用。同时,痕量元素显示这一系列玄武岩主要受到部分熔融的控制,大量的结晶分异并未发生,且源区残留石榴子石。分析认为玄武岩岩浆应该是原生岩浆,而不是演化岩浆,影响整个岩浆的形成的过程可能是部分熔融而不是分离结晶。基于目前已发表的实验岩石学结果和理论分析认为汉诺坝玄武岩与辉石岩类相平衡,源区主要矿物相为单斜辉石和石榴子石,可能存在少量的橄榄石。 相似文献
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Rare dunite and 2-pyroxene gabbro xenoliths occur in banded trachyte at Puu Waawaa on Hualalai Volcano, Hawaii. Mineral compositions suggest that these xenoliths formed as cumulates of tholeiitic basalt at shallow depth in a subcaldera magma reservoir. Subsequently, the minerals in the xenoliths underwent subsolidus reequilibration that particularly affected chromite compositions by decreasing their Mg numbers. In addition, olivine lost CaO and plagioclase lost MgO and Fe2O3 during subsolidus reequilibration. The xenoliths also reacted with the host trachyte to form secondary mica, amphibole, and orthopyroxene, and to further modify the compositions of some olivine, clinopyroxene, and spinel grains. The reaction products indicate that the host trachyte melt was hydrous. Clinopyroxene in one dunite sample and olivine in most dunite samples have undergone partial melting, apparently in response to addition of water to the xenolith. These xenoliths do not contain CO2 fluid inclusions, so common in xenoliths from other localities on Hualalai, which suggests that CO2 was introduced from alkalic basalt magma between the time CO2-inclusion-free xenoliths erupted at 106±6 ka and the time CO2-inclusion-rich xenoliths erupted within the last 15 ka. 相似文献
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The Shiribeshi Seamount off northwestern Hokkaido, the Sea of Japan, is a rear-arc volcano in the Northeast Japan arc. This seamount is composed of calc-alkaline and high-K basaltic to andesitic lavas containing magnesian olivine phenocrysts and mantle peridotite xenoliths. Petrographic and geochemical characteristics of the andesite lavas indicate evidence for the reaction with the mantle peridotite xenoliths and magma mixing between mafic and felsic magmas. Geochemical modelling shows that the felsic end-member was possibly derived from melting of an amphibolitic mafic crust. Chemical compositions of the olivine phenocrysts and their chromian spinel inclusions indicate that the Shiribeshi Seamount basalts in this study was derived from a primary magma in equilibrium with relatively fertile mantle peridotites, which possibly represents the mafic end-member of the magma mixing. Trace-element and REE data indicate that the basalts were produced by low degree of partial melting of garnet-bearing lherzolitic source. Preliminary results from the mantle peridotite xenoliths indicate that they were probably originated from the mantle beneath the Sea of Japan rather than beneath the Northeast Japan arc. 相似文献
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内蒙古四子王旗东八号中新世含深源捕虏体富钾橄榄玄武岩的发现及其意义 总被引：6，自引：0，他引：6
内蒙古四子王旗东八号地区最近发现含有深源捕虏体的富钾橄榄玄武岩。玄武岩为灰黑色致密块状,以富碱(K2O+Na2O5．91％～6．47％)、高钾(K2O2．82％～3．12％)和较高的钛(TiO2 2．22％—2．36％)为特征,属钾玄岩系列,全岩K—Ar年龄为21．9±1．7Ma。捕虏体主要为尖晶石二辉橄榄岩、二辉橄榄岩等。根据矿物平衡温压计算表明：捕虏体形成温度为1100—1250℃,压力为1．7—2．0GPa,应源自于岩石圈地幔。四子王旗橄榄玄武岩较高的TiO2和K2O,暗示其岩浆可能源于幔柱作用。推测华北板块北缘自中生代开始可能受到来自深部的幔柱作用,大量上升的岩浆因受到阻挡而保留在岩石圈底部,底侵作用和部分继续上升的岩浆,将岩石圈地幔的捕虏体携出地表。 相似文献
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Upper mantle xenoliths from Wikieup, AZ, provide abundant evidence for magmatic modification of the uppermost mantle beneath
the Transition Zone between the Colorado Plateau and the southern Basin and Range province. Upper mantle lithologies in this
xenolith suite are represented by spinel peridotite, wehrlite, plagioclase peridotite, and Al-augite group pyroxenites. Isotopic
data for these xenoliths yield relatively uniform values and suggest a common petrogenesis. Al-augite-bearing gabbro and pyroxenite
xenoliths from this locality are interpreted to have formed by crystal fractionation processes from parent alkali basalts
similar to the Wikieup host basalt. Mineral and whole rock compositions show consistent trends of increasing incompatible
element contents (Fe, Al, Ca, Na, K, LIL, and LREE), and decreasing compatible element contents (Mg, Cr, Ni) from spinel peridotite
to wehrlite to plagioclase peridotite to the host basalt composition. These compositional trends are interpreted as resulting
from varying degrees of magma-mantle wall rock interaction as ascending mafic magmas infiltrated upper mantle peridotite.
Small degrees of melt infiltration resulted in slightly modified spinel peridotite compositions while moderate degrees metasomatized
spinel peridotite to wehrlite, and the highest degrees metasomatized it to plagioclase peridotite. Whole rock compositions
and clinopyroxene, plagioclase, and whole rock isotopic data suggest that the infiltrating magmas were the same as those from
which the gabbros and pyroxenites crystallized, and that they were alkalic in composition, similar to the Wikieup host alkali
olivine basalts. Relatively uniform 143Nd/144Nd for the mineral separates and whole rocks in spite of the significantly wide range in their 147Sm/144Nd (0.71–0.23 in clinopyroxene) suggests that the Wikieup xenoliths including gabbro, pyroxenite, peridotite, wehrlite, and
plagioclase peridotite, are all relatively young rocks formed or metasomatized by a relatively recent magmatic episode.
Received: 21 May 1996 / Accepted: 23 December 1996 相似文献
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Shoji Arai Yohei Shimizu Tomoaki Morishita Yoshito Ishida 《Contributions to Mineralogy and Petrology》2006,152(3):387-398
We found fine-grained Fe-rich orthopyroxene-rich xenoliths (mainly orthopyroxenite) containing partially digested dunite fragments of Group I from Takashima, Southwest Japan. Orthopyroxenite veinlets, some of which contain plagioclase at the center, also replace olivine in dunite and wehrlite xenoliths of Group I. This shows high reactivity with respect to olivine of the melt involved in orthopyroxenite formation, indicating its high SiO2 activity. The secondary orthopyroxene of this type is characterized by low Mg# [= Mg/(Mg + total Fe) atomic ratio] (down to 0.73) and high Al2O3 contents (5–6 wt%). It is different in chemistry from other secondary orthopyroxenes found in peridotite xenoliths derived from the mantle wedge. Clinopyroxenes in the Fe-rich orthopyroxenite show a convex-upward REE pattern with a crest around Sm. This pattern is strikingly similar to that of clinopyroxenes of Group II pyroxenite xenoliths and of phenocrystal and xenocrystal clinopyroxenes, indicating involvement of similar alkali basaltic melts. The Fe-rich orthopyroxenite xenoliths from Takashima formed by reaction between evolved alkali basalt melt and mantle olivine; alkali basalt initially slightly undersaturated in silica might have evolved to silica-oversaturated compositions by fractional crystallization at high-pressure conditions. The Fe-rich orthopyroxenites occur as dikes within the uppermost mantle composed of dunite and wehrlite overlying pockets of Group II pyroxenites. The orthopyroxene-rich pyroxenites of this type are possibly common in the uppermost mantle beneath continental rift zones where alkali basalt magmas have been prevalent. 相似文献
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Rates of magma ascent and depths of magma reservoirs beneath La Palma (Canary Islands) 总被引：2，自引：0，他引：2
Peridotitic mantle xenoliths from historic and prehistoric eruptions on La Palma show many similarities. Prolonged reactions of the xenoliths with their host magmas have been used to place constraints on the magma transport system beneath the island. All xenoliths show crystalline selvages and 0.9–2.6 mm wide diffusion zones in olivine along most of their surface. Diffusion kinetics in olivine, combined with fluid inclusion barometry, document that selvages and diffusion zones formed at crustal levels within 8 to about 100 years. Some xenolith fractures lack selvages and were in contact with the host magma for less than 4 days. A multistage magma ascent is proposed: (i) peridotite wall rock was fragmented and became incorporated into the ascending magma years to decades prior to the eruption; (ii) the xenoliths were rapidly transported to, and deposited in, crustal magma reservoirs, forming selvages and diffusion zones at the xenolith rims; (iii) renewed fragmentation of the xenoliths occurred days to hours prior to eruption, possibly by decompressive strain fracturing during rapid ascent. 相似文献
19.
Potassic latite in the transition zone of the Colorado Plateau near Chino Valley, Arizona, contains abundant eclogite and amphibolite xenoliths and minor websterite and pyroxenite xenoliths. One unit contains peridotite xenoliths; analyzed samples have mg-ratios of 68 and 71, 58 and 63 wt% SiO2, and are enriched in potassium and other large ion lithophile (LIL) elements. Rare earth element (REE) patterns are light REE enriched with La greater than 100 times chondritic abundance. The peridotite xenoliths are partly to totally altered, but contain remnant olivine, orthopyroxene, and clinopyroxene; one harzburgite nodule also contains spinel. Mineral compositions from the xenoliths are relatively refractory and similar to those in other spinel peridotite xenoliths from the Colorado Plateau. Geothermometry on olivine-spinel and two-pyroxene pairs indicates equilibration temperatures of less than 800° C for the peridotite nodules. The relatively low temperatures calculated from mineral equilibria are consistent with temperature estimates for other mantle nodules from under the Colorado Plateau.Peridotite xenoliths, mg-ratios, and Ni contents are evidence that the latite magma was derived from mantle peridotite. The potassic nature of the magma probably accounts for its silica-rich composition. The potassic, silica-rich nature of the latite and its enrichment in LREE and other LIL elements are consistent with a source which was metasomatically enriched in these elements either before or during partial melting. The source could have been either spinel or garnet peridotite. 相似文献
20.
Hualalai Volcano, Hawaii, is best known for the abundant and varied xenoliths included in the historic 1800 Kaupulehu alkalic basalt flow. Xenoliths, which range in composition from dunite to anorthosite, are concentrated at 915-m elevation in the flow. Rare cumulate ultramafic xenoliths, which include websterite, olivine websterite, wehrlite, and clinopyroxenite, display complex pyroxene exsolution textures that indicate slow cooling. Websterite, olivine websterite, and one wehrlite are spinel-bearing orthopyroxene +olivine cumulates with intercumulus clinopyroxene +plagioclase. Two wehrlite samples and clinopyroxenite are spinel-bearing olivine cumulates with intercumulus clinopyroxene+orthopyroxene + plagioclase. Two-pyroxene geothermometry calculations, based on reconstructed pyroxene compositions, indicate that crystallization temperatures range from 1225° to 1350° C. Migration or unmixing of clinopyroxene and orthopyroxene stopped between 1045° and 1090° C. Comparisons of the abundance of K2O in plagioclase and the abundances of TiO2 and Fe2O3in spinel of xenoliths and mid-ocean ridge basalt, and a single 87Sr/ 86Sr determination, indicate that these Hualalai xenoliths are unrelated to mid-ocean ridge basalt. Similarity between the crystallization sequence of these xenoliths and the experimental crystallization sequence of a Hawaiian olivine tholeiite suggest that the parental magma of the xenoliths is Hualalai tholeiitic basalt. Xenoliths probably crystallized between about 4.5 and 9 kb. The 155°–230° C of cooling which took place over about 120 ka — the age of the youngest Hualalai tholeiitic basalt — yield maximum cooling rates of 1.3×10–3–1.91×10–3 °C/yr. Hualalai ultramafic xenoliths with exsolved pyroxenes crystallized from Hualalai tholeiitic basalt and accumulated in a magma reservoir located between 13 and 28 km below sealevel. We suspect that this reservoir occurs just below the base of the oceanic crust at about 19 km below sealevel. 相似文献