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1.
The boron isotopic composition of zoned tourmaline in two metasediments from the island of Syros, determined by secondary-ion mass spectrometry (SIMS), reflects the sedimentary and metamorphic record of the rocks. Tourmaline from a silicate-bearing marble contains small (≤20 μm) detrital cores with highly variable δ 11B values (−10.7 to +3.6‰), pointing to a heterogeneous protolith derived from multiple sources. The sedimentary B isotopic record survived the entire metamorphic cycle with peak temperatures of ∼500°C. Prograde to peak metamorphic rims are homogeneous and similar among all analysed grains (δ 11B ≈ +0.9‰). The varying δ 11B values of detrital cores in the siliceous marble demonstrate that in situ B isotope analysis of tourmaline by SIMS is a potentially powerful tool for provenance studies not only in sediments but also in metasediments. A meta-tuffitic blueschist bears abundant tourmaline with dravitic cores of detrital or authigenic origin (δ 11B ≈ −3.3‰), and prograde to peak metamorphic overgrowth zones (−1.6‰). Fe-rich rims, formed during influx of B-bearing fluids under retrograde conditions, show strongly increasing δ 11B values (up to +7.7‰) towards the margins of the grains. The δ 11B values of metamorphic tourmaline from Syros, formed in mixed terrigenous–marine sediments, reflect the B signal blended from these two different sources, and was probably not altered by dehydration during subduction.  相似文献   

2.
Tourmalinites from the Golden Dyke Dome,Northern Australia   总被引：1，自引：0，他引：1  
Tourmalinites occur at five stratigraphic levels within the low metamorphic grade multiply deformed Lower Proterozoic metasediments and metavolcanics of the Golden Dyke Dome. The geological setting, exhalite associations, sedimentary structures and tourmaline chemistry all preclude a granitic origin. Tourmalinite derived from the isochemical metamorphism of an exhalite comprising silica and tourmaline. Tourmalinite and other exhalites are hosted by carbonaceous pelitic metasediments and were deposited in deeper basinal areas. The ore fluid was probably dolerite-heated seawater which leached a thick pile of argillaceous sediments and acquired metals and boron by leaching. The first and second increase in geothermal gradient produced tourmalinite, the third produced auriferous tourmalinite and iron formations with tourmalinite and exhalative Pb-Zn deposits forming during the period of maximum geothermal gradient. More tourmalinite formed during the subsequent decline in geothermal gradient. Tourmalinites are regarded as B-rich iron formations which can be the host for or associated with exhalative deposits of Au and base metals.  相似文献   

3.
Evidence for anisotropy in the super-thick sedimentary basin under the northern Bay of Bengal is presented. Surface wave group velocity data given by Brune and Singh (1986) is better fit by an anisotropic model than an isotropic one. This lends support to the hypothesis that the mid-crustal rocks are metasediments and that the section of sediments and metasediments is more than 20 km thick.  相似文献   

4.
SHRIMP (Sensitive High‐Resolution Ion MicroProbe) analytical procedures have been developed to enable dating of the small, early diagenetic xenotime overgrowths that commonly occur on zircons in siliciclastic sedimentary rocks. The method will be particularly useful in Precambrian terranes, where diagenetic xenotime dating could play a role equivalent to biostratigraphic dating in the Phanerozoic. Reliable 207Pb/206Pb data are more readily obtained than 206Pb/238U, which also favours application to the Precambrian. However, it is demonstrated that 206Pb/238U dating of larger overgrowths (>10 μm) is also viable and applicable to Phanerozoic samples. SHRIMP Pb/Pb geochronology of authigenic xenotime in an unmetamorphosed Palaeoproterozoic sandstone in the Kimberley Basin has constrained diagenesis to a precision of ± 7 Ma. In contrast, greenschist‐facies metasediments of the Archaean Witwatersrand Basin, South Africa, contain both authigenic and alteration xenotime that record a complex history of growth from early diagenesis to the last major thermal event to affect the basin.  相似文献   

5.
Three types of tourmaline occurrence have been identified in the area of Bin Yauri, Nigeria, mesothermal lode-gold mineralization. These are: (1) stratabound tourmalinites in pelitic metasediments, (2) tourmaline in a hydrothermal alteration assemblage within hornfelsed wall rocks, (3) tourmaline in auriferous quartz and quartz-carbonate veins. Although the tourmaline occurrences are all within or close to the contact aureole of a granodiorite intrusion, geochemical characteristics of the tourmalines are broadly similar and reflect a common metasedimentary source. Two stages of tourmalinization are envisaged. The earlier (ca. 1100 Ma) involved syngenetic-diagenetic formation of tourmalinites, while the later (ca. 500 Ma) involved epigenetic (hydrothermal) tourmaline-gold mineralization, possibly derived by dehydration and devolatilization of metasedimentary sequences containing tourmaline-rich rocks or tourmalinites. Electron microprobe analyses indicate that the tourmalines are intermediate members of the schorl-dravite solid solution series. Plots involving FeO, MgO, and/or Al2O3 from these analyses are used to constrain the sources and processes of tourmalinization. Two metallogenic implications are derived from this study. One is that, although the tourmalinites are barren of gold and base metal mineralization, their occurrences nevertheless encourages exploration for syngenetic-exhalative massive sulphide deposits in the region. The other implication applies to the potential use of tourmaline in deciphering the physico-chemical conditions of gold-mineralizing fluids in the Bin Yauri area.  相似文献   

6.
In this provenance study of late Palaeozoic metasediments of the Eastern Andean Metamorphic Complex (EAMC) along the south Patagonian proto-Pacific margin of Gondwana, the palaeogeological setting of the continental margin in Devonian–Carboniferous and Permian times is reconstructed. The study is based on detrital heavy mineral contents, chemical compositions of tourmaline grains, and whole rock element and Nd-Sr isotopic compositions. Element and isotopic compositions reveal that Devonian–Carboniferous metaturbidites deposited before the development of a Late Carboniferous–Permian magmatic arc along the margin were mainly fed from felsic, recycled, old continental rocks. The last recycling phase involved erosion of metasediments that were exposed in Patagonia. Feeder systems to the basin cut either through epidote-rich or garnet-rich metasediments. In Permian time, EAMC metaturbidites were deposited next to the evolving magmatic arc and were derived from felsic, crustal rocks. Two provenance domains are recognised. The metasediments of the northern one are chemically similar to those of the Devonian–Carboniferous metasediments. This domain was fed from the metasedimentary host rocks of the magmatic arc. The southern domain probably was fed from the arc proper, as indicated mainly by the dominance of metaplutonic lithic fragments, abundant detrital biotite, and the major element composition of the metasediments.  相似文献   

7.
Chemical compositions of tourmaline from the vein-type tungsten deposits of the Kaneuchi mine in Japan are obtained with an electron probe microanalyzer. Tourmaline occurring at this mine belongs to the dravite-schorl series. Magnesium contents are high compared with tourmaline from granitic zones. This suggests that ore-forming solutions are not formed directly from magmatic fluid and reacted with sedimentary rocks. Compositions of tourmaline in quartz veins are similar to those in host rocks, and the bulk compositions of host rocks do not indicate magnesium metasomatic reactions. It can therefore be concluded that water/rock interactions occurred at a deeper level which remains unexplored.  相似文献   

8.
Heavy mineral analysis of the late Paleozoic Barakar and Raniganj sandstones from the Singrauli Gondwana sub-basin shows relative abundance of garnet, epidote, zircon, tourmaline and muscovite in the Raniganj Sandstone and epidote, garnet, rutile and tourmaline in the Barakar sandstones. Stratigraphically, the heavy mineral crops donot exhibit marked variation in their relative abundance, though garnet, epidote and muscovite form the bulk of the heavy minerals. Significant interspecific association among heavy minerals and provenance of the Barakar and Raniganj sandstones are evaluated by using σ-M multivariate model. Quantitative result suggests that the Barakar Sandstone are characterized by the basic pair match significantly more than expected due to chance alone (p value <<0.05) are garnet-tourmaline and epidote-rutile, whereas, the succeeding Raniganj sandstone are characterized by zircon-rutile and epidote-garnet. These basic pairs may be regarded as interspecific association among the heavy minerals. The basic pairs deduced from heavy mineral suites suggest that the source rocks of late Paleozoic Barakar and Raniganj sandstones have been principally derived from the acid plutonic rocks and low to high grade metasediments lying to the south and southeast of the Singrauli Gondwana sub-basin.  相似文献   

9.
The Qiman Tagh W-Sn belt lies in the westernmost section of the East Kunlun Orogen, NW China, and is associated with early Paleozoic monzogranites, tourmaline is present throughout this belt. In this paper we report chemical and boron isotopic compositions of tourmaline from wall rocks, monzogranites, and quartz veins within the belt, for studying the evolution of ore-forming fluids. Tourmaline crystals hosted in the monzogranite and wall rocks belong to the alkali group, while those hosted in quartz veins belong to both the alkali and X-site vacancy groups. Tourmaline in the walk rocks lies within the schorl-dravite series and becomes increasingly schorlitic in the monzogranite and quartz veins. Detrital tourmaline in the wall rocks is commonly both optically and chemically zoned,with cores being enriched in Mg compared with the rims. In the Al-Fe-Mg and Ca-Fe-Mg diagrams,tourmaline from the wall rocks plots in the fields of Al-saturated and Ca-poor metapelite, and extends into the field of Li-poor granites, while those from the monzogranite and quartz veins lie within the field of Li-poor granites. Compositional substitution is best represented by the MgFe_(-1), Al(NaR)_(-1), and AlO(Fe(OH))_(-1) exchange vectors. A wider range of δ~(11)B values from -11.1‰ to -7.1‰ is observed in the wall-rock tourmaline crystals, the B isotopic values combining with elemental diagrams indicate a source of metasediments without marine evaporates for the wall rocks in the Qiman Tagh belt. The δ~(11)B values of monzogranite-hosted tourmaline range from -10.7‰ and-9.2‰, corresponding to the continental crust sediments, and indicate a possible connection between the wall rocks and the monzogranite. The overlap in δ~(11)B values between wall rocks and monzogranite implies that a transfer of δ~(11)B values by anataxis with little isotopic fractionation between tourmaline and melts. Tourmaline crystals from quartz veins have δ~(11)B values between -11.0‰ and-9.6‰, combining with the elemental diagrams and geological features, thus indicating a common granite-derived source for the quartz veins and little B isotopic fractionation occurred. Tourmalinite in the wall rocks was formed by metasomatism by a granite-derived hydrothermal fluid, as confirmed by the compositional and geological features.Therefore, we propose a single B-rich sedimentary source in the Qiman Tagh belt, and little boron isotopic fractionation occurred during systematic fluid evolution from the wall rocks, through monzogranite, to quartz veins and tourmalinite.  相似文献   

10.
泥灰岩中自生方解石的稀土元素酸溶方法研究   总被引：1，自引：0，他引：1  
碳酸盐岩稀土元素是沉积环境示踪的理想参数,但由于自生沉积碳酸盐矿物的稀土元素含量远低于陆源黏土等其他矿物,在样品处理过程中少量陆源黏土矿物的溶解,将影响沉积环境的示踪。因此,如何在样品处理过程中避免陆源黏土矿物中稀土元素的释放,从而获得海洋环境自生沉淀形成的碳酸盐矿物中的元素方法非常重要。本文应用地层中常见的同一泥灰岩样品,分别用5%醋酸、5%盐酸、2%和5%硝酸浸取,采用0.5 h、1 h、2 h、3 h、6 h和24 h的反应时间,用X射线衍射法（XRD）分析酸不溶残渣矿物组成、电感耦合等离子体原子发射光谱法（ICP-AES）测定酸可溶相溶液的主元素和微量元素含量、电感耦合等离子体质谱法（ICP-MS）测定酸可溶相溶液的稀土元素含量,结果表明所有酸溶均可完全溶解泥灰岩中的方解石矿物,并有少量黏土发生溶解,导致稀土总量和Ce/Ce＊增高,但对Eu/Eu＊、LaN/YbN和Gd/Gd＊等参数没有影响。泥灰岩中自生方解石的稀土元素理想溶样条件是5%醋酸反应1 h以内,溶液的ICP-MS分析结果适用于示踪沉积环境的氧化还原条件。  相似文献   

11.
Tourmaline bearing leucogranite occurs as a pluton with pegmatitic veins intruding the Archaean granodiorite in the Bastipadu area, Kurnool district of Andhra Pradesh. We present field and petrographic relations, mineral chemistry and geochemical data for the leucogranite. It is essentially a two-mica granite, composed of quartz, perthite, microcline, albite, tourmaline and muscovite along with minor biotite and titanite. The euhedral tourmalines are regularly distributed in the rock. The geochemical studies show that the leucogranite is calc-alkaline, peraluminous to metaluminous which formed in a syn-collisional to volcanic arc-related setting. It displays strong ‘S’ type signatures with high K/Na ratios, moderately fractionated light rare earth elements, relatively flat heavy rare earth elements with \(\hbox {[Ce/Yb]}_\mathrm{N} \le 27.8\) and a strong negative Eu anomaly. The geochemical characteristics indicate that the leucogranite melt might have been generated from partial melting of metasediments. Electron probe microanalyser data show the presence of alkali group tourmaline in leucogranite represented by schorl and dravite. Tourmaline compositions plot in the Li-poor granitoids and associated pegmatites and aplites and metapelites/metasammites fields. Partial melting of boron-enriched source rocks is linked with the development of tourmalines in the leucogranite.  相似文献   

12.
在内蒙古西乌珠穆沁旗晚石炭世—早二叠世阿木山组第三段泥晶灰岩中发现有海绿石。对海绿石的微观特征分析表明,阿木山组海绿石呈团粒状结构,同时呈胶体产出于方解石周边,显示了原生海绿石的基本特点。电子探针的组分分析表明,阿木山组中的海绿石为高成熟度的海绿石。通过对不同地区和不同环境下海绿石的组分特征分析,建立了一种海绿石沉积的理想模式,同时揭示了阿木山组第三段海绿石化作用是在含氧量不够充分的弱还原状态下的正常浅海中进行的。本区阿木山组的下碎屑岩段和上灰岩段是在海水两进两退环境下的沉积,阿木山组灰岩中发现的海绿石则有可能代表了一个海进的开始。本区海绿石的发现及研究,对于进一步研究该区层序地层特征、地层格架及区域地层对比具有重要意义。  相似文献   

13.
前寒武纪沉积岩中自生独居石的发现及其意义   总被引：5，自引：1，他引：5  
由于受到葛家屯组中发现自生方铅矿的启发 ,首次于大连前寒武纪震旦系十三里台组泥岩中发现了自生独居石 ,这一发现为在中国北方前寒武纪沉积岩中寻找自生独居石提供了重要的线索。它为进一步探索 U、Th- Pb同位素测年拓展了新的研究领域和提供了可能性。本文列举了中国北方前寒武纪沉积岩中 Ce元素异常以及 REE较高的例证 ,认为上述地区都有可能发现自生独居石。同时介绍了最近又在北京十三陵中元古代的常州沟组和串岭沟组所发现自生独居石的新资料。研究表明 ,自生独居石的电子探针扫描形态 ,与岩浆岩、变质岩及砂矿中截然不同。在地质年代分布上 ,元古宙 REE相对丰度较高 ,特别是 L REE较高的泥质岩多数来自古陆壳上。资料对比结果显示 :在 L a+Ce+Nd、Yb+Y、Sm+Gd+Dy三角图中 ,北京十三陵元古宙泥质岩、大连震旦系十三里台组泥岩和辽南 -辽西中元古代泥质岩都属于近古陆的沉积类型。首次提出 ,中国北方元古宙沉积与南方震旦系磷块岩沉积环境存在明显的不同并反映在三角图中 ,前者离 L a+Ce+Nd端点近 ,而后者由于成因上属于洋流上升沉积物而远离该端点。按照大连震旦系十三里台组沉积环境特点 ,自生独居石应为生物成矿作用的产物 ,含矿物泥岩形成于总体氧化环境中的局部还原亚环境中。基于此 ,建立了  相似文献   

14.
大连震旦系十三里台组首次发现自生稀土元素矿物独居石后 ,在北京十三陵中元古代长城系常州沟组、串岭沟组和大红峪组又发现了自生的独居石以及其他磷酸盐和硅酸盐稀土矿物。自生稀土矿物的形成和岩石中稀土元素含量较高有关 ;电子探针背散射图像和 P、Th、L a、Ce、Nd、Y等元素面分布图像研究表明 ,沉积岩中的自生稀土矿物与岩浆岩、变质岩和碎屑成因的截然不同。本文首次报道了元古宙长城系常州沟组沉积岩中碎屑锆石边部成岩过程中形成的自生磷钇矿。中国北方元古宙泥砂质碎屑沉积岩普遍具有高稀土组合 ,许多地区都可能存在独居石等自生稀土矿物 ,如天津蓟县、辽西、辽南和宣化等地 ,为利用离子探针 (SHRIMP)确定其同位素地质年代提供了可能。此外 ,本文对比了大连震旦系自生独居石和内蒙白云鄂博矿区东矿的独居石晶形和化学成分的相似性 ,再一次提出中国北方元古宙富稀土地层可能是内蒙古白云鄂博巨型稀土元素矿床的矿源层问题。  相似文献   

15.
普宜地区位于上扬子腹地——四川盆地东南缘,区内晚三叠世碎屑岩记录了上扬子前陆盆地演化信息,是研究盆地东缘盆山耦合的理想对象.二桥组主要由三角洲平原-三角洲前缘相砂岩组成,交错层理恢复的物源主要来自东侧,砂岩岩屑主要由岩浆岩岩屑和变质岩岩屑组成,碎屑重矿物主要由锆石、电气石、金红石、白钛石、黄铁矿、锐钛矿、石榴子石、铬铁...  相似文献   

16.
电气石的LA—MC—ICPMS原位微区硼同位素分析方法是最近几年新兴的一种高效经济的硼同位素分析方法。对上堡晚白垩世含电气石二云母花岗岩的电气石进行LA—MC—ICPMS原位微区的硼同位素研究发现,其具有非常均一的¨B／mB比值（3．9908～3．9979）~H万¨B值（加权平均为（一12．86＋0．19）‰）。结合区域地质资料以及其他已有的硼同位素资料,提出上堡花岗岩中硼来源于沉积岩,可能的源区是邻近花岗岩体的石炭一二叠系的沉积地层或深埋在地壳中的沉积物质。在晚白垩世,华南处于伸展的背景中,幔源岩浆的底侵带来的巨大的热源使地壳中的沉积物质发生熔融,形成强过铝质的花岗质浆,在岩浆演化的晚期形成电气石。  相似文献   

17.
Authigenic Carbonate Formation in the Ocean   总被引：1，自引：0，他引：1  
Oceanic authigenic carbonates are classified according to the origin of carbonate carbon source using a complex methodology that includes methods of sedimentary petrography, mineralogy, isotope geochemistry, and microbiology. Mg-calcite (proto-dolomite) and aragonite predominate among the authigenic carbonates. All authigenic carbonates are depleted in heavy carbon isotope 13 and enriched in heavy oxygen isotope 18O (in PDB system), indicating biological fractionation of isotopes during the carbonate formation. Results obtained show that authigenic carbonate formation is a biogeochemical (microbial) process, which involves carbon from ancient sedimentary rocks, abiogenic methane, and bicarbonate-ion of hydrothermal fluids into the modern carbon cycle.  相似文献   

18.
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19.
Tourmaline rocks of previously unclear genesis and spatially associated with W- (Cu)-bearing calc-silicate rocks occur in Palaeoproterozoic supracrustal and felsic intrusive rocks in the Bonya Hills in the eastern Arunta Inlier, central Australia. Tourmalinisation of metapelitic host rocks postdates the peak of regional low-pressure metamorphism (M1/D1, ~500 °C, ~0.2 GPa), and occurred synkinematically between the two main deformation events D1 and D2, coeval with emplacement of Late Strangways (~1.73 Ga) tourmaline-bearing leucogranites and pegmatites. Tourmaline is classified as schorl to dravite in tourmaline–quartz rocks and surrounding tourmaline-rich alteration zones, and as Fe-rich schorl to foitite in the leucogranites. Boron metasomatism resulted in systematic depletion of K, Li, Rb, Cs, Mn and enrichment of B, and in some samples of Na and Ca, in the tourmaline rocks compared to unaltered metasedimentary host rocks. Whole-rock REE concentrations and patterns of unaltered schist, tourmalinised schist and tourmaline–quartz veins—the latter were the zones of influx of the boron-rich hydrothermal fluid—are comparable to those of post-Archaean shales. Thus, the whole-rock REE patterns of these rocks are mostly controlled by the metapelitic precursor. In contrast, REE concentrations of leucogranitic rocks are low (10 times chondritic), and their flat REE patterns with pronounced negative Eu anomalies are typical for fractionated granitic melts coexisting with a fluid phase. REE patterns for tourmalines separated from metapelite-hosted tourmaline–quartz veins and tourmaline-bearing granites are very different from one another but each tourmaline pattern mirrors the REE distribution of its immediate host rock. Tourmalines occurring in tourmaline–quartz veins within tourmalinised metasediments have LREE-enriched (LaN/YbN=6.3–55), shale-like patterns with higher REE (54–108 ppm). In contrast, those formed in evolved leucogranites exhibit flat REE patterns (LaN/YbN=1.0–5.6) with pronounced negative Eu anomalies and are lower in REE (5.6–30 ppm). We therefore conclude that REE concentrations and patterns of tourmaline from the different tourmaline rocks studied are controlled by the host rock and not by the hydrothermal fluid causing boron metasomatism. From the similarity of the REE pattern of separated tourmaline with the host rock, we further conclude that incorporation of REEs in tourmaline is not intrinsically controlled (i.e. by crystal chemical factors). Tourmaline does not preferentially fractionate specific REEs or groups of REEs during crystallisation from evolved boron- and fluid-rich granitic melts or during alteration of clastic metasediments by boron-rich magmatic-hydrothermal fluids.Editorial responsibility: J. Hoefs  相似文献   

20.
我国电气石矿床类型及其地质特征   总被引：4，自引：0，他引：4  
卢宗柳 《矿产与地质》2008,22(2):174-178
在研究我国电气石矿产产出地质环境、成矿地质过程和电气石矿物组分特征的基础上,总结了我国电气石矿产成矿类型：花岗伟晶岩型、岩浆热液型、火山次火山热液型、热水沉积型和表生残积砂矿型。并阐述了各类型电气石矿床类型产出的时代、成矿地质特征和电气石矿物化学特征。  相似文献   

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