玲珑花岗岩体的变形磁组构特征及其与金矿的关系

本文利用磁组构的方法对玲珑花岗岩体的磁组构特征及其与金矿的关系进行研究.玲珑岩体的磁化率各向异性度P的平均值为1.2872,具有典型的构造变形成因特点;磁面理围绕其西北侧的北截花岗闪长岩展布,倾角平缓;磁线理呈SW向近水平展布.玲珑岩体的变形磁组构的特征表明玲珑岩体的变形磁组构是由于后期侵入的北截郭家岭花岗闪长岩体侵入造成的.研究还发现除了断裂的控矿作用以外,位于玲珑岩体内部和边缘的金矿和磁化率各向异性间存在密切的空间对应关系.金矿往往位于磁化率各向异性度P值高的区域,而磁化率各向异性度P值低的区域金矿很少.     

花岗岩构造研究及花岗岩构造动力学刍议

花岗岩可以视为一种很好的构造标志体,犹如褶皱、断裂一样。从花岗岩浆的形成、融体分离、岩浆上升到岩体定位以及变形改造的全过程都蕴含着丰富的构造动力学信息。研究花岗岩浆上升、迁移和定位可以探讨构造块体抬升及区域构造动力学。岩体生长方式与构造块体的运动学、动力学有密切的关系,极性生长揭示了上、下构造块体或岩石圈之间的相对的近水平方向剪切运移。变形花岗岩体是一种区域尺度的应变标志体,可以进行岩石有限应变测量和流变学参数估算,为分析区域构造变形特征提供应变参数。以对不同期次、不同变形程度花岗岩体为间接标志体,通过锆石定年可以限定变形的时间,特别是有可能确定早期变形的时间。岩体定位深度的系统研究有利于了解构造块体的抬升和深部构造作用。花岗岩构造与花岗岩成因类型特别是其演变研究的结合是判别构造块体动力学背景以及其转换的有效途径。通过这几方面的系统研究和有机结合,可以提供丰富的构造动力学信息,是否可能发展成较系统的花岗岩构造动力学值得探讨。     

Chemical weathering of granite under acid rainfall environment, Korea

Chemical weathering was investigated by collecting samples from five selected weathering profiles in a high elevation granitic environment located in Seoul, Korea. The overall changes of chemistry and mineralogical textures were examined reflecting weathering degrees of the samples, using polarization microscopy, X-ray diffraction (XRD), electron probe micro analysis (EPMA), X-ray fluorescence spectroscopy (XRF), and inductively coupled plasma–mass spectroscopy (ICP–MS). The chemical distribution in the weathering profiles shows that few trace elements are slightly immobile, whereas most major (particularly Ca and Na) and trace elements are mobile from the beginning of the granite weathering. On the other hand, there were mineralogical changes initiated from a plagioclase breakdown, which shows a characteristic circular dissolved pattern caused by a preferential leaching of Ca cation along grain boundaries and zoning. The biotite in that region is also supposed to be sensitive to exterior environmental condition and may be easily dissolved by acidic percolated water. As a result, it seems that some rock-forming minerals in the granitic rock located in Seoul are significantly unstable due to the environmental condition of acidic rainfall and steep slopes, where they are susceptible to be dissolved incongruently leading some elements to be highly depleted.     

Magma sources and gold mineralisation in the Mount Leyshon and Tuckers Igneous Complexes, Queensland, Australia: U-Pb and Hf isotope evidence

In situ LAM-ICPMS U-Pb, Hf-isotope and trace-element analyses of zircon have been used to evaluate the relative contributions of juvenile mantle and crustal sources to the intrusive rocks of the mafic to intermediate, gold-poor Tuckers Igneous Complex (TIC), and the spatially and temporally related, felsic Mount Leyshon Igneous Complex (MLIC), which hosts a gold-rich porphyry system.

The TIC intrusions range in age from 304.2 ± 9.1 Ma to 288.5 ± 6.4 Ma, and the MLIC intrusions from 291.0 ± 4.8 Ma to 288 ± 6 Ma. Cross-cutting relationships define the intrusion sequence from oldest to youngest; Diorite, Monzodiorite, Mafic Granodiorite and Biotite Microgranite within the TIC; Early Dyke, Southern Porphyry and Late Dyke within the MLIC.

Zircons from the earliest rock type within each complex have a wide range in _Hf (5.2 to 14.8 for the TIC Diorite, 2.0 to 12.4 for the MLIC Early Dykes) suggesting the mixing of juvenile and crustal magmas. This interpretation is supported by trace-element data that show the presence of two distinct zircon populations in the MLIC Early Dyke. The later intrusive rocks have narrower ranges in _Hf (typically < 4 _Hf units) and trace-element patterns of zircon. This homogeneity suggests derivation from magmas produced by further mixing and fractional crystallisation of the TIC Diorite and the MLIC Early Dyke magmas respectively. A greater crustal contribution to the gold-rich MLIC is inferred from the range of median _Hf (3.2 to 4.5 for the MLIC, 5.4 to 8.7 for the TIC). We suggest that the MLIC was derived by melting of more felsic crustal rocks, and with less input from juvenile mantle, then the TIC; it was not derived by fractional crystallisation of an intermediate to mafic TIC-like magma. Modelling of Hf isotope data yields a mean model age of 1040 ± 10 Ma (at ¹⁷⁶Lu/¹⁷⁷Hf = 0.015) for the crustal component in both complexes.

Gold was precipitated in the MLIC Breccia during the emplacement of the Late Dykes. The isotopically homogenous nature of the Late Dykes suggests that no additional juvenile-mantle input was involved at the mineralisation stage. This supports a model in which gold and other metals were indigenous to the Late Dykes magma and were concentrated by magma differentiation and fluid-evolution processes.     

太行-五台山区不同时代花岗岩类岩石学和地球化学的特征对比及陆壳演化

通过对太行－五台山区太古宙、元古宙和中生代等不同时代的花岗岩类岩石学和地球化学特征的对比，并将晚太古时期花岗岩类同国内外同时期花岗岩类进行对比，确定了本区晚太古时期花岗岩类岩石组合为英云闪长岩－奥长花岗岩－花岗闪长岩或英云闪长岩－奥长花岗岩－花岗闪长岩－花岗岩，并以奥长花岗岩演化趋势为主，叠加了部分钙碱性演化；而元古宙、中生代花岗岩类岩石组合则主要为花岗闪长岩－花岗岩或花岗岩，以钙碱性演化趋势为特征。可以认为晚太古时期的太行－五台山区正处于陆壳演化的初始阶段和成熟阶段之间的过渡性阶段。     

万洋山—诸广山花岗岩带铀成矿的区域地质背景

万洋山—诸广山复式花岗岩带,经历多期次的构造-岩浆活动,受到东西向和南北向的深部构造控制。岩带内北东、北北东、东西、南北及北西向五组线型断裂构造及规模不一的中心型环状构造发育。铀成矿的时空分布,受中生代南北向和东西向构造-岩浆活动带交汇区的宏观制约。矿床定位与中心型小环状构造交切及不同方向的线型断裂交叉密切有关。矿源既来自铀源层和花岗岩,也来自上地幔岩浆源。区域内地质-成矿事件复杂,经过了槽、台、洼三大演化阶段。地洼阶段构造-岩浆活动次数最多,最强烈。铀成矿作用形成于地洼阶段中晚期,即白垩-第三纪。铀成矿以内生热液(热水)为主,叠加有后生淋积矿化。     

新宁—灰汤断裂带花岗斑岩与煌斑岩脉的分布特征及其找矿意义

新宁一灰汤断裂南东盘,分布有数条北西向的花岗斑岩脉带,每条岩脉带内,产出有相同的矿床组合及类似的分带规律,构成一个北东向的多金属成矿带。成矿带北西部分为锑金成矿区,南东侧是铅锌铜钨成矿区。新宁—灰汤断裂与桃江—城步断裂控制的煌斑岩脉,具有明显区别,在某些地段具有钾镁煌斑岩主要特征,它对我省金刚石原生矿的突破,是一条重要线索与新途征。     

Comparative analysis of coatings on granitic substrates from urban and natural settings (NW Spain)

Rock coatings are frequent on natural rock outcrops and even more on stone surfaces of historical buildings and monuments. They are interesting as some of them have a protective effect against erosion. In the last 30 years, research on rock coatings has been performed separately on either buildings or natural outcrops. This paper studies and compares thin coatings found on granitic rock surfaces of historical buildings with coatings found on natural granite outcrops in a same climatic area (NW Spain) by analysing their surface and cross-sections. As rock surfaces of buildings have known age they can be used to assess rates of weathering and coating growth. This is the first comparative study of formation of coatings on natural and built surfaces in the same region. Both endogenous (rock characteristics) and exogenous factors (climatic conditions, air pollution) that could affect the coatings formation are considered to assess the origin and formation of coatings. X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) analyses of the underlying rocks, XRD analyses of the coatings and Scanning Electron Microscopy (SEM) observations of surface and cross-sections of the coatings, performing Energy Dispersive Spectrometry (EDS) and X-ray maps, were carried out to establish their composition. Fieldwork and results indicate that natural outcrops are widely covered by biological coatings or coatings formed due to rock weathering, while coatings found on rock ashlars are highly variable with air pollution, other building materials, organic droppings and micro-environmental factors contributing to coatings on rock ashlars in a more significant way than substrate characteristics and exposure time.     

A Pan-African alkaline pluton intruding the Saramuj Conglomerate,south-west Jordan

The geological setting, petrography and bulk mineral chemistry of a monzodiorite and a presumably consanguineous megaporphyry with large (up to 25 cm) labradorite megacrysts, both intruding the upper Proterozoic Saramuj Conglomerate in south-west Jordan (south eastern shore of the Dead Sea), were examined. The crystallization temperatures of the monzodiorite and the megaporphyry as determined from pyroxene thermometry and supported by contact metamorphic mineralogy are about 700 and 900°C, respectively. The intrusion depth of the monzodiorite is about 3–4 km. The monzodiorite was emplaced in the Saramuj Conglomerate at about 595 + 2 Ma ago according to Rb/Sr and U/Pb age determinations.The stratigraphic positions of the monzodiorite, megaporphyry and their host rock (the Saramuj Conglomerate) were compared with time-equivalent lithologies in the Arabian-Nubian Shield. Correspondence to: H. Wachendorf     

Eocene I-type magmatism in the Eastern Pontides,NE Turkey: insights into magma genesis and magma-tectonic evolution from whole-rock geochemistry,geochronology and isotope systematics

ABSTRACT

The Eastern Pontides orogenic belt in NE Turkey hosts numerous I-type plutons of Eocene epoch. Here, we report new U–Pb SHRIMP zircon ages and in situ zircon Lu-Hf isotopes along with bulk-rock geochemical and Sr-Nd-Pb-O isotope data from the Kemerlikda??, Ayd?ntepe and Pelitli plutons and mafic microgranular enclaves (MMEs) to constrain their parental melt source(s) and evolutionary processes. U-Pb SHRIMP zircon dating yielded crystallization ages between 45 and 44 Ma for the studied plutons and their MMEs. The plutons range from gabbro to granite and have I-type, medium to high-K calc-alkaline, and metaluminous to slightly peraluminous characteristics. On the primitive mantle-normalized multi-trace-element variations, the plutons and their MMEs are characterized by signi?cant enrichment in LILE/HFSE. Chondrite-normalized REE patterns of the plutons and their MMEs are close to each other and show moderate enrichment with variable negative Eu anomalies. The studied plutons have fairly homogeneous isotope composition (⁸⁷Sr/⁸⁶Sr_(i) = 0.70502 to 0.70560; εNd_(i) = +0.9 to – 1.4; δ¹⁸O = +5.0 to +8.7‰, εHf_(i) = – 2.2 to +13.5). The MMEs show medium to high-K calc-alkaline and metaluminous character. Although the isotope signatures of the MMEs (⁸⁷Sr/⁸⁶Sr_(i) = 0.70508 to 0.70542; εNd_(i) = +0.9 to ?1.1; δ¹⁸O = +5.8 to +8.0, εHf_(i) = +4.3 to +10.4) are very similar to those of the host rocks. Fractionation of plagioclase, amphibole, pyroxene and Fe-Ti oxides played an important role in the evolution of the plutons. The isotopic composition of the studied plutons and MMEs are similar to I-type plutons derived from mantle sources. The MMEs show incomplete magma mixing/mingling, representing small bodies of mafic parental magma. The parental magma(s) of the studied plutons were generated from the enriched lithospheric mantle and then modified by fractional crystallisation, and lesser assimilation and mixing/mingling in the crustal magma chambers.