High-density nitrogen inclusions in barite from a giant siderite vein: implications for Alpine evolution of the Variscan basement of Western Carpathians, Slovakia

Contrasting compositions and densities of fluid inclusions were revealed in siderite–barite intergrowths of the Dro?diak polymetallic vein hosted in Variscan basement of the Gemeric unit (Central European Carpathians). Primary two‐phase aqueous inclusions in siderite homogenized between 101 and 165 °C, total salinity ranged between 18 and 27 wt%, and CaCl₂/(NaCl + CaCl₂) weight ratios were fixed at 0.1–0.3. By contrast, mono‐ and two‐phase aqueous inclusions in barite exhibited total salinities between 2 and 22 wt%, and the CaCl₂/NaCl ratios ranged from NaCl‐ to CaCl₂‐dominated compositions. The aqueous inclusions in barite were closely associated with very high‐density (0.55–0.745 g cm^?3) nitrogen inclusions, in some cases containing up to 16 mol.% CO₂. Crystallization P–T conditions of siderite (175–210 °C, 1.2–1.7 kbar) constrained by the vertical oxygen isotope gradient along the studied vein, isochores of fluid inclusions and the K/Na exchange thermometer corresponded to minimal palaeodepths between 4.3 and 6.3 km, assuming lithostatic load and average crust density of 2.75 g cm^?3. Maximum fluid pressure during barite crystallization attained 3.6–4.4 kbar at 200–300 °C, and the most dense nitrogen inclusions maintained without decrepitation the residual internal pressure of 2.2 kbar at 25 °C. Contrasting fluid compositions, increasing depths of burial (～4–14 km) and decreasing thermal gradients (～40–15 °C km^?1) during initial mineralization stages of the Dro?diak vein reflect Alpine orogenic processes, rather than an incipient Permian rifting suggested in previous metallogenetic models. Siderite crystallized at rising P–T in a closed, rock‐buffered hydrothermal system developed in the Variscan basement during the north‐vergent Cretaceous thrusting and thickening of the Gemeric crustal wedge. Variable salinities of the barite‐hosted inclusions reflect a fluid mixing in open hydrothermal system, and re‐equilibration textures (lengths of decrepitation cracks proportional to fluid inclusion sizes) correspond to retrograde crystallization trajectory coincidental with transpression or unroofing. Maximum recorded fluid pressures indicate ～12‐km‐thick pile of imbricated nappe units accumulated over the Gemeric basement during the Cretaceous collision.     

Passive and active margin history of the northern Tatricum (Western Carpathians,Slovakia)

The Tatricum, an upper crustal thrust sheet of the Central Western Carpathians, comprises pre-Alpine crystalline basement and a Late Paleozoic-Mesozoic sedimentary cover. The sedimentary record indicates gradual subsidence during the Triassic, Early Jurassic initial rifting, a Jurassic-Early Cretaceous extensional tectonic regime with episodic rifting events and thermal subsidence periods, and Middle Cretaceous overall flexural subsidence in front of the orogenic wedge prograding from the hinterland. Passive rifting led to the separation of the Central Carpathian realm from the North European Platform. A passive margin, rimmed by peripheral half-graben, was formed along the northern Tatric edge, facing the Vahic (South Penninic) oceanic domain. The passive versus active margin inversion occurred during the Senonian, when the Vahic ocean began to be consumed southwards below the Tatricum. It is argued that passive to active margin conversion is an integral part of the general shortening polarity of the Western Carpathians during the Mesozoic that lacks features of an independent Wilson cycle. An attempt is presented to explain all the crustal deformation by one principal driving force - the south-eastward slab pull generated by the subduction of the Meliatic (Triassic-Jurassic Tethys) oceanic lithosphere followed by the subcrustal subduction of the continental mantle lithosphere.     

Siderite mineralization of the Gemericum superunit (Western Carpathians, Slovakia): review and a revised genetic model

The Gemericum is a segment of the Variscan orogen subsequently deformed by the Alpine–Carpathian orogeny. The unit contains abundant siderite–sulphide and quartz–antimony veins together with stratabound siderite replacement deposits in limestones and stratiform sulphide mineralization in volcano-sedimentary sequences. The siderite–sulphide veins and siderite replacement deposits of the Gemericum represent one of the largest accumulations of siderite in the world, with about 160 million tonnes of mineable FeCO₃. More than 1200 steeply dipping hydrothermal veins are arranged in a regional tectonic and compositional pattern, reflecting the distribution of regional metamorphic zones. Siderite–sulphide veins are typically contained in low-grade (chlorite zone) sedimentary, volcano-sedimentary or volcanic Lower and Upper Paleozoic rocks. Quartz–antimony veins are hosted by higher-grade units (biotite zone). Siderite–sulphide veins are dominated by early siderite followed by a complex set of stages, including quartz–sulphide (chalcopyrite, tetrahedrite), barite, tourmaline–quartz, and sulphide-remobilization stages. The temporal evolution of these stages is difficult to study because of the widespread and repeated tectonic processes, within-vein replacement and recrystallization. Siderite–sulphide veins show considerable vertical (up to 1200 m) and lateral (up to 15 km) extent, and a thickness typically reaching several metres. Carbonate-replacement siderite deposits of the Gemericum are hosted by a Silurian limestone belt and are similar to stratabound siderite deposits of the Eastern Alps (e.g., Erzberg, Austria).Based on a review of geological, petrological and geochronological data for the Gemericum, and extensive stable and radiogenic isotope data and fluid inclusion data on hydrothermal minerals, the siderite–sulphide veins and siderite replacement deposits are classified as metamorphogenic in a broad sense. The deposits were formed during several stages of regional crustal-scale fluid flow. Isotope (S, C, Sr, Pb) fingerprinting identifies the metamorphosed rock complexes of the Gemericum as a source of most components of hydrothermal fluids. Fluid inclusion and stable isotope data evidence the participation of several contrasting fluid types, and the existence of contrasting P–T conditions during vein evolution. A high-δ¹⁸O, medium- to high-salinity, H₂O-type fluid is the most important component during siderite deposition, whereas H₂O–CO₂-type fluid inclusion containing dense liquid CO₂ and corresponding to minimal pressures between 1 and 3 kbar were found in a younger tourmaline–quartz stage. Younger quartz–ankerite(±siderite)–sulphide stages are characterized by high-salinity (17 to 35 wt.% NaCl equivalent) and low-temperature (T_h=90 to 180 °C) H₂O-type fluids.The vein deposits are interpreted as a result of multistage hydrothermal circulation, with Variscan and Alpine mineralization phases. Based on available indirect data, the most important mineralization phase was related to regional fluid flow during the uplift of a Variscan metamorphic core complex, producing siderite–sulphide (±barite) mineralization, while tourmaline–quartz stage and sulphide remobilization stages are related to Alpine processes. Two phases of vein evolution are evident from two groups of ⁸⁷Sr/⁸⁶Sr isotope ratios of Sr-rich, Rb-poor hydrothermal minerals: 0.71042–0.71541 in older barite and 0.7190–0.7220 in late-stage celestine and strontianite.     

Late Cretaceous to Early Tertiary palaeogeography of the Western Carpathians (Slovakia) and the Eastern Alps (Austria): implications from heavy mineral data

The Late Cretaceous Brezová and Myjava Groups of the Western Carpathians in Slovakia and formations of the Gosau Group of the Northern Calcareous Alps in Lower Austria comprise similar successions of alluvial/shallow marine deposits overlain by deep water hemipelagic sediments and turbidites. In both areas the heavy mineral spectra of Late Cretaceous sediments contain significant amounts of detrital chrome spinel. In the Early Tertiary the amount of garnet increases. Cluster analysis and correspondence analysis of Coniacian/Santonian and Campanian/Early Maastrichtian heavy mineral data indicate strong similarities between the Gosau deposits of the Lunz Nappe of the north-eastern part of the Northern Calcareous Alps and the Brezova Group of the Western Carpathians. Similar source areas and a similar palaeogeographical position at the northern active margin of the Adriatic/Austroalpine plate are therefore suggested for the two tectonic units.Basin subsidence mechanisms within the Late Cretaceous of the Northern Calcareous Alps are correlated with the Western Carpathians. Subsidence during the Campanian-Maastrichtian is interpreted as a consequence of subduction tectonic erosion along the active northern margin of the Adriatic/Austroalpine plate. Analogous facies and heavy mineral associations from deep water sandstones of the Manin Unit and the Klape Unit indicate accretion of parts of the Pieniny Klippen Belt during the Late Cretaceous along the Adriatic/Austroalpine margin.     

斯洛伐克西喀尔巴阡山Kosice-Medvedia菱镁矿床的矿物学、流体包裹体和碳-氧-锶同位素研究

Kosice矿床是斯洛伐克第二大的菱镁矿床(150Mt),位于Gemeric的东部.其镁质碳酸盐矿体赋存于石炭纪石灰石和含白云石的石灰石中,同时下盘黑色片岩中也含有被铁质碳酸盐交代的薄层碳酸盐透镜体.在华力西期造山运动(M1)中,古生代岩石受到了低级变质作用(绿泥石带).镁交代作用始于白云岩1的结晶作用,其后形成菱镁矿,最终沿裂隙形成铁菱镁矿.铁质碳酸盐包括早期铁白云石-白云石,铁白云石和后期含方解石和石英的菱铁矿.根据碳酸盐矿物对地质温度计,白云石l结晶作用发生在300～340℃.这一结果与M1的变质矿物组合(绿泥石,白云母-伊利石)吻合.铁白云石的结晶作用发生在320～370℃.少量细脉中可见白云石2,绿泥石和伊利石-多硅白云母,它们是由于阿尔卑斯期造山运动M2变质作用形成的更晚的矿物组合.菱镁矿的流体包裹体(FI)研究,显示存在不同成分的热卤水,卤水成分变化相当于NaCl含量21～42wt%,但其它成分的盐含量高于NaCl,溶解的CO2含量也有变化.两相包裹体均一温度(Th)的范围为164～217℃,含石盐子晶包裹体均一温度的范围为217～344℃.富CO2包裹体(盐度相当于NaCl含量1～22wt%,CO2的密度为0.28～0.77g·cm-3,均一温度为289～344℃)在菱镁矿中是次要的,但这种包裹体在与矿石伴生的石英中是主要的,并且与含石盐子晶流体包裹体共生.在后期镁交代过程中流体中的CO2逐渐增加.和铁质碳酸盐伴生的石英中只有两相包裹体,包裹体中CO2含量有所变化,盐度范围为17～24wt%的NaCl(或者34～36 wt%的MgCl2),均一温度为152～195℃.包裹体的数据结合碳酸盐地质温度计显示镁交代作用的压力范围是180～320MPa(7～12km),铁交代作用的压力范围是280～420MPa(10～16km),说明地热梯度约为25～35℃/km.包裹体浸出液的分析表明Cl/Br和Na/Br的比值存在变化,但仍旧说明富镁的卤水来源是上二叠纪和下三叠纪的分馏蒸发岩来源.铁质碳酸盐流体的高溴和高碘含量,说明在铁交代过程中周围黑色片岩的明显影响.菱镁矿和铁交代作用,表明交代流体中的碳和二氧化碳,主要是海洋沉积的来源.菱铁矿的"Sr/86Sr比值((0.71124～0.71140),说明锶的多来源,最初应是石炭纪和二叠纪的海水,但它被当地其它陆壳中的锶混染.     

Ordovician K-bentonites in the upper-plate active margin of Western Gondwana, (Famatina Ranges): Stratigraphic and palaeogeographic significance

Numerous, thin-bedded, tabular pale-yellowish clay bands are interlayered with black shales in a biostratigraphically constrained Early Ordovician volcano-sedimentary succession at Famatina, western Argentina. This region was part of a fairly continuous upper-plate, convergent volcanic chain that fringed western Gondwana. Mineralogy on both clay and non-clay fractions, whole rock chemistry and field observations on these distinctive event-beds indicate that they originated as relatively coarse fallout tephras, altered first into bentonites and later, through burial metamorphism, into K-bentonites (metabentonites). These tephras were deposited as single crystals and glassy dust or pumiceous fragments in a restricted subtidal environment. The region of Famatina has previously been inferred as the source of abundant distal K-bentonites recorded in the adjacent lower-plate allochthonous Precordillera terrane. However, these K-bentonites within the proximal arc site were unknown and rather unexpected since they are generally better preserved like distal deposits, associated either with central vent plinian–ultraplinian eruptions or with accompanying co-ignimbrite ash clouds. Their chemistry and comparison with those K-bentonites in the Precordillera allow tracing an evolution from volcanic arcs into continental crust. K-bentonites described in this paper are much older than those recorded in the adjacent Precordillera terrane and seem to be associated with a first eruptive period along western Gondwana that has no counterpart in the Argentine Precordillera, suggesting a significant longitudinal separation between these two regions by the Early Ordovician.     

Stages in the Magura Basin: a case study of the Polish sector (Western Carpathians)

The Magura Basin domain developed in its initial stage as a Jurassic-Early Cretaceous rifted passive margin that faced the eastern parts of the oceanic Alpine Tethys. In the pre- and syn-orogenic evolution of the Magura Basin the following prominent periods can be distinguished: Middle Jurassic-Early Cretaceous syn-rift opening of basins (1) followed by Early Cretaceous post-rift thermal subsidence (2), latest Cretaceous–Paleocene syn-collisional inversion (3), Late Paleocene to Middle Eocene flexural subsidence (4) and Late Eocene - Early Miocene synorogenic closing of the basin (5). The driving forces of tectonic subsidence of the basin were syn-rift and thermal post-rift processes, as well as tectonic loads related to the emplacement of accretionary wedge. This process was initiated at the end of the Paleocene at the Pieniny Klippen Belt (PKB)/Magura Basin boundary and was completed during Late Oligocene in the northern part of the Magura Basin. During Early Miocene the Magura Basin was finally folded, thrusted and uplifted as the Magura Nappe.     

Superdense CO2 inclusions in Cretaceous quartz–stibnite veins hosted in low-grade Variscan basement of the Western Carpathians, Slovakia

CO₂ inclusions with density up to 1,197 kg m⁻³ occur in quartz–stibnite veins hosted in the low-grade Palaeozoic basement of the Gemericum tectonic unit in the Western Carpathians. Raman microanalysis corroborated CO₂ as dominant gas species accompanied by small amounts of nitrogen (<7.3 mol%) and methane (<2.5 mol%). The superdense CO₂ phase exsolved from an aqueous bulk fluid at temperatures of 183–237°C and pressures between 1.6 and 3.5 kbar, possibly up to 4.5 kbar. Low thermal gradients (∼12–13°C km⁻¹) and the CO₂–CH₄–N₂ fluid composition rule out a genetic link with the subjacent Permian granites and indicate an external, either metamorphogenic (oxidation of siderite, dedolomitization) or lower crustal/mantle, source of the ore-forming fluids.According to microprobe U–Pb–Th dating of monazite, the stibnite-bearing veins formed during early Cretaceous thrusting of the Gemeric basement over the adjacent Veporic unit. The 15- to 18-km depth of burial estimated from the fluid inclusion trapping PT parameters indicates a 8- to 11-km-thick Upper Palaeozoic–Jurassic accretionary complex overlying the Gemeric basement and its Permo-Triassic autochthonous cover.     

Cretaceous evolution of a metamorphic core complex,the Veporic unit,Western Carpathians (Slovakia): P–T conditions and in situ40Ar/39Ar UV laser probe dating of metapelites

Alpine metamorphism, related to the development of a metamorphic core complex during Cretaceous orogenic events, has been recognized in the Veporic unit, Western Carpathians (Slovakia). Three metamorphic zones have been distinguished in the metapelites: 1, chloritoid + chlorite + garnet; 2, garnet + staurolite + chlorite; 3, staurolite + biotite + kyanite. The isograds separating the metamorphic zones have been modelled by discontinuous reactions in the system K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O (KFMASH). The isograds are roughly parallel to the north‐east‐dipping foliation related to extensional updoming along low‐angle normal faults. Thermobarometric data document increasing P–T conditions from c. 500 °C and 7–8 kbar to c. 620 °C and 9–10 kbar, reflecting a coherent metamorphic field gradient from greenschist to middle amphibolite facies. ⁴⁰Ar/³⁹Ar data obtained by high spatial resolution in situ ultraviolet (UV) laser ablation of white micas from the rock slabs constrain the timing of cooling and exhumation in the Late Cretaceous. Mean dates are between 77 and 72 Ma; however, individual white mica grains record a range of apparent ⁴⁰Ar/³⁹Ar ages indicating that cooling below the blocking temperature for argon diffusion was not instantaneous. The reconstructed metamorphic P–T–t path is ‘clockwise’, reflecting post‐burial decompression and cooling during a single Alpine orogenic cycle. The presented data suggest that the Veporic unit evolved as a metamorphic core complex during the Cretaceous growth of the Western Carpathian orogenic wedge. Metamorphism was related to collisional crustal shortening and stacking, following closure of the Meliata Ocean. Exhumation was accomplished by synorogenic (orogen‐parallel) extension and unroofing in an overall compressive regime.     

Petrogenesis of Ordovician magmatic rocks in the southern Chiapas Massif Complex: relations with the early Palaeozoic magmatic belts of northwestern Gondwana

The recent discovery of Early Ordovician S-type granites in the southwest of the Chiapas Massif Complex adds a new perspective to the Palaeozoic history of the Maya block, inasmuch as no rocks of such age had previously been reported in this region. New geologic mapping west of Motozintla, Chiapas, revealed pelitic to psammitic metasedimentary successions (Jocote Unit) intruded by granitoids and metabasites. The Jocote Unit is unconformably underlain by the newly defined Candelaria Unit, which comprises deformed calc-silicate rocks and interlayered folded amphibolites. The Candelaria Unit is the oldest rock succession so far recognized in the southern Maya block. We used laser-ablation multicollector inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating to determine the ages of the rock, yielding Early Ordovician (ca. 470 Ma) and Late Ordovician (ca. 450 Ma) ages.

Major and trace element geochemistry, as well as Nd and Sr isotope data, suggest that folded amphibolites of the Candelaria Unit are mantle-derived and are probably related to rifting. The Early Ordovician bimodal magmatism of the Jocote Unit is more strongly differentiated; it reflects crustal contamination and volcanic-arc chemical signatures. A granitic stock (Motozintla pluton) intruded the area in the Late Ordovician. Its geochemical composition indicates less crustal contamination and a mixed signature between volcanic-arc and within-plate settings. Magmatic rocks analogous in age and chemical character crop out in the Rabinal and the Altos Cuchumatanes areas of Guatemala, suggesting the existence of a semi-continuous Ordovician magmatic belt from Chiapas to central Guatemala. Similar but somewhat younger granites also occur in the Maya Mountains of Belize, suggesting that magmatism migrated in the Silurian from the Chiapas–Guatemala belt towards the Maya Mountains.     

Petrology of two granite types from the Tribeč Mountains,Western Carpathians: An example of allanite (+ magnetite) versus monazite dichotomy

Two granitoid series have been distinguished in the Tribeč Mountains (Western Carpathians) on the basis of the contrasting petrological behaviour of their accessory minerals. The allanite–magnetite-bearing (AM) tonalite–granodiorite–granite series typically contains dark magmatic enclaves and is produced from oxidizing, more hydrous (about 5.2 wt.% water) melts that were emplaced at depths equivalent to 350 ± 100 MPa. The monazite-bearing (M) tonalite–granodiorite–granite series contains only metamorphic xenoliths and comes from reduced and drier (about 2.3 wt.% water) melts that were probably emplaced at a shallower depth. The inferred magma properties probably reflect source rock effects. The mineralogical discrimination scheme between the AM and M series corresponds broadly to I- and S-type subdivision and may be useful not only for the granitoid bodies in the Western Carpathians but also for the whole Variscan orogenic belt.     

黑龙江北部多宝山矿区奥陶系的岩石特征和构造意义

黑龙江北部多宝山矿区广泛发育奥陶系,因含有铜、钼矿源层而受到地质界的注意.本文概述了其生物地层和沉积特征,重点探讨了其火山岩的岩石化学特征.该套火山岩总体上属钙碱性系列,部分（主要是酸性岩）可能属拉斑玄武岩系.下旋回（窝里河组）火山岩以相对低K、La和Eu负异常为特征,总体属大陆边缘岛弧,局部显示出大洋岛弧安山岩的性质.上旋回（多宝山组）的弧则属大陆边缘岛弧与安第斯型山弧的过渡类型,部分地区可能有安第斯型山弧发育.分5个阶段重塑了该区奥陶纪大地构造演化,早古代洋壳向东偏北消减于布列亚一佳木斯地块之下,因后退式的消减而火山弧向西偏南迁移,构造线方向为北北西向.     

Cambrian to Devonian Geologic Evolution of the Sierra de Comechingones, Eastern Sierras Pampeanas, Argentina: Evidence for the Development and Exhumation of Continental Crust on the Proto-Pacific Margin of Gondwana

Crystalline rocks from the Sierra de Comechingones, eastern Sierras Pampeanas, evolved through three distinct orogenic cycles during the Eopalaeozoic: (1) the first tectono-thermal event named Pampean orogeny (550 to 505 Ma), which peaked in the Early Cambrian, was responsible for extensive metamorphism, partial melting, juvenile magmatism, rapid decompression, and persistent tectonic activity. Large part of the crustal section that was residing at middle levels (c. 27 km) was heated above 800 °C during the thermal peak stage of the Pampean orogeny; decompression of the Pampean orogen's core took place at this high temperature. The exhumation mechanism that assisted rapid uplifting combined the effects of ongoing tectonic forces with a buoyant instability created by a large amount of anatectic magmas in the middle to lower crust. (2) Beginning at the Early Ordovician, the Famatinian orogeny produced an overall shortening, causing pervasive textural reworking of the Cambrian metamorphic sequences under a high-strain regime. By being adjacent to the Famatinian magmatic arc, the western border of the Cambrian crystalline package absorbed imposed deformation along a crustal scale ductile shear zone. Within this zone, the high-grade metamorphic rocks were reworked and re-hydrated to lower temperature assemblages (<600°C and 3–6 kbar). Early Ordovician subduction-related igneous activity, even though manifested as small plutons, intruded Cambrian crystalline sequences, and experienced textural reworking during Late Famatinian tectonic exhumation. Late Famatinian convergence resulted in west-vergent ductile shear zones that placed Cambrian onto Ordovician crystalline sequences. (3) During post-Famatinian times (360–400 Ma) enduring crustal perturbation produced intra-crustal-derived granitic magmatism. West- to northwest-directed thrusting was concentrated in belts nucleated along crustal-scale tectonic boundaries formed between older tectono-stratigraphic units. As a result, Devonian anatectic granites were formed and tectonically extruded among Pampean and Famatinian crystalline sequences. The post-Famatinian event is also characterised by the intrusion of batholith-scale monzogranites into Pampean and Famatinian crystalline sequences residing in the upper crust.

Crystalline rocks currently exposed in the Sierra de Comechingones show that they crystallised and were exhumed in a setting where tectono-thermal activity lasted, even though it might have waned, until the Middle Palaeozoic. From the latest Neoproterozoic (c. 550 Ma) until the Late Devonian (c. 360 Ma) tectonic activity was intermittently acting, indicating continuous convergence along the proto-Pacific margin of Gondwana.     

The role of structural inheritance in continental break-up and exhumation of Alpine Tethyan mantle(Canavese Zone,Western Alps)

The Canavese Zone(CZ)in the Western Alps represents the remnant of the distal passive margin of the Adria microplate,which was stretched and thinned during the Jurassic opening of the Alpine Tethys.Through detailed geological mapping,stratigraphic and structural analyses,we document that the continental break-up of Pangea and tectonic dismemberment of the Adria distal margin,up to mantle rocks exhumation and oceanization,did not simply result from the syn-rift Jurassic extension but was strongly favored by older structu ral inheritances(the Proto-Canavese Shear Zone),which controlled earlier lithospheric weakness.Our findings allowed to redefine in detail(i)the tectono-stratigraphic setting of the Variscan metamorphic basement and the Late Carbonife rous to Early Cretaceous CZ succession,(ii)the role played by inherited Late Carboniferous to Early Triassic structures and(iii)the significance of the CZ in the geodynamic evolution of the Alpine Tethys.The large amount of extensional displacement and crustal thinning occurred during different pulses of Late Carbonife rous-Early Triassic strike-slip tectonics is wellconsistent with the role played by long-lived regional-scale wrench faults(e.g.,the East-Variscan Shear Zone),suggesting a re-discussion of models of mantle exhumation driven by low-angle detachment faults as unique efficient mechanism in stretching and thinning continental crust.     

西盟地区奥陶纪花岗片麻岩的锆石U-Pb年代学、Hf同位素组成特征及其大地构造意义

对云南西部侵入于原西盟群帕可组的花岗片麻岩开展主量元素、锆石U-Pb年龄及原位Hf同位素组成分析。岩石地球化学特征显示其为高钾钙碱性强过铝质S型花岗岩,两件代表性样品分别给出了461.4±2.5 Ma和461.5±3.3 Ma的206Pb/238U加权平均年龄,相应的锆石εHf(t)值分别介于-6.45~-1.90和-5.60~-1.44之间,二阶段模式年龄(tDM2)分别为1.57~1.86 Ga和1.54~1.90 Ga。这些数据表明西盟地区侵入于原西盟群帕可组内的花岗片麻岩并非前人所认为的中元古代岩石,而是中奥陶世产物,其源岩可能是元古宙变质杂砂岩。结合前人研究成果,作者推测西盟地区早古生代花岗片麻岩是环冈瓦纳大陆边缘安第斯型造山作用的产物。     

斯洛伐克西喀尔巴阡山脉内侧Veporicum地区的地球动力学演化序列与菱镁矿和滑石矿床成因

本文总结并报导了斯洛伐克西喀尔巴阡山脉内侧的石炭纪岩石中产出的菱镁矿和滑石成因的最新资料.这些矿床赋存于Veporicum构造超单元中和该超单元与Gemericum的接触带中.北部Sinec成矿带是主要的菱镁矿和滑石矿化区,产出的主要矿床有Kokava,Sinec,Samo,Hnsta-Mutnik等矿床.而南部的Ochtina成矿带只产有菱镁矿床,主要矿床包括在Dubrava地体上的Dubrava,Mikov?JedL'vec;Luben韐,Ochtina,Kosice-Bankov,Banisko,Medvedia等矿床.菱镁矿形成于变质M1期石炭系中方解石被白云石和菱镁矿连续交代过程(北矿带成矿温度为280～400℃,南矿带成矿温度为370～420℃;Radvanec＆Prochska,2001;Kodera＆Radvanec,2002).Permoscythian蒸发卤水提供了Mg.成矿事件和华力西期碰撞后运动有关.拉伸构造和高热流值促使成矿热液系统的产生.滑石矿化则形成于稍晚的不同期变质事件(M2),成矿流体来源也与菱镁矿化不同.构造的、微构造的、变质的以及地质年代学的数据将滑石成矿作用和阿尔卑斯上白垩系的构造地热事件AD2联系在一起.AD2事件是阿尔卑斯碰撞(AD1)地壳加厚和变质核杂岩体起源的结果,体现在地壳不整合面上的区域拉伸,及开放系统中大规模热液流动.这一过程在更靠近Veporic热穹的北带区域(Sinec剪切带)很显著,而向着Veporic热穹的周围部分(南Ochtina带),M2变质过程和块滑石化则逐渐减弱.Sinec剪切带是北Sinec带中突出的AD2-AD3结构,白云石/菱镁矿透镜体(在M1期交代造成的)和相伴随的岩石夹杂在AD1中更坚硬的基底岩石之中.本研究证明了AD2中块滑石化的普遍性,滑石和白云石2形成于拉伸显微构造中(变质过程M2;温度为490～540℃,压力为240～330MPa).在Sinec带中AD3阶段的对偶剪切作用形成了该带中的滑石矿.它是AD2事件从去顶到区域扭压剪切的动力学转变过程的逐步延续.北Sinec带使AD3变形处于由坚硬岩石包围的软岩石的狭窄的剪切带中,而在南Ochtina带中AD3变形产生在由里面漂浮着坚硬碳酸盐块的软的岩石柱中.在Ochtina带中,在AD2和AD3阶段由于M2期较低的P-T条件和变形梯度导致了该区有经济价值的滑石矿化不发育.总之,现有的研究结果能用作阿尔卑斯型地体中菱镁矿和滑石找矿的基本标志.     

Pegmatite Emplacement in the Seridó Belt, Northeastern Brazil: Late Stage Kinematics of the Brasiliano Orogen

Geometric and kinematic analysis was performed in an area located in the central part of the Seridó Belt (NE Brazil), where supracrustal rocks affected by polyphase deformation are well exposed. The first event recognized in this area (and regionally known as the D₂ deformation) is characterized by top to the south thrust tectonics while a second one (D₃ deformation) is marked by upright folds, strike-slip or transpressive shear zones and the development of flower structures. Major pegmatite swarms were emplaced during and late as regards the second event (dated ca. 580 Ma), being part of the Brasiliano orogeny; similar dyke swarms are known from the Nigerian Shield. These pegmatite swarms provide reliable kinematic markers of the late evolutionary stage of the Neoproterozoic Trans-Sahara-Borborema collisional belt. Mineralogical, geometric and kinematic features support two stages of pegmatite emplacement during the strike-slip event: (i) older, syn-D₃ homogeneous pegmatites intruded mostly along lithological and structural discontinuities, such as foliation surfaces; (ii) late, D₃ heterogeneous pegmatites were emplaced along tension gashes and other dilation structures. The heterogeneous pegmatites are economically more important, being exploited for precious metals and stones, as well as industrial minerals.     

Structural,petrological and chemical analysis of syn‐kinematic migmatites: insights from the Western Gneiss Region,Norway

Evidence of melting is presented from the Western Gneiss Region (WGR) in the core of the Caledonian orogen, Western Norway and the dynamic significance of melting for the evolution of orogens is evaluated. Multiphase inclusions in garnet that comprise plagioclase, potassic feldspar and biotite are interpreted to be formed from melt trapped during garnet growth in the eclogite facies. The multiphase inclusions are associated with rocks that preserve macroscopic evidence of melting, such as segregations in mafic rocks, leucosomes and pegmatites hosted in mafic rocks and in gneisses. Based on field studies, these lithologies are found in three structural positions: (i) as zoned segregations found in high‐P (ultra)mafic bodies; (ii) as leucosomes along amphibolite facies foliation and in a variety of discordant structures in gneiss; and (iii) as undeformed pegmatites cutting the main Caledonian structures. Segregations post‐date the eclogite facies foliation and pre‐date the amphibolite facies deformation, whereas leucosomes are contemporaneous with the amphibolite facies deformation, and undeformed pegmatites are post‐kinematic and were formed at the end of the deformation history. The geochemistry of the segregations, leucosomes and pegmatites in the WGR defines two trends, which correlate with the mafic or felsic nature of the host rocks. The first trend with Ca‐poor compositions represents leucosome and pegmatite hosted in felsic gneiss, whereas the second group with K‐poor compositions corresponds to segregation hosted in (ultra)mafic rocks. These trends suggest partial melting of two separate sources: the felsic gneisses and also the included mafic eclogites. The REE patterns of the samples allow distinction between melt compositions, fractionated liquids and cumulates. Melting began at high pressure and affected most lithologies in the WGR before or during their retrogression in the amphibolite facies. During this stage, the presence of melt may have acted as a weakening mechanism that enabled decoupling of the exhuming crust around the peak pressure conditions triggering exhumation of the upward‐buoyant crust. Partial melting of both felsic and mafic sources at temperatures below 800 °C implies the presence of an H₂O‐rich fluid phase at great depth to facilitate H₂O‐present partial melting.     

昌宁-孟连结合带奥陶纪洋岛玄武岩的识别及其构造意义——来自地球化学和锆石U-Pb年龄的证据

西南三江昌宁-孟连构造带传统被认为是晚古生代古特提斯洋的缝合带。在该构造带中段铜厂街蛇绿混杂岩东侧勐勇—芒红一带,新识别出一套近南北向展布的灰绿色气孔-杏仁状玄武岩、安山玄武岩和硅质岩、浅变质泥质粉砂岩组成的火山-沉积岩系。对杏仁状玄武岩样品进行LA-ICP-MS锆石U-Pb定年,获得其~(206)Pb/~(238)U年龄加权平均值为449.3±8.4Ma(MSWD=3.5),表明该套火山岩喷发于奥陶纪。元素地球化学特征表现为富铝(12.11%~15.04%)、富钠(K_2O/N_2O=0.03~0.44)、高Mg~#值(45.9~61.7),同时,该套火山岩中MgO=6.78%~12.34%,平均为9.43%,Cr=58.6×10~(-6)~636×10~(-6),平均为310.3×10~(-6),Ni=57.4×10~(-6)~410×10~(-6),平均为202.1×10~(-6),Nb=18.9×10~(-6)~32.8×10~(-6),平均为25.06×10~(-6),具有轻稀土元素强烈富集的"直线状"稀土元素配分模式,(La/Yb)_N=5.25,(Ce/Yb)_N=4.42,(Ce/Sm)_N=1.68,稀土元素总量随全碱含量增大有升高的趋势,表明其为亚速尔型洋岛。总体上,该套火山岩具碱性OIB(洋岛玄武岩)的特征,可能是大洋板内热点前部熔融的产物。亚速尔型洋岛玄武岩的出现代表了特提斯洋盆内洋岛发育早期阶段的物质记录,为重新认识滇西南昌宁—孟连地区特提斯主洋盆开阔多岛洋的格局提供了丰富的岩石学依据。