Green Rocks Research Articles

Black adzes in the Early Neolithic of Belgium: Contribution of the Raman microspectrometry and petrography in characterization and sourcing

Early Neolithic (Linear Pottery Culture) adzes originate from settlements and workshops accompany the neolithization of Belgium. They are made from a wide range of extraregional lithic raw materials such as metamorphic green rocks (amphibolite) and black volcanic rocks (“basalt’) beside more local or regional raw material as flints, light-coloured (sedimentary and lightly metamorphic) quartzites, black lydites (Cambrian nodular phtanite of Céroux-Mousty and Lower Namurian banded phtanites) and dark grey Lower Namurian silicified sandstones previously called “Micaceous sandstones of Horion-Hozémont’. The discovery of the workshop of Noirfontaine near the city of Liège in the 1970s and 1980s provides exceptional assemblage available for updating analytical studies. This research focuses on the multi-scale characterization, the discrimination and sourcing both Cambrian and Namurian black sedimentary rocks rich in secondary silica composing Early Neolithic adzes found in Belgium. Their black colour results from finely dispersed organic matter, but the absence of palynomorphs does not allow a biostratigraphic ascription. Additional petrographical analyses (Optical Petrography, Scanning Electron Microscope), X-ray diffraction, chemical analyses (Energy Dispersive Spectroscopy) and measuring the degree of graphitization of the organic matter through Raman microspectrometry have been decisive in identifying the geological and geographical provenances by comparing the acquired results with geological reference samples collected in the field or through reference collections. Cambrian lydites are coming from a very restricted area and were preferred to other more local rock sources.

The oxidation state and distribution of Fe in pumpellyite from the Northern Chichibu Belt in the Hijikawa district, western Shikoku, Japan

AbstractIntracrystalline distribution of ferrous and ferric iron within pumpellyites (VIIW8VIX4VIY8IVZ12O56–n(OH)n, Z = 1) from low-grade metamorphic green rocks of the Kanogawa unit in the Northern Chichibu Belt, Hijikawa district, western Shikoku, Japan, was investigated using electron microprobe analysis, X-ray Rietveld refinement, and 57Fe Mössbauer spectroscopic analysis to verify the regularity of the distribution of Fe within the octahedral X and Y sites in pumpellyite and its effect on the pumpellyite structure. Two Fe-rich pumpellyite samples, labelled CLW and CHG, with average total Fe2O3 of 10.01±1.69 and 16.07±1.08 wt.%, respectively, were separated from the rock samples. The site occupancies at the X and Y sites in the CLW and CHG pumpellyites, refined using powder X-ray diffraction data, are X[Mg0.298Fe0.298(5)Al0.405]Y[Fe0.191Al0.809] and X[Mg0.244Fe0.42(1)Al0.34]Y[Fe0.32Al0.68], respectively. The Fe2+:Fe3+ ratio of the CLW pumpellyite, determined using Mössbauer spectroscopy, is 12(1):88(3). By combining the average chemical composition data, the site occupancies at the X and Y sites, and the Fe2+:Fe3+ ratio of the CLW pumpellyite, the chemical formulae of CLW and CHG pumpellyites are constructed as (Ca7.96K0.02Na0.01)Σ7.99(Mg1.19Mn2+0.09Fe2+0.39Fe3+0.71Al1.62)Σ4.00(Al6.47Fe3+1.50V0.02Ti0.01)Σ8.00Si12.26O43.33(OH)12.67 and (Ca8.01K0.01)Σ8.02(Mg0.97Mn2+0.02Fe2+0.63Fe3+1.03Al1.19)Σ4.01(Al5.44Fe3+2.55V0.01)Σ8.00Si12.02O42.69OH)13.31, respectively, implying that the proper name of both pumpellyites is pumpellyite-(Al). The intracrystalline distribution coefficients of Fe3+ versus Al between the X and Y sites, KD = (Fe3+/Al)X/(Fe3+/Al)Y, are 1.62 and 1.90 for the CLW and CHG pumpellyites, respectively, implying stronger X-site preference of Fe3+ than Al3+. In the CHG pumpellyite, where the Fe contents at the X and Y sites are higher than in the CLW pumpellyite, the mean <X–O> and <Y–O> distances are 2.06 and 1.98 Å, respectively, which are larger than <X–O> = 2.040 and <Y–O> = 1.944 Å in the CLW pumpellyite. The unit-cell parameters of the CHG pumpellyite are a = 8.8672(3), b = 5.9562(2), c = 19.1899(6) Å, β = 97.473(2)° with V = 1004.9(2) Å3 and are larger than those of the CLW pumpellyite, a = 8.8456(4), b = 5.9393(2), c = 19.1613(8) Å, β = 97.461(3)° with V = 998.14(7) Å3.

The propylitic alteration in the Ponce Enriquez Gold Mining district, Azuay province, Ecuador: genetic constraints from a mineral chemistry and fluid inclusions study

Wide areas of the Southern sector of Ecuador are characterized by Cretaceous mafic volcanic rocks, pervasively altered by a propylitic mineralogical assemblage with epidote, chlorite, and quartz with minor titanite, illite and prehnite. These propylitically altered rocks host significant gold mineralization in veins, deeply exploited in the last decades. Porphyry Au-Cu deposits also occur in the area. This work focuses on the study of this propylitic alteration to assess the genetic conditions and the relation with the distance from the porphyry system, through the chemical composition of the secondary minerals (particularly trace elements in epidote and chlorite) and fluid inclusion data. The aim is to improve knowledge of the trace element geochemistry of secondary minerals in propylitic alteration and their relationship to the causative porphyry systems. The results of this work indicate that alteration affecting the rocks of the Pallatanga Fm. can be related to the propylitic hydrothermal alteration halo of porphyry copper deposits. Fluid inclusion investigation in quartz veins associated with epidote and chlorite evidenced at least two pulses of hydrothermal fluids characterized by temperature around 345°C for the first one and around 305°C for the second one. The salinity of the fluids is always low (around 1.5 wt% NaClequiv.) suggesting a dominantly meteoric component. Evidence of boiling processes have not been observed. We hypothesize that the hydrothermally altered “green rocks” of the Ponce Enriquez Mining District could be envisaged as the propylitic halo of the Miocene hornblende-bearing Au-Cu porphyry deposits of Gaby-Papa Grande, and discuss the epidote and chlorite trace element composition in this scenario. The results help improving the general knowledge of the propylitically altered rocks in southern Ecuador and add new data for the use of trace element chemistry of epidote and chlorite in mineral exploration elsewhere.

Stratigrafie sedimentů doprovázejících vulkanity těšínitové asociace u Bruzovic

The rocks of the teschenite association form smaller scattered occurrences in the upper part of the Hradiště Formation of the Silesian Unit. The age of the igneous rocks corresponds to Berriasian to Barremian (Menčík et al. 1983). The teschenite association includes a relatively heterogeneous group of rocks with variable abundances of felsic and mafic minerals. Three outcrops of the teschenite association rocks (both typical teschenites and strongly altered ultramafic types) embedded in non- volcanic sediments were studied in the bed of the Pazderůvka River between Bruzovice and Žermanice (Bz1, Bz2, and Bz3; Fig. 1). At Bz1 and Bz2 outcrops, bodies of teschenite are hosted by sedimentary rocks affected by caustic metamorphism. The volcanic rocks at Bz3 are represented by strongly altered, markedly clayey dark green rocks with a macroscopically apparent high proportion of dark micas and pyroxenes. The bedrock of the outcrop is composed of calcareous claystone, limestone, and sandy limestone, likely representing Těšín Limestones. The phase composition of the volcanic rocks from the Bz1 and Bz2 localities is to a certain extent similar, which indicates that the same body was observed at both localities. Macroscopically, the rocks are medium- to coarse-grained with a variable proportion of dark minerals, indicating internal differentiation of the body. The very high proportions of natrolite (up to about 35 %, up to 54 % in the leucocratic type) are particularly notable. The volcanic rocks from the Bz3 locality are quite different. Their composition corresponds to strongly argilitised mafic rocks (and their volcaniclastic derivates), containing more than 50 % of clay component with a dominance of smectite, as documented by X-ray diffraction data. As for the primary components, pyroxene, biotite, plagioclase, and accessory amphibole were detected. Calcareous dinoflagellate cysts Cadosina semiradiata fusca, Colomisphaera vogleri, and Cadosina semiradiata representing the lower Valanginian to upper Barremian were identified in polished sections of the calcareous rock. Non-calcareous dinoflagellate cysts in Bz1 and Bz2 samples are almost black, reflecting the strong thermal effects of the teschenite intrusion at the contact with with the sediments. The dinoflagellate cysts in the Bz3 outcrop are very well preserved with no evidence of thermal alteration. The overlying body of the volcanic rock can be therefore considered as effusive. Circulodinium vermiculatum, Cymososphaeridium validum, Muderongia tabulata, Oligosphaeridium albertense, Oligosphaeridium asterigerum, Pseudoceratium pelliferum, Systematophora palmula from the Bz3 outcrop can be considered as stratigraphically significant. Based on the first occurrence of C. validum and the last occurrences of Circulodinium vermiculatum and Systematophora palmula, Leereveld (1995) delineates a dinoflagellate zone of Cymososphaeridium validum which represents the upper Valanginian to the lowermost Hauterivian. The composition of palynofacies, in which palynomorphs predominate, is characteristic of a distal well-oxygenated shelf.

ANALISIS KANDUNGAN SiO2 PADA BATUAN GREEN TUFF DENGAN METODE GRAVIMETRIK

Research has been conducted on the content of Silica dioxide (SiO2) in Green Tuff rocks from Bone of South Sulawesi Province. This Green Tuff rock is a type of sedimentary rock formed from volcanic ash released from a pit during a volcanic eruption. This research uses the gravimetric method which is analytical chemical method by weighing the sample that has been melted as much as 0.5 grams then adding enough distilled water, 10 ml of HCl and 5 ml of HNO3, after that it is heated to dry and added 5 mL of HCl. Reheat until the volume becomes half of the initial volume and added distilled water afterwards, cooled and filtered. The purpose of adding HCl and HNO3 is so that the silica content can be separated from the impurities so that a larger crystal-shaped silica precipitate and a yellowish-colored solution containing impurities are present in the precipitate. So that in this study the results of the analysis of the content of Silica dioxide (SiO2) of 76.50%.

Exploration Targeting in Porphyry Cu Systems Using Propylitic Mineral Chemistry: A Case Study of the El Teniente Deposit, Chile

Abstract The mineral chemistry of epidote and chlorite from the propylitic halo at El Teniente, in samples collected at distances up to 6.6 km from the deposit center, was determined by microprobe and laser ablation-inductively coupled plasma-mass spectrometry. Results show that both minerals systematically incorporated a range of trace elements that define a much larger footprint to the system than is easily recognized using conventional means such as whole-rock geochemistry. Apart from Fe and Mg in chlorite, there is no significant control of mineral chemistry by bulk-rock composition. For chlorite, geothermometry temperatures and Ti and V concentrations are high proximal, whereas Li, As, Co, Sr, Ca, and Y are low proximal and elevated in distal positions. Ratios of these elements define gradients toward ore varying over three to five orders of magnitude. The proximal-high Ti content is thought to reflect crystallization temperature, whereas proximal-low signatures are believed to characterize elements that are relatively fluid mobile in the inner parts of the propylitic halo in the presence of mildly alkaline to mildly acidic and oxidized fluids so that they are not incorporated into crystallizing chlorite, despite being generally compatible within the mineral structure. These elements begin to substitute into chlorite in the distal parts of the propylitic halo where fluids are largely rock buffered in terms of major element chemistry. In epidote, As defines a broad proximal low and is generally elevated at distances of at least 3 km from the edge of the ore shell. Zinc, La, Yb, Y, and Zr in epidote, among others, appear to define a geochemical shoulder that surrounds the deposit. These patterns are broadly similar to those observed in previous work at Batu Hijau and in the Baguio district, suggesting that these minerals behave consistently in porphyry systems and can therefore provide useful exploration tools within propylitic green rocks.

Local production and long-distance procurement of beads and pendants with high mineralogical diversity in an early Saladoid settlement of Guadeloupe (French West Indies)

The preventive excavation of an archaeological site located at the Gare Maritime of Basse-Terre (Guadeloupe, French West Indies) revealed a series of stone artifacts including finished beads and pendants, as well as pieces representing several stages of the chaîne opératoire. This work is an integrated study of the mineralogy and typo-technology of these objects. The artifacts have been recovered from layers interpreted as midden deposits of an early Saladoid coastal settlement dated to 250–400 cal. A.D. Non-invasive analyses by Raman spectroscopy have shown that the 50 artifacts belong to 13 different gemstones which are, in decreasing order of frequency: serpentine, amethyst, turquoise, sudoite, rock crystal, calcite, feldspar, diorite, jasper, aventurine, chlorite, paragonite and nephrite. All these materials’ mineralogy, and in particular the great diversity of the so called “green rocks”, could only be reliably determined through an analytical characterization. The diversity of lithic materials used and abandoned in the Gare Maritime site dump is the largest known to date in the Caribbean archipelago. The presence of seven objects in turquoise is particularly noteworthy in view of its rarity in the other known sites in the region. The chaîne opératoire for each of these raw materials could be approached for the first time in the Caribbean area by emancipating ourselves from the “greenstone” category, which has been too often used in the past because of the lack of reliable mineralogical identification. These results make it possible to integrate the Gare Maritime site into the group of Saladoid sites which have delivered a large set of ornamental elements. On the one hand, the various shapes of artifacts fit the regional cultural pattern, both for beads and pendants shapes, the latter being mainly stylized frogs. On the other hand, the use of 13 semi-precious stones in the lapidary production is exceptional for the region and confirms the use at this period of many exotic raw materials. The provenance of these materials, although difficult to pinpoint properly due to the incomplete mapping of regional resources, documents a mixture of regional and even distant (continental) origins, thus strengthening the idea of a pan-Caribbean network for the exchange of raw materials for lapidary art.

Clay Minerals Occurred in Landslide Areas on Mikabu Green Rocks

Clay Minerals Occurred in Landslide Areas on Mikabu Green Rocks

Utilización de rocas ornamentales en Costa Rica desde tiempos precolombinos hasta el siglo XX

Las rocas ornamentales y para la construcción se han utilizado en Costa Rica desde al menos hace 4000 años. Las rocas ígneas (principalmente lavas), los aluviones y en menor grado las rocas sedimentarias, lasintrusivas y las metamórficas de bajo grado (cornubianitas) incluyendo rocas hidrotermalizadas, se utilizaron enmonumentos, enchapes, sitios habitacionales, tumbas, caminos, escultura, así como objetos de uso doméstico (hachas, metates, mesas, etc.). Los denominados jades precolombinos son en realidad rocas verdes de diversostipos, tanto foráneos (jadeitas, nefritas y serpentinitas de Guatemala y México) como de origen local (areniscasy calcedonias, entre otras). Previo a la prohibición de su venta, los utensilios precolombinos fueron utilizados y comercializados como ornamento de jardines e interiores. Durante la Conquista y la Colonia, Costa Rica era unterritorio pobre con escasa mano de obra indígena, lo cual no permitió el desarrollo de una arquitectura elaborada, dentro de la cual se utilizaron las rocas como elemento constructivo. A finales del siglo XIX y hasta mediados del XX, las principales obras arquitectónicas del Valle Central (monumentos, edificios, iglesias, callesy aceras) se construyeron principalmente con lavas de los volcanes Barva e Irazú, ignimbritas del Río Grande, seguido de calizas (Barra Honda, El Viejo-Península de Santa Elena, Turrialba y San Miguel de Patarrá) y de mármoles importados de Carrara (Italia). Los mármoles y los travertinos han estado igualmente difundidos enla industria funeraria. El uso de rocas ornamentales en construcciones habitacionales está circunscrito principal-mente a enchape de muros y fachadas, aceras y jardines, estando representadas predominantemente por escorias rojizas (procedentes de Sabana Redonda de Poás), los cantos rodados de ríos, lavas (lajas y lavas vesiculares dela Cordillera Central) y el molejón (areniscas cuarcíferas). Otras rocas ornamentales utilizadas en diversas obras(granitos, gabros, serpentinas, etc.), son de uso limitado y de procedencia foránea, por lo que su costo es elevado. Un cambio en la economía y en la sociedad a partir de la década de los ochentas del siglo XX, se tradujo enuna construcción más abierta, dinámica y ligera, lo que implicó un menor uso de rocas ornamentales, no solo enedificios, sino en un nuevo tipo de cementerios: los camposantos. Sin embargo, Costa Rica posee un potencialque no ha sido evaluado adecuadamente en lo que corresponde al uso de rocas ornamentales nativas, tierra virgen para futuras investigaciones específicas.

The nature and age of the Suroyam clinopyroxenite massif (Middle Urals)

The Suroyam alkaline ultrabasitesyenite (mainly pyroxenite) massif, including the Suroyam apatitetita� nomagnetite deposit, is a part of the Nyazepetrovsk structural-formational zone located on the western slope of the Middle Urals, within the Ufimskii promon� tory of the East European Platform. The Nyazepetrovsk complex tectonically overlaps the sedimentary shelf and bathyal deposits of the mar� gin of the Paleozoic continent (Fig. 1) and is the uppermost tectonic sheet developed here. The com� plex is made of volcanogenic-sedimentary and intru� sive rocks of Ordovician-Early Devonian age, approximately correlated with the Early and Late islandarc oceanic formations of the Tagil zone (1). According to the chemical composition and metallo� genic features, the Suroyam massif located in the area of these formations can be compared with massifs of a palladiumbearing "branch" of the Platinum belt (Ural PGEbearing belt) in the Urals. The Rb-Sr iso� chrone age of the massif is 415.2 ± 1.1 Ma. Recent data obtained provide confirmation of the allochthonous origin of the Suroyam massif and its positional con� nection with the Tagil zone. The stratigraphic section of the Nyazepetrovsk zone is represented by volcanic and volcanogenic- sedimentary formations with subordinate siliceous rocks, siltstone, and sandstones. The section is distin� guished into three formations (from ancient to young): basalt, basalt-andesitebasalt, and trachybasalttra� chyte. Based on rare findings of radiolarians, con� odonts, and macrofauna, the age of the formations is regarded as Ordovician-Early Devonian. The Suroyam massif is located in the southern area of the axial part of the Nyazepetrovsk zone, and it is mainly composed of apatitetitanomagnetite clinopy� roxenites, subjected to strong superimposed potassium and sodium metasomatism, connected with manifes� tations of alkaline magmatism (2). The nature of the massif is under discussion. There were ideas expressed in (3, 4) about its platform origin, but more convincing evidence is needed. We have identified, however, sim� ilarities of the Suroyam massif with some specific mas� sifs of the Platinum belt with titanomagnetite mineral� ization. In particular, among the most widespread types in the Suroyam massif (Fig. 2) are highferrugi� nous clinopyroxenites, green and dark green rocks, characterized by fine to coarse grained structure, as well as pegmatoid structure. The main rockforming minerals are clinopyroxene, titanomagnetite, apatite, and phlogopite. The quantitative ratios of these miner� als vary greatly. The central part of the Suroyam massif is composed of coarsegrained titanomagnetite cli� nopyroxenites (like kosvites) with a titanomagnetite content of 6-25%; the marginal part is characterized mainly by apatitetitanomagnetite types of rocks, con� taining 2.9-19.5% of apatite. The undeformed rocks have sideronitic and granoblastic texture. Clinopyroxene forms short and long prismatic grains. According to the chemical composition, cli� nopyroxene is represented by diopsidehedenbergite, containing 25-30% of the hedenbergite molecule. The iron content in pyroxene ranges from 14 to 26% (20 at. % on average). There was noted a high content of alumina (2.49-5.05%) with variations in the augite content from 6 to 11%. The titanomagnetite is lowtitanium, and it is rep� resented by xenomorphic grains with sideronitic tex� ture. In addition it forms finegrained, platy, den� dritic, and dropshaped inclusions in clinopyroxene. In general, titanomagnetite is distributed uniformly in the rock. However, there are sections with a banded distribution of ore minerals. In titanomagnetite there are inclusions of xenomorphic clinopyroxene and prismatic apatite. Sometimes, the ore mineral forms

Chemical composition of the green rocks in the Nedamo Terrane, Northeast Japan

The Nedamo Complex, an Early Carboniferous accretionary complex, contains green rocks of Late Devonian age. The complex consists of two lithotectonic units: the Takinosawa Unit and Tsunatori Unit. We analyzed the chemical composition of the green rocks in both units, as this has yet to be done for the Takinosawa Unit, and has only been done for some of the green rocks of the Tsunatori Unit. The chemical composition of green rocks in the Takinosawa Unit shows features of phyric within-plate tholeiite ; that in the Tsunatori Unit shows features of phyric alkali basalt, phyric within-plate tholeiite, and aphyric MORB.

Petrology, petrography and mineralographical studies of “Choghart Iron Ore Mine”, Bafgh area, Iran

The Choghart Iron Ore is located in Precambrian Formation of Central Iranian Plateau and their country rocks are sedimentary, volcanic, intrusive, schist, marble and gneisses. This complex is influenced by metamorphism (Contact and Burial) and metasomatism processes and has caused great variety of rocks and minerals around Choghart area. But as a whole, the complex which make the country rocks of the ore body has completely two different facies; these two facies are mostly green and light rocks which are applied generally with different names by geologists. The study of petrographical performance with respect to mineralogical study upon these two facies show that, the light rocks which are made up of high percent of quartz and feldspar have under gone a very intrusive metasomatism which is named as Cratophyer. Furthermore, these studies also show that the greatest part of the green rocks of the area, have been formed due to the low grade metamorphism of igneous rocks, and due to the mineralogical and textural composition, it is named as Greenstone.

Chlorite exhibits a little swelling property formed in green rock distributed in the Nishinotani landslide area, Ehime, SW Japan

Green rocks that have originated from basalt and tuff are distributed in the Nishinotani landslide area . Chlorite is the major constituent mineral of green rocks, and it is formed in the phenocrysts found in these rocks. The chlorite in these rocks exhibits a little swelling property because it includes several smectite components. Thus, it is proposed that the landslide activity is induced not only by smectite, but also by chlorite, which exhibits a little swelling property.

Iron speciation related to color of Jurassic sedimentary rocks in Turpan Basin, northwest China

Mesozoic-Cenozoic reddish and green beds are widely distributed in northwest China. Mossbauer spectroscopy revealed that the composition of iron species varies with color in the middle-upper Jurassic sedimentary rocks from the Turpan Basin. Three main kinds of iron species were identified: (1) ferric iron of hematite (hem-Fe3+), (2) paramagnetic ferric iron (para-Fe3+), and (3) paramagnetic ferrous iron (para-Fe2+). Pyrite iron (pyr-Fe2+) was revealed only in a few samples. In general, there is a direct correlation between rock color, iron species and total iron content, however, in detail, this relationship is more complicated. The reddish rocks contain higher contents of total iron and hem-Fe3+, whereas the gray rocks contain much more para-Fe2+. However, relatively low hematite content cannot give red color to rocks, probably due to suppression by other pigments such as organic matter in black or chlorite in green. The dark or green rocks normally contain either only paramagnetic Fe2+ and paramagnetic Fe3+ species or these two species associated with hematite Fe3+, but the relative content of hematite species is lower. The variations of different iron species control lithological properties such as color and also may reflect the sedimentary conditions. Moreover, iron speciation in these rocks is one of the main factors, which result the color features of rocks in remote sensing imagery.

Low‐temperature alteration of mesozoic oceanic crust, Ocean Drilling Program Leg 185

Basalts drilled from the Mesozoic crust at Ocean Drilling Program (ODP) Sites 801 and 1149 during Leg 185 have been affected by a succession of submarine, variably oxidative alteration processes by cold seawater. The low‐temperature alteration resulted in various combinations of secondary minerals both as replacements of igneous phases, and as void and crack fillings. Mg‐smectite, calcite, celadonite and Fe‐oxyhydroxide are the dominant secondary minerals. Quartz, chalcedony and phillipsite are always very minor phases that fill open spaces. The rocks generally exhibit concentric haloes, 0.5 to 1 cm in thickness, around gray inner cores and usually adjacent to exposed surfaces. Color zonations result from the abundance of various secondary mineral assemblages present in each zone. The green rocks are dominated by celadonitic phyllosilicates, whereas the dusky red haloes are characterized by abundant iddingsite and Fe‐oxyhydroxides replacing the fine clinopyroxene. Finally Mg‐smectite ± calcite, are the most common secondary phases in the inner gray cores. The most unusual effects of the low‐temperature alteration of the study rocks are the pervasive, pale green to gray green color and the relatively abundant dusky red haloes surrounding inner reddish gray cores. Alteration of Mesozoic crust cored during Leg 185 is comparable with low‐temperature alteration of 310 m thick uppermost volcanic section of the 5.9 My old crust of Hole 504B. Except the renewed precipitation of calcite in veins, the aging of oceanic crust does not depend on time probably because it occurs during the first few millions of years after the accretion, and ceases when the crust is sealed off.

Petrology and P-T condition of white mica-chlorite schists from Vlasina series - Surdulica, SE Serbia

This paper reports structural, textural, petrological and metamorphic data from Vlasina Series of greenschists rocks (as part of the Upper Complex of the Serbo-Macedonian Massif) within which group of white mica-chlorite schist are extensively developed. This group of rocks made the ground of series in which various types of green rocks appear as a lenses and small irregular mass, rarely as dykes. Other features, that characterize these rocks, are the common occurrence of albite and garnet (subordinate) porphyroblasts, as well as development of quartz segregation. Group of white mica-chlorite schist makes about 75 vol. % of Series. Among them, according to mode and mineral composition, the following schist varieties are distinguished: albite-white mica-chlorite (?garnet), white mica-chlorite (?garnet), albite-white mica, sericite-chlorite (?albite), graphite-sericite as well as phyllites and calcshists. Their metamorphic evolution is characterized by the development of a metamorphic episode during Carboniferous - c. 350-330 Ma (Milovanovic et al., 1988) of low to medium P and T. The mineral assemblages of first phase (low PT) is preserved as a very thin Si=S1 foliation included in albite porphyroblast or as small polygonal arcs of S1 in S2 foliation. Textural, mineralogical and petrological data indicate that original volcanoclastic-sedimentary series was transformed during three phase of deformation and metamorphism in the temperature range from 320-415?C, locally 450-500?C and pressures 3 to 5 kbar.

Petrologic characteristics and geologic age of green rocks including chert xenoliths in the Pippu area, central Hokkaido, Japan

Petrologic characteristics and geologic age of green rocks including chert xenoliths in the Pippu area, central Hokkaido, Japan

Stratigraphie et paléogéographie d'un bassin d'avant-arc ordovicien, Estrie-Beauce, Appalaches du Québec

Two new formations, the Frontière and Etchemin formations, have been found to lie below the Beauceville and Saint-Victor formations, the two known formations of the Magog Group. The Frontière Formation, at the base of the group, is made up of centimeter-thick beds of medium- to coarse-grained litharenite and of greyish green mudstone; the sandstone, greyish green, contains abundant felsic volcanic rock fragments and chromite grains. The Etchemin Formation is composed mostly of centimeter-thick dusky yellow green siliceous mudstone; at the base, there is also a purple mudstone, and meter-thick beds of dusky green volcaniclastic rocks rich in intermediate to felsic volcanic rock fragments and crystals of feldspar and quartz occur near its top. The Beauceville Formation consists of interbedded centimeter-thick beds of black clayslate and centimeter- to meter-thick beds of black volcaniclastic rocks. The Saint-Victor Formation consists of classic turbidite beds with few meter-thick yellowish volcaniclastic rock beds similar to those of the Beauceville Formation; the sandstone is a litharenite rich in quartz grains and sedimentary rock fragments. Most rocks of the Frontière and Etchemin formations as well as the volcaniclastic rocks of the Beauceville and Saint-Victor formations were derived from a magmatic arc located to the southeast. However, the shale of the Beauceville Formation and the turbidites of the Saint-Victor Formation were derived from an orogenic source located to the northwest. The Magog Group is located between the Saint-Daniel Mélange and the Ascot Complex interpreted as remnants of an accretionary prism and a magmatic arc, respectively. The sediments of this group were thus deposited in a fore-arc basin active during the Taconian orogeny of the Middle to Late Ordovician.

関東山地越生地域の御荷鉾緑色岩および吾野地域の秩父帯緑色岩の残留単斜輝石

The original igneous rocks of weakly metamorphosed greenstones are basalt-dolerite and limburgite in Mikabu Green Rocks of the Ogose area, and basalt-dolerite-bostonite and limburgite in the Chichibu melange zone of the Agano area, both of Kanto Mountains. Relict phenocrystic clinopyroxenes of basaltic and limburgitic rocks of both areas are chromian augite (Cr2O3 0.4-0.8 wt.%) to chrome augite (Cr2O3 more than 0.8 wt.%), but, in general, comparatively poor in TiO2 (less than 0.1 wt.%). However, limburgitic pyroxenes of the Chichibu melange zone are slightly richer in TiO2 and Cr2O3 and higher in Mg/(Fe+Mg) than those of the Mikabu rocks. The phenocrystic clinopyroxenes are generally similar in Cr2O3/TiO2 ratios to clinopyroxenes of ocean-floor basalts and of peridotite xenoliths derived from the mantle.

Laramide Tectonic Evolution of San Juan Sag, Colorado: Implications of Animas and Blanco Basin Formations: ABSTRACT

The lower member of the Animas Formation (McDermott Member) is a volcaniclastic sequence derived from a north-northwest source (San Juan-La Plata area). It consists of purple andesitic debris flows, green fan-delta sandstones and mud rocks, and dark gray conglomerates with clast compositions indicating that the Precambrian core of the source uplift was exposed. The upper member is a sand-dominated alluvial plain sequence deposited by southwest-flowing braided streams. It includes green-gray-brown carbonaceous mudstones and pebbly sandstones containing clasts of mudstone, andesite, and detritus from Precambrian and Mesozoic sources in the Brazos-San Luis uplift to the east and northeast. by the end of Animas deposition, the San Juan sag (then a northeastern extension of the San Juan basin) was a broad, southwest-plunging synclinal downwarp bounded by hogback monoclines to the north and east. An erosional period followed Animas deposition; the greatest thickness of Animas was preserved along the axis of this synclinal feature. Bright-red sandy mudstones and yellow-gray pebbly sandstones and cobble conglomerates comprise the proximal alluvial-fan deposits of the Blanco Basin Formation. They unconformably overlie Precambrian through Paleocene rocks and clast compositions reflect these sources. Renewed uplift and segmentation of the Brazos-San Luis uplift resulted in the shedding of detritus southwestwardmore » into the San Juan sag and eastward into a narrow, asymmetrical, north-trending wrench basin within the uplift. Following Blanco Basin deposition, the last Laramide event is represented by the separation of the San Juan sag from the San Juan basin by uplift of the Archuleta anticlinorium.« less