南极碳质球粒陨石中两个富尖晶石球粒状难熔包体的岩石学和矿物化学特征

富尖晶石球粒状CAI(富Ca-Al难熔包体)是球粒陨石中一种特殊类型的CAI,在南极格罗夫山碳质球粒陨石GRV020025和GRV021579中共发现两个富尖晶石球粒状CAI———GRV020025-3RI8和GRV021579-3RI5。GRV020025-3RI8具有占统治地位的尖晶石,在球粒的最外边存在严重蚀变的不规则边,钙钛矿主要分布在靠近边的位置。与GRV020025-3RI8比较,GRV021579-3RI5的尖晶石中的钙钛矿消失,深绿辉石出现,薄薄的蚀变层位于尖晶石核和富钙辉石边之间。两个富尖晶石球粒状CAI的尖晶石均具有低含量FeO和ZnO的特征,而且GRV021579-3RI5具有较GRV020025-3RI8更高的TiO2含量。岩石学和矿物化学特征表明,GRV020025-3RI8和GRV021579-3RI5都经历过熔融结晶过程,它们的蚀变均发生在非氧化的含水或无水的环境中。     

Palaeoclimatic reconstruction from Loch Lomond Readvance glaciers in the West Drumochter Hills,Scotland

Geomorphological mapping in the West Drumochter Hills provides evidence of a readvance of locally nourished glaciers during the Loch Lomond (Younger Dryas) Stade, in the form of an icefield 67.7 km² in area drained by outlet glaciers. The icefield limits accord broadly with those proposed by Sissons (1980) but all geomorphic, stratigraphic and sedimentological evidence conflicts with a recent proposal that the landforms in the area reflect southwestwards retreat of the last ice sheet. Up‐valley continuity of recessional moraines indicates that the ice remained active and close to climatic equilibrium during the earlier stages of glacier retreat, consistent with slow warming following the coldest part of the stade. The pattern of equilibrium line altitudes (ELAs) across the icefield is consistent with transfer of snow by westerly and southerly winds. The ELA of the reconstructed icefield as a whole is 622–629 m, although this figure is likely to be lower than the regional (climatic) ELA because the icefield probably received additional snow blown from adjacent plateau surfaces and slopes. Inclusion of potential snow‐blow areas in the ELA calculation yields a value of 648–656 m; the climatic ELA is therefore likely to have lain between 622 and 656 m. Mean June to August temperature at the ELA, based on chironomid assemblages at two sites, falls within the range 4.0 ± 0.7°C. Empirical relationships between temperature and precipitation at modern glacier ELAs indicate that mean annual precipitation (MAP) at the ELA was 1977 ± 464 mm, statistically indistinguishable from modern values. Comparison with precipitation values calculated for the Isle of Mull on the west coast suggest that the precipitation gradient across the Central Highlands of Scotland was steeper during the Loch Lomond Stade than at present, probably as the result of efficient scavenging of precipitation from westerly airflows by the West Highland Icefield. Copyright © 2005 John Wiley & Sons, Ltd.     

The Loch Lomond Readvance on the Isle of Skye,Scotland: Glacier reconstruction and palaeoclimatic implications

Geomorphological mapping of southern Skye indicates evidence for a single readvance of locally-nourished glaciers. These comprised a major icefield that occupied c. 155 km² of the main mountain area, a small icefield c. 10 km² in extent in the Kyleakin hills and ten corrie glaciers with a total area of c. 16 km². The absence of Lateglacial pollen sites, shorelines and periglacial features within the limits of local glaciation implies a Loch Lomond Readvance age for this glacial event. The area-weighted mean equilibrium line altitude (ELA) of the reconstructed Loch Lomond Readvance glaciers (319 m) conforms with a regional eastwards rise in ELAs that indicates dominant westerly airstreams during the Loch Lomond Stadial. An easterly decline in ELAs across the former icefields is interpreted in terms of easterly transfer of snow across ice-sheds by westerly winds, though the altitudes of corrie glacier ELAs suggest that the dominant snow-bearing winds were southerlies. Calculations based on the area-weighted mean ELA for the major icefield (308 m) indicate a stadial mean July sea-level temperature of c. 6 °C. The anomalously low gradients of certain former icefield outlet glaciers are attributed to deformation of subglacial sediment, an effect that may vitiate the assumption of linear ablation/accumulation gradients in the calculation of former ELAs for reconstructed glaciers.     

The Loch Lomond Readvance on the Isle of Mull,Scotland: glacier reconstruction and palaeoclimatic implications

Geomorphological mapping of Mull provides evidence for an icefield 143 km² in area flanked by six corrie glaciers with a total area of ca. 13 km². The absence of Lateglacial periglacial features, shorelines and pollen sites from the area occupied by this readvance, together with radiocarbon dating of shell fragments, confirm that it occurred during the Loch Lomond (Younger Dryas) Stade. The thickness of glacigenic deposits within the area of the readvance is attributed to reworking of paraglacial sediments. Up‐valley continuity of recessional moraines indicates that the ice remained active and near to equilibrium during retreat, consistent with slow warming following the coldest part of the stade. Reconstructed equilibrium line altitudes (ELAs) imply vigorous snow‐blowing by westerly winds, and are consistent with a general southwestwards decline in ELAs across the Scottish Highlands. An ELA of 250 m was calculated for the Mull Icefield using an ablation:accumulation balance ratio (ABR) approach. Palaeotemperature and palaeoprecipitation estimates were derived by calculating a theoretical regional ELA from meteorological data and assuming that the combination of temperature and precipitation implied by the theoretical ELA approximates conditions at 250 m on Mull during the Loch Lomond Stade. The result indicates a mean July sea‐level temperature of 5.7 ± 0.5°C and a mean annual precipitation at 250 m of ca. 2700–3800 mm (best estimate 3200 mm), indicating higher precipitation totals than at present owing to more vigorous atmospheric circulation. Copyright © 2002 John Wiley & Sons, Ltd.     

6块新回收沙漠陨石的矿物岩石学特征及类型划分

干旱沙漠地区与南极冰盖均有利于陨石样品保存。2013年4-5月,通过首次新疆哈密沙漠陨石考察,回收了陨石样品47块。文中报导其中6块样品的矿物岩石学特征,并划分它们的化学岩石类型。Arlatager004、006、0014、0022和TuzLeik001等5块样品主要由橄榄石、辉石、长石、铁镍金属和陨硫铁组成,具有典型的普通球粒陨石岩石结构特征,其球粒结构不明显,表明经历过较强的热变质,岩石类型划分为5型;根据样品中橄榄石Fa值,低钙辉石Fs值和样品的金属含量等,将Arlatager004、006、0014、0022划分为L5型普通球粒陨石;TuzLeik001划分为H5型普通球粒陨石。Kumtag005具有典型的球粒结构,结合橄榄石Fa值和低钙辉石Fs值以及岩石学特征,将其划分为L3型普通球粒陨石。根据橄榄石Fa值与其百分标准平均方差(PMD)之间的关系,将Kumtag005的岩石类型亚型划分为L 3.4。这6块样品代表了3个化学群,结合该地区回收到的其他陨石分析结果,表明新疆哈密沙漠是一个新的陨石富集区,这些沙漠陨石的发现和研究,必将极大促进中国陨石学和天体化学的发展。     

Dynamics and palaeoclimatic significance of a Loch Lomond Stadial glacier: Coire Ardair,Creag Meagaidh,Western Highlands,Scotland

The extent, basal conditions and retreat history of a Loch Lomond Stadial glacier are reconstructed based on detailed geomorphological and sedimentological assessment. We present new evidence from the vicinity of Coire Ardair that supports the former existence of a warm-based, locally-fed valley glacier, with probable cold-based ice on the surrounding plateau. This is broadly consistent with modelled creep-dominated flow in the upper catchment and sliding-dominated flow throughout much of the valley. A dense suite of moraines, primarily formed in ice-marginal environments, records a multi-phase recessional history: (1) active and oscillatory retreat; (2) a prolonged ice stillstand; (3) partial ice stagnation with occasional minor readvances; (4) increased oscillatory retreat with a substantial readvance event; and (5) rapid and uninterrupted retreat. We propose that a Coire Ardair glacier responded to sub-centennial scale climate fluctuations, possibly associated with the periodic delivery of warmer air masses to the region, rather than to a single, prominent shift in climate.     

富钙长石-橄榄石型包体与典型富Ca,Al包体的矿物岩石学特征对比研究

本文研究了2个富钙长石-橄榄石型包体和2个富黄长石-尖晶石型和富尖晶石-辉石型包体（分别来自宁强和南极格罗夫山碳质球粒陨石）的矿物岩石学特征,并对它们进行了对比。富钙长石-橄榄石型包体的矿物模式组成具有富橄榄石和缺失黄长石的特征,其可能是球粒和典型难熔包体之间的中间产物,是认识它们之间相互关系的钥匙。矿物岩石学特征表明富黄长石-尖晶石型和富尖晶石-辉石型包体可能是星云直接凝聚的产物,而富钙长石-橄榄石型包体经历过熔融结晶过程。富钙长石-橄榄石型包体的初始物质可能是富Al的球粒或含难熔组分的蠕虫状橄榄石集合体。矿物化学组成对比研究发现,GRV 022459-RI6中的尖晶石具有最富FeO的特征,表明包体的蚀变可能发生在高氧逸度的星云环境。     

Loch Lomond Stadial and Flandrian shorelines in the inner Moray Firth area,Scotland

Morphological mapping and stratigraphical investigations have identified surface and buried relict marine features in the inner Moray Firth area. The features consist of a buried gravel layer formed during the Loch Lomond Stadial, a buried beach of early Flandrian age, and surface beaches and estuarine flats of mid-late Flandrian age. Analysis of the altitudes of morphological features has identified two buried and five (possibly six) surface glacio-isostatically tilted raised shorelines. The steepest shoreline is associated with the buried gravel layer and slopes down towards N20°E at a gradient of 0.20m/km. Younger shorelines have lower gradients between 0.16–0.03m/km. The shoreline sequence combined with published data defines relative sea-level movements in the area during the last 11000 years. The inner Moray Firth shorelines are correlated with similar features in other areas of Scotland which include the Main Lateglacial, Main Buried and Main Postglacial Shorelines.     

A preliminary study of PGE in the Late Caledonian Loch Borralan and Loch Ailsh alkaline pyroxenite-syenite complexes,north-west Scotland

The Siluro-Ordovician Loch Borralan (c. 430 Ma) and Loch Ailsh Complexes (c. 439 Ma) comprise a suite of intrusive rocks ranging in composition from clinopyroxenites, through potassic melasyenites to quartz syenites. The rock suite at Loch Borralan also includes nepheline syenite. Geochemical data in the literature indicate that the intrusions are alkaline, with pronounced enrichments in LILE and LREE relative to contemporaneous calc-alkaline magmatic centres further to the south-east, although they share similar high LILE/Nb, subduction-related characteristics. The Loch Borralan Complex is associated with marginal gravity and magnetic anomalies which can be interpreted in terms of a shallow body less than 400 m thick. Analysis of rocks and drill core revealed widespread elevated Pt and Pd values in pyroxenites and syenites in both complexes. The highest concentrations, up to about 900 ppb Pt+Pd, occur in pyroxenites in the Loch Borralan Complex. Extensive archived drill core provides an excellent section through the marginal pyroxenites, which host the PGE at Loch Borralan. The pyroxenites show unusual petrological features; early clinopyroxene is followed by biotite, apatite, magnetite, sphene and plagioclase with later garnet, which might be metasomatic in origin. Sulphides occur in minor amounts. High-temperature shearing produced local granulation and mylonitisation. Later brittle deformation caused extensive micro-fracturing and the introduction of minor carbonate veining. Platinum-group minerals (PGM) were located in a number of samples with high PGE assay values. These occur as clusters of grains around 1–2 m in diameter, and are difficult to identify uniquely. A few grains appear to be magmatic; these are Pt and PtPd sulphides that occur enclosed in clinopyroxene or garnet. All other grains occur in late fractures or along grain boundaries. These include sperrylite (PtAs₂), Pd antimonides and PdBi tellurides, along with hessite (Ag₂Te). They occur in microfractures accompanied by carbonate and barite and fine-grained sulphides and are probably of secondary origin. The PGE in the pyroxenites may have been introduced during the magmatic phase of the intrusion but the observed distribution of PGM results from low-temperature, hydrothermal remobilisation following brittle deformation and introduction of fluids.

川西九龙打枪沟锂铍矿床赋矿伟晶岩矿物学和矿物化学特征

打枪沟伟晶岩型锂铍矿床是九龙地区典型的中型锂铍矿床,是松潘-甘孜锂成矿带的重要组成部分。该矿床含矿伟晶岩主要为钠长石伟晶岩和钠长石-锂辉石伟晶岩,主要矿石矿物为锂辉石和绿柱石。在翔实的野外地质调查的基础上,选取打枪沟锂铍矿床典型矿脉（ⅠLi,Be和ⅡBe矿脉）开展岩相学、矿物学和矿物化学研究,以揭示其矿物生成顺序和成矿阶段。电子探针分析结果显示,含锂矿物主要为锂辉石,矿物中Li2O含量为7.94%~8.29%,平均为8.12%;云母类矿物为白云母和锂-多硅白云母,白云母中Li2O含量为0.08%~0.35%,平均为0.21%,Rb2O含量为0.13%~0.35%,平均为0.24%,锂-多硅白云母中Li2O含量为1.11%~1.43%,平均为1.28%,Rb2O含量为0.79%~0.94%,平均为0.87%;电气石为铁电气石-锂电气石系列,Li2O含量为0.48%~0.85%,平均为0.64%。在详细的矿物显微特征研究并结合电子探针分析的基础上,分析认为伟晶岩中稀有金属矿物由绿柱石→绿柱石+锂辉石→锂辉石→锂辉石+锂-多硅白云母转变,云母由白云母向锂-多硅白云母转变,电气石由铁电气石向锂电气石过渡,长石矿物由微斜长石+钠长石→钠长石→交代钠长石转变,石英由原生石英→后期热液石英变化。综合分析认为,打枪沟锂铍矿床经历了多阶段的演化过程,主要划分为结晶分异阶段、交代阶段、热液阶段,其中锂铍等稀有金属矿物的形成主要发生在结晶分异阶段和交代阶段。     

Deglaciation of the younger dryas or Loch Lomond Stadial ice-field in the northern Highlands,Scotland

When viewed from the air, Scottish ‘hummocky moraine’ can be resolved into a series of linear ridges that resemble those found at the margins of actively retreating glaciers today. Recent work has supported the interpretation of these linear ridges as ice-marginal landforms and the authors believe that the majority of ‘hummocky moraine’ deposits can be interpreted in this way. Consequently the pattern of deglaciation can be established fairly precisely from the pattern of linear ridges. This approach is applied to the landforms of the northern part of the Loch Lomond Stadial ice-field in order to reconstruct the regional pattern of deglaciation. This leads to important inferences about the significance of topographic control during deglaciation and more importantly it provides fresh insight into the environment of the British Isles during the Loch Lomond Stadial.     

新疆西天山智博铁矿床蚀变矿物学、矿物化学特征及矿床成因探讨

智博铁矿床是西天山东部阿吾拉勒铁成矿带新发现的大型磁铁矿矿床之一。赋矿围岩为下石炭统大哈拉军山组火山岩及火山碎屑岩。围岩蚀变广泛发育,识别出3个阶段:第一阶段以辉石+钠长石+磁铁矿为主;第二阶段以角闪石+钾长石+绿帘石+磁铁矿+黄铁矿为主;第三阶段以绿帘石+绿泥石+方解石+石英+黄铁矿+赤铁矿±黄铜矿为主。电子探针分析表明,智博铁矿与其他岩浆-热液成因铁矿床具有类似的蚀变矿物化学成分。辉石以透辉石为主(Di=62.97%~83.56%),含少量钙铁辉石(Hd=16.44%~36.45%);火山岩中斜长石(Ab47.57-57.82An41.5-51.87Or0.56-0.68)蚀变形成钠长石(Ab77.89-99.33An0.46-2.48Or0.21-20.3);与热液作用有关的钾长石叠加改造早期蚀变矿物;角闪石主要为阳起石;晚期发育富铁绿帘石〔Fe/(Fe+Al)=0.2~0.36〕以及绿泥石蚀变矿物。与火山岩中的磁铁矿〔w(TiO2)3.08%〕相比,矿体中磁铁矿具有低w(TiO2)(0.23%)的特点,部分早期浸染状磁铁矿与火山岩中的磁铁矿w(V2O5)相当,暗示该矿化阶段的铁质部分来源于围岩。矿物学及矿物化学表明,热液交代作用对成矿具有重要的贡献。同时,智博铁矿具有一些暗示铁矿浆成因的结构特征,如块状磁铁矿与围岩呈截然接触,磁铁矿胶结围岩角砾,磁铁矿条带呈流动状分布以及板条状磁铁矿等。结合铁矿带区域地质特征,认为智博铁矿可能主要由富铁岩浆流体形成,在形成大量块状富铁矿体的同时,伴随有广泛的围岩蚀变。矿区内大量的磁铁矿矿化与晚石炭世大陆岛弧岩浆活动有密切的成因联系。     

Geochemistry and mineral chemistry of Pan-African amphibolites of South Sinai,Egypt

In the Wadi Feiran area, amphibolites occur as inclusions, bands, linear bodies of variable thickness and irregular lenses in para-geneisses. Chemical evidence indicates that these amphibolites display an igneous origin and were derived from magma essentially of tholelitic rather than alkaline composition; transitional in character between continental and island-arc. The chemistry of amphiboles, related to pressure and temperature conditions of meta-morphism, showed that they were formed under low pressure and high temperature conditions.     

Petrogenetic modelling of in situ fractional crystallization in the zoned Loch Doon pluton,Scotland

The late Caledonian Loch Doon granitic intrusion ranges in composition from hypersthene diorite at the margin, through quartz diorite, granodiorite and granite to cordierite microgranite at its core. Petrogenetic modelling of trace element variations and least squares analysis of major elements indicate that two distinct magmas are involved, each magma controlled by crystallization of plag-opx-cpx-bio. Late stage rocks related to the second magma include the cordierite microgranites and aplites, which are interpreted as the final residue which crystallized rapidly after a build up and loss of volatiles.Analyses of whole rocks and minerals for REE's and other elements of moderate-high ionic potential indicate that these elements are strongly controlled by minor phase crystallization; apatite, zircon, sphene and allanite are dominant at intermediate compositions but other accessory minerals such as monazite and xenotime may also become important at acid compositions.It is probable that within each magma the mechanisms of crystal settling and filter pressing operated, the former being initially dominant, and the latter becoming more important with increasing degree of fractional crystallization.     

Petrography and mineral chemistry of Ca-rich inclusions in the Allende meteorite

There are two types of white, coarse-grained, Ca-Al-rich inclusions in Allende. Type A inclusions contain 80–85 per cent melilite, 15–20 per cent spinel, 1–2 per cent perovskite and rare plagioclase, hibonite, wollastonite and grossularite. Clinopyroxene, if present, is restricted to thin rims around inclusions or cavities in their interiors. Type B inclusions contain 35–60 per cent pyroxene, 15–30 per cent spinel, 5–25 per cent plagioclase and 5–20 per cent melilite. The coarse pyroxene crystals in Type B's contain >15 per cent Al₂O₃ and >1.8 per cent Ti, some of which is trivalent. Type A pyroxenes contain <9 per cent Al₂O₃ and <0.7 per cent Ti.Electron microprobe analyses of 600 melilite, 39 pyroxene, 35 plagioelase, 33 spinel and 20 perovskite grains were performed in 16 Type A, 1 intermediate and 9 Type B inclusions in Allende and 1 Type A in Grosnaja. Melilite composition histograms from individual Type A inclusions are usually peaked between Ak10 and Ak30 and are 15–20 mole % wide while those from Type B inclusions are broader, unpeaked and displaced to higher åkermanite contents. Most pyroxenes contain < 1 per cent FeO. All plagioclase is An 98 to An 100. Spinel is almost pure MgAl₂O₄. Perovskite contains small (< 1 per cent) but significant amounts of Mg, Al, Fe, Y, Zr and Nb.Inferred bulk chemical compositions of Type A inclusions are rather close to those expected for high-temperature condensates. Those of Type B inclusions suggest slightly lower temperatures but their Ca/Al ratio seems less than the Type A's, indicating that the Type B's may not be their direct descendants. Some textural features suggest that the inclusions are primordial solid condensetes while others indicate that they may have been melted after condensation. Fragmentation and metamorphism may have also occurred after condensation.     

Mineral chemistry,crystallization conditions and magma mixing‐mingling at Orduzu volcano (Malatya), Eastern Anatolia,Turkey

The Middle Miocene Orduzu volcanic suite, which is a part of the widespread Neogene Yamadağ volcanism of Eastern Anatolia, consists of a rhyolitic lava flow, rhyolitic dykes, a trachyandesitic lava flow and basaltic trachyandesitic dykes. Existence of mafic enclaves and globules in some of the volcanic rocks, and microtextures in phenocrysts indicate that magma mingling and mixing between andesitic and basaltic melts played an important role in the evolution of the volcanic suite. Major and trace element characteristics of the volcanic rocks are similar to those formed in convergent margin settings. In particular, incompatible trace element patterns exhibit large depletions in high field strength elements (Nb and Ta) and strong enrichments in both large ion lithofile elements (Ba, Th and U) and light rare earth elements, indicating a strong subduction signature in the source of the volcanic rocks. Furthermore, petrochemical data obtained suggest that parental magmas of rhyolite lava and dykes, and trachyandesite lava and basaltic trachyandesite dykes were derived from subduction‐related enriched lithospheric mantle and metasomatized mantle (± asthenosphere), respectively. A detailed mineralogical study of the volcanic suite shows that plagioclase is the principal phenocryst phase in all of the rock units from the Orduzu volcano. The plagioclase phenocrysts are accompanied by quartz in the rhyolitic lava flows and by two pyroxenes in the trachyandesitic lava flows and basaltic trachyandesitic dykes. Oxide phases in all rocks are magnetite and ilmenite. Calculated crystallization temperatures range from 650°C to 800°C for plagioclase, 745°C–1054°C for biotite, 888°C–915°C for pyroxene and 736°C–841°C for magnetite–ilmenite pairs. Calculated crystallization pressures of pyroxenes vary between 1.24–5.81 kb, and oxygen fugacity range from −14.47 to −12.39. The estimates of magmatic intensive parameters indicate that the initial magma forming the Orduzu volcanic unit began to crystallize in a high‐level magma chamber and then was stored in a shallow reservoir where it underwent intermediate‐mafic mixing. The rhyolitic lava flow and dykes evolved in relatively shallower crustal magma chambers. Copyright © 2007 John Wiley & Sons, Ltd.     

火星陨石NWA11288岩石矿物学和冲击变质特征

NWA 11288 是一块2015 年发现的玄武岩质辉玻无球粒陨石,具有典型的次辉绿结构,主要由辉石(面积比68. 6%)和熔长石(面积比28. 1%)组成,含少量磷酸盐(面积比 1. 35%)、不透明矿物(面积比 1. 45%)和二氧化硅等副矿物.通过扫描电子显微镜、电子探针和拉曼光谱等实验分析方法,对NWA 112...     

Petrochemistry and mineral chemistry studies on metamorphic ultramafic rocks in Yanghou area, Northern Fujian, China

Petrochemical studies indicate that the Yanghou metamorphie ultramafic rocks are composed of metamorphosed harzburgite and ultramafic cumulate.Trace element geochemistry and mineral chemistry of the metamorphic harzburgite indicate that they are relicts of depleted mantle.Systematic petrochemical,mineral chemical and geochronological studies led to such a conclusion that the Yanghou metamorphic ultramafic rocks may be the components of Late Sinian-Early Paleozoic ophiolite in South China.