Batholith Research Articles

Petrogenesis of the Pa'a batholiths in the Geji area, western segment of the Bangong Co-Nujiang River suture zone: Constraints by geochemistry, zircon U-Pb geochronology and Hf isotope

班公湖-怒江结合带是藏北一条重要的特提斯主洋残余，在洋盆消减过程中发生了强烈岩浆作用，在其南缘形成了沿狮泉河-永珠缝合带两侧广泛分布的白垩纪大规模岩浆岩和火山岩，为了解班公湖-怒江特提斯洋俯冲和闭合过程提供了良好窗口。本文对出露于革吉地区帕阿花岗闪长岩岩基进行了详细的野外地质填图、全岩元素地球化学、锆石U-Pb年代学和Hf同位素组成研究。研究结果表明，花岗闪长岩和其闪长质包体的锆石206Pb/238U年龄分别为155.7±1.0Ma（谐和年龄，MSWD=0.26，N=18）和156.5±2.3Ma（年龄加权平均值，MSWD=2.6，N=16），岩浆侵位于晚侏罗世，不是以往所认为的白垩纪岩浆产物。花岗闪长岩主要属于高钾钙碱性系列，高铝饱和指数（A/CNK=0.91~1.04），显示了过铝质特征。花岗闪长岩富集轻稀土元素（LREE/HREE）=5.51~8.54，（La/Yb）N=6.27~20.2）和大离子亲石元素，亏损Nb、Ta、Sr、Ti等高场强元素，具有中等至弱Eu负异常（δEu=0.61~0.85）。锆石Hf同位素分布集中，花岗闪长岩和闪长质包体的锆石eHf（t）均为负值，分别为（-9.4~-6.3）和（-10.9~-8.6），Hf地壳模式年龄分别为（1.32~1.48Ga）和（1.44~1.56Ga），指示了帕阿花岗闪长岩岩基主体系古老地壳基底部分熔融产物，存在少量地幔物质的加入，形成于弧环境，可能属于班公湖-怒江洋盆南向俯冲到拉萨地块古老结晶基底重熔形成的一套具弧属性的未分异Ⅰ型花岗岩。

مطالعه کانی شناسی و فرآیندهای اسکارنی شدن در اسکارن مس- آهن آوان، شمالخاور خاروانا، شمال باختر ایران

اسکارن مس- آهن آوان در نتیجه نفوذ باتولیت گرانیتوئیدی قره داغ به‌ داخل سنگهای کربناته ناخالص کرتاسه بالایی تشکیل شده است. اسکارن آوان متشکل از پهنه های مرمر، اگزواسکارن و اندواسکارن بوده و بخش اصلی آن پهنه اگزواسکارن، است. بررسیهای کانی شناسی بیانگر آن است که پهنه اگزواسکارن شامل زیرپهنه های گارنت اسکارن، پیروکسن- گارنت اسکارن و کانه اسکارن است. مهمترین کانی کالک سیلیکاته بی آب در پهنه اگزواسکارن، گارنت و ترکیب آن اوگراندیتی (Ad53-89) است. برخی بلورهای گارنت، منطقه‌بندی دارد و ترکیب آنها به طرف حاشیه‌ها به آندرادیت خالص (Ad99) میل می‌کند. کلینوپیروکسن موجود در زیرپهنه پیروکسن- گارنت اسکارن از نوع دیوپسید (Di75-96) است. زیرپهنه کانه اسکارن از کانه‌های مگنتیت، هماتیت، پیریت، کالکوپیریت، بورنیت، مالاکیت و گوتیت تشکیل شده است. وجود میزان محدود ولاستونیت در مجموعه کانی شناسی اسکارن آوان، هم‌رشدی بلورهای گارنت و کلینوپیروکسن و نبود هاله واکنشی بین این دو کانی و نبود بافتهای جانشینی نشان‌دهنده آن است که این کانیها به‌صورت هم‌زمان در محدوده دمایی C°600- 430 و فوگاسیته اکسیژن بیشتر از 10-26 تشکیل شده‌اند.

The Capilla del Monte pluton, Sierras de Córdoba, Argentina: the easternmost Early Carboniferous magmatism in the pre-Andean SW Gondwana margin

Fil: Dahlquist, Juan Andres. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Cordoba. Facultad de Ciencias Exactas Fisicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina

Highly Potassic Melagranite of Bintang Batholith, Main Range Granite, Peninsular Malaysia

Highly Potassic Melagranite of Bintang Batholith, Main Range Granite, Peninsular Malaysia

Evolução metamórfica e estrutural do Complexo Várzea do Capivarita, Cinturão Dom Feliciano, Encruzilhada do Sul, RS

O Complexo Várzea do Capivarita está representado por paragnaisses dispostos como megaxenólitos nos granitos da Suíte Encruzilhada do Sul e como fragmentos menores nos granitos Quitéria e Cordilheira. Essas unidades graníticas afloram no extremo norte do Batólito Pelotas, porção leste do Cinturão Dom Feliciano, próximo a Encruzilhada do Sul. O complexo é constituído por gnaisses pelíticos, com ocorrência subordinada de gnaisses calci-silicáticos, mármores, gnaisses quartzo-feldspáticos e raros quartzitos. Os gnaisses pelíticos possuem injeções de corpos tabulares de muscovita leucogranitos peraluminosos com espessuras centimétricas a métricas. Neste trabalho foram feitas análises petrográficas e microestruturais de seções delgadas representativas das litologias do complexo e a caracterização estrutural da área de estudo. A integração desses dados permitiu avaliar a migmatização dos paragnaisses e a geração das injeções leucograníticas. As condições metamórficas estabelecidas com base nas paragêneses identificadas indicam temperaturas da ordem de 850 a 1000°C e pressões entre 6 e 10 kbar, caracterizando um metamorfismo orogênico de fácies granulito, da série de pressão intermediária e de ultra-alta temperatura (UAT). A concordância estrutural entre o bandamento (S2) dos paragnaisses e a foliação ígnea (S0 ) do leucogranito indica que ambas foram formadas no mesmo evento, implicando que a migmatização dos paragnaisses do Complexo Várzea do Capivarita gerou os leucogranitos peraluminosos durante o ápice do metamorfismo orogênico colisional.

When did India-Asia Collide and Make the Himalaya?

Critical evaluation and comparison of the available geological and geochronological data from the northern parts of the Himalaya and Trans-Himalaya mountains highlight that these mountains did not initially evolve by the collision of continents of the Indian and Asian plates. Instead, subducted Tethyan oceanic lithosphere in front of the Indian continent melted to produce the calc-alkaline suite of the Shyok-Dras volcanic arc and the Ladakh batholith. Hence, the Indian plate initially subducted beneath and started building up the then existing intra-oceanic island arc. Timing of the first impingement of the Indian and Asia plates has been better constrained at around 57.5 Ma by comparing (i) the bulk ages from the Ladakh batholith (product of partial melting of the Tethyan oceanic lithosphere) with (ii) the subducted continental lithospheric and UHP metamorphosed Indian crust in the Tso Morari, and (iii) biostratigraphy of the youngest marine sedimentation in Zanskar. Thus, the Himalaya witnessed its first rise and emergence from deeply exhumed terrain in the Tso Morari after around 53 Ma, followed by sequential imbrication of the Indian continental lithosphere and associated exhumation during rise of the Himalayan mountains from north to the south since 45 Ma.

Phanerozoic palinspastic reconstructions of Great Basin geotectonics (Nevada-Utah, USA)

Palinspastic reconstructions of Phanerozoic geotectonic elements in the Great Basin (Nevada-Utah, USA) to restore the effects of Basin and Range extension, Sevier thrust telescoping, and evolution of the Cordilleran magmatic arc and forearc region to the west provide the following insights: (1) the position of the Neogene Walker Lane incipient transform system was controlled by thermal weakening of the lithosphere beneath the extinct southern segment of the ancestral Cascades arc; (2) Eocene to Miocene magmatism swept across the Great Basin from northeast to southwest, in a direction normal to the continental margin, rather than from north to south parallel to the continental margin; (3) the elevated Paleogene Nevadaplano and Sevier thrust belt between the Sierra Nevada and the Sevier foreland basin was comparable in width to the modern Altiplano and Subandean thrust belt between the Andean volcanic chain and the Brazilian foreland; (4) the late Mesozoic Sierra Nevada and Idaho batholiths formed in the roots of the Cordilleran magmatic arc as segments of a linear batholith belt that lacked curvature; (5) early to middle Mesozoic backarc basins, thrusts, and plutons were coordinated geodynamically with arc accretion and closure of a suture belt in the Sierran foothills, Klamath Mountains, and Blue Mountains of the Cordilleran arc terrane to the west; and (6) Devonian–Mississippian Roberts Mountains and Permian–Triassic Golconda thrusts and allochthons, emplaced successively from the west upon the flank of the Cambrian–Devonian miogeoclinal belt, were formed as linear features subparallel to the Wasatch hinge line marking the western edge of undeformed craton.

POST-VARISCAN MAFIC DIKES FROM THE LATE OROGENIC COLLAPSE TO THE TETHYAN RIFT: EVIDENCE FROM SARDINIA

Dolerite dikes cut the Lower Paleozoic medium- to high-grade metamorphic basement, the Sardinia-Corsica batholith and the Stephanian - Autunian calcalkaline effusives (1st volcanic episode, according e.g. to Bonin, 1989; Cabanis et al., 1990) with a N-S trend and subvertical dip. Their occurrence is reported from several areas of Sardinia, from the N to the SE. The basic dikes are associated with diorite to rhyolite dikes having trends ranging from E-W to N-S. A late Triassic lamprophyric dike intruded the garnet-staurolite-kyanite micaschists near Mt. Nieddu and has a 40°N direction. Two 40Ar-39Ar age determinations for the dolerite dikes were carried out on amphibole. Ages between 253.8±4.9 and 248±8 Ma (Permian - Early Triassic) probably correspond to the emplacement interval. A continental within-plate geochemical signature, with prevalent tholeiitic to transitional (dolerites) and minor alkalic (lamprophyre) terms, has been determined. The relative LILE and REE enrichment compared with the MORBs and Nd isotopic ratios (4 bulk samples; initial 143Nd/144Nd ratios between 0.512529±0.000025 and 0.513143±0.000023) is consistent with a source in a sub-continental lithospheric mantle. The remarkable compositional and isotopic variability can be explained by the partial melting of a heterogeneous source. Crustal contamination variably affects some transitional dikes; the host Arzachena monzogranite probably represents the major contaminant source. On the whole, the geochemical data support an anorogenic geochemical affinity, in accordance with the extensional regional tectonics, for the Permo-Triassic dikes in Sardinia. The E-W emplacement patterns correspond to the major fractures and primarily R and RI structures associated with the late Variscan transcurrent-extensional E-W faults. The N-S emplacement trend is consistently associated with a generalized E-W extension of the Sardinian crust: in a predrift restoration it coincides with the patterns of extension between the European and Insubric crust at the beginning of the Tethyan rift. In Sardinia, the lamprophyre dike is significantly younger than the late Variscan alkaline volcanites and dikes of the rest of the Mediterranean domain (e.g. Eastern Provence: 278-264 Ma, 40Ar/39Ar isotope dating on feldspar from rhyolites and on plagioclase from mafic flow, Zheng et al., 1992; Western Pyrenean Axial Zone: 271-266 Ma, K-Ar isotope dating on kaersutite phenocrysts from mafic dikes, Debon and Zimmermann, 1993), in accordance with the diachronism of both the first and second volcanic episodes in different areas of the Mediterranean domain. The overlap between the calc-alkaline events and the volcanic and sub-volcanic alkalic event, is not exclusive to Sardinia and Corsica (e.g. the Pyrenees and Pan-African orogen).

Weathering of Devonian monzogranites as recorded in the geochemistry of saprolites from the South Mountain Batholith, Nova Scotia, Canada

Parent mineralogy, paleoenvironment, and subsequent diagenetic and erosional history contribute to the nature of the paleoweathering profiles (saprolites) developed on the South Mountain Batholith. Saprolites of three different ages (pre-Carboniferous, pre-Triassic, and pre-Pleistocene) developed on Devonian monzogranite and exhibit increases in oxidation and hydration and decreases in rare earth elements with increasing weathering. In addition, changes in Ca, Ba, Rb, Zn, Pb, Co, and other elements in the oldest saprolite indicate element mobility during weathering. Re-exposure of these partially weathered profiles at surface in today's acidic and oxygen-rich environment may result in further migration of elements from these saprolites.
 
 RÉSUMÉ
 
 La minéralogie originelle, le paléoenvironnement, et les antécédents diagénétiques et d'érosion subséquents sont autant de facteurs qui déterminent les profils de paléométéorisation (saprolithes) observés dans le batholithe de South Mountain. Des saprolithes de trois époques différentes (antérieures au Carbonifère, à l'ère triasique, et au Pléistocène) se sont formées sur du monzogranite. On observe une oxydation et une hydratation accrues, une diminution de la présence des éléments du groupe des terres rares, et une météorisation plus grande. De plus, des altérations de Ca, Ba, Rb, Zn, Pb, Co et d'autres éléments dans les saprolithes plus anciens indiquent le caractère meuble des éléments pendant la météorisation. Une nouvelle exposition de ces profils en partie météorisés dans le milieu acide et riche en oxygène d'aujourd'hui pourrait entraîner une autre migration des éléments contenus dans ces saprolithes.
 
 [Traduit par la rédaction]

Emplacement of the Fogo Island Batholith, Newfoundland

The Siluro-Devonian Fogo Island Batholith is a high-level, bimodal, sill-like unit about 7 km thick, intruded by a slightly younger, heterogeneous mafic unit. Stratigraphic evidence suggests emplacement of the batholith by raising of the roof without strong deformation of the host rocks. Large composite gabbro-microgranite dykes below the sill, intruded along axial planar cleavage, probably served as feeders. The upper 3– 4 km of the sill comprise homogeneous to slightly zoned, coarse, hastingsite-biotite granite. Ignimbrite sheets of similar composition above the sill suggest that the granite was emplaced beneath cover rocks no more than 1 km thick. The lower 3 km of the sill consist of heterogeneous, locally layered, mafic rocks. Metre-scale, non-intrusive sheets of contrasting composition mark the contact between the granitic upper and mafic lower part of the sill. A late influx of mafic magma disrupted older mafic rocks and hybridised with granite, producing complex, heterogeneous "diorite". The local presence of A-type compositions in the granitic portion of the batholith may reflect diffusion during this process. A model for emplacement of the batholith assumes crustal anatexis above mantle-derived, underplated mafic magma, followed by passive emplacement of composite magma along tensional fractures related to movements on the Dog Bay Line, a dextral terrane boundary. Later movements on this feature controlled emplacement of further batches of magma, and finally tipped the batholith about 25° to the north, producing its present configuration. RÉSUMÉ Le Batholithe siluro-dévonien de l'île Fogo forme une unité à l'aspect d'un filon-couche bimodale de niveau élevé et d'environ sept kilomètres d'épaisseur, dans laquelle fait intrusion une unité mafique hétérogène légèrement plus récente. Les observations stratigraphiques laissent supposer une mise en place du batholithe par soulèvement du toit sans déformation marquée des roches hôtes. Des dykes composites de gabbro-rhyolite de fortes dimensions au-dessous du filon-couche, ayant subi une intrusion le long de la schistosité de plan axial, ont probablement servi de voies de passage. Les trois à quatre kilomètres supérieurs du filon-couche sont constitués de granite à hastingsite-biotite grossier allant d'homogène à légèrement zoné. Des couches de tuf consolidé d'une composition semblable au-dessus du filon-couche permettent de supposer que la mise en place du granite s'est faite sous des roches de couverture d'au plus un kilomètre d'épaisseur. Les trois kilomètres inférieurs du filon-couche sont constitués de roches mafiques hétérogènes, localement stratifiées. Des nappes non intrusives de quelques mètres d'une composition différente marquent la zone de contact entre le sommet granitique et la base mafique du filon-couche. Un afflux tardif de magma mafique a perturbé les roches mafiques âgées et a entraîné une hybridation avec le granite, produisant des « diorites » hétérogènes complexes. La présence locale de compositions de type A dans la partie granitique du batholithe pourraient témoigner d'une diffusion au cours de ce processus. Un modèle de mise en place du batholite suppose une anatexie crustale au-dessus d'un magma mafique reposant sur des plaques et d'origine mantellique, suivie de la mise en place passive de magma composite le long de fractures de tension apparentées à des mouvements survenus le long de la ligne Dog Bay, une ligne de démarcation de terrane dextre. Des mouvements ultérieurs le long de cette ligne ont déterminé la mise en place d'autres mélanges de magma et ont finalement incliné le batholithe d'environ 25 degrés vers le nord, pour produire sa configuration existante.

Deep drill hole in the Devonian South Mountain batholith, Nova Scotia: a potential for hidden mineral deposits within the batholith

The drill hole near Digby in southwestern Nova Scotia is the deepest on-shore hole in the Canadian Appalachians, and penetrated to a depth of about 1.5 km. The site of the drill was selected at the periphery of the Devonian South Mountain batholith, which contains important mineralization of tin and uranium. The drill hole intersected texturally uniform megacrystic biotite granodiorite, which does not display any pronounced primary vertical zonation. At depth, the drill core contains zones of alteration, fracturing, and brecciation. The alteration is mainly due to fluid flow along the fractures. Some fractures are mineralized and contain galena, sphalerite, pyrrhotite, chalcopyrite, pyrite, hematite, quartz, and carbonate minerals. Common occurrence of alteration zones in the hole suggests that such zones are widespread in the batholith and point to abundant hydrothermal activity deep within the massif. It is inferred that the potential for hidden economic mineral deposits within the batholith is much greater than is suggested by surface features. The association of mineralization as seen in the drill core with the most primitive rocks of the batholith further indicates that mineral deposits in granitoid rocks are not always hosted by the most evolved and fractionated rocks. Extensive fracturing demonstrates that the batholith is not a suitable candidate for the storage of radioactive waste material. High temperature measured in the drill hole (~68°C at a depth of about 1,450 m) suggests that the pluton has promise as a source of geothermal energy. RESUMÉ Le puits de forage creusé#xE9; prè#xE8;s de Digby dans le Sud-Ouest de la Nouvelle-É#xC9;cosse constitue le puits sur rivage le plus profond dans les Appalaches canadiennes; il s’enfonce à#xE0; une profondeur d’environ 1,5 kilomè#xE8;tre. L’emplacement du trou de forage a é#xE9;té#xE9; choisi à#xE0; la pé#xE9;riphé#xE9;rie du batholite dé#xE9;vonien du mont South, qui abrite une miné#xE9;ralisation importante d’é#xE9;tain et d’uranium. Le trou de forage a entrecoupé#xE9; de la granodiorite à#xE0; biotite phé#xE9;nocristalline à#xE0; texture uniforme qui n’affiche aucun rubanement vertical primaire prononcé#xE9;. En profondeur, la carotte de forage pré#xE9;sente des zones d’alté#xE9;ration, de fissuration et de bré#xE9;chification. L’alté#xE9;ration est principalement due à#xE0; un é#xE9;coulement de fluides le long des fissures. Certaines fissures sont miné#xE9;ralisé#xE9;es et renferment de la galè#xE8;ne, de la sphalé#xE9;rite, de la pyrrhotine, de la chalcopyrite, de la pyrite, de l’hé#xE9;matite, du quartz et des carbonates. La pré#xE9;sence fré#xE9;quente de zones d’alté#xE9;ration dans le trou permet de supposer que ces zones sont ré#xE9;pandues dans le batholite et elle signale une activité#xE9; hydrothermale abondante en profondeur à#xE0; l’inté#xE9;rieur du massif. On en dé#xE9;duit que le potentiel de gî#xEE;tes miné#xE9;raux rentables caché#xE9;s à#xE0; l’inté#xE9;rieur du batholite est beaucoup plus vaste que ce que laissent supposer les caracté#xE9;ristiques à#xE0; la surface. L’association de la miné#xE9;ralisation avec les roches les plus primitives du batholite dont té#xE9;moigne la carotte ré#xE9;vè#xE8;le par ailleurs que les gî#xEE;tes miné#xE9;raux dans des roches granitiques ne sont pas toujours inclus dans les roches les plus é#xE9;volué#xE9;es et les plus fractionné#xE9;es. Le degré#xE9; de fissuration prononcé#xE9; ré#xE9;vè#xE8;le que le batholite ne constitue pas un candidat convenable pour le stockage des dé#xE9;chets radioactifs. La tempé#xE9;rature é#xE9;levé#xE9;e relevé#xE9;e dans le trou de forage (~68°#xB0;C à#xE0; une profondeur de 1 450 m) laisse supposer que le pluton repré#xE9;sente une source prometteuse d’é#xE9;nergie gé#xE9;othermique.

SHRIMP U-Pb and 40Ar/39Ar Age Constraints for Relating Plutonism and Mineralization in the Boulder Batholith Region, Montana

SHRIMP U-Pb and 40Ar/39Ar Age Constraints for Relating Plutonism and Mineralization in the Boulder Batholith Region, Montana

Two-mica F–Li–B-rich monzogranite apophysis of the Larderello batholith cored from 3.5km depth

Two-mica F–Li–B-rich monzogranite apophysis of the Larderello batholith cored from 3.5km depth

SIGNIFICANCE OF SANDSTONES INTERBEDDED IN THE JURASSIC BASALTS OF THE BALAGNE OPHIOLITIC NAPPE (CORSICA, FRANCE)

The Balagne Nappe which includes a thick ophiolitic succession, has an isolated external western position and is underlain by Eocene rocks over the autochthonous Corsican basement. The nappe consists, from base to top, of: 1) basaltic pillow lavas up to 1 km thick, 2) oceanic sediments (radiolarites, limestones showing diverse facies, particularly pelagic, pelites with interbeds of “Palombini”-type limestones, and 3) detrital formations ranging from the Albian- Cenomanian to Middle Eocene. The trace element content of the basalts of the Balagne Nappe s.l. is characteristic of enriched mid-oceanic ridge basalts (EMORB). In contrast, lavas of the more eastern Ligurian Units, such as the Inzecca Unit (Upper ‘Schistes lustres’), have an N-MORB character. We can thus define a marginal “Balagne-Ligurian domain”. In their lower part close to the gabbroic substratum, near Piana di Castifao, the Jurassic basalts have a level of feldspathic and micaceous quartzitic sandstone with calcareous cement (Baud, 1975). This level, 3 m thick, is intercalated within two 8-m layers of basaltic breccia (exploded pillows), sandwiched between flows of pillow lavas in places showing normal polarity. This rules out a tectonic hypothesis for the contacts at the base and top of the sandstones, as both contacts are clearly stratigraphic. The top of the sandstones is coarse grained, with lithic debris of continental origin and basalt fragments. The heavy minerals originate either from the oceanic or continental material. Zircons are particularly abundant and well preserved, which indicates limited transport. The typological study, according to Pupin’s diagram (1980), reveals that zircons plot in the field overlapping that of zircons from calc-alkaline granites (s.l.), highly abundant in the Corsican-Sardinian batholith. The Piana di Castifao sandstone interbed is the only known example in the Corsican Ligurian ophiolites. A similar thin bed has been described from the top of the ophiolitic sequence of the “Lago Nero-Replatte Nappe” to the east of Briancon in the French-Italian Alps. Similarly, in the Queyras region West of Mount Viso were reported sands and gravels with granite clasts, here there are underlying pillow basalts extruded over a serpentinite substratum. In both cases (east of Briancon and Queyras), no geological nor geochemical indications were found to constrain the position of the continent that supplied the detrital material. The detrital material originated from a continental source similar to that of Piana di Castifao. The Balagne-Ligurian domain of the Ligurian Ocean must therefore have been situated, during the Jurassic, relatively close to the Western European continental margin, as indicated by the geochemical facies of the EMORB, the basement fragments within the San Colombano supra-ophiolitic limestones, and the Piana di Castifao quartzitic interbed. The eastern margin of the Ligurian Ocean was also characterized by continental detritus as shown in the Cretaceous External Ligurides in the Northern Apennines.

Petrogenesis of late Hercynian calc-alkaline dykes of mid-eastern Sardinia: petrographical and geochemical data constraining hybridization process

During the final stages of the emplacement of the Hercynian batholith, a calc-alkaline dyke swarm intersected the crystalline basement of Sardinia. In mid-eastern Sardinia, these dykes range in composition from basaltic andesite to dacites-rhyolites with oligophyric and porphyritic textures, respectively. Plagioclase is the dominant phase among the phenocrysts, with subordinate brown and green amphibole; biotite, K-feldspar and quartz are abundant in more differentiated compositions. The biotite Rb-Sr age of this magmatism ranges between 291 and 271 Ma. Compositional data can be modelled using two separate trends: 1) AFC-type processes with fractionation of An-rich plagioclase, orthopyroxene and Cr-rich clinopyroxene are responsible for compositional variations amongst the most basic rocks; 2) andesitic to rhyolitic magmas evolve starting from basic magmas which are aligned along the first trend due to hybridization process. The complex and long-lived mafic magma and the crust interaction indicate a MASH-like scenario characterized by different magma chambers, as proposed for the late-Hercynian magmatism in other areas.

New constraints on the age and origin of the Dunbrack Pb-Cu-Zn-Ag deposit, Musquodoboit Batholith, southern Nova Scotia

Mineralization at the Dunbrack Pb-Zn-Cu-Ag deposit occurs within a ca. 1 m wide quartz vein characterized by comb, cockade, crustiform, and breccia textures. The mineralized vein, NW-trending and steeply dipping, has a medium- to coarsegrained, biotite – muscovite ± cordierite monzogranite phase of the 370 Ma Musquodoboit batholith as its hanging wall and a fine-grained felsie dyke rock as its footwall. Silicate mineralogy in the vein is dominated by quartz with trace amounts of K-feldspar (Or86-100), muscovite (≤2 wt. % FeO, ≤0.8 wt. % F), chlorite, and kaolinite, whereas sulphides include Fe-poor sphalerite (≤4 wt. % Fe), galena, chalcopyrite, and a variety of secondary Cu sulphides. Dating (40Ar/39Ar) of vein muscovite and the footwall dyke rock indicate similar ages of 370 Ma; therefore, vein formation and dyke injection are interpreted to be coincident with emplacement of the 370 Ma Musquodoboit Batholith.
 
 Fluid inclusion studies of aqueous, L-V inclusions indicate homogenization temperatures of ca. 140 ± 5°C and salinities of 20 ± 2 wt. % eq. NaCI, but minor amounts of inclusions with higher (24 to 27 wt. %) and lower (8-16 wt. %) salinities occur. First melting temperatures and analysis of decrepitate mounds indicate two fluid types, a more abundant NaCI-H2O fluid and a less abundant NaCI-CaCl2-KCI-H2O fluid.
 
 Sulphur isotopes for hypogene galena, chalcopyrite, and sphalerite are uniform and equate to δ34SH2s of +4.2 to +6.6%o (at 300°C), which is similar to data for other granite-related sulphide mineralization in the Meguma Zone. Vein quartz has an δ18 value of+15.3 ± 1.2%o (n=10), which equates to δ18Owater of +9 to +11.5%o at 300°C, whereas fluid inclusion extracts indicate δD values of -90 to -113%o (n=6).
 
 Collectively, the timing of mineralization (i.e. 370 Ma) and the dominantly magmatic isotopic and geochemical signature for the vein-forming fluid suggest a genetic association with the Musquodoboit Batholith. However, the Ca-rich nature of some fluid inclusions and low δD values of fluid extracts suggest involvement of another reservoir, possibly reflecting a fluid that equilibrated with the country rock of the Meguma Group.
 
 RÉSUMÉ
 La minéralisation au dépôt de Pb-Zn-Cu-Ag Dunbrack se produit dans une veine de quartz d'une largeur c. 1 m caractérisée par des textures de peignes, cockade, croûteuses et de brèches. La veine minéralisée en direction nord-ouest a un pcndage à pente forte, et une phase à grain grossier, de biotite-muscovite±cordierite monzogranite provenant du batholite Musquodoboit de 370 Ma en tant que lèvre supérieure et a un dyke a grain fin de roche felsique en tant que sa lèvre inférieure. La minéralogie de silicate dans la veine est dominée par le quartz avec des traces de K-feldspath (Or86-100), muscovite (≤2 poids en pour-cent de FeO, ≤0.8 poids en pour-cent de F), chlorite, et kaolinite, tandis que les sulfures inclucnt la sphalérite pauvre en Fe (≤4 poids en pour-cent de Fe), la galène, la chalcopyrite, et une variété de sulfures secondaires de Cu. La datation (40Ar/39Ar) de la veine de muscovite et du dyke de roche a lèvre infeérieure indiquent des âges semblables de 370 Ma ; done, la formation de veine et l'injection de dyke sont interprétérs pour ètre comcidentes avec la mise en place Batholite Musquodoboit de 370 Ma.
 
 Les études d'inclusions fluides « L-V » et aqueuses, indiquent les températures d'homogeneisation de c.140 ± 5°C et salinités de 20 % équivalent poids en pour-cent ± 2 NaCI, mais a des quantités mineures d'inclusions avec plus haut (24 à 27 poids %) et abaissement (8-16 poids %) des salinités produites. Les premières températures et analyse de fonte des monticules décrépités indiquent deux types de liquides, un fluide plus abondant de NaCI-H2O et un fluide moins abondant de NaCl-CaCI2-KCI-H2O.
 
 Les isotopes de soufre pour la galene hypogee, la chalcopyrite, et la sphalerite sont uniformes et egalisent a δ34SH2s of +4.2 to +6.6% (à 300°C), semblable a des données pour d'autre minéralisation de sulfure jumelcr au granite dans la zone de Meguma. Le quartz de veine a une valeur de δ18O +15.3 ± 1.21 (n= 10), qui égalise à δ18Oeau de +9 à + 11.51à 300°C, tandis que les extraits liquides d'inclusion indiquent des valeurs de δD de -90 à -1131 (n=6).
 
 Collectivcment. la synchronisation de la minéralisation (c.-a-d., 370 Ma) et la signature isotopique et géochimique principalement magmatique pour le fluide provenant de veine suggérent une association gentHiquc avec le Batholite de Musquodoboit. Cependant, la nature riche en calcium de quelques inclusions liquides et valeurs basses δD d'extraits liquides suggérent la participation d'un autre réservoir, refiétant probablement un fluide qui a équilibré avec la roche de la region du Groupe de Meguma.
 
 [Traduit par la rédaction]

A Permo-Carboniferous U-Pb age for part of the Guanta Unit of the Elqui-Limari Batholith at Rio del Transito, Northern Chile

ABSTRACT. A U-Pb zircon age 0f 285.7+/-1.5 Ma is presented for granodiorite from the Chanchoquin pluton of the Guanta Unit, Elqui Superunit of the Elqui-Limari Batholith. This is the first U-Pb zircon age reported from this batholith and is interpreted as dating emplacement of part of its oldest unit, very close to the time of the Carboniferous-Permian boundary. The age is similar to published Rb-Sr ages for the Palaeozoic batholiths of the Coast Range in Central Chile, in the Algarrobo and Nahuelbuta areas, indicating a widespread episode of plutonic activity along the Gondwana margin of Northern and Central Chile. If the new age were applicable to the whole of the Guanta unit, the other units of the Elqui Superunit (Cochiguas and El Volcan units) would have been emplaced during Permian or later times. A new Rb-Sr whole-rock isochron of 256+/-10 Ma for the Cochiguas Unit in Rio Los Molles, at the southern end of the batholith, is in agreement with this, although previous evidence for the Cochiguas Unit in its type section indicated a Carboniferous age. This suggests either that the Rb-Sr system in Los Molles has been reset, or that the mapped units of the batholith, although lithologically similar in different areas, are not contemporaneous. Further U-Pb dating is needed to resolve these questions. RESUMEN. Edad U-Pb permo-carbonifera para parte de la Unidad Guanta del Batolito Elqui-Limari en Rio del Transito, norte de Chile. Se presenta una nueva edad (U-Pb en circon de 285,7+/-1,5 Ma) para una granodiorita del pluton Chanchoquin de la Unidad Guanta (Superunidad Elqui del Batolito Elqui-Limari). Representa la primera determinacion de U-Pb en circon del batolito, y se interpreta como la edad de cristalizacion de parte de la unidad mas antigua, muy proxima al limite Carbonifero-Permico. Es, ademas, muy similar a las edades obtenidas en los batolitos paleozoicos de la Cordillera de la Costa de Chile, en las localidades de Algarrobo y Nahuelbuta, verificando, por lo tanto, una intensa actividad magmatica a lo largo del margen gondwanico del norte y centro de Chile. Si la nueva edad pudiera interpretarse como de toda la Unidad Guanta, las restantes unidades de la Superunidad Elqui (unidades Cochiguas y El Volcan) deberian haberse emplazado durante el Permico o mas recientemente. Una nueva isocrona Rb-Sr en roca total de 256+/-10 Ma para la Unidad Cochiguas en Rio Los Molles, en el extremo austral del batolito, esta de acuerdo con esto, aunque evidencias previas de la Unidad Cochiguas en su seccion tipo indican una edad carbonifera. Se sugiere que los sistemas Rb-Sr en el area de Rio Los Molles, se han ajustado o que distintas unidades mapeadas del batolito, aunque coherentes litologicamente, no son contemporaneas. Se requieren dataciones U-Pb adicionales para resolver estas interrogantes.

Continental crust subduction and collision along Shangdan Tectonic Belt of East Qinling, China——Evidence from Pb, Nd and Sr isotopes of granitoids

The East Qinling orogenic belt can be divided into North and South Qinling erogenic belts by the Shangdan fault. The granitoids, especially the late Paleozoic - early Mesozoic granitoids, are widely distributed in North Qinling and South Qinling orogenic belts. Pb, Nd and Sr isotopic compositions and some trace element ratios for the collision-type granitoids were measured. The data are used to evaluate the granitic magma source and to probe the chemical composition of deep crust where the granitic intrusions were emplaced. The studies indicate that the South Qinling collision-type granitoids came from the South Qinling middle-lower crust and the North Qinling collision-type granitic batholiths were also derived from the South Qinling middle-lower crust rather than from the North Qinling block itself. These results provide direct evidence for the South Qinling continental crust underplating beneath the North Qinling block in the continent-continent interaction stage of the East Qinling orogenic belt.

Introduction to the geological map of the north Karakorum terrain from the Chapursan valley to the Shimshal pass 1:150,000 scale

These notes introduce a new geological map at 1:150,000 scale of a large part of the Upper Hunza valley (Karakorum, Pakistan). The mapped area includes the Permian to Cretaceous sedimentary cover of the Karakorum, which is located north of the Karakorum Axial Batholith. The mapped sedimentary and intrusive complexes form four major tectonic units, stacked in a very complex system, due to polyphase events, spanning from Cretaceous to Cenozoic. These events are linked to repeated collisions against the Asian margin of the Kohistan Arc during the Cretaceous and of the Indian Plate during the Cenozoic. Beyond the stratigraphic and structural characteristics of the deformed units, our map also considers the general setting of quaternary deposits.

An overview of recent bedrock mapping and follow-up petrological studies of the South Mountain Batholith, southwestern Nova Scotia, Canada

Recent detailed geological mapping has provided insight into the evolution of the South Mountain Batholith of southwestern Nova Scotia. Mapping has resulted in the delineation of 49 map units consisting of: biotitegranodiorite, biotite monzogranite, muscovite-biotitc monzogranite, coarse- and fine-grained leucomonzogranite and leucogranite; 49 map units have been assigned to thirteen plutons which have been grouped into two stages, including early stage 1 (mostly granodiorite and monzogranite) and late stage 2 (mostly monzogranite, leucomonzogranite, leucogranite). Follow-up petrographic and geochemical studies indicate a continuous sequence from least evolved biotite granodiorite to most evolved leucogranite.
 
 In spite of a definitive sequence of emplacement for the plutons and their units, an evaluation of published geochronological data indicates that all plutons were intruded and crystallized during a very short time interval (<5 Ma) at ca. 370 Ma. Various structural characteristics, including the shape and distribution of plutons, the coincidence of several stage 2 plutons with major fault zones, and the orientation of primary and secondary structural features (e.g., megacryst alignment, joints, veins), indicate that the batholith was subjected to regional stresses associated with the waning stages of the Acadian Orogeny during intrusion.
 
 The various rock types within the plutons have broadly similar compositions; however, detailed petrographic and geochemical studies have revealed unique compositional characteristics. These differences are explained by variations in protolith composition. Similarly, the style of mineralization in the sundry plutons is interpreted as reflecting the protolith composition and the physio-chemical conditions that prevailed during their crystallization. Accordingly, the economic potential of the thirteen plutons must be evaluated individually.
 
 RÉSUMÉ
 Une nouvelle cartographie géologique détaillée a fourni des données sur l’évolution du batholite du mont South du sud-ouest de la Nouvelle-Écosse. La cartographie a permis de suivre 49 unités qui consistent en: granodiorite à biotite, monzogranite à biotite, monzogranite à biotite et muscovite, leucomonzogranite et leucogranite à grain grossier et fin; les 49 unités ont été assignées à treize plutons qui sont regroupés en deux stades: le stade 1, préeoce (principalement granodiorite et monzogranite), et le stade 2, tardif (principalement monzogranite, leucomonzogranite et leucogranite). Les études pétrographiques et géochimiqucs d'appoint indiquent une suité continue allant des granodio rites a biotite, peu évoluées, aux leucogranitcs, les plus évolués.
 
 En dépôt d'une séquence d'intrusion bien définie pour les plutons et leurs unités, une évaluation des données géochronologiques pubiées indique que tous les plutons se sont mis en place et ont cristallisé pendant un interval le très court (<5 Ma), il y a environ 370 Ma. Diverses caractéristiques structurales, dont la forme et la distribution des plutons, la coincidence de plusieurs plutons de stade 2 avec des zones de failles majeures et 1 'orientation des structures primaires et secondares (e.g., alignement des mégacristaux, joints, veines) indiquent que le batholite était soumis, lors de sa mise en place, aux contraintes régionales associées aux stades finaux de l'orogénèse acadienne.
 
 Les diverses lithologies à l'intérieur des plutons ont des compositions proches. Cependant, des études pétrogra-phiques et géochimiques détaillées ont révèles des compositions particulières. Ces différences sont expliquées par des variations dans la composition des protolites. De la même maniere, les patrons de minéralisations associées aux divers plutons sont interpréts comme reflétanl la composition du protolite et les conditions physico-chimiques lors de la cristallisation. En conséquence, le potentiel économique des 13 plutons doit &#xEQ;tre évalué individuellement.
 
 [Traduit par le journal]