超基性岩中含铜、钴块状硫化物矿床——德尔尼铜矿成因新认识

长期以来对德尔尼铜矿的成因存在着不同认识。从矿石组成和结构、构造来看,应属典型的块状硫化物矿石,矿床亦应属于含铜黄铁矿型矿床。但从其地质产状来看又与一般的黄铁矿型矿床大不相同,与一般的岩浆熔离铜镍硫化物矿床也有较多差异。这就是本矿床类型独特之处。近年来通过工作又取得一些新资料,特别是超基性岩和矿石的同位素年龄数据。本文在综合新老资料基础上,提出新看法,认为该矿床形成于上地幔,再就位于地壳浅部。其成因类型暂定为:“深部熔离—构造侵位矿床”。鉴于本矿床与一般块状硫化物矿床相比有其独特性,建议命名为“德尔尼型”。     

The emplacement of intermediate volume ignimbrites: A case study from Roccamonfina Volcano,Southern Italy

A model is presented for the emplacement of intermediate volume ignimbrites based on a study of two 6 km³ volume ignimbrites on Roccamonfina Volcano, Italy. The model considers that the flows were slow moving, and quickly deflated from turbulent to non-turbulent conditions. Yield strength and density increased whereas fluidisation decreased with time and runout of the pyroclastic flows. In proximal locations, on the caldera rim, heterogeneous exposures including discontinuous lithic breccias, stratified and cross-stratified units interbedded with massive ignimbrite suggest deposition from turbulent flows. In medial locations thick, massive ignimbrite occurs associated with three types of co-ignimbrite lithic breccia which we interpret as being emplaced by non-turbulent flows. Multiple grading of different breccia/lithic concentration types within single flow units indicates that internal shear occurred producing overriding or overlapping of the rear of the flow onto the slower-moving front part. This overriding of different parts of non-turbulent pyroclastic flows could be caused by at least two different mechanisms: (1) changes in flow regime, such as hydraulic jumps that may occur at breaks in slope; and (2) periods of increased discharge rate, possibly associated with caldera collapse, producing fresh pulses of lithic-rich material that sheared onto the slower-moving part of the flow in front.We propose that ground surge deposits enriched in pumice compared with their associated ignimbrite probably formed by a flow separation mechanism from the top and front of the pyroclastic flow. These turbulent clouds moved ahead of the non-turbulent lower part of the flow to form stratified pumice-rich deposits. In distal regions well-developed coarse, often clast-supported, pumice concentrations zones and coarse intra-flow-unit lithic concentrations occur within the massive ignimbrite. We suggest that the flows were non-turbulent, possessed a relatively high yield strength and may have moved by plug flow prior to emplacement.     

辽宁庄河鞍子山超单元岩浆侵位变形构造

鞍子山超单元由4个单元组成，各单元不同程度地发育岩浆侵位变形构造。侵位变形构造主要由叶理构造组成，闪长质包体，钾长石斑晶总体按优选方位定向，三者产状一致，平行接触带分布。从早期单元至晚期单元，随着岩浆侵位叶理构造变形强度减弱，闪长质包体数量减少，压扁变形程度降低，钾长石斑晶从明显按优选方位定向到杂乱分布。根据上述特征，将该超单元浆侵位变形、中等侵位变形、弱侵位变形及基本无侵位变形4个带。     

辽宁海城地区辽河群底部大型韧性滑脱带的构造演化

通过对辽宁海城地区赵家堡子－马风－什司县一带早元古宙辽河群底部地层和变质深成侵入体的详细构造研究，确认了辽河群底部与太古宙之间大型韧性滑脱带的存在。卷入滑脱带的地质体有辽河群底部浪子山岩组和早元古宙变质深成侵入体。滑脱带的构造演化可划分为：①吕梁运动早期沿太古宙与早元古宙接触带部位发生大规模拉伸顺层滑脱变形作用；②拉伸滑脱变形中晚期早元古宙深成侵入体沿滑脱带顺层同构造就位；③吕梁运动晚期滑脱带的收缩变形作用三大阶段。     

塔中地区油气运聚特征

塔中地区主要受塔中Ⅰ号、Ⅱ号及Ⅲ号三条大断层控制 ,形成巨型复式背斜 ,隆起高部位地层遭受了强烈的风化剥蚀。背斜之上 ,断裂和局部构造发育。可划分出两个主要成藏期 :第Ⅰ成藏期为寒武系—下奥陶统烃源岩成熟生烃运移期 ,生排烃高峰为志留纪 ;第Ⅱ成藏期为中—上奥陶统烃源岩在燕山期—喜马拉雅期成熟生烃运聚。第Ⅰ成藏期形成的油藏有两个特征 :在塔中Ⅰ号断裂带、北部斜坡带油气注入奥陶系及志留系圈闭中 ,形成原生油气藏 ;构造高部位 (如中央断垒带 )的油气藏在后期构造运动中遭受破坏。第Ⅱ成藏期形成的油藏可分为两类 :对早期油藏的再次充注 ;聚集形成新油藏。塔中地区的油气运移通道主要有断裂和不整合面 ,油气的分布也主要受断裂和不整合面所控制。塔中Ⅰ号构造带和北部斜坡带是较为有利的勘探区带     

北京云蒙山片麻状花岗岩锆石SHRIMP定年及其地质意义

应用锆石SHRIMP定年方法对云蒙山片麻状花岗岩进行年代学研究 ,得到 4组年龄 :14 4± 4Ma、16 0～ 16 3Ma、193～ 2 18Ma和 2 4 16Ma。其中 14 4± 4Ma代表了云蒙山岩体的侵位时间 ,16 0～ 16 3Ma和 193～ 2 18Ma两组年龄可能是岩浆侵位过程中捕虏锆石的年龄。 2 4 16Ma与Davis等的锆石U_Pb法上交点年龄 (190 0～ 2 4 0 0Ma)一致 ,可能反映了原岩的时代 ,说明该花岗岩来源于晚太古代片麻岩的局部熔融或者是岩浆侵位过程中捕获了晚太古代的锆石。     

A brief comparison of lava flows from the Deccan Volcanic Province and the Columbia-Oregon Plateau Flood Basalts: Implications for models of flood basalt emplacement

The nature and style of emplacement of Continental Flood Basalt (CFB) lava flows has been a matter of great interest as well as considerable controversy in the recent past. However, even a cursory review of published literature reveals that the Columbia River Basalt Group (CRBG) and Hawaiian volcanoes provide most of the data relevant to this topic. It is interesting to note, however, that the CRBG lava flows and their palaeotopographic control is atypical of other CFB provinces in the world. In this paper, we first present a short overview of important studies pertaining to the emplacement of flood basalt flows. We then briefly review the morphology of lava flows from the Deccan Volcanic Province (DVP) and the Columbia-Oregon Plateau flood basalts. The review underscores the existence of significant variations in lava flow morphology between different provinces, and even within the same province. It is quite likely that there were more than one way of emplacing the voluminous and extensive CFB lava flows. We argue that the establishment of general models of emplacement must be based on a comprehensive documentation of lava flow morphology from all CFB provinces.     

The Shape and Volume of the Skaergaard Intrusion, Greenland: Implications for Mass Balance and Bulk Composition

Re-examination of the Skaergaard intrusion in the context ofits regional setting, combined with new data from explorationdrilling, has resulted in a revised structural model for theintrusion. It is modelled as an irregular box, c. 11 km fromnorth to south, up to 8 km from east to west, and 3·4–4km from the lower to the upper contact. The walls of the intrusionare inferred to follow pre-existing and penecontemporaneoussteep faults, and the floor and roof seem largely controlledby bedding planes in the host sediments and lavas, similar toregional sills. The suggested shape and volume are in agreementwith published gravimetric modelling. Crystallization alongall margins of the intrusion concentrated the evolving meltin the upper, central part of the intrusion, best visualizedas an ‘onion-skin’ structure inside the box. Thetotal volume is estimated to c. 280 ± 23 km³, of which13·7% are referred to the Upper Border Series (UBS),16·4% to the Marginal Border Series (MBS) and 69·9%to the Layered Series (LS). In the LS, the Lower Zone (LZ) isestimated to constitute 66·8%, the Middle Zone (MZ) 13·5%and the Upper Zone (UZ) 19·7%. The new volume relationshipsprovide a mass balance estimate of the major and trace elementbulk composition of the intrusion. The parental magma to theSkaergaard intrusion is similar to high-Ti East Greenland tholeiiticplateau basalts with Mg number c. 0.45. The intrusion representsthe solidification of contemporary plateau basalt magma trappedand crystallized under closed-system conditions in a crustalreservoir at the developing East Greenland continental margin. KEY WORDS: bulk composition; emplacement; mass proportions; Skaergaard intrusion; structure     

Genetic significance of fluid inclusions in the CSA Cu–Pb–Zn deposit, Cobar, Australia

CSA mine exploits a ‘Cobar-type’ Cu–Pb–Zn±Au±Ag deposit within a cleaved and metamorphosed portion of the Cobar Supergroup, central New South Wales. The deposit comprises systems of ‘lenses’ that encompass veins, disseminations and semi-massive to massive Cu–Pb–Zn ores. The systems and contained lenses truncate bedding, are approximately coplanar with regional cleavage and similarly oriented shear zones and plunge parallel to the elongation lineation. Systems have extreme vertical continuity (>1000 m), short strike length (400 m) and narrow width (100 m), exhibit vertical and lateral ore-type variation and have alteration haloes. Models of ore formation include classical hydrothermalism, structurally controlled remobilisation and polymodal concepts; syntectonic emplacement now holds sway.Fluid inclusions were examined from quartz±sulphide veins adjacent to now-extracted ore, from coexisting quartz–sulphide within ore, and from vughs in barren quartz veins. Lack of early primary inclusions precluded direct determination of fluids associated with D₂–D₃ ore and vein emplacement. Similarly, decrepitation (by near-isobaric heating) of the two oldest secondary populations precluded direct determination of fluid phases immediately following D₂–D₃ ore and vein emplacement. Post-decrepitation outflow (late D₃ to early post-D₃) is recorded by monophase CH₄ inclusions. Entrained outflow of deeply circulated meteoric fluid modified the CH₄ system; modification is recorded by H₂O+CH₄ and H₂O+(trace CH₄) secondary populations and by an H₂O+(trace CH₄) primary population. The contractional tectonics (D₂–D₃) of ore emplacement was superseded by relaxational tectonics (D_4P) that facilitated meteoric water penetration and return flow.Under D₂ prograde metamorphism, entrapment temperatures (Tt) and pressures (Pt) for pre-decrepitation secondary inclusions are estimated as Tt300–330 °C and Pt1.5–2 kbar≈Plith (the lithostatic pressure). Decrepitation accompanied peak metamorphism (T350–380 °C) in mid- to late-D₃, while in late-D₃ to early post-D₃, essentially monophase CH₄ secondary inclusions were entrapped at Tt350 °C and Pt=1.5–2 kbar≈Plith. Subsequently, abundant CH₄ and entrained meteoric water were entrapped as H₂O+CH₄ secondaries under slowly decreasing temperature (Tt330–350 °C) and constant pressure (Pt1.5–2 kbar). Finally, with increasingly dominant meteoric outflow, H₂O+(trace CH₄) populations record decreasing temperatures (Tt>300 to <350 down to 275–300 °C) at pressures of Phydrostatic<Pt (1 kbar) <Plith (1.5 kbar).The populations of inclusions provide insight into fluid types, flow regimes and P–T conditions during parts of the deposit's evolution. They indirectly support the role of basin-derived CH₄ fluids in ore formation, but provide no insight into a basement-sourced ore-forming fluid. They fully support post-ore involvement of meteoric water. The poorly constrained entrapment history is believed to span 10 Ma from 395 to 385 Ma.     

Granitoid emplacement by multiple sheeting during Variscan dextral transpression: The Saint-Laurent – La Jonquera pluton (Eastern Pyrenees)

The structural study of the Saint-Laurent – La Jonquera pluton (Eastern Pyrenees), a Variscan composite laccolithic intrusion emplaced in metasedimentary and gneissic rocks of the Roc de Frausa dome, by means of the anisotropy of magnetic susceptibility (AMS) technique has allowed the determination of the nature and orientation of its magmatic fabrics. The magmatic foliation has a predominant NE–SW strike and the mean lineation is also NE–SW trending with a shallow plunge. A strain gradient is measured so that the tonalites to granodiorites that form the basal parts of the pluton, and are intruded into amphibolite-facies metamorphic rocks, recorded the highest anisotropies, whereas the monzogranites and leucogranites, emplaced into upper crustal, low-grade metamorphic rocks, are weakly deformed. These results point to the synkinematic sequential emplacement of multiple granitoid sheets, from less to more differentiated magmatic stages, during the Late Carboniferous D₂ event characterized by an E–W-trending dextral transpression. The magmatic foliation appears locally disturbed by the effects of two tectonic events. The first of them (D₃) produced mylonitization of granitoids along NW–SE retrograding shear zones and open folds in the host Ediacaran metasediments of the Roc de Frausa massif, likely during late Variscan times. Interference between D₂ and D₃ structures was responsible for the dome geometry of the whole Roc de Frausa massif. The second and last perturbation consisted of local southward tilting of the granitoids coupled to the Mesozoic–Cenozoic cover during the Alpine.