Quartz Schist Research Articles

Detrital zircon U–Pb dating of low-grade metamorphic rocks in the Sulu UHP belt: evidence for overthrusting of the North China Craton onto the South China Craton during continental subduction

The Shiqiao–Pingshang low-grade metasedimentary rocks sporadically crop out in the Sulu ultrahigh-pressure (UHP) belt in east–central China. Major and trace element data indicate that they were deposited in a passive margin basin, probably located at the southern margin of the North China Craton. Sensitive high-resolution ion microprobe (SHRIMP) U–Pb dating of detrital zircons from a quartzite (SD53) from Pingshang and a quartz schist (SD54) from Shiqiao records ages ranging from 2800 to 1900 Ma. Three age populations are defined: at 2660–2500, 2350–2150 and 2100–1900 Ma, with peak ages at 2522, 2212 and 2020 Ma, respectively. Muscovite Ar–Ar dating of the quartz schist (SD54) yields a plateau age of 265.9 ± 1.2 Ma. These data support the view that the Shiqiao–Pingshang low-grade metasedimentary rocks originated from the North China Craton, and underwent deformation in the Permian during subduction of the South China Craton (Yangtze block) beneath the North China Craton. This requires that the low-grade metasedimentary rocks were overthrust for several tens of kilometres onto the South China Craton, explaining why source materials from the North China Craton are common in Triassic to Jurassic sedimentary basins adjacent to the Dabie–Sulu orogenic belt.

Bayesian Statistical Framework to Construct Probabilistic Models for the Elastic Modulus of Concrete

The commonly used Pauw’s formula to predict elastic modulus of concrete is very general and does not address the complexity of modern concretes, such as high-strength concrete, use of different types of aggregates and admixtures, etc. This paper develops a statistical framework to construct probabilistic models for the elastic modulus of concrete and evaluates the influence of different aggregate types, based on a large number of experimental data. The proposed framework to construct probabilistic models expands upon Pauw’s formula and properly accounts for both aleatory and epistemic uncertainties. Bayesian updating is used to assess the unknown model parameters based on experimental data. A Bayesian stepwise deletion process is used to identify important explanatory functions and construct parsimonious models. As an application, the approach is used to develop a probabilistic model for concretes made using crushed limestone and crushed quartz schist coarse aggregates.

Zircon U-Pb geochronology of basement metamorphic rocks in the Songliao Basin

Zircon LA-ICP MS U-Pb dating of six metamorphic rocks and a metagranite (breccia) from southern basement of the Songliao Basin are reported in order to constrain the formation ages of basement. The basement metamorphic rocks in the Songliao Basin mainly consist of metagabbro (L45-1), amphibolite (SN117), metarhyolitical tuff (G190), sericite (Ser) schist (N103), chlorite (Chl) schist (T5-1), biotite (Bi)-actinolite (Act)-quartz (Q) schist (Y205), and metagranite (L44-1). The cathodoluminesence (CL) images of the zircons from metagabbro (L45-1) and metagranite (L44-1) indicate that they have cores of magmatic origin and rims of metamorphic overgrowths. Their U-Pb isotopic ages are 1808±21 Ma and 1873±13 Ma, respectively. The zircons with oscillatory zoning from amphibolite (SN117) and Chl schist (T5-1), being similar to those of mafic igneous rocks, yield ages of 274 ± 3.4 Ma and 264 ± 3.2 Ma, respectively. The zircons from metarhyolitical tuff (G190) and Ser schist (N103) display typical magmatic growth zoning and yield ages of 424 ± 4.5 Ma and 287 ± 5.1Ma, respectively. Most of zircons from Bi-Act-Q schist (Y205) are round in shape and different in absorption degree in the CL images, implying their sedimentary detritals. U-Pb dating yield concordant ages of 427 ± 3.1Ma, 455 ± 12 Ma, 696 ± 13 Ma, 1384±62 Ma, 1649±36 Ma, 1778±18 Ma, 2450±9 Ma, 2579±10 Ma, 2793±4 Ma and 2953±14 Ma. The above-mentioned results indicate that the Precambrian crystalline basement (1808–1873 Ma) exists in the southern Songliao Basin and could be related to tectonic thrust, and that the Early Paleozoic (424–490 Ma) and Late Paleozoic magmatisms (264–292 Ma) also occur in the basin basement, which are consistent with the ages of the detrital zircons from Bi-Act-Q schist in the basement.

Lithofacies analysis of the Dezadeash Formation (Jura–Cretaceous), Yukon, Canada: The depositional architecture of a mud/sand-rich turbidite system

The Dezadeash Formation is a northwest trending belt of predominantly Jura–Cretaceous deep-marine siliciclastic rocks in southwestern Yukon, Canada. It is truncated to the southwest by the Denali Fault System, a major transcurrent fault along which ∼ 370 km of dextral slip occurred in post-Early Cretaceous time, and it is flanked to the northeast by the Kluane Schist, a mainly mica–quartz schist assemblage of unknown age and origin. This study provides a robust quantitative description of lithofacies comprising a point-source mud/sand-rich turbidite system: approximately 16 335 m of measured strata from 75 sections throughout the Dezadeash Formation indicate that up to 29 lithofacies types are present and these are dominated by thin- to thick-bedded sandstone–mudstone couplets and medium- to thick-bedded sandstone. The various lithofacies are grouped into conglomerate, sandstone, sandstone–mudstone, and siltstone–mudstone lithofacies associations, which are interpreted as slide, channel-lobe transition, lobe, and overbank architectural elements, respectively. Stacked channel-lobe transition and lobe elements predominate, but the depositional architecture displays no apparent, overall vertical trend. The Dezadeash Formation represents mainly the lower middle and lower subdivisions of a point-source, mud/sand-rich turbidite system that records a single stage of fan growth as it prograded transversely from a volcano-plutonic arc into the basin.

4.1 Ga old detrital zircon in western Tibet of China

4.1 Ga old detrital zircon was found by SHRIMP U-Pb dating for quartz schist from Buring County in western Tibet, Southwest China. This is the oldest zircon U-Pb age found in China so far. The detrital zircon is a zircon of magmatic origin because its Th/ U ratios are 0.76 to 0.86. Two dates older than 4.0 Ga were measured only in one grain. U-Pb ages of 35 measured spots in 24 zircons can be subdivided into 6 groups, corresponding to at least 6 episodes of magmatic activity in the target area. The present results provide an important geochronological constraint on the geological evolution of Qinghai-Tibet Plateau.

Controls on hydrothermal Fe oxide–Cu–Au–Co mineralization at the Guelb Moghrein deposit, Akjoujt area, Mauritania

The Guelb Moghrein Fe oxide–Cu–Au–Co deposit, with a total resource of 23.6 Mt at 1.88% Cu, 1.41 g/t Au, and 143 g/t Co, is hosted by an extensive metacarbonate body. However, it is restricted to up to 30-m wide tabular breccia zones developed parallel to discrete shear zones that transect the host metacarbonates. The Fe–Mg clinoamphibole–chlorite schists represent up to 1-m thick interlayer metasediments and localized viscous shearing in these shear zones. Siderite of the metacarbonate body was deformed into a breccia and was replaced by an ore and alteration assemblage comprised of Fe–Mg clinoamphibole, magnetite, pyrrhotite, chalcopyrite, graphite, Fe–Co–Ni arsenides, arsenopyrite, cobaltite, uraninite, and Bi–Au–Ag–Te minerals. In contact with wall rock amphibolites, the metacarbonate body is enveloped by an alteration halo up to 40 m wide, consisting of biotite, actinolite, grunerite, chlorite, calcite, albite, and quartz. The Guelb Moghrein ore body is structurally controlled by shear zones that developed in the footwall of a regional thrust zone. This thrust separates greenschist facies quartz–sericite schists and biotite–garnet–quartz schists of the Sainte Barbe volcanic unit in the hanging wall from amphibolite facies metavolcanic rocks, metacarbonates, and the Guelb Moghrein ore body of the Akjoujt metabasalt unit in the footwall. Peak temperatures of the latter unit are estimated by hornblende–plagioclase thermometry at 580±40°C. Thrusting was retrograde for the Akjoujt metabasalt unit, but prograde for the Sainte Barbe volcanic unit at P–T conditions of about 410±30°C and 2–3 kbar (garnet–biotite thermometry). Structural and petrological evidences suggest that the ore fluids migrated along the shear zones and reacted with the siderite in the metacarbonate. This evolution and the setting of Guelb Moghrein in the fold-and-thrust belt of the Pan-African to Variscan Mauritanides (Mauritania, West Africa) resemble Proterozoic Fe oxide–Cu–Au–Co deposits such as examples from the Tennant Creek and Mount Isa Inliers, Australia.

Environmental Assessment of Sewage Disposal Systems Using 2D Electrical-Resistivity Imaging and Geochemical Analysis: A Case Study from Ibadan, Southwestern Nigeria

A case study is presented of integrated use of 2D electrical-resistivity imaging and geochemical analysis in environmental impact assessment of sewage disposal systems. This involved geoenvironmental studies around a septic tank in Ibadan, southwestern Nigeria. The area is underlain by quartzites and quartz schists, whereas the weathered profile consists of sandy and silty clay with some gravel. Twenty-two multi-electrode resistivity profiling lines were taken using the Wenner array. The electrode spacing ranged from 1 to 8 m with a station interval of 1 m. Resistivity data analysis involved inversion using a rapid least-square technique and construction of iso-apparent resistivity contour maps. Four pits were dug, with two of the pits located on points of resistivity lows and the other two pits on points of high resistivity values. The pits were dug to a total depth of 2 m and soil samples collected from each pit at 0.5-, 1.0-, 1.5-, and 2.0-m depths. The samples were analyzed for conductivity and for Pb, Fe, Cu, Cr, and nitrate concentrations. The resistivity survey yielded low resistivity values at locations close to the septic tank and higher values farther from it. This agreed with the electrical conductivities measured for soil samples. Statistical analyses of the conductivity variation with distance from the septic tank yielded a negative correlation coefficient of between −0.92 and −0.52, indicating an inverse relationship between the two quantities. Similar relationships were established for analyzed chemical constituents. The environment is impacted by the septic system as shown by soil sampling and geophysical results. The results demonstrate that pollution mapping in a basement complex environment can be carried out using the approach described in this paper.

Quartz lattice preferred orientation patterns and static recrystallization: Natural examples from the Ryoke belt, Japan

Research Article| July 01, 2006 Quartz lattice preferred orientation patterns and static recrystallization: Natural examples from the Ryoke belt, Japan Miharu Otani; Miharu Otani 1Department of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8602, Japan Search for other works by this author on: GSW Google Scholar Simon Wallis Simon Wallis 1Department of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8602, Japan Search for other works by this author on: GSW Google Scholar Author and Article Information Miharu Otani 1Department of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8602, Japan Simon Wallis 1Department of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8602, Japan Publisher: Geological Society of America Received: 14 Nov 2005 Revision Received: 13 Feb 2006 Accepted: 03 Apr 2006 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 The Geological Society of America, Inc. Geology (2006) 34 (7): 561–564. https://doi.org/10.1130/G22430.1 Article history Received: 14 Nov 2005 Revision Received: 13 Feb 2006 Accepted: 03 Apr 2006 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Miharu Otani, Simon Wallis; Quartz lattice preferred orientation patterns and static recrystallization: Natural examples from the Ryoke belt, Japan. Geology 2006;; 34 (7): 561–564. doi: https://doi.org/10.1130/G22430.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Quartz c-axis lattice preferred orientation (LPO) patterns have been widely used to analyze different aspects of mid-crustal ductile deformation. However, despite the common presence of annealed microstructures in high-grade metamorphic belts, the effects of static recrystallization on such quartz LPOs are unclear. A suite of samples of quartz schist from the Nukata area of the Ryoke metamorphic belt was collected along profiles of several kilometers that reach the postorogenic Shinshiro tonalite. The samples show an increase in grain size and changes in microstructure, such as straightening of grain boundaries and formation of quartz-in-quartz inclusions that represent annealing related to contact metamorphism. In contrast to the clear microstructural changes, quartz c-axis LPO patterns show only very minor modifications even after strong annealing. This result implies that quartz LPO patterns should not be obliterated by static recrystallization and quartz-rich tectonites that lack such LPO patterns deformed by processes other than dislocation creep. Likely processes in high-grade rocks are grain boundary sliding assisted by melt migration and diffusion creep, both of which are characterized by Newtonian rheologies. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Quartz lattice preferred orientation patterns and static recrystallization: Natural examples from the Ryoke belt, Japan

Quartz c-axis lattice preferred orientation (LPO) patterns have been widely used to analyze different aspects of mid-crustal ductile deformation. However, despite the common presence of annealed microstructures in high-grade metamorphic belts, the effects of static recrystallization on such quartz LPOs are unclear. A suite of samples of quartz schist from the Nukata area of the Ryoke metamorphic belt was collected along profiles of several kilometers that reach the postorogenic Shinshiro tonalite. The samples show an increase in grain size and changes in microstructure, such as straightening of grain boundaries and formation of quartz-in-quartz inclusions that represent annealing related to contact metamorphism. In contrast to the clear microstructural changes, quartz c-axis LPO patterns show only very minor modifications even after strong annealing. This result implies that quartz LPO patterns should not be obliterated by static recrystallization and quartz-rich tectonites that lack such LPO patterns deformed by processes other than dislocation creep. Likely processes in high-grade rocks are grain boundary sliding assisted by melt migration and diffusion creep, both of which are characterized by Newtonian rheologies.

Empirical analysis of electromagnetic profiles for groundwater prospecting in rural areas of Ibadan, southwestern Nigeria

The Slingram electromagnetic (EM) survey using a coil separation of 60 and 100 m was carried out in ten villages in the Akinyele area of Ibadan, southwestern Nigeria to aid in the development of groundwater. Five main rock types including an undifferentiated gneiss complex (Su), biotite-garnet schist/gneiss (Bs), quartzite and quartz schist (Q), migmatized undifferentiated biotite/hornblende gneiss (M) and pegmatite/quartz vein (P) underlie the study area. A total of 31 EM profiles was made to accurately locate prospective borehole sites in the field.

Late-Svecofennian transpressive deformation in SW Finland—evidence from late-stage D3 structures

Late-Svecofennian deformation was investigated in the Bjensböle area of SW Finland. The deformation history was revealed by following marker horizons of amphibolite, marble and black schist, in addition to microscopic studies and U-Pb monazite geochronology. The D1 structures are transposed and overprinted by D2 structures. The mesoscopic F2 folds are tight to isoclinal with fold axes plunging 20-40[ddot] NE-ENE. Regional large-scale open F3 folds formed during the main D3 phase, and the macroscopic structure in Bjensböle is an F2-F3 interference pattern formed by N-S compression. The area consist of low P/high T amphibolite facies sillimanite gneiss and low P/low T amphibolite facies quartz schist, separated by a low P/low T amphibolite horizon in the central part of the area. The sillimanite gneiss yielded a U-Pb monazite age of 1824±5 Ma. This age gives a timing for the peak metamorphism and the D3 folding on the Kemiö Island. After the peak metamorphism some deformational structures developed. A NE-SW directed crenulation cleavage in the quartz schist and the amphibolite, small open folds in the marble, a foliation in the sillimanite gneiss and a muscovite orientation in the quartz schist all have the same direction. These structures are interpreted as late-stage D3 (D3L). The angle between the NE-SW directed D3L structures and the locally predominant S0 + S1 + S2 schistosity is ca. 25[ddot]. The structural evidence related to the D3L point to a dextral sense of shearing along roughly E-W directed zones with a NW-SE compression. This is related to a regional ductile shearing signifying the vaning stages of the late-Svecofennian transpressive deformation in SW Finland.

Sexual risk behaviour and infection: epidemiological considerations

The Heilongjiang Complex is a high-pressure accretionary belt composed mainly of serpentinite, glaucophane-bearing metabasalt, epidote-glaucophane-albite schist, greenschist, marble, two-mica schist, muscovite-albite schist, quartz schist, and quartzite (chert), located along the...

Southward extrusion of eclogite-bearing mafic–ultramafic bodies in the Sanbagawa belt, central Shikoku, Japan

Several mafic rock masses, which have experienced eclogite facies metamorphism, are distributed in flat-lying non-eclogitic schists in an intermediate structural level (thermal core) of the Sanbagawa belt. The largest, Iratsu mass, and an associated peridotite, the Higashi-Akaishi mass, extend E–W for about 8 km, and N–S for about 3 km, and are surrounded by pelitic, basic and quartz schists. The Iratsu mass consists of metabasites of gabbroic and basaltic origin, with intercalations of ultramafic rocks, felsic gneiss, quartz schist and metacarbonate. The Iratsu mass can be divided into two layers along a WNW-trending metacarbonate layer. The Higashi-Akaishi mass consists of peridotite with intercalations of garnet clinopyroxenite. It is situated beneath the western half of the Iratsu mass, and their mutual boundary dips gently or steeply to the N or NE. These masses underwent eclogite, and subsequent epidote-amphibolite facies metamorphism as has been reported elsewhere. The Iratsu–Higashi-Akaishi masses and the surrounding rocks underwent ductile deformation under epidote-amphibolite facies (or lower P– T) metamorphic conditions. Their foliation generally trends WNW and dips moderately to the NNE, and the mineral lineation mostly plunges to the N and NE. In non-eclogitic schists surrounding the Iratsu–Higashi-Akaishi masses, the foliation generally trends WNW and dips gently or steeply to the N or S and the mineral lineation mostly plunges to the NW, N and NE. Kinematic analysis of deformation structures in outcrops and oriented samples has been performed to determine shear senses. Consistent top-to-the-north, normal fault displacements are observed in peridotite layers of the Higashi-Akaishi mass and eclogite-bearing epidote amphibolite layers of the Iratsu mass. Top-to-the-northeast or top-to-the-northwest displacements also occur in non-eclogitic pelitic–quartz schists on the northern side of the Iratsu mass. In the structural bottom of the Iratsu–Higashi-Akaishi masses and to the south, reverse fault (top-to-the-south) movements are recognized in serpentinized peridotite and non-eclogitic schists. These observations provide the following constraints on the kinematics of the rock masses: (1) northward normal displacement of Iratsu relative to Higashi-Akaishi, (2) northward normal displacement of non-eclogitic schists on the north of the Iratsu mass and (3) southward thrusting of the Iratsu–Higashi-Akaishi masses upon non-eclogitic schists in the south. The exhumation process of the Iratsu–Higashi-Akaishi masses can be explained by their southward extrusion.

Geology and geochemistry of the Changba SEDEX Pb-Zn deposit, Qinling orogenic belt, China

The Changba Pb-Zn SEDEX deposit occurs in the Middle Devonian sequence of the Anjiaca Formation of the Western Qinling Hercynian Orogen in the Gansu Province, China. The Changba-II orebody is hosted in biotite quartz schist and is the largest of 143 stratiform orebodies that are hosted either in biotite quartz schist or marble. The Changba-II comprises two types of mineralization: a bedded facies and an underlying breccia lens. The bedded section exhibits three sulfide sub-facies zoned from bottom to top: 1) banded sphalerite intercalated with quartz albitite; 2) interbedded massive pyrite and sphalerite ore; and 3) banded sphalerite ore intercalated with banded baritite. Major metallic minerals are sphalerite, pyrite, galena, with minor arsenopyrite, pyrrhotite, boulangerite, and rare chalcopyrite. The bedded sulfides are underlain by a lens of brecciated and albitized biotite-quartz schists cemented by sulfides and tourmaline.

The effects on human health and hydrogeochemical characteristics of the Kirkgeçit and Ozancik Hot Springs, Canakkale, Turkey.

This investigation was carried out to determine the hydrogeochemical characteristics of the Kirkgeçit and Ozancik hot springs. The study areas are located northeast and southwest of the town of Can, Canakkale. During the investigation, geological maps of the hot springs and its surroundings were prepared, and hot waters and rock samples were collected from the study sites. The Paleogene-Neogene aged andesite, trachyandesite, andesitic tuff, silicified tuff and tuffites form the basement rocks in the Ozancik hot spring area. In the Kirkgeçit hot spring area, there are Lower Triassic aged mica and quartz schists at the basement rocks. The unit is covered by limestones and marbles of the same age. They are overlain by Quaternary alluvial deposits. A chemical analysis of the Kirkgeçit hot water indicates that it is rich in SO(4)2- (1200.2 mgL-1), Cl- (121.7 mgL-1), HCO3- (32.5 mg L-1), Na+ (494 mg L-1), K+ (30.2 mg L-1), Ca2+ (102 mg L-1), Mg2+ (15.2 mg L-1), and SiO2 (65.22 mg L-1). Chemical analysis of the Ozancik hot water indicates that it is rich in SO(4)2- (575 mg L-1), Cl- (193.2 mg L-1), HCO3- (98.5 mg L-1), Na+ (315 mg L-1), K+ (7.248 mg L-1), Ca2+ (103 mg L-1), Mg2+ (0.274 mg L-1), and SiO2 (43.20 mg L-1). The distribution of ions in the hot waters on the Schoeller diagram has an arrangement of r(Na(+) + K+) > rCa2+ > rMg2+ and r(SO(4)2-) > rCl- > r(HCO3-). In addition, the inclusion of Fe2+, Cu2+, Cr3+, Mn2+, Ni2+ and Hg2+ in the hot water samples indicates potential natural inorganic contamination. The water analysis carried out following the ICPMS-200 technique was evaluated according to the World Health Organisation and Turkish Standards. The use and the effects of the hot water on human health are also discussed in the paper.

Contact Metamorphism of the Daulet Suite by Solid-State Emplacement of the Kokchetav UHP-HP Metamorphic Slab

The andalusite-sillimanite-type low-pressure Daulet Suite underlies the Kokchetav ultrahigh-pressure—high-pressure (UHP-HP) massif of northern Kazakhstan. The Daulet Suite is composed of pelitic-psammitic gneisses or schists and quartz schist with minor amounts of metacarbonate and metabasite. About 300 thin sections were examined from the Daulet metapelites; rocks were divided into two mineral zones. Zone A is characterized by andalusite + cordierite + biotite, and zone B by sillimanite + cordierite + biotite with excess K-feldspar, quartz, and plagioclase in both zones. K-feldspar appears with andalusite at lower temperatures than the first formation of sillimanite. Pressure-temperature conditions of the Daulet metamorphism range from 580 to 680°C at a nearly constant pressure of ~2 kbar. Comparison of compositions of solid-solution minerals with a buffered assemblage indicates that the metamorphic grade increases towards the boundary with the overlying UHP-HP unit. Detailed mapping revealed that the primary structure of both the Kokchetav UHP-HP massif and its surrounding units is subhorizontal; the UHP-HP unit has been thrust over the Daulet Suite with a top-to-the-north movement. The thermal structure of the Daulet Suite is subhorizontal and metamorphic grade increases upwards—i.e., toward the boundary with the UHP-HP unit—whereas the thermobaric maximum of the UHP-HP unit occurs at an intermediate structural level. The upward increase in metamorphic grade within the Daulet Suite implies contact metamorphism by the tectonic juxtaposition of the "hot" Kokchetav UHP-HP unit at shallow crustal levels.

Geotechnical properties of lateritic soil developed over quartz schist in Ishara area, south western Nigeria

Geotechnical properties of lateritic soil developed over quartz schist in Ishara area, south western Nigeria

O magmatismo alcalino Neoproterozóico na Ilha do Cardoso, Sudeste do Estado de São Paulo

This work focuses on the geology and geochronology of rocks cropping out on Cardoso Island, on the southeastern coast of Sao Paulo State, close to the boundary with Parana State. The island, with an area of about 151 km² is a protected area administered by the Institute of the Secretariat for the Environment of the State of Sao Paulo. It is mountainous, with a peak at 814 m, and is covered by denseAtlantic Forest vegetation. The island is made up mainly of an igneous complex with light grey leucocratic, inequigranular, medium to coarse-grained syenites. The Tres Irmaos Syenite (STI), composed of pyroxene, hornblende, and perthitic to mesoperthitic microcline, predominates has magmatic flow structures, and is cut by the pinkish grey, leucocratic medium-grained Cambriu alkali-feldspar granites (GC). Geochemical analysis of STI and GC demonstrate their metaluminous alkaline nature and late orogenic to anorogenic character. The bodies formed between 620 and 570 Ma according to U-Pb dating of zircons and cooled between 597 and 531 Ma (K-Ar in amphiboles). Whole rock Sm-Nd analyses yield Meso - and Paleoproterozoic TDM ages (1,500 - 2,200 Ma). A belt of low-grade metasedimentary rocks occurs in the northern part of the island. Quartz schist, quartz-mica schist and mica-quartz schist, often-containing andalusite and cordierite, predominate.Geochemical and geochronological data suggest that the sources of the metasediments were continental arc andesites of whose protoliths separated from the mantle between 1,800 and 2,200 Ma during the Paleoproterozoic. These metasediments probably continue on the continent in the Taquari region and extend southwards in narrow strips between the granitoids of the Paranagua Domain.

Permian volcanism in the Mongolian orogenic zone, northeast China: geochemistry, magma sources and petrogenesis

Lower Permian volcanism was the first magmatic activity to occur after the collision events in the Mongolian orogenic zone, east China. The Permian volcanic rocks are therefore a key to understanding the dynamics of the unified continental lithosphere. The volcanic rocks consist of basic and intermediate rocks. The intermediate rocks with high initial 87Sr/86Sr ratios (0.7051 to 0.7052) and low εNd values (−0.73 to −3.57) generally overlie the basic rocks in the field. The basic rocks have relatively low initial 87Sr/86Sr ratios (0.7034 to 0.7051) and high εNd values (2.72 to −0.10). Two parallel Rb–Sr isochrons give almost the same age, about 270 Ma. One consists of the basic rocks giving an initial isochron 87Sr/86Sr ratio of 0.7035. The other consists of the intermediate rocks and one sample of basalt, which give an initial isochron 87Sr/86Sr value of 0.7051. The strong correlations between SiO2 and other major elements suggest that fractional crystallization played an important role in the magmatic processes. However, fractional crystallization cannot explain the geochemistry of most incompatible trace elements and Sr–Nd isotope characteristics. The positive correlation between Th/Nb and (La/Sm)N ratios demonstrates the direct relation between the enrichment of the light rare earth elements and the contamination of continental sediments. The high contents of large ion lithosphere elements (LILE) in the Permian volcanic rocks may suggest an additional ‘crust + fluid’ component, especially in the intermediate rocks, which are highly enriched in Ba (> 400 ppm) relative to the basic rocks (> 200 ppm). We propose that the subduction slab dropped into depleted mantle and released fluid, which induced the mantle metasomatism and LILE enrichment. The metasomatized mantle partially melted and formed the ‘primary’ magma. This primary magma assimilated with the Proterozoic biotite–quartz schist during its rise, and finally formed the Permian volcanic rocks. Magma assimilated with the Proterozoic biotite–quartz schist in small amounts could have produced the basic rocks, while assimilation of larger amounts of magma (because of longer assimilation time) would generate intermediate rocks.

A Cretaceous back-arc basin in the Coast Belt of the northern Canadian Cordillera: evidence from geochemical and neodymium isotope characteristics of the Kluane metamorphic assemblage, southwest Yukon

The Coast Belt of the northern Cordillera in Canada is the locus of the boundary between accreted and ancient North American margin rocks. The largest exposure of metasedimentary rocks in the Coast Belt is the Kluane metamorphic assemblage (KMA), a northwest-striking belt 160 km long of graphitic mica–quartz schist and gneiss with minor interfoliated olivine serpentinite. The KMA does not appear to correlate with other sedimentary or metamorphic rock assemblages in the Canadian Cordillera. To determine its tectonic setting and protolith provenance, we analyzed trace element, rare earth elements, and neodymium isotope compositions of the KMA, of the adjacent pericratonic Aishihik metamorphic suite (AMS) of the Yukon–Tanana terrane, and of adjacent slates of the Dezadeash Formation (DF), filling a Late Jurassic – Early Cretaceous flysch basin. The εNd(0) values of analyzed KMA samples range from –1.4 to –5.6 and depleted mantle model ages (TDM) range from 1.16 to 1.45 Ga. KMA samples are intermediate between more evolved AMS samples (average εNd(0) –25, TDM = 2.6 Ga) and more juvenile DF samples (εNd(0) = +1.9, TDM = 0.95 Ga). The intermediate characteristics of the KMA samples cannot be linked to a known source region and are interpreted to reflect homogeneous mixing from predominantly juvenile and minor evolved sedimentary sources. A compatible tectonic setting is a back-arc basin within influence of a continental source. Eastward subduction of the KMA beneath ancient North America collapsed the back-arc basin by latest Cretaceous time.