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关于东南极拉斯曼丘陵夕线片麻岩类原岩恢复问题的讨论 总被引：2，自引：0，他引：2
南极拉斯曼丘陵及其邻区的(含)夕线片麻岩类的原岩可以是杂砂岩、亚杂砂岩、石英砂岩、泥质岩或页岩等。粘土岩或页岩之类的富铝沉积岩与富夕线片麻岩并没有直接对应关系。没有一种泥质岩的化学组成可以与富夕线片麻岩相对应。研究区内夕线石片麻岩的形成主要与黑云斜长片麻岩有关,影响夕线石出现的决定性因素是特定温压条件下的变形变质改造过程,而不是原岩成分。夕线石片麻岩在很大程度上是黑云斜长片麻岩经长英质组分迁移之后的滞留-残留体。夕线石化过程中岩石组分发生了改造,相关变质作用已经明显偏离等化学过程,基本上属于开放体系。原岩中Al2O3的含量也不能控制夕线石的出现与否,含夕线石的岩石未必富铝,反之亦然,岩石富铝也可以不出现夕线石;但是夕线石化过程往往是Al2O3相对增加的过程,这些认识对于夕线石片麻岩成岩环境的确定和原岩建造的重建都具有重要意义。 相似文献
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东南极拉斯曼丘陵出露的中-高级变质岩是普里兹湾基底岩系的主要组成部分,是研究普里兹湾高级区组成与演化的理想对象。本文对拉斯曼丘陵米洛半岛地区的夕线石榴二长片麻岩进行了岩石学、相平衡模拟和地质年代学研究。研究结果表明拉斯曼丘陵夕线石榴二长片麻岩矿物组合为石榴子石+堇青石+斜长石+钛铁矿+夕线石+石英±黑云母±钾长石,经历了格林威尔期(～980Ma)高温变质,其峰期阶段(M1)的矿物组合为石榴子石+斜长石+钾长石+钛铁矿+夕线石+石英,变质温压条件为:～820℃、～9. 6kbar。夕线石榴二长片麻岩的岩浆锆石比变质锆石具有更低的LREE和更高的HREE含量,其原岩的沉积年龄不早于～1073Ma,物源主要为中元古代岩浆岩(S-型花岗岩)。拉斯曼丘陵在格林威尔期经历了陆-陆碰撞,进而快速折返、剥蚀作用的过程。 相似文献
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南极拉斯曼丘陵高级长英质变质岩中出现的磷灰石-斜方辉石(Ap-Opx)组合表明岩石经历了麻粒岩相条件下的变质作用,长英质片麻岩发生了强烈的脱水深熔作用。随着熔体的迁出,长英质片麻岩中的残留或者镁铁质岩石中的分异产物,均可形成Ap-Opx组合。残留矿物如磷灰石、金属氧化物等具有丰富的稀土元素,强烈影响着岩石中的稀土元素配分型式。磷灰石-斜方辉石组合的存在说明体系中有适量但不是很充足的有效钙质组分。由磷灰石、磁铁矿-钛铁矿、石榴石,直至斜方辉石,一方面反映了活动组分-残留组分的不断变化,另一方面,也说明高级变质作用过程中体系的失水程度逐渐增加;变质作用中富含该组合的岩石是经变质过程形成的特有岩石,没有固有的原岩可对应。 相似文献
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在欧龙布鲁克地块乌兰北部地区察汗河岩群中识别出麻粒岩相石榴夕线堇青石片麻岩,其矿物组合为石榴子石、夕线石、堇青石、黑云母、斜长石、钛铁矿和少量钾长石等。岩相学观察显示,M1阶段矿物组合有斜长石±钾长石+石榴子石+夕线石+石英,M2阶段矿物组合有斜长石±钾长石+石榴子石+夕线石+石英+钛铁矿+黑云母,M3阶段矿物组合有堇青石+黑云母+钛铁矿+石英+石榴子石+斜长石±钾长石。相平衡模拟计算结果显示,该岩石的峰期温压条件为p=0.92～1.08 GPa,峰期温度t>790℃,峰期之后经历升温降压的p-T演化轨迹。锆石和独居石LA-ICP-MS U-Pb年代学研究获得的变质年龄分别为1 133±14 Ma和1 125±37 Ma, 1 133～1 125 Ma应代表了该期麻粒岩相变质作用的时代。结合区域地质资料和已有的研究成果,我们认为乌兰北部察汗河岩群的石榴夕线堇青石片麻岩可能形成于大洋俯冲作用下的弧或弧后构造环境,乌兰北部的岩浆-变质杂岩带经历了从中元古代晚期-新元古代早期俯冲增生到碰撞造山的演化过程,是全球Rodinia超大陆汇聚过程的响应。 相似文献
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长英质片麻岩中堇青石的一种可能的形成机制——以南极拉斯曼丘陵高级区为例 总被引：2，自引：0，他引：2
本文通过对南极拉斯曼丘陵长英质片麻岩变质过程中堇青石与其它矿物之间结构关系的研究 ,识别出明显不同的两种组合Pl Kfs Qtz(Grt)和Crd Opq Spl±Qtz,认为区内高级变质作用向深熔作用转化过程中发生了长英质组分和镁铁质组分的分凝。分凝出的长英质熔体与堇青石的形成没有直接关系 ;镁铁质组分较富Mg、Fe ,贫Si、Ca ,当镁铁质组分达到一定的富集程度时即形成堇青石。时间上 ,堇青石形成于降压过程中发生的深熔作用的晚期 相似文献
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东南极拉斯曼丘陵麻粒岩相岩石中早期残留矿物组合的特征及其变质… 总被引：4，自引：1，他引：4
东南极拉斯曼丘陵出露的麻粒岩相泥质片麻岩和镁铁质麻粒岩经历了复杂的变形变质历史。代表前进的增厚事件的早期残留变质构造Ｄ１形成于１０００Ｍａ期间。对应于Ｄ１的变质峰期Ｍ１的变质组合以泥质片麻岩的石榴石和尖晶石变斑晶中的堇青石和夕线石包裹体以及镁铁质麻粒岩的石榴石变斑晶中的斜方辉石和斜长石包裹体为特征。在该区斯托罗斯半岛的紫苏黑云石英岩的粗粒紫苏辉石中发现了包裹的假蓝宝石＋磁铁石和假蓝宝石＋尖晶石＋夕 相似文献
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华北地台太古代麻粒岩相带的堇青石-夕线石组合:低压麻粒岩相的标志 总被引：3，自引：4，他引：3
华北地台北缘麻粒岩相带中,西起贺兰山东至辽吉地区,凡有高铝变质沉积岩发育的地方几乎都普遍存在堇青石-夕线石组合,它分别出现在含堇青石石英岩、片麻岩、麻粒岩和S-型花岗岩中;堇青石-石榴石-夕线石组合也极常见。用石榴石-堇青石矿物对计算的变质作用P-T条件约5.3×10~8～7.5×10~8Pa,700～810℃,地热梯度约30～40℃/km。这些数据与共生岩石中其他矿物对所得温压条件基本一致。堇青石-夕线石组合是低压变质作用的标志。因此该麻粒岩相带大部分属于低压麻粒岩相。 相似文献
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沂水杂岩中变泥砂质岩石的岩石化学特征及年代 总被引：4，自引：3，他引：1
含夕线石十字石榴二云斜长片麻岩是沂水杂岩中首次发现的一种少见的变泥砂质岩石,包裹于沂水生心官庄岩浆杂岩体中,为残留的变质表壳岩透镜体,它经历了两期变质作用的改造.早期高角闪岩相变质与区域麻粒岩相变质有关,峰期矿物共生组合主要为:石榴子石(中心域)+黑云母±白云母+斜长石+石英,M1峰期变质温压条件为:T=660±10℃,P=5.7±0.3kb;晚期角闪岩相变质矿物共生组合为:十字石+石榴子石(边部域)+黑云母±白云母+斜长石±夕线石+石英,以形成大量自形-半自形十字石和具有明显的成分环带的石榴子石为特征,晚期石榴子石的形成由核部→边部经历了一降温降压过程,石榴子石核部:T=650±10℃,P=7.7±0.5Kb,石榴子石边部:T=578±10℃,P=4.7±0.1kb;晚期变质作用早期(石榴子石成核)阶段与埋深导致的部分熔融有关,晚期石榴子石生长阶段与岩浆热事件有关.锆石SHRIMP U-Pb定年结果表明:碎屑锆石不一致线上交点年龄为2695±32Ma,代表变泥砂质岩石源区岩浆岩的结晶年龄,变泥砂质岩石的早期变质变质作用年龄小于此值;晚期变质作用年龄为2537±5Ma. 相似文献
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周喜文 《吉林大学学报(地球科学版)》2001,31(4):416-416
夕线石(Sil)是泥质变质岩的重要特征变质矿物,一直被视作高温变质矿物的典型,并常以其在岩石中的首次出现作为变质作用进入峰期的标志.然而近来发现有些夕线石并非产于高温变质岩之中,而是出现于变质程度较低的黑云片岩或二云片岩之中.因而有必要对夕线石的成因机制作深入分析,以便准确建立变质矿物的生成演化序列. 自然界产出的夕线石按其形态和产状不同主要有如下几种:(1)巨晶板柱状或竹节状夕线石,主要以变班晶形式存在于夕线石榴钾长片麻岩之中,形态规则、产出量大,共生矿物有石榴石(Gt)、钾长石(Kf)和黑云母(Bt)等,无堇青石(Crd).(2)针柱状或乳滴状夕线石集合体,常以包体形式存在于大颗粒的茧青石、钾长石或石英之中.集合体形态多样,有时规则排列,有时则强烈弯曲甚至形成小褶皱.该夕线石主要产于夕线石榴茧青黑云钾长片麻岩之中.(3)纤维毛发状夕线石聚集体,常与黑云母残片交生在一起,彼此呈渐变过渡关系.该种夕线石可产出在两种截然不同的岩石之中,反映其不同的成因特征.一种为夕线石榴(堇青)黑云片麻岩,夕线石沿黑云母解理缝方向呈纤维状分布,由里向外夕线石粒径逐渐变细,表现出一种熔融特征;另一种为含石榴夕线黑云片岩或二云片岩,这种夕线石和黑云母往往遭受了强烈的揉皱,呈不规则的毛团状和扫帚状,夕线石粒径极细以至在光学镜下很难分辨.由于矿物组合中缺少十字石(Stau)、堇青石和钾长石等特征矿物,表明其变质温度较低(相当于绿片岩相-低角闪岩相). 相似文献
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东南极拉斯曼丘陵高级变质长英质岩石中铁钛氧化物的局部聚集与高级变质作用过程中的深熔作用有关,并非原岩富集这些组分。深熔作用造成惰性组分如铁钛氧化物滞留原地或略有聚集及活动性组分的迁移,而流体挥发组分优先聚集于熔体之中。当体系中水含量较低、处于不饱和状态时,深熔作用过程中形成局部"熔体",其结晶所成的浅色体不具低共结组分,没有熔体结晶结构,不是真正的熔体,可能是(准)熔体。较粗粒的浅色体或伟晶岩也是与深熔作用有关的产物,其形成早于花岗岩脉或岩体,而与花岗质岩浆分异无关。伴随(准)熔体的出现,体系中组分的萃取、分异效果较为明显,即可造成组分分异,形成截然不同的异地、二相分异结构,分别形成固相残留物(组成可以不固定)和(准)熔体相。固相残留体中富铝、铁组分,形成矽线石和铁钛氧化物团块,其中少或无挥发分;与此对应,短距离迁移浅色体中往往贫铁钛组分,可见石榴子石、偶见铁钛氧化物矿物。这种挥发分不饱和状态下的深熔作用基本属于封闭体系,整体失水不显著,高级变质岩中的一些特征矿物如矽线石、石榴子石、堇青石、尖晶石的形成也与这种分异作用有关,但组分迁移范围有限,并可保存组分分异各阶段的产物。拉斯曼丘陵长英质岩系中大量铁钛氧化物和矽线石类矿物组合的形成,反映了临界状态下的局部或差异抬升,变形作用的非均匀性及相伴随的组分分异作用,很可能相当于早期格林维尔期构造的泛非期再活动。 相似文献
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S. BABA 《Journal of Metamorphic Geology》1998,16(6):819-841
The Leverburgh Belt and South Harris Igneous Complex in South Harris (northwest Scotland) experienced high-pressure granulite facies metamorphism during the Palaeoproterozoic. The metamorphic history has been determined from the following mineral textures and compositions observed in samples of pelitic, quartzofeldspathic and mafic gneisses, especially in pelitic gneisses from the Leverburgh Belt: (1) some coarse-grained garnet in the pelitic gneiss includes biotite and quartz in the inner core, sillimanite in the outer core, and is overgrown by kyanite at the rims; (2) garnet in the pelitic gneiss shows a progressive increase in grossular content from outer core to rims; (3) the AlVI/AlIV ratio of clinopyroxene from mafic gneiss increases from core to rim; (4) retrograde reaction coronas of cordierite and hercynite+cordierite are formed between garnet and kyanite, and orthopyroxene+cordierite and orthopyroxene+plagioclase reaction coronas develop between garnet and quartz; (5) a P–T path is deduced from inclusion assemblages in garnet and from staurolite breakdown reactions to produce garnet+sillimanite and garnet+sillimanite+hercynite with increasing temperature; and (6) in sheared and foliated rocks, hydrous minerals such as biotite, muscovite and hornblende form a foliation, modifying pre-existing textures. The inferred metamorphic history of the Leverburgh Belt is divided into four stages, as follows: (M1) prograde metamorphism with increasing temperature; (M2) prograde metamorphism with increasing pressure; (M3) retrograde decompressional metamorphism with decreasing pressure and temperature; and (M4) retrograde metamorphism accompanied by shearing. Peak P–T conditions of the M2 stage are 800±30 °C, 13–14 kbar. Pressure increasing from M1 to M2 suggests thrusting of continental crust over the South Harris belt during continent–continent collision. The inferred P–T path and tectonic history of the South Harris belt are different from those of the Lewisian of the mainland. 相似文献
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John A. Percival 《Contributions to Mineralogy and Petrology》1979,69(2):177-184
The increase in metamorphic grade toward the Hackett River gneiss dome indicates that the structural dome is also a metamorphic culmination. In pelitic rocks east of the dome, the prograde sequence is chlorite, biotite, staurolite-cordierite, sillimanite. To the southwest the sequence is andalusite-staurolite-cordierite, sillimanite. In quartzofeldspathic gneisses which are closer to the dome than the sillimanite isograd, kyanite occurs as corroded relics, cross-cut by sillimanite and rimmed by cordierite and plagioclase.The pelites were metamorphosed under regional low-pressure conditions at the same time the quartzo-feldspathic rocks underwent higher-pressure metamorphism. A lateral variation in geothermal gradient during metamorphism is postulated to account for the change in facies-series. High heat flow beneath oceanic crust produced the low-pressure assemblages in the pelites; higher-pressure assemblages formed in a region of suppressed isotherms around a relatively cool, proto-continental trondhjemitic body. Low-pressure conditions were imposed on the kyanite-bearing gneisses during continuing metamorphism and diapiric uplift.Spatial association of late Archean kyanite-bearing rocks with early Archean sodic proto-cratons has also been noted in the Churchill and Superior Provinces of Canada as well as the Rhodesian Craton. 相似文献
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In the Boi Massif of Western Timor the Mutis Complex, which is equivalent to the Lolotoi Complex of East Timor, is composed of two lithostratigraphical components: various basement schists and gneisses; and the dismembered remnants of an ophiolite. Cordierite-bearing pelitic schists and gneisses carry an early mineral assemblage of biotite + garnet + plagioclase + Al-silicate, but contain no prograde muscovite; sillimanite occurs in a textural mode which suggests that it replaced and pseudomorphed kyanite at an early stage and some specimens of pelitic schist contain tiny kyanite relics in plagioclase. Textural relations between, and mineral chemistries of, ferro-magnesian phases in these pelitic chists and gneisses suggest that two discontinuous reactions and additional continuous compositional changes have been overstepped, possibly with concomitant anatexis, as a result of decrease in Pload during high temperature metamorphism. The simplified reactions are: garnet and/or biotite + sillimanite + quartz + cordierite + hercynite + ilmenite + excess components. P-T conditions during the development of the early mineral assemblage in the pelitic gneisses are estimated to have been P + 10 kbar and T > 750°C, based upon the plagioclase-garnet-Al-silicate-quartz geobarometer and the garnet-biotite geothermometer. P-T conditions during the subsequent development of cordierite-bearing mineral assemblages in the pelitic gneisses are estimated to have been P + 5 kbar and T + 700°C with XH2O < 0.5, based upon the Fe content of cordierite occurring in the assemblage quartz + plagioclase + sillimanite + biotite + garnet + cordierite coexisting with melt. Final equilibration between some of the phases suggests that conditions dropped to P > 2.3 kbar and T > 600°C. A similar exhumation P-T path is suggested for the pelitic schists with early metamorphic conditions of P > 6.2 kbar and T > 745°C and subsequent development of cordierite under conditions in the range P = 3-4 kbar and T = 600-700°C. The tectonic implications of these P-T estimates are discussed and it is concluded that the P-T path followed by these rocks was caused by decompression during rifting and synmetamorphic ophiolite emplacement resulting from processes during the initiation and development of a convergent plate junction located in Southeast Asia during late Jurassic to Cretaceous time. 相似文献
16.
通过对聂拉木高喜马拉雅结晶岩系石榴子石带-十字石带-蓝晶石带-夕线石带倒转变质的研究,认为除夕线石带以外的其它变质带主要由固相变质反应形成。夕线石的出现并非蓝晶石或十字石带递增变质所致。"倒转变质"不应包括所谓的夕线石带。实际上,夕线石化与深熔作用之后的溶液（或熔体）活动更为密切。时间顺序上应是递增变质作用及分带→深熔作用→夕线石化,夕线石的出现不是深熔作用的开始,而是深熔作用的结束。夕线石的形成主要与变形作用过程中黑云母和／或钾长石的分解及碱（土）金属组分的迁移有关,关键在于溶液（或熔体）组分沿裂隙迁移过程中发生的组分逐步沉淀,最早沉凝的Al、Si组分形成夕线石和石英,之后陆续有其它的组分的结晶;细夕线石粗粒化即进一步转化形成柱状夕线石的同时形成蠕英结构和斜长石生长边。夕线石化可能与深熔花岗（片麻）岩的上升过程有关。 相似文献
17.
Cordierite gneisses of southern Kerala,India: petrology,fluid inclusions and implications for crustal uplift history 总被引：2，自引：0，他引：2
M. Santosh 《Contributions to Mineralogy and Petrology》1987,96(3):343-356
The cordierite-bearing gneisses occurring as elongate patches in an 8- to 10-km-wide zone along the Achankovil fault-lineament at the northern margin of the southern Kerala crustal segment represent an important lithological unit in the Archaean granulite terrane of south India. The textural relationships in these rocks are consistent with the following main reactions: (1) garnet+quartz=cordierite+hypersthene; (2) garnet+sillimanite+quartz=cordierite; (3) hypersthene+sillimanite+quartz=cordierite; (4) sillimanite+spinel=cordierite+corundum; and (5) biotite+quartz+sillimanite=cordierite+K-feldspar. Many of the mineral associations and reaction textures, including the remarkable preservation of symplectites, are indicative of partial replacement of high-pressure assemblages by cordierite-bearing lower-pressure ones during an event of rapid decompression. Temperature estimates from coexisting mineral phases show 710° (garnet-biotite), 791° (garnet-cordierite) and 788° C (garnet-orthopyroxene). Pressure estimates from mineral assemblages range from 5.4 to 7 kb. Detailed fluid inclusion studies in quartz associated with cordierite show high-density CO2 (0.80–0.95 g/cm3) as the dominant fluid phase, with traces of probable CH4 (?) in the sillimanite-bearing rocks. The isochore for the higher-density fluid inclusions defines a pressure of 5.5 kb. The fracture-bound CO2 and CO2-H2O (±CH4?) inclusions indicate simultaneous entrapment at 400° C and 1.7 kb in the cordierite-hypersthene assemblage and 340° C and 1.2 kb in the cordierite-sillimanite assemblage. The P-T path delineated from combined solid and fluid data corresponds to the piezothermic array of the gneisses and is characterized by T-convex nature, indicative of rapid and virtually isothermal crustal uplift, probably aided by extensional tectonics. 相似文献
18.
东南极拉斯曼丘陵硼硅酸盐矿物组合硅硼镁铝矿-硼柱晶石-电气石的形成过程及其岩石学意义 总被引：1，自引：0，他引：1
东南极拉斯曼丘陵长英质片麻岩中产出大量的电气石-硼柱晶石-硅硼镁铝矿之硼硅酸盐矿物组合,这些矿物(电气石除外)的形成晚于变质峰期一般的硅酸盐矿物。电气石可多次出现,硅硼镁铝矿之后形成硼柱晶石,很少见两种以上的硼硅酸盐矿物能够同时结晶,各种硼硅酸盐矿物在同一期、甚至同一阶段内呈递进关系。在硼硅酸盐矿物的结晶过程中,B2O3和Al2O3较为活动从而SiO2的活度相对受到抑制,即存在组分的分异和活性波动,表明络阴离子SiO44-、PO43-、BO33-活动高峰并非同步因而,挥发分组分对深熔作用的影响可能是有限的;同时,结晶的金属阳离子组分不断发生分异。不同的硼硅酸盐矿物形成的介质条件有所差异:电气石形成于富钙的弱酸性溶液,硅硼镁铝矿应为近中-碱性溶液介质,而硼柱晶石形成于含少量氟的偏碱性介质环境。除温压因素外,流体挥发分种类和介质条件也影响到硼硅酸矿物的多期次、多阶段的变化,从而造成矿物组合的复杂性。本区长英质岩石中硼(B)及其他挥发分组分的较高含量可由原岩成分决定,亦可经由变质-深熔作用引起,即深熔作用时熔体的整体优先吸收硼(硼的第一次富集)及随后熔体结晶阶段的局部残留和富集硼(硼的第二次富集)。Gdd-Prs-Trn硼硅酸盐矿物组合的存在,表明发生了以脱水为主的高级变质作用,同时伴随强烈的深熔作用。挥发分组分在露头尺度体系中可能属于开放性质,而在更大尺度和范围内则基本封闭;在深熔作用中,硼等挥发分的存在影响了熔体的组成使得岩浆熔点降低、熔融成分调整粘度有所降低,更容易运移;而且,熔体可以携带这些挥发分,当熔体结晶时挥发分析出、结晶局部富集而形成硼硅酸盐矿物,尤其是沿着一些构造有利部位发生显著的聚集。 相似文献
19.
Abstract Small unexploited copper-lead-zinc deposits, characterized by a distinctive wall-rock association of cordierite quartzite, silica-undersaturated rocks, calc-silicate rocks and impure marbles, occur in quartzofeldspathic gneisses and mafic granulites of the Strangways Metamorphic Complex, central Arunta Block, central Australia. Available data support the hypothesis that these are metamorphosed volcanogenic ore bodies. The chemical compositions of the quartzofeldspathic gneisses are comparable with those of less metamorphosed felsic igneous rocks, particularly the felsic igneous rocks emplaced in the North Australian Orogenic Province in the interval 1880–1800 Ma; and the mafic granulites are chemically similar to basalts (olivine-normative tholeiites). The wall-rock suite can be correlated from chemistry and lithological association with the suites of wall rocks found in unmetamorphosed volcanogenic ore deposits. That the protolith of the cordierite quartzites may well have been leached tuff, similar to the illite-chlorite-quartz tuff found in volcanogenic ore deposits, is also shown by retrogression of the granulitefacies assemblage: cordierite-garnet-ortho-pyroxene-biotite-quartz in the cordierite quartzites to cordierite-anthophyllite-bearing assemblages and thence to chlorite-muscovite-quartz assemblages. Lenses of silica-undersaturated rocks with spinel and, less commonly, sapphirine are interpreted as the metamorphosed equivalents of chlorite-rich pods found within leached tuffs in volcanogenic ore deposits. The wall rocks form sheet-like bodies; this suggests that they were deposited in relatively shallow water, thus precluding the formation of massive sulphides. 相似文献