江西银山多金属矿床伊利石的形成与流体成矿作用的初步研究

江西银山多金属矿床的热液蚀变粘土矿物主要由伊利石组成,伊利石主要由流体作用过程中长石的伊利石化形成,其结晶度与成矿流体作用密切相关.银山第1期铅锌银成矿作用,水/岩比相对较低,成矿流体以孔隙渗透为主,溶质迁移慢,形成含有少量膨胀层的伊利石;第2期铜金成矿作用,水/岩比相对较高,流体的运移方式以通道式或裂隙式为主,溶质迁移的速度快,形成不含膨胀层的伊利石.研究表明成矿作用过程中的伊利石化主要与铅锌银矿化有关,而绿泥石化与铜金矿化有关.     

黔东南凯里-榕江-从江前寒武系甚低级变质作用研究

根据碎屑岩甚低级变质作用原理,运用伊利石结晶度、绿泥石结晶度、伊利石-白云母多型、伊利石(白云母)b_0值、绿泥石温度计等碎屑岩低温变质研究的方法,分析研究了黔东南前寒武系67个2μm的粘土样品,得到黔东南凯里-榕江-从江一带下江群伊利石结晶度为0.221~0.607°Δ2θCu Kα、绿泥石结晶度为0.239~1.393°Δ2θCu Kα,变质带伊利石-白云母多型均为2M_1型,伊利石(白云母)b_0值为0.9001~0.9048nm,平均0.9021nm。根据伊利石(白云母)b_0值的累积频率曲线得出研究区下江群遭受的变质作用为典型的中压变质类型。由Cathelineau(1988)绿泥石温度计估算出下江群浅变质带峰期变质温度为362~382℃。以上结果表明凯里-榕江-从江一带下江群经历了成岩-高近变质-浅变质作用,基于Warr和Rice标样的成岩/变质界限,剖面可划分为一个成岩带、两个近变质带、一个转变带和一个浅变质带。结合华南地区新元古代构造运动,推断新元古界下江群经历的成岩-变质作用与晋宁运动引起的扬子地块与华夏地块碰撞拼贴有关。     

Precambrian fossils from the Hamersley range,Western Australia,and their use in stratigraphic correlation

The palaeontology, correlation and sedimentation of the Proterozoic sequence in the Hamersley Range, Western Australia, are discussed. Fossil calcareous algal growths, such as stromatolites and onkolites are described, as well as possible medusoid impressions. These indicate shallow water accumulation of the sediments and provide evidence of the extensive existence of plant and animal life in the Late Precambrian of Western Australia.

Distinctive stromatolites are shown to characterize various levels in the Proterozoic succession. A descending sequence of stromatolite assemblages is proposed denoted by:

• Collenia frequens—Conophyton cf. inclinatum

• Collenia australasica—C. undosa

• C. cf. kona—C. brockmani

• C. sp. aff. multiflabella.

Emphasis is placed on the possible significance of these calcareous algae for correlation and age subdivision of the Proterozoic of Western Australia and its relation to other Precambrian successions.     

Characterization of juvenile pyroclasts from the Kos Plateau Tuff (Aegean Arc): insights into the eruptive dynamics of a large rhyolitic eruption

Silicic pumices formed during explosive volcanic eruptions are faithful recorders of the state of the magma in the conduit, close to or at the fragmentation level. We have characterized four types of pumices from the non-welded rhyolitic Kos Plateau Tuff, which erupted 161,000 years ago in the East Aegean Arc, Greece. The dominant type of pumice (>90 vol.%) shows highly elongated tubular vesicles. These tube pumices occur throughout the eruption. Less common pumice types include: (1) “frothy” pumice (highly porous with large, sub-rounded vesicles), which form 5–10 vol.% of the coarsest pyroclastic flow deposits, (2) dominantly “microvesicular” and systematically crystal-poor pumices, which are found in early erupted, fine-grained pyroclastic flow units, and are characterized by many small (<50 μm in diameter) vesicles and few mm-sized, irregular voids, (3) grey or banded pumices, indicating the interaction between the rhyolite and a more mafic magma, which are found throughout the eruption sequence and display highly irregular bubble shapes. Except for the grey-banded pumices, all three other types are compositionally identical and were generated synchronously as they are found in the same pyroclastic units. They, therefore, record different conditions in the volcanic conduit leading to variable bubble nucleation, growth and coalescence. A total of 74 pumice samples have been characterized using thin section observation, SEM imagery, porosimetry, and permeametry. We show that the four pumice types have distinct total and connected porosity, tortuosity and permeability. Grey-banded pumices show large variations in petrophysical characteristics as a response to mingling of two different magmas. The microvesicular, crystal-poor, pumices have a bimodal bubble size distribution, interpreted as reflecting an early heterogeneous bubble nucleation event followed by homogeneous bubble nucleation close to fragmentation. Finally, the significant differences in porosity, tortuosity and permeability in compositionally identical tube and frothy pumices are the result of variable shear rates in different parts of the conduit. Differential shear rates may be the result of either: (1) pure shear, inducing a vertical progression from frothy to tube and implying a relatively thick fragmentation zone to produce both types of pumices at the same time or (2) localized simple shear, inducing strongly tubular vesicles along the wall and near-spherical bubbles in the centre of the conduit and not necessarily requiring a thick fragmentation zone.     

关于伊利石结晶度诸指数的评价

本文根据结晶学原理、Ｓｃｈｅｒｒｅｒ定律、Ｗａｒｒｅｎ－Ａｖｅｒｂａｃｈ理论和Ｘ射线衍射峰形态学原理提出任何衍射峰都是由五个基本要素组成的,即：衍射峰位置;最大衍射强度;半高宽;衍射峰形态和对称性。各衍射峰要素都具有其自身的物理学意义,其中,只有半高宽和衍射峰形态是与晶体内部结构和大小即结晶度相联系的。据此,分析评价了与Ｘ射线衍射相关的Ｋüｂｌｅｒ指数、Ｗｅｂｅｒ－ＤｕｎｏｙｅｒｄｅＳｅｇｏｎｚａｃ－Ｅｃｏｎｏｍｏｕ指数、Ｗｅａｖｅｒ指数、Ｍｉｌｉｅｒｓ指数、Ｗｅｂｅｒ指数、分解ＨＷ及纯Ｃ轴厚度等伊利石结晶度指数的理论基础、使用前提和条件、特点及误差源。指出Ｋüｂｌｅｒ指数、Ｗｅｂｅｒ－ＤｕｎｏｙｅｒｄｅＳｅｇｏｎｚａｃ－Ｅｃｏｎｏｍｏｕ指数和分解ＨＷ为非条件性单一结晶度指数;Ｗｅａｖｅｒ指数、Ｗｅｂｅｒ指数和高宽比为条件性单一结晶度指数;消除晶体内部微应变影响的ｃ轴厚度为全面描述伊利石结晶度指数;而Ｍｉｌｉｅｒｓ指数不可描述伊利石结晶度。     

Very Low-grade Metamorphism in Basement Greywacke Terranes of the Northern and Central North Island, New Zealand

Metamorphism in the late Permian to early Cretaceous North Island basement greywackes has been investigated using petrography and clay mineral crystallinity. Several terranes are represented in the North Island greywackes and the study area includes Murihiku, Manaia Hill, Bay of Islands and Omahuta terranes and the Mélange Zone. Very low-grade metamorphic events in the greywackes have produced mineral assemblages of zeolite to pumpellyite-actinolite greywacke facies. Zeolite facies greywackes are characterized by the assemblage Zeo (Lmt, Anl, Hul)+Qtz±Ab±Cal± Chl±I±I/S* observed in the entire Murihiku terrane and in the eastern part of the Bay of Islands terrane and the Mélange Zone. The entire Manaia Hill, most of the Bay of Islands, the eastern area of the Omahuta terranes and the central part of the Mélange Zone are at prehnite-pumpellyite facies with mineral assemblages of Prh+Qtz+Chl+Pmp+Ab+± Ill±Cal±Lmt. Pumpellyite-actinolite facies with the mineral assemblage of Pmp±Act+Qtz+Ab+Chl±Ep±Ill±Cal±Chl occurs in the western part of the Mélange Zone and the Omahuta terrane.

Illite (IC) and chlorite (ChC) crystallinity values of greywackes are very similar and range from diagenetic zone to anchizone. Metamorphic conditions indicated by the IC and ChC and mineral facies are in excellent agreement and correlate as follows: crystallinity diagenetic-zone with the zeolite mineral facies, crystallinity lower anchizone with prehnite-pumpellyite mineral facies and crystallinity upper anchizone with pumpellyite-actinolite mineral facies. The general increase in the metamorphic grade from east to west, except in Murihiku terrane, is compatible with the sequence of accretion expected in a subduction environment.     

糜棱岩化过程中细粒白云母多型与结晶度的演变——以郯庐断裂带南段为例

郯庐断裂带南段韧性剪切带出现在大别山东缘与张八岭隆起高压变质带之上。根据韧性剪切带糜棱岩中同构造矿物组合、黑云母的存在以及长石的变形行为,推测其变形-变质温度为400-450℃。b_0值分析表明,这些糜棱岩是在低压环境下形成的。对一系列糜棱岩样品的XRD分析显示,糜棱岩中同构造细粒白云母的多型类型皆为1M 2M_1型,指示即使在400℃以上环境下1M型仍没有消失。糜棱岩化过程中不断新生的细粒白云母初始时刻为1M型,接着发生向2M、型的转变。由于新生细粒白云母的不断产生,即使在较高温度环境下形成的糜棱岩仍含有1M型。所分析糜棱岩结晶度Kubler指数介于0.23～0.42°△2θ,多属于近变带范畴,显示其结晶程度差于实际所经历的温度。本文所测定的细粒白云母结晶度值与粒径成反比,由于糜棱岩化中细粒白云母不断的新生与结晶生长常不充分,实测的结晶度是不同时刻形成的、具不同结晶度的细粒白云母的混合结晶度。糜棱岩化过程中时间短、富流体活动、新生矿物不断发生等特性,使其中细粒白云母多型与结晶度的演变规律不同于沉积岩的甚低级变质。     

高岭石的结晶度和精泥流变性能的关系

造纸涂料分气刀和刮刀涂料两种,它们的主要区别在于固含量高低和流变性能的好坏。刮刀涂料要求固含量高,流变性能好,即粘度低,一般小于500mpa.s。实践证明,流变性能的好坏,与高岭石的结晶度密切有关。结晶度高,则流变性能好。因此,可以用“x衍射”法测定高岭石的d(001)半高宽(w)代入公式c=100(1/w)计算高岭石的结晶度(c),进而判断精泥的硫变性能及其用途。     

The structure and the phyllosilicates (chemistry, crystallinity and texture) of Talas Ala-Tau (Tien Shan, Kyrgyz Republic): comparison with more recent subduction complexes

Geological mapping and structural analysis of the Talas Ala Tau (Tien Shan, Kyrgyz Republic) have revealed a complex structure composed of folds with axial-plane cleavage and thrust faults verging towards the NE. The main structures of the range correspond to minor Tertiary and Carboniferous–Permian deformation superimposed on the main deformation event that took place during the Baikalian orogeny. The pervasive axial-plane cleavage diminishes in penetrativity from the hinterland to the foreland in both the Uzunakhmat and Karagoin sheets. The main thrusts developed phyllonitic shear-related rocks on the hangingwall immediately above the thrust planes. A crystal-chemical study of the phyllosilicates growth during the Baikalian deformation event along a cross-section revealed changes in the crystallinity, composition and lattice parameters of them. The phyllosilicates present in the Talas Ala Tau rocks were crystallized in very low-grade metamorphic conditions, that is below 300 °C, as indicated by their Kübler Index (KI), which decreases from SW towards the NE. Detailed TEM study of the phyllosilicates reveals a clear textural difference at the lattice level between samples with higher or lower KI parameters. There is also a clear difference in crystal-chemical parameters (KI and b) and composition between the phyllosilicates growth in relation to the axial-plane cleavage and the ones belonging to the thrust-related phyllonites. The first ones are more affected by the ferrimuscovitic vector than the phyllosilicates of phyllonites, closer to the theoretical phengitic component. Huge ranges of values of phengitic content of micas at sample level are interpreted as the result of a decompression path from at least 8 kbar. We propose a subduction geodynamic environment for the regional deformation and the origin of the phyllosilicates, as they are similar to those obtained in more recent accretionary complexes.