Granite and associated mafic phases, North River pluton, Cobequid Highlands, Nova Scotia

The North River pluton is one of a series of upper Devonian - lower Carboniferous granite and gabbro/diorite plutons in the Cobequid Highlands. It lies within a regional zone of east-west strike-slip faulting associated with the Cobequid Fault. The pluton consists of a single main granite unit that intruded small marginal bodies of gabbro. The southern part of the pluton is locally foliated and pervasively fractured. Diabase and microgranite sheets and dykes cut the pluton and adjacent country rock. A relative sequence of intrusion can be determined from cross-cutting relationships with foliated or fractured granite. Hybrid rocks demonstrate that some of the mafic magma was intruded synchronously with granitic magma. The pluton is geochemically similar to other Devono-Carboniferous plutons in the Cobequid Highlands, although it represents a deeper structural level than most of the other plutons. The granite is a subalkalic A-type granite. The mafic rocks show "within-plate" geochemical characteristics; early intrusions resemble olivine-normative continental tholeiites, but later dykes are highly fractionated and show strong enrichment in incompatible elements. Enrichment in Rb and K in the northeastern part of the pluton reflects a late metasomatic event associated with the growth of secondary biotite. The Devono-Carboniferous plutons of the Cobequid Highlands differ from other published examples of shear zone plutonism in that magma generation appears to have been related to either local or more probably regional extension rather than the shear zone having tapped a magma that originally resulted from either subduction or continental collision. RÉSUMÉ Le pluton de North River est l'un des batis dévoniens supérieurs à carbonifères inférieurs constituent une suite de plutons granitiques et gabbrolques/dioritiques présente dans les Monts Cobequid. Il git au sein d'une zone régionale de décrochement est-ouest associée à la faille de Cobequid. Le pluton consiste en une unité principale unique de granite qui fit intrusion dans de petits batis gabbrolques marginaux. La portion méndionale du pluton montre une foliation locale et une fracturation penetrative. Des lames ainsi que des flkms de diabase et de microgranite recoupent le pluton et la roche encaissante adjacente. Les recoupements du granite folié ou fracturé permettent de déterminer une séquence relative d'intrusion. Des roches hybrides démontrent qu'une fraction du magma mafique fit intrusion au même moment que le magma granitique. La géochimie du pluton est semblable à celle des autres plutons dévono-carbonifères présents dans les Monts Cobequid, et ce bien qu'il représente un niveau structural plus profond que celui des autres plutons. Le granite est un granite subalcalin de type A. Les roches mafiques montrent des caractéristiques géochimiques "intraplaques"; les intrusions précoces ressemblent à des tholéiites continentales à olivine normative mais les filons plus tardifs ont subi un fractionnement prononcé et ils sont fortement enrichis en éléments incompatibles. Un enrichissement en Rb et en K dans la région nord-est du pluton reflete un événement métasomatique tardif associé à la croissance d'une biotite secondaire. Les plutons dévono-carbonifères des Monts Cobequid diffèrent des autres exemples publiés de plutonisme associé à une zone de cisaillement en ce que la venue du magma semble avoir été reliée à une extension locale ou, de façon plus vraisemblable, régionale plutôt qu'au captage par la zone de cisaillement d'un magma résultant à l'origine soil d'une subduction, so it d'une collision continentale. [Traduit par le journal

The Pre- Carboniferous rocks of the western Cobequid Hills, Avalon zone, Nova Scotia

Pre-Carboniferous rocks of the western Cobequid Hills outcrop north of the Cobequid Fault, are cut by several major east-west faults, and are onlapped unconformably to the north by the Late Carboniferous Cumberland Group. The oldest rocks comprise the Late Hadrynian Jeffers Formation. In the south, this unit consists of mafic and felsic volcanic rocks, interbedded with mudstones and carbonates, that are overlain by turbidites. To the north, the Jeffers Formation consists of a thick sequence of felsic volcanogenic turbidites. This stratigraphic succession of volcanic rocks passing up into turbidites differs from some other Late Hadrynian Avalonian sequences In the predominance of sedimentary rocks, but does resemble the Georgevllle Group of the Antigonish Highlands. Mafic dykes and sills, and associated porphyritlc rbyolite Intrusions, Intruded the Jeffers Formation prior to the formation of a regional flat-lying cleavage. The Late Hadrynian Jeffers Brook Pluton, which post-dates this cleavage, consists of diorite with marginal granitic phases that also occur as dyke-like intrusions beyond the main pluton. Several smaller intrusions petrographically similar to the Jeffers Brook Pluton also occur. At least two series of later dykes, probably pre-Silurlan in age, cut the Jeffers Formation and the Late Hadrynian intrusions. The Silurian Wilson Brook Formation outcrops only at the extreme northern edge of the Cobequid Hills: it consists of fossiliferous fine-grained sandstones and shales which overlie thin rhyolites, basalts and red clastic sediments. This sequence is very similar to the lower part of the Arisaig Group north of the Antigonish Highlands to the east. It is overlain unconformably by the Devono-Carboniferous Fountain Lake Group of volcanic rocks and by Carboniferous sedimentary rocks which are significantly deformed only near the Cobequid Fault. Carboniferous granite plutons appear spatially related to the Kirkhill and Cobequid Faults. They are in places foliated and contain abundant mafic sills and dykes that appear to reflect continuing motion on the Cobequid Fault during emplacement and cooling of the granites. RÉSUMÉ Dans l'Ouest des Honts Cobequid, les roches précarbonifères affleurent su nord de la Faille de Cobequid, sont recoupées par plusieurs failles majeures de direction est-ouest et sont recouvertes en discordance, au nord, par le Groupe de Cumberland d'âge tardicarbonifère. Les roches les plus vieilles englobent la Formation de Jeffers du Tardihadrynien. Au sud, cette derniére se compose de volcanites mafiques et felsiques interlitées avec des mudstones et des carbonates, le tout couronne de turbidites. Vers le nord, la Formation de Jeffers renferme une pulssante assise de turbidites volcanogènes felsiques. Cette succession stratigraphique de volcanites passant vers le haut à des turbidites différe certes de quelques autres séquences tardihadrynlennes avalonlennes par la prédominance, en son sein, de roches sédimentalres male rappelle aussi le Groupe de Georgevllle dans les Monts Antigonish. La mise en place de dykes et filons-couches mafiques, ainsi que des intrusifs de rhyollte qui lcur sont associés. eut lieu avant la formation d'un clivage régional horizontal. Le Pluton tardihadrynien de Jeffers Brook, qui est postérieur à ce cllvage, est formé de diorite avec des phases granitiques marginales qui se présentent aussi au-delà du pluton principal sous formé d*intrusions ressemblant à des dykes. On rencontre aussl plusieurs intrusifs plus petlis mais de pétrographle similaire au Pluton de Jeffers Brook. Au molns deux ensembles de dykes plus tardlfs. probablepent d'âge presilurien, recoupent la Formation de Jeffers et les intrusifs tardlhadryniens. On n'observe la Formation silurienne de Wilson Brook qu'a la llsiere la plus au nord des Monts Cobequid: elle englobe des grès fins fosslliferes et des argilites qui recouvrent, tous deux, de minces rhyolites, basaltes et sédiments clastiques rouges. Cette séquence rappelle fortement la partie inférieure du Groupe d'Arisaig au nord des Monts Antigonish plus à l'est. Bile est recouverte en discordance par le Groupe de volcanites dévono-carbonifères de Fountain Lake et par des roches sédimentalres carbonifères qui ne sont déformées de façon importante qu'auprés de la Faille de Cobequid. Les plutons granitiques carbonifères semblent rattachés dans l'espace aux failles de Kirkhill et Cobequid. lis sont folies par endroits et contieiment d'abondants filons-couches et dykes mafiques qui semblent tradulre le jeu continu de la Faille de Cobequid durant la mise en place et le refroidissement des granites. [Traduit par le journal

Geochemistry of metavolcanic rocks of the Ross Island and Ingalls Head formations, Grand Manan Island, New Brunswick

Southeastern Grand Manan Island consists of explosive and effusive volcanic rocks of the Ross Island and Ingalls Head formations that include syn-eruptive sediments and hyaloclaslites Lavas are commonly amygdaloidal and/or microporphyritic with phenocrysts of feldspar and. more rarely, pyroxene or quartz, set in a glassy to microcrystalline groundmass. They are compositionally similar to orogenic andesites with elevated TiO2 (up to 1.5%). The andesites are divisible in two groups that differ in CaO, Na2O, P2O5, Cr and Sr contents, and in the enrichment of Ba relative to Rb and Th. Among the chemically similar andesite samples, those with higher MgO also contain higher amounts of incompatible elements. Unusually for such rocks, there is no evidence for a significant role of feldspar in the evolution from andesite (6l% SiO2) to dacite (66% Si)2). A sample from a mafic dyke cutting the Ingalls Mead Formation contains high FeO(>l2% vs. ≤9% in the host rocks) and TiO2 (>2%). The incompatible element pattern of the dyke sample exhibits troughs at Nb-Ta and Sr similar to those shown by the andesite and dacite samples, but not at Ti. The geochemical characteristics of andesite and the time-space-compositional relationship of the dyke with the host andesite are considered to reflect the origin of these rocks by partial melting of hydrous mafic crust under moderate to low pressure (<8 kbar). The melts may have formed in equilibrium with olivine + orthopyroxene + clinopyroxene ± amphibolc ± plagioclasc ± apatite ± Fe-Ti oxide. Some of the volcanic rocks resemble late Cambrian to late Ordovician rocks of the New River belt on the northwestern margin of the Avalon composite terrane. RÉSUMÉ Le sud-est de l’ile Grand Manan est constitué de roches volcaniques d'épanehement et d'explosion des formations de Ross Island et d'lngalls Head, qui comprennent des sédiments syn-éruptifs el des hyaloclaslites. Les laves sont communément amygdaloides ou microporphyriques et component des phénocristaux de feldspath et, plus rarement de la pyroxene ou du quartz à 1'intériuer d'une matrice rocheuse vitreuse à microcristalline. Les roches ont une composition semblable aux andésites orogiéniques avec des teneurs élevées en TiO2 (jusqu'à 1.5 %). On peut subdiviser les andésites en deux groupes dont les teneurs en CaO, Na2O, P2O5, Cr et Sr et l’enrichissement en Ba comparativement à celui en Rb et Tn différent. Parmi les échantillons d'andésite qui se ressemblent dc prés du point de vue chimique ceux plus riches en MgO renferment également des quantiés supérieures d'éléments incompatibles. Fait éceptionnel dans le cas de magmas de ce genre, on ne relève aucun indice è l’eflet que le feldspath aurait joué un role déterminant dans l’énvolution de l'andéstie (61% de SiO2) au dacite (66% de SiO2). Un échaniillon provenant dun dyke mafique recoupant la Formation d'lngalls Head renferme une proportion élvée de FeO (>12 % par opposition a ≤9% dans les roches hôtes) et de TiO2 (>2 %). La configuration en éléments incompatibles de l'échantillon de dyke présente des creux face au Nb-Ta et au Sr à I'instar des échantillons d'andésite et de dacite mais non par rapport au Ti. Les caractéristiques géochimiques de I'andésite et le rapport de composition temps-distance de l'échantillon de dyke avec I'andésite hôle sont considérés comme des attribuis révélateurs de l'origine de ces roches qui proviennent d'une fusion partielle de la croute mafique hydrique sous une pression moyenne à faible (<8 khars) Les laves se sont sans doute formées en équilibre avec de I'olivine + orthopyroxene + clinopyroxene ± amphibolc ± plagioclasc ±apatite ± oxyde de Fe-Ti. Quelques-unes des roches volcaniques ressemblent aux roches du Cambrien supérieur a I'Ordovicien supérieur de la ceinture de New River, le long de la marge nord-ouesl du terrane composite d'Avalon Traduit par la rédactio

Deformation of the Cape Chignecto Pluton, Cobequid Highlands, Nova Scotia: thrusting at the Meguma-Avalon boundary

The Early Carboniferous Cape Chignecto pluton, at the western end of the Cobequid Highlands in the Avalon Terrane of Nova Scotia, consists predominantly of two-feldspar biotite granite. Intrusion of smaller diorite bodies locally melted and hybridized the granite. Diabase and microgranite dykes cut the plutons. Much of the pluton has a flat-lying mylonitic foliation, with a mineral elongation lineation trending between north and west. Quartz is dynamically recrystallized, but feldspars show predominantly brittle deformation. The phiton was probably deformed under greenschist facies conditions, after cooling. C-S fabrics observed in the field, and tails on porphyroclasts seen in thin section, indicate northward overthrusting. The Hadrynian Jeffers Group is thrust over the south edge of the phiton in the Fowler Brook inlier. At its north edge, the pluton is probably thrust over volcanic rocks of die Fountain Lake Group. The deformation of the pluton is constrained by stratigraphic relationships and isotopic dates to a Namurian or possibly early Westphalian age. Deformation within the pluton is correlated with Namurian uplift of the Cobequid and Caledonia Highlands. It records either transpression resulting from the curvature of the Meguma-Avalon boundary or a major component of convergent movement between the Meguma and Avalon terranes. RÉSUMÉ Le pluton de Cape Chignecto, daté du début du Carbonifere et situé à l'extremité occidentale des Monts Cobequid (Lanière d'Avalon, Nouvelle-Écosse), est formé en majeure partie de granite à biotite à deux feldspaths. Le granite subit une fonte et une hybridation locales lore de l’ intrusion de batis dioritiques de plus faibles dimensions. Des dykes de diabase et de microgranite recoupent les plutons. La majeure partie du pluton présente une foliation mylonitique horizontale, avec une linétion d'éirement orientée entre le nord et l’ouesL On note une recristallisation dynamique du quartz mais la déformation des feldspaths est surtout fragile. Le pluton fut probablement déformé sous des conditions appartenant au faciès des schistes verts, et ce après son refroidissement. Des fabriques planaires C-S, observées sur le terrain, et des ombres de pression dissymdtriques, vues en lame mince, indiquent un charriage vers le nord. Le Groupe hadrynien de Jeffers chevauche l'extrémité méridionale du pluton dans la fenetre de Fowler Brook. A son extrémité septentrionale, le pluton chevauche probablement les volcanites du Groupe de Fountain Lake. Les relations stratigraphiqueset des datations radiométriques limitent l'âge de la déformation du pluton au Namurien ou possiblement au début du Westphalien. On corrèle la déformation au sein du pluton avec la surrection namurienne des monts Cobequid et Caledonia. Cette déformation enregistre soil une transpression résultant de la cambrure de la jonction Meguma-Avalon, soil une forte composanle de mouvement convergent entre les lanières de Meguma et d* Avalon. [Traduit par le journal

Late Miocene magmatic activity in the Attic-Cycladic Belt of the Aegean (Lavrion, SE Attica, Greece): implications for the geodynamic evolution and timing of ore deposition

Numerous post-metamorphic Miocene granitoids occur in the area of Lavrion, SE Attica, at the western end of the Attic-Cycladic Belt of the Aegean. U-Pb ion microprobe-dating (SHRIMP) of zircon from a granitoid sill in the hanging-wall of a regional detachment fault reveals two distinct ages: (1) 11.93 ± 0.41 Ma, obtained from inherited zircon cores with metamorphic characteristics (homogeneous cathodoluminescence, low Th/U ratios) and granulite-type (round/resorbed) morphology. This age is interpreted as the time of a likely granulite-facies metamorphism of the precursor rock. (2) 8.34 ± 0.20 Ma, obtained by oscillatory zoned zircon domains with cathodoluminescence and Th/U characteristics typical for magmatic origin. This age is interpreted as the crystallization time of the granitoid sills. Although a granulite-facies metamorphic event has not been recognized so far for rocks of the Attic-Cycladic Belt, it seems to be the most plausible hypothesis to explain both the zircon systematics and age results. This hypothesis is consistent with an extensional regime predominating in the Aegean from Late Miocene times onwards. A possible granulite-facies metamorphism can be related to magmatic underplating at the initial stages of extension, setting an upper age of c. 12 Ma for the operation of the detachment fault. The 8.34 ± 0.20 Ma zircon crystallization age is, statistically, marginally different to a previous K-Ar feldspar date of hornblende-bearing dykes (9.4 ± 0.3 Ma) and identical to a 8.27 ± 0.11 Ma K-Ar biotite date of the main granitoid stock in the area, thus being generally consistent with prior age constraints from the region. Operation of the detachment fault in the Lavrion area is therefore bracketed between c. 11.9 Ma and at least 8.3 Ma. This time range is in line with the time of operation of detachment faults suggested previously for the Cycladic islands. Carbonate-hosted replacement-type massive sulphide Pb-Zn-Ag ores are spatially associated with the detachment fault and related extensional structures in the Basal Unit. Therefore, these Pb-Zn-Ag ores probably also formed within the above time span of c. 11.9 to at least 8.3 Ma. U-Pb ion microprobe (SHRIMP) dating of zircon from an orthogneiss within the metaclastic subunit of the Basal Unit in Lavrion yielded a protolith age of 240 ±4 Ma, consistent with ages of Triassic volcanism elsewhere in Greec

Genetic relationships between skarn ore deposits and magmatic activity in the Ahar region, Western Alborz, NW Iran

Publisher's Version/PDFPaleocene to Oligocene tectonic processes in northwest Iran resulted in extensive I-type calc-alkaline and alkaline magmatic activity in the Ahar region. Numerous skarn deposits formed in the contact between Upper Cretaceous impure carbonate rocks and Oligocene&mdash;Miocene plutonic rocks. This study presents new field observations of skarns in the western Alborz range and is based on geochemistry of igneous rocks, mineralogy of the important skarn deposits, and electron microprobe analyses of skarn minerals. These data are used to interpret the metasomatism during sequential skarn formation and the geotectonic setting of the skarn ore deposit related igneous rocks. The skarns were classified into exoskarn, endoskarn and ore skarn. Andraditic garnet is the main skarn mineral; the pyroxene belongs to the diopside-hedenbergite series. The skarnification started with pluton emplacement and metamorphism of carbonate rocks followed by prograde metasomatism and the formation of anhydrous minerals like garnet and pyroxene. The next stage resulted in retro gradation of anhydrous minerals along with the formation of oxide minerals (magnetite and hematite) followed by the formation of hydrosilicate minerals like epidote, actinolite, chlorite, quartz, sericite and sulfide mineralization. In addition to Fe, Si and Mg, substantial amounts of Cu, along with volatile components such as H2S and CO2 were added to the skarn system. Skarn mineralogy and geochemistry of the igneous rocks indicate an island arc or subduction-related origin of the Fe-Cu skarn deposit.</p

Ophiolitic mélanges in crustal-scale fault zones: implications for the Late Palaeozoic tectonic evolution in West Junggar, China

Publisher's Version/PDFThe Baijiantan and Darbut ophiolites in West Junggar are exposed in steep fault zones (&gt;70&deg;) containing serpentinite m&eacute;lange, in contact on either side with regionally distributed Upper Devonian-Lower Carboniferous ocean floor peperitic basalts and overlying sedimentary successions. The ophiolitic m&eacute;langes show classic structural features created by strike-slip faulting and consistent shear sense indicators of left-slip kinematics. Sandstone blocks within the m&eacute;langes resemble the surrounding sediments in lithology and age, indicating that the ophiolitic m&eacute;langes consist of locally derived rocks. The ophiolitic m&eacute;langes therefore originated from left-slip fault zones within a remnant basin and are not plate boundaries nor subduction suture zones. Sandstone is the youngest lithology involved in the m&eacute;lange and provides a maximum age for the m&eacute;lange of 322 Ma, whereas stitching plutons are younger than 302 Ma. Multiple clusters in zircon ages from single gabbro blocks in the m&eacute;lange at ~375, ~360, ~354, and ~340 Ma are inconsistent with accretionary incorporation of subducting ocean crust but rather suggest that episodic movement of the faults provided pathways for magma from the mantle into magma chambers. Late Paleozoic tectonic evolution of West Junggar involved Late Devonian to Carboniferous relative motion between the Junggar block and West Junggar ocean basin, which triggered the left-slip fault zones within a remnant ocean basin, along which the oceanic crust was disrupted to form linear ophiolitic m&eacute;langes. Final filling of this remnant ocean basin and its dismemberment by strike-slip faulting occurred in the late Carboniferous, followed by crustal thickening by juvenile granites at the Carboniferous-Permian boundary

Beta Cells within Single Human Islets Originate from Multiple Progenitors

BACKGROUND: In both humans and rodents, glucose homeostasis is controlled by micro-organs called islets of Langerhans composed of beta cells, associated with other endocrine cell types. Most of our understanding of islet cell differentiation and morphogenesis is derived from rodent developmental studies. However, little is known about human islet formation. The lack of adequate experimental models has restricted the study of human pancreatic development to the histological analysis of different stages of pancreatic development. Our objective was to develop a new experimental model to (i) transfer genes into developing human pancreatic cells and (ii) validate gene transfer by defining the clonality of developing human islets. METHODS AND FINDINGS: In this study, a unique model was developed combining ex vivo organogenesis from human fetal pancreatic tissue and cell type-specific lentivirus-mediated gene transfer. Human pancreatic progenitors were transduced with lentiviruses expressing GFP under the control of an insulin promoter and grafted to severe combined immunodeficient mice, allowing human beta cell differentiation and islet morphogenesis. By performing gene transfer at low multiplicity of infection, we created a chimeric graft with a subpopulation of human beta cells expressing GFP and found both GFP-positive and GFP-negative beta cells within single islets. CONCLUSION: The detection of both labeled and unlabeled beta cells in single islets demonstrates that beta cells present in a human islet are derived from multiple progenitors thus providing the first dynamic analysis of human islet formation during development. This human transgenic-like tool can be widely used to elucidate dynamic genetic processes in human tissue formation