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Absolute ages of migmatization in the polymetamorphic, parautochthonous basement of the Sveconorwegian Province, Sweden, have been determined using U–Pb ion probe analysis of zircon domains that formed in leucosome of migmatitic orthogneisses. Migmatite zircon was formed by recrystallization whereas dissolution–reprecipitation and neocrystallization were subordinate. The recrystallized migmatite zircon was identified by comparison of zircon in mesosomes and leucosomes. It is backscatter electron‐bright, U‐rich (800–4400 ppm) with low Th/U‐ratios (generally 0.01–0.1), unzoned or ‘oscillatory ghost zoned’, and occurs as up to 100 μm‐thick rims with transitional contacts to cores of protolith zircon. Protolith ages of 1686 ± 12 and 1668 ± 11 Ma were obtained from moderately resorbed, igneous zircon crystals (generally Th/U = 0.5–1.5, U < 300 ppm) in mesosomes; protolith zircon is also present as resorbed cores in the leucosomes. Linkage of folding, synchronous migmatization and formation of recrystallized zircon rims allowed direct dating of south‐vergent folding at 976 ± 7 Ma. At a second locality, similar recrystallized zircon rims in leucosome date pre‐Sveconorwegian migmatization at 1425 ± 7 Ma; an upper age bracket of 1394 ± 12 Ma for two overprinting phases of deformation (upright folding along gently SSW‐plunging axes and stretching in ESE) was set by zircon in a folded metagranitic dyke. Lower age brackets for these events were set at 952 ± 7 and 946 ± 8 Ma by zircon in two crosscutting and undeformed granite–pegmatite dykes. Together with previously published data the present results demonstrate: (i) Tectonometamorphic reworking during the Hallandian orogenesis at 1.44–1.42 Ga, resulting in migmatization and formation of a coarse gneissic layering. (ii) Sveconorwegian continent–continent collision at 0.98–0.96 Ga, involving (a) emplacement of an eclogite unit, (b) regional high‐pressure granulite facies metamorphism, (c) southvergent folding, subhorizontal, east–west stretching and migmatization, all of which caused overprint or transposition of older Mesoproterozoic and Sveconorwegian structures. The Sveconorwegian migmatization and folding took place during or shortly after the emplacement of Sveconorwegian eclogite and is interpreted as a result of north–south shortening, synchronous with east–west extension and unroofing during late stages of the continent–continent collision. 相似文献
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K. HISADA L. L. PERCHUK T. V. GERYA D. D. VAN REENEN B. K. PAYA 《Journal of Metamorphic Geology》2005,23(5):313-334
Metapelites, migmatites and granites from the c. 2 Ga Mahalapye Complex have been studied for determining the P–T–fluid influence on mineral assemblages and local equilibrium compositions in the rocks from the extreme southwestern part of the Central Zone of the Limpopo high‐grade terrane in Botswana. It was found that fluid infiltration played a leading role in the formation of the rocks. This conclusion is based on both well‐developed textures inferred to record metasomatic reactions, such as Bt ? And + Qtz + (K2O) and Bt ± Qtz ? Sil + Kfs + Ms ± Pl, and zonation of Ms | Bt + Qtz | And + Qtz and Grt | Crd | Pl | Kfs + Qtz reflecting a perfect mobility (Korzhinskii terminology) of some chemical components. The conclusion is also supported by the results of a fluid inclusion study. CO2 and H2O ( = 0.6) are the major components of the fluid. The fluid has been trapped synchronously along the retrograde P–T path. The P–T path was derived using mineral thermobarometry and a combination of mineral thermometry and fluid inclusion density data. The Mahalapye Complex experienced low‐pressure granulite facies metamorphism with a retrograde evolution from 770 °C and 5.5 kbar to 560 °C and 2 kbar, presumably at c. 2 Ga. 相似文献
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山东招掖金矿带稀土元素地球化学特征初步研究 总被引：1，自引：0，他引：1
本文提出了解决本区某些地质问题的新信息。认为不同地质体具有大体相似的稀土元素配分模型,成岩成矿关系密切,具有继承性演化特点。各类花岗质岩石由胶东群变质岩经混合岩化作用形成。成矿热液富含[CO_3]~(2-)或[HCO_3]~-,金在黄铁矿和石英中富集,与∑REE、LREE的含量及∑Ce/∑Y、Ce/Yb、La/Yb比值呈正相关。上述参数可用作该类金矿床矿化富集规模和强度的评价标志。 相似文献
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本文提出了冀东黑云母片麻岩—H2O系统在0.1一0.2GPa压力下熔融买验的相关系。其固相线温度分別为0.1GPa时762℃,0.2GPa时712℃。黑云母消失的温度分別为0.1GPa时787℃,0.2GPa时737℃,石英消失的温度分别为0.1GPa时837.℃,0.2GPa时787.℃。采用Burn-ham模型计算的在液相线温度下岩浆饱和水的含量分別为0.1GPa时3.8%与0.2GPa时5.8%。根据实验结果以及早前寒武纪时冀东陆壳的古地温可知,该区早前寒武纪角阿岩相岩石分布的地区广泛出现的混合岩化作用应主要归因于陆壳岩石(黑云母片麻岩等)的局部熔融作用。由实验结果以及现代冀东陆壳的地温可推知,壳内低速层可能不是由岩石局部熔融所引起,而是由岩石中含有隙间水流体引起。 相似文献
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新疆阿克陶红蓝宝石矿床矿物学研究 总被引：3，自引：0，他引：3
新疆阿克陶红蓝宝石矿床含矿岩石具有典型的眼球状、条带状混合岩化构造。浅色脉体中的钾长石有序度很低，属单斜正长石，其中部分发育钠长石出溶条纹。基体中出现富铝矿物矽线石和电气石，黑云母中Ａｌ２Ｏ３含量高；斜长石Ａｎ值低，为钠长石。含矿岩石为富铝贫硅低钙质岩石。脉体中的红蓝宝石晶体中发现大量流体熔融包裹体。红蓝宝石矿床为混合岩化作用成因，形成于高温低压条件下 相似文献
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试论阜平杂岩的深熔作用 总被引：2，自引：0，他引：2
阜平杂岩中广泛产出浅色脉体,从而显示强烈的混合岩化作用。前人把引起混合岩化作用的机制归因于岩汁交代、重熔或无水深熔作用,似乎与实际的岩相结构不是很一致。矿物自形晶、钠长石净边结构和一些典型的矿物转化反应表明,阜平杂岩的混合岩化作用实际上经历了复杂的过程,主要表现为有水条件下的深熔作用。所形成的熔体有较大的流动性,可迁移一定的距离而进入邻近的岩石,对这些部位而言相当于发生了外来熔体的注入活动,造成熔体注入式混合岩化作用,形成一些交代反应和结构。因此,阜平杂岩混合岩化作用中的变质反应过程既包括长英质矿物的熔融(溶解),还涉及一种含水矿物(如黑云母)转化形成另外一种含水矿物(如角闪石)的化学反应。阜平杂岩的混合岩化作用最重要的机制是水致熔融或含水深熔作用,溶解性重熔或无水深熔作用则较为次要。 相似文献
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M. BRÖCKER R. KLEMD M. COSCA W. BROCK A. N. LARIONOV N. RODIONOV 《Journal of Metamorphic Geology》2009,27(5):385-403
The Orlica–?nie?nik complex (OSC) is a key geological element of the eastern Variscides and mainly consists of amphibolite facies orthogneisses and metasedimentary rocks. Sporadic occurrences of eclogites and granulites record high‐pressure (HP) to ultrahigh‐pressure (UHP) metamorphic conditions. A multimethod geochronological approach (40Ar–39Ar, Rb–Sr, Sm–Nd, U–Pb) has been used to gain further insights into the polymetamorphic evolution of eclogites and associated country rocks. Special attention was given to the unresolved significance of a 370‐ to 360 Ma age group that was repeatedly described in previous studies. Efforts to verify the accuracy of c. 370 Ma K–Ar phengite and biotite dates reported for an eclogite and associated country‐rock gneiss from the location Nowa Wie? suggest that these dates are meaningless, due to contamination with extraneous Ar. Extraneous Ar is also considered to be responsible for a significantly older 40Ar–39Ar phengite date of c. 455 Ma for an eclogite from the location Wojtowka. Attempts to further substantiate the importance of 370–360 Ma zircon dates as an indicator for a melt‐forming high‐temperature (HT) episode did not provide evidence in support of anatectic processes at this time. Instead, SHRIMP U–Pb zircon dating of leucosomes and leucocratic veins within both orthogneisses and (U)HP granulites revealed two age populations (490–450 and 345–330 Ma respectively) that correspond to protolith ages of the magmatic precursors and late Variscan anatexis. The results of this study further underline the importance of Late Carboniferous metamorphic processes for the evolution of the OSC that comprise the waning stages of HP metamorphism and lower pressure HT overprinting with partial melting. Eclogites and their country rocks provided no chronometric evidence for an UHP and ultrahigh‐temperature episode at 387–360 Ma, as recently suggested for granulites from the OSC, based on Lu–Hf garnet ages ( Anczkiewicz et al., 2007 ). 相似文献
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潼关地区混合岩可划分为四大类及若干亚类,混合岩化的程度与南北向构造挤压力的强弱相关,且随着分布在不同的构造部位而具分带性,混合岩化在宏观上、微观上都表现了多期性;曾称的“花岗伟晶岩”系混合岩作用的产物,应称混合花岗岩。 相似文献