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赣中周潭群副变质岩碎屑锆石U-Pb年代学 总被引：5，自引：3，他引：2
对赣中周潭群副变质岩中的碎屑锆石开展了LA-ICP-MS U-Pb定年工作,两个石榴黑云母片岩和一个黑云母片岩三个样品中碎屑锆石给出的最年轻的年龄峰值分别为834±11Ma、830±11Ma和809±15Ma.这些碎屑锆石具有与江南造山带内冷家溪群及其相当地层类似的年龄谱型式和相近的最年轻的年龄峰值,表明周潭群应与它们有相似的形成历史和源区,产生于相似的构造环境.因此,周潭群在新元古代扬子地块与华夏地块拼接的过程中,应与冷家溪群、双桥山群等地层一样靠近扬子一侧,而不应属华夏地块.从黑云母片岩部分碎屑锆石的变质边获取的年龄分别为444±11Ma和438±11Ma,表明周潭群地层的变质作用发生在加里东期,与华夏地块其他地区的角闪岩相变质岩的变质年龄一致.相反,与周潭群同期的双桥山群、冷家溪群等地层均未达到角闪岩相变质.这表明,在扬子和华夏地块新元古代的拼接之后,二块体在(现在的)赣中地区又裂开,从而导致了周潭群和相邻的冷家溪群及双桥山群在加里东时期有不同的变质响应. 相似文献
3.
笔者等对周潭群沉积变质岩及其中脉体的微量元素、氧同位素地球化学进行了研究,结果表明,变质石英脉继承了其围岩的稀土元素及氧同位素地球化学特征,表明形成石英脉的流体来源于围岩;脉体的微量元素对Zr-Hf、U-Th、Nb-Ta和Y-Ho与变质岩有一定的差异,且有一定的分异,指示脉体是流体作用的产物。变质流体通过侧向扩散作用形成了周潭群变沉积岩中的变质脉体。 相似文献
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Rare earth element distributions among coexisting granulite facies minerals,Scourian complex,NW Scotland 总被引：1，自引：0，他引：1
The major rock-forming mineral phases (pyroxenes, plagioclase, garnet, hornblende) of a suite of granulite-facies gneisses from the Scourian complex, NW Scotland, have been analyzed for their rare earth element (REE) content. Although host rock compositions range from felsic to ultramafic, REE abundances and patterns for each mineral group show only limited variation. The REEs exhibit regular and consistent distribution patterns for each mineral which suggest, together with major element and textural considerations, that the observed distribution coefficients approach equilibrium. Total REE content follows the sequence hornblende>clinopyroxene>garnet>plagioclase >orthopyroxene and mass balance calculations show that even in the felsic gneisses>60% of the REEs reside in the major rock-forming minerals. Comparisons of both relative REE abundances and distribution coefficients with those in other rock types reveal a striking resemblance with patterns observed in mineral-liquid pairs of dacitic rocks. These similarities may have arisen during a partial melting episode in which granite-granodiorite melts were generated and removed from the Scourian complex; leaving a residuum which is severely depleted in the incompatible elements, including the REEs. 相似文献
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滇西六合地区新生代正长斑岩中深源包体的矿物学特征与成因意义 总被引：16，自引：0，他引：16
在云南省鹤庆县六合乡河东村的正长斑岩中产出多种含石榴石的深源包体。文中详细介绍了这些包体的岩相学特征和退变质特征 ,提供了包体中主要造岩矿物的化学成分分析结果。根据包体中的矿物组合及主要造岩矿物的化学成分特征划分出了 5种包体类型 ,并运用单斜辉石地质温压计、角闪石地质压力计和石榴石单斜辉石Fe Mg交换地质温度计计算了包体形成和退变质的温压条件 ,初步确定石榴石透辉岩及石榴辉石岩来源于上地幔 (87～ 95km) ,在快速上升到下地壳时被正长斑岩岩浆捕获 ;石榴石透辉角闪岩、麻粒岩形成于下地壳 (45～ 5 5km ) ,石榴石斜长角闪岩形成于中下地壳 (约 30km) ,为壳源岩石包体。除石榴辉石岩外 ,其余 4种包体均经历了退变质作用。根据它们的显微结构特征、矿物化学特征及温压计算结果 ,划分了两个变质期次 ,构筑了包体形成及退变质作用的 p T轨迹 ,讨论了退变质过程中压力 深度的变化及意义 ,并推断在退变质过程中包体经历了富Na流体的交代作用。 相似文献
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扬子地块西南缘大红山群石榴白云母-长石石英片岩的白云母40Ar-39Ar定年及其地质意义 总被引：1，自引：1，他引：0
大红山群是扬子地块西南缘出露的古元古代结晶基底,主要经历了绿片岩相-低角闪岩相变质作用.本研究对大红山群老厂河组变质中酸性岩和变质沉积岩——石榴白云母-长石石英片岩中的白云母进行了40Ar-39Ar测年,得到三个样品的坪年龄和40Ar/39Ar等时线年龄结果较统一,坪年龄代表的变质年龄分别为837.7±4.2Ma、839.6±4.2Ma和844.2±4.2Ma.变质沉积岩和变质中酸性岩的变质时代类似,均介于837～845Ma.大红山群变质基性岩中变质锆石的U-Pb定年年龄为849±12Ma(杨红等,2012),40Ar-39Ar测年数据与锆石定年数据相结合,说明大红山群古元古代结晶基底中的火山岩和沉积岩均在新元古代经历了同期变质作用,其主期低角闪岩相变质作用发生于新元古代837～850Ma.结合前人发表的扬子西缘～750Ma的变质年龄,扬子西缘从北向南的区域变质作用时限可扩展到750 ～850Ma.此外,扬子西缘存在750～850Ma的岩浆事件,本文研究结果说明,扬子地块西缘在新元古代不仅发生了大规模岩浆作用,也发生了750～850Ma的区域变质作用,扬子西缘存在新元古代的岩浆-变质事件.岩浆事件与变质事件之间可能存在相关性,即新元古代岩浆作用引起了扬子西缘的区域动力热流变质作用. 相似文献
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Adriana Heimann Paul G. Spry Graham S. Teale Colin H. H. Conor Norman J. Pearson 《Mineralogy and Petrology》2011,101(1-2):49-74
Garnet-rich rocks occur throughout the Proterozoic southern Curnamona Province, Australia, where they are, in places, spatially related to Broken Hill-type Pb-Zn-Ag deposits. Fine-scale bedding in these rocks, their conformable relationship with enclosing metasedimentary rocks, and their enrichment in Mn and Fe suggest that they are metamorphosed chemical precipitates. They formed on the floor of a 1.69?Ga continental rift basin from hydrothermal fluids mixed with seawater and detritus. Garnet in garnet-quartz and garnet-amphibole rocks is generally light rare earth element (LREE) depleted, and has flat heavy REE (HREE) enriched chondrite-normalized REE patterns, and negative Eu anomalies (Eu/Eu*?<?1). Garnet in garnet-rich rocks from the giant Broken Hill deposit has similar REE patterns and either positive (Eu/Eu*?>?1) or negative Eu anomalies. Manganese- and Mn-Ca-rich, Fe-poor garnets in garnetite, garnet-hedenbergite, and garnet-cummingtonite rocks at Broken Hill have Eu/Eu*?>?1, whereas garnet in Mn-poor, Fe-rich quartz garnetite and quartz-garnet-gahnite rocks from Broken Hill, and quartz garnetite from other locations have Eu/Eu*?<?1. The REE patterns of garnet and its host rock and interelement correlations among REEs and major element contents in garnet and its host rock indicate that the Eu anomaly in garnet reflects that of its host rock and is related to the major element composition of garnet and its host rock. The value of Eu/Eu* in garnet is related to its Mn, Fe, and Ca content and that of its host rock, and the distribution of REEs among garnet and accessory phases (e.g., feldspar). Positive Eu anomalies reflect high amounts of Eu that was preferentially incorporated into Mn- and Mn-Ca-rich oxides and carbonates in the protolith. In contrast, Eu/Eu*?<?1 indicates the preferential discrimination against Eu by Fe-rich, Mn-poor precursor minerals. Precursors to Mn-rich garnets at Broken Hill formed by precipitation from cooler and more oxidized hydrothermal fluids compared to those that formed precursors to Mn-poor, Fe-rich garnet at Broken Hill and the other locations. Garnet from the Broken Hill deposit is enriched in Zn (> 400?ppm), Cr (> 140?ppm), and Eu (up to 6?ppm and positive Eu anomalies), and depleted in Co, Ti, and Y compared to garnet in garnet-rich rocks from other localities. These values, as well as MnO contents ?>?15 wt. % and Eu/Eu*?>?1 are only found at the Broken Hill deposit and are good indicators of the presence of Broken Hill-type mineralization. 相似文献
8.
赣中周潭群石榴石、斜长石和黑云母微区化学成分特征及其地球动力学意义 总被引：5，自引：0，他引：5
周潭群变质岩中石榴石、斜长石和黑云母微区化学成分变化明显，石榴石变斑晶具典型的生长环带，由晶体中心向两侧边缘XMg、XFe值以光滑曲线递增，XCu、XMn值以光滑曲线递减，反映其增温过程；晶体最边缘的化学成分反映变质峰期的温度条件。通过石榴石变斑晶生长环带剖面分析，应用Grt-Bi温度计和GASP压力计，确定本区变质作用PT轨迹为顺时针形式，发生于大陆碰撞造山带环境。 相似文献
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辽东弓长岭—岫岩地区位于胶—辽—吉造山带东段,区内发育厚层古元古代变质沉积岩系,本文对这些变质沉积岩进行了岩相学和U-Pb年代学等方面的研究。岩相学特征显示这些岩石变质程度普遍偏低,多为绿片岩相变质条件,未发现高级特征变质矿物。岩石中主要矿物颗粒为石英,其中北辽河群碳酸盐矿物较为发育。根据辽东弓长岭-岫岩地区古元古代变沉积岩碎屑锆石阴极发光（CL）图像,这些锆石普遍具有清晰的振荡环带和较高的Th/U值（>0.3）,表明其原岩来自岩浆岩。结合LA-ICP-MS U-Pb年代学,得到里尔峪组、高家峪组、大石桥组和盖县组碎屑锆石分别呈现出2 159、2 500、2 189/2 530和2 044/2 197 Ma的年龄峰值,表明其沉积物来源于古元古代花岗质岩石和相邻的太古宙杂岩。结合前人资料,本文认为南、北辽河岩群形成于相同的环境并经历了相同的构造演化过程,古元古代弧-陆碰撞模式可能更适用于胶—辽—吉造山带的构造演化。 相似文献
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大别山区变质岩中蓝晶石的几种退变质反应及其所指示的动力学过程 总被引：3，自引：2，他引：3
蓝晶石在大别山含柯石英和不含柯石英的榴辉岩、高压变质的副片麻岩、非高压变质的宿松群的变质沉积岩中都是重要的变质矿物。它们多有冠状或其它的变质反应结构，形成多样化的退变质反应矿物。有些退变质反应是十分罕见的。本文报道了８种蓝晶石的矿物组合和退变质反应，推测和计算了变质反应的温度－压力条件，从而探讨了它们代表的近等温降压、升温降压和流体为重要因素的降温降压的不同的动力学过程。这些数据与用其它变质矿物所得到的温度压力条件和ＰＴｔ演化基本一致。为探讨大别山超高压变质带的构造演化提供了新的依据。 相似文献
11.
北秦岭松树沟榴辉岩的确定及其地质意义 总被引：9，自引：8，他引：1
松树沟石榴石角闪岩(榴闪岩)呈透镜状产于松树沟超镁铁岩旁侧的斜长角闪岩中,一直以来被认为是形成于接触交代变质或麻粒岩相变质过程。详细岩相学及矿物元素分析,在榴闪岩的基质矿物、石榴石幔部及锆石包体中发现残留的绿辉石,而且石榴石也保存了明显的进变质主、微量元素成分环带,表明松树沟榴闪岩为榴辉岩退变质的产物,至少经历了从角闪岩相到榴辉岩相再到角闪岩相的三阶段顺时针PT演化过程。锆石定年结果得到榴辉岩的变质年龄为500±8Ma,原岩结晶时代为796±16Ma,与秦岭岩群北侧官坡超高压榴辉岩的变质年龄和原岩年龄完全一致,也与北秦岭区域高压-超高压变质时代和原岩的结晶时代一致。表明松树沟榴辉岩与北秦岭造山带已发现的高压-超高压变质岩石一起都应是古生代大陆深俯冲作用的结果,而松树沟超镁铁岩可能是俯冲的大陆板片在折返过程中携带的俯冲隧道中的交代地幔岩。 相似文献
12.
The geochemical patterns of major and trace elements in zonal garnets and the mineral inclusions in them formed by progressive and regressive metamorphism of pelites are established. It is shown that an increase in temperature and pressure led to a decrease in the Y and HREE contents in garnets, and the increase in their contents is related to a decrease in the PT-parameters of their formation. A negative correlation between the CaO and REE contents in garnet indicates their isomorphism. The main reason for the sharp increase in the CaO content in garnets during collision metamorphism is mass transfer between the garnet and the plagioclase. The deviations from this situaiton, which are expressed in simultaneous increase in the grossular component in garnet and the anorthite component in plagioclase, are caused by metamorphic reactions related to the epidote decomposition. The mass transfer of major and trace elements between the reacting phases in metamorphic reactions mostly occurred with preservation of the balance of matter. The mirror shape and the character of the REE patterns of the rock-forming minerals relative to the composition of the rock indicate the equilibration of the HREE and Y contents between garnet, the major concentrator of these elements in the rock, and other phases. The balance between the LREEs and HREEs in the rock is achieved by the presence of variable amounts of monazite. 相似文献
13.
《International Geology Review》2012,54(2):95-119
Eclogites are often the only tangible high-pressure evidence we have from a paleosubduction zone, and they potentially preserve important geochemical information from the descending slab. Selected Group B/C eclogites and metapelites from the Trescolmen locality in the Adula nappe in the central Swiss Alps were chosen for a detailed investigation to determine oxygen isotope ratios and major- and trace-element compositions of the main rock-forming minerals. Complex major-element zonation patterns in garnet porphyroblasts indicate a pre-Alpine, medium-pressure growth history coupled with a high-pressure modification during the Alpine orogeny. Garnet REE patterns are notably HREE depleted in rim regions, with high overall REE content, particularly in the cores of grains. Omphacites are relatively homogenous in major elements, and show LREE- and HREE-depleted patterns, but with overall abundances of REEs lower than in garnets. These patterns are best explained by partitioning of the HREEs into garnet and the LREEs into zoisite. Oxygen-isotope systematics indicate limited fluid flow in eclogites and surrounding metapelites. δ18O values of quartz and garnet at the interface between eclogites and metapelites are indistinguishable and point to fluid exchange. Oxygen equilibrium conditions among rock-forming minerals, particularly between quartz and garnet in eclogites and metapelites, were reached, and fractionation indicates temperatures of ～600°C. The δ18O of unaltered eclogites (5.5 to 7.5 ‰) suggests a basaltic, MORB-type protolith. 相似文献
14.
Along with eclogitized gabbro and gabbronorite bodies, boudinaged metaultramafites such as garnet-pyroxene rocks and orthopyroxenites were revealed in the Archean plagiogneiss strata of the Gridino complex. The garnet-pyroxene rock crope out as a boudin on Vysokii Island. The early stage of the rock evolution is documented by inclusions of diabantite (Fe-Si chlorite), a mineral that occurs in metasomatized peridotites. Diabantite was found in all rock-forming minerals in paragenesis with mineral phases enriched in REE (Ce, Nd, La, etc.), U, and Th. The confinement of ore phases to the inclusion rims and the development of two systems of cracks, radial and concentric, around the inclusions in pyroxenes point to the transformation of the inclusions after their trapping. Thermobarometric studies of the crystal cores revealed that the anhydrous paragenesis garnet + orthopyroxene + clinopyroxene, which replaced the chlorite-bearing rock, formed at ~690 ºC and ~17 kbar. The rims of the rock-forming minerals reflect isothermal decompression to ~12 kbar, which was followed by decompression cooling to ~650 ºC and ~9 kbar with the formation of regressive amphibole-garnet-pyroxene paragenesis. The giant-grained orthopyroxenites compose chains of boudinaged bodies on Izbnaya Luda Island. The orthopyroxene crystals host abundant amphibole, quartz, biotite, and pyrite inclusions pointing to amphibolite metamorphism at the early stage of the rock evolution. There are two types of amphibole: magnesian hornblende and anthophyllite. The hornblende is a primary mineral, whereas the low-temperature anthophyllite forming rims around the quartz inclusions was produced at the regressive stage of metamorphism. There are no indicators of the PT-conditions of the peak metamorphism in the orthopyroxenite. The reaction enstatite + quartz + H2O = anthophyllite allows deciphering water activity of anthophyllite formation, a ≤ 0.5. 相似文献
15.
Yu. M. Lebedeva V. A. Glebovitskii S. A. Bushmin E. S. Bogomolov E. V. Savva K. I. Lokhov 《Doklady Earth Sciences》2010,432(1):602-605
The Sm-Nd isotope-chronological method is used for the first time to investigate the whole rock and rock-forming minerals
from metasomatic sillimanite orthopyroxene rocks in the Por’ya Guba nappe of the Lapland granulite belt. As a result isochrone
values of the age are obtained, which allows estimate the minimum time intervals that have passed from the moment of formation
of the investigated rocks. They indicate that peak conditions of collision metamorphism in fluid-permeable shear zones of
the LGB occurred in the Paleoproterozoic Svekofennian age when high-temperature high-pressure sillimanite-orthopyroxene metasomatic
rocks were formed. The obtained data make it possible to assume that, with regard to the measurement errors, high-pressure
metasomatism did not last over 10 Ma, and this process did not coincide in time with older medium pressure metamorphism. 相似文献
16.
The major and trace element compositions of nine eclogites from the Dabie–Sulu ultrahigh pressure (UHP) metamorphic terrane in eastern China were determined for both whole rock and the main constituent minerals, garnet and clinopyroxene. The results indicate that the eclogite protoliths originated from a basaltic magma, which formed in a continental setting as shown by isotopic and immobile element data. Based on the garnet REE characteristics, the eclogites can be roughly divided into two groups. Group 1 has LREE enrichment with no Eu anomaly for whole rock, and smooth LREE depletion but HREE enrichment pattern for garnet, whereas group 2 shows a depletion of LREE with a pronounced positive Eu anomaly and flat HREE pattern for both whole rock and garnet. From these features, we suggest that the protoliths for group 2 are Fe–Ti–gabbros with relatively high cumulus plagioclase and Fe–Ti oxide, whereas the group 1 eclogites are probably from basalts. Therefore, the unusual garnet REE pattern observed in group 2 can be considered as an important signature for identifying gabbro protoliths for eclogites. The identification of gabbro protoliths from the eclogites in the Dabie–Sulu terrane provides evidence for Neoproterozoic rift magmatism in the northern margin of the Yangtze craton. During ultrahigh pressure metamorphism in the Dabie–Sulu terrane, LILEs (including Ba, Rb, Th, U, K) had high mobility, but REEs and HFSEs were immobile, and trace element distribution equilibrium was approached between garnet and clinopyroxene. An estimate of mass balance indicates that garnet and clinopyroxene host the majority of HREEs and Y, and clinopyroxene is a significant host for Sr, but minor and accessory minerals predominantly account for LREEs, Th, U, and Zr. 相似文献
17.
Metabasic rocks related to pre-Cambrian protoliths from the lower portion of the deep crust of the Serre (Calabria, southern Italy) contain porphyroblastic garnet up to 5–6 cm in diameter. Garnet forms coronas around the inclusions of clinopyroxene and is in contact with various matrix minerals. Both inner and outer coronas formed under granulite facies conditions after the thermal peak during the Hercynian reworking. Six porphyroblastic garnets (≥1 cm in diameter) from four samples have been dated with the Sm-Nd method to constrain the distinct metamorphic stages and, possibly, to investigate the diffusion of Sm and Nd in garnet. They show in the core major element flat profiles whereas one of these, analyzed for REEs, preserves only a feeble zoning. This suggests that the diffusion rates of REEs are effective at the crystal scale. The apparent Nd ages range from 354 to 88 Ma, without any reproducibility in each and in all rock samples. The oldest age of 354 Ma is interpreted as the primary isotopic signatures linked to prograde metamorphism. The interpretation of younger ages (309, 272, 215, 143 and 88 Ma) requires a detailed discussion about: (i) possible modification of chemical and isotopic composition of the rocks during and after garnet growth, (ii) possible contamination by inclusions in garnet, (iii) inherited isotopic disequilibrium, (iv) new growth or recrystallization of garnet and (v) possible isotopic resetting of large crystals which, in principle, is hampered by the slow diffusion of REE’s in garnet. Some of the Nd ages are similar to U-Pb ages of zircon from the metabasic rocks of deep crustal rocks of the Serre (350, 300 and 280 Ma). This convergence of apparent ages can hardly be considered as simply fortuitous. Thus, since: (i) corona formation was fluid-assisted and (ii) all porphyroblasts were broken up into several fragmented subgrains by sets of fractures resulting in smaller volumes, the volume diffusion and the possible role of high-T fluids on the resetting of Sm-Nd ages are discussed. The calculated ages of 354, 309 and 272 Ma are considered as geologically meaningful and related to the thermal peak and subsequent decompression and cooling stage of the Variscan metamorphism. 相似文献
18.
The Makbal Complex in the northern Tianshan of Kazakhstan and Kyrgyzstan consists of metasedimentary rocks, which host high‐P (HP) mafic blocks and ultra‐HP Grt‐Cld‐Tlc schists (UHP as indicated by coesite relicts in garnet). Whole rock major and trace element signatures of the Grt‐Cld‐Tlc schist suggest a metasomatized protolith from either hydrothermally altered oceanic crust in a back‐arc basin or arc‐related volcaniclastics. Peak metamorphic conditions of the Grt‐Cld‐Tlc schist reached ~580 °C and 2.85 GPa corresponding to a maximum burial depth of ~95 km. A Sm‐Nd garnet age of 475 ± 4 Ma is interpreted as an average growth age of garnet during prograde‐to‐peak metamorphism; the low initial εΝd value of ?11 indicates a protolith with an ancient crustal component. The petrological evidence for deep subduction of oceanic crust poses questions with respect to an effective exhumation mechanism. Field relationships and the metamorphic evolution of other HP mafic oceanic rocks embedded in continentally derived metasedimentary rocks at the central Makbal Complex suggest that fragments of oceanic crust and clastic sedimentary rocks were exhumed from different depths in a subduction channel during ongoing subduction and are now exposed as a tectonic mélange. Furthermore, channel flow cannot only explain a tectonic mélange consisting of various rock types with different subduction histories as present at the central Makbal Complex, but also the presence of a structural ‘dome’ with UHP rocks in the core (central Makbal) surrounded by lower pressure nappes (including mafic dykes in continental crust) and voluminous metasedimentary rocks, mainly derived from the accretionary wedge. 相似文献
19.
江西南城震旦系周潭群变质岩地球化学特征 总被引：1，自引：0，他引：1
周潭群变质岩其主要岩石类型的ＳｉＯ２含量为５８％～７３％,Ｋ２Ｏ＋Ｎａ２Ｏ大多为４％～６％。稀土配分型式均为右倾负斜率轻稀土富集型,全部样品出现负Eu异常。岩石中Ｓｎ、Ｓｂ、Ｓ、Ｃｏ、Ｎｉ、Ｈｇ、Ｍｏ含量低于克拉克值,而Ｌｉ、Ｒｂ、Ｃｓ等碱性元素含量偏高,特别是微量元素组合Ａｎ、Ａｇ、Ａｓ、Ｐｈ、Ｚｎ含量明显高于克拉克值。周潭群变质岩形成年龄为６７２±７２Ｍａ,相当于震旦系底部层位,变质相应属低角门岩相,其原岩体系应为一套复理石或类复理石泥砂岩建造。 相似文献
20.
Geochemical studies on REE, trace elements and oxygen isotopes from metamorphic veins and their host metasedimentary rocks in the Zhoutan Group at two localities, Xiangshan and Yihuang, in central Jiangxi Province have been conducted in this paper. The results show that the metamorphic quartz veins inherited the REE and oxygen isotope geochemical characteristics from their host rocks, suggesting that the vein-forming fluids were derived from the host rocks. Additionally, fractionation degrees of the trace element pairs Zr-Hf, Nb-Ta, Y-Ho and U-Th in the veins are different from those of their host rocks. It is also indicated that the veins are the products of the fluids. The metamorphic veins within the Zhoutan Group metasedimentary rocks were formed principally as a result of lateral diffusion of the metamorphic fluids. 相似文献