Zircon U–Pb and Lu–Hf isotopic constraints on Archean crustal evolution in the Liaonan Complex of northeast China
En MengFulai LiuJianhui LiuPinghua LiuYing CuiChaohui LiuHong YangFang WangJianrong ShiQing-Bo KongTao Lian
46
Citation
173
Reference
10
Related Paper
Citation Trend
Keywords:
Protolith
Microflore of Pre-Cambrian LImestones of the Duszniki Zdroj Region (The Central Sudeten)
Metamorphic rocks of the Bystrzyckie Mountains, which also comprise crystalline limestones of Duszniki Zdroj, have been known to many authors. H. Wolf (1864) included these rocks among the Pre-Cambrian; at the same time he distinguished red and augen gneisses as older ones, while mica-schists with limestone lenticles, hornblende schists and gneisses were considered to be younger ones. L. Lepla (1910) included metamorphic rocks of this region among the Archaean. W. Petrascheck (1910, 1944) distinguished the older, axial part built of gneisses, and the younger one — a cover of mica-schists with limestone lenticles; he included both parts among the Pre-Cambrian. K. Smulikowski (1951) included mica-schists among the Algonkian, with a reservation, however. J. Gierwielaniec (1957, 1965) supposes that crystalline limestones of the Duszniki Zdroj region are of the Cambrian age, although their affiliation to the Algonkian is not unlikely. A synthetic stratigraphical-lithological profile of metamorphic rocks of the Bystrzyckie Mountains was drawn up by M. Dumicz (1964). This author includes the metamorphic rocks of the Bystrzyckie Mountains among the Pre-Cambrian; at the same time he remarks that micaschists with limestone lenticles are older than gramte-gneisses. J. Obere (1966) included mica-schists of this region among the Proterozoic, while H. Teisseyre (1968) claims their Pre-Cambrian age. The author of the present paper has carried out his studies in one of non-working limestone quarries situated in the Duszniki Zdroj region (fig. 1). Shaly limestones, compact and brecciated, dark-pink and lightgray in colour occur in this outcrop (fig. 2). In .microsections directional arrangement of mineral grains have been found (table I, fig. 1, 2), among which calcite prevails, quartz constitutes about 25%, while micas and feldspars are less numerous. Ferric oxides form pigment that gives colour to the rock. Brecciated limestones are outcropped on one of the walls (table I, fig. 3). Samples for micropalaentologic studies were taken from all outcrop ped layers. The samples were used for making cubes of a size 8 X 5 X 6 cm; the latter were then dissolved in hydrochloric acid, in acetic acid and in EDTA. Some were frozen in liquid nitrogen and then unfrozen. 550 preparations and also 35' microsections and 40 surficial sections were made; the former were then preserved in the Canada balsam. The microflore found there is usually poorly preserved. Sporangia and fructifications of Fungi and Sphaeromorphidae are comparatively best preserved, while Cyanophyta are much worse. The Sphaeromorphida group is the most abundant one in genera and species. Species: Prostosphaeridium flexuosum T i m., Protosphaeridium laccatum Tim. according to B. W. Timofiejew (1966, 1969) are widely spread in Vendian and Riphaean (late Precambrian), but there are only few in the Cambrian. Others, such as: Protosphaeridium vermium Tim. , Pterosperomopsimorpha annulare T i m., Leiosphaeridium — type R. Pf lug, Synsphaeridium sorediforme T i m., are quoted by this author from Riphaean. Among Cyanophyta the genera: Cephalophytarion, Paleonacystis, Sphaerophycus parvum S с h., Catinella polymorpha — the form F. Pf lug, Miliaria implexa Pflug were described by J. W. Schopf (1968), J. W. Schopf et J. M. Blacic (1969), H. Pflug (1966) from the Upper Proterozoic of Australia and the Rocky Mountains in North America. The genera: Gunflintia grandis Bargh., Gunflintia minuta and Eosphaera come from the Lower Proterozoic of Canada (E. S. Barghorn et S. A. Tyler 1965). Also the genera Fibularix, Scintilla and Tormentella were described by H. Pflug from the Upper Proterozoic. The genus Belaiaella, described by P. N. Kolosow (1970), as well as Phycomycetes, presented by B. W. Timofiejew (1969), come from the Riphaean of Siberia. Ascomycetes have not been quoted from the Pre-Cambrian, so far. Having analysed the stratigraphie range of the described genera of microflora (vide specification of the described microflora), the Archaean age of limestones, suggested by A. Lepla (1910), should be thus excluded. Assemblages characteristic of the Cambrian are also absent here, which would not confirm J. Gierwielaniec’ s suggestion (1957, 1965) of the possible Cambrian age of limestones, either. The Upper Proterozoic age seems to be the most reasonable one, which is indicated by the prevalence of genera and species of the microflora. At the present stage of investigations it is difficult to decide whether other crystalline limestones in this area are of the same age as the ones described from the Duszniki region, or whether they are younger or older. Further studies will allow a solution of this problem.
Hornblende
Outcrop
Cite
Citations (2)
Quartzofeldspathic gneisses near zinc–lead–gold mineral deposits at Montauban-les-Mines, Quebec, have been examined geochemically to determine whether their protoliths were dominantly sedimentary or igneous. The gneisses are generally similar in average compositions to both rhyolitic rocks and sandstones (greywackes in particular). The most useful methods of protolith discrimination were found to be: (1) log (SiO 2 /Al 2 O 3 ) versus log [(CaO + Na 2 O)/K 2 O]; (2) Niggli si versus mg; (3) normative quartz; (4) Shaw's discriminant function. Application of these criteria indicates that the Montauban quartzo-feldspathic gneisses were derived dominantly from quartzose sandstone or greywacke protoliths (or both).
Protolith
Cite
Citations (5)
This study describes the La, Ce, Nd, Sm, Eu, Tb, Yb and Lu concentrations in six iron-formation rocks (Fetot^> 15 °/o), four ferriferous schists (Fetofx.10-15°/o) and two schist interbeds of the Archean Ukkolanvaara iron formation, as well as in seven associated schists of the Ilomantsi Schist Belt.For the same elements, two samples were analysed from the Archean Siivikkovaara iron formation in Kuhmo, one sample from the Archean Otravaara pyrite ore and one sample from the Karhusaari pyrite ore, probably Middle Precambrian in age.All the iron-formation samples and the Otravaara pyrite ore show a marked positive Eu anomaly compared with the composite of North American shale (NAS) and are relatively poor in rare-earth elements (REE).The REE concentrations in the Ilomantsi schists are largely similar to those in the Sheba greywackes from the analogous ironformation-bearing association of the Archean Fig Tree Group, South Africa.The ferriferous schists show a marked positive Eu anomaly compared with the NAS, but contain the other REE in as high abundances as the Ilomantsi schists on average.The results confirm the general Eu excess in the Archean iron formations compared with younger iron-rich metasediments.The REE concentrations in the Archean schists characterized by an Eu excess in relation to younger pelitic schists are considered indicative of their general immaturity and a source area dominantly graniticgranodioritic in composition.
Banded iron formation
Cite
Citations (13)
The region discussed in this paper lies in Chester County, Pa., and is included in the eastern half of the Coatesville quadrangle. (See fig. 3.) It is within the belt of crystal-line schists and gneisses of the Piedmont Plateau. The northern half of the area, which will be called the Doe Run region, from the village of that name (see Fig. 4, p. 15), has been surveyed by Eleanora F. Bliss in connection with the problem of the relation of the Wissahickon mica gneiss to the Octoraro schist.
BLISS
Quadrangle
Cite
Citations (5)
Mr. Geo. G. Holmes and others have observed the remarkable and highly suggestive fact that not only do the schists (which contain in many places interlaminated beds of quartzites and massive crystalline limestone, e.g. in the Dwarsberg on the Magalakwin River in the Northern Transvaal) appear interbedded in the gneisses, but that the strike foliation and planes of schistosity of these old schists and of the gneisses seem invariably to be parallel.
Foliation (geology)
Cite
Citations (0)
Tonalitic orthogneiss from the Brookville Gneiss in southern New Brunswick has an igneous protolith age of $$605 \pm 3 Ma$$ based on U-Pb dating of zircon. Metamorphic titanite from the same sample gives a minimum age of $$564 \pm 6 Ma$$ for upper amphibolite facies metamorphism of the unit. Based on U-Pb analyses of single detrital zircons, a maximum sedimentary protolith age of about 641 Ma is suggested for associated paragneiss. These ages indicate that the igneous protolith of the orthogneiss was at most 35 Ma younger than the sedimentary rocks it intruded, and that the Brookville Gneiss is younger than the Green Head Group to which it was previously considered basement. Both orthogneiss and paragneiss in the Brookville Gneiss contain Proterozoic and Archean detrital zircon grains, suggesting an old, heterogeneous continental source. We conclude that the Brookville Gneiss does not represent the basement to the Avalon Terrane.
Cite
Citations (55)