黑龙江省东部马家街群碎屑锆石年代学及其大地构造意义

马家街群分布在黑龙江省东部佳木斯地块桦南隆起的西南缘,主要由一套经历了接触变质作用的富铝、富碳沉积碎屑岩所组成。区域上,这套接触变质岩系具有变质矿物分带特征,由西向东依次出现十字石、红柱石、石榴石和黑云母。红柱石碳质板岩和石榴云母石英片岩2件样品获得的LA-ICP-MS U-Pb碎屑锆石年龄谱均显示有272~310Ma、479~533Ma和>800Ma三组年龄。根据两件样品显示的最小年龄均未小于272Ma,而且二者的最小年龄组（272~310Ma）具有类似的峰值年龄,分别为276Ma和279Ma,这限定了马家街群主体岩石沉积年龄的下限应在中二叠世之前。侵入马家街群的花岗岩的锆石年龄为259Ma,说明其接触变质作用时代为晚二叠世早期,限定了马家街群形成时代的上限。479~533Ma年龄组中,2件样品的峰值年龄分别为499Ma和522Ma,这是佳木斯地块麻山群中最为重要的高级变质和花岗质岩浆作用年龄。>800Ma的年龄组具有多个峰值年龄,说明源区（佳木斯地块）具有前寒武纪-早前寒武纪地壳。上述证据表明,马家街群是晚二叠世早期形成的一套接触变质岩系,而非前寒武纪区域变质岩系。鉴于479~533Ma的麻山群在佳木斯地块中普遍存在,说明以麻山群为代表的早古生代变质结晶岩系既是马家街群沉积的基底,也是重要的物源区;而276~279Ma的早二叠世火山岩在佳木斯地块东缘分布广泛,表明其对马家街群的沉积也具有一定的贡献。     

The Neogene and Lower Pleistocene crags of Upper Normandy: Biostratigraphic revision and paleogeographic implications

The biostratigraphic revision of the benthic foraminifera present in the coastal Cenozoic quartzose and shelly sands (crags) at Fécamp and Valmont (Seine-Maritime) reveals Early Pliocene (Fécamp) and Early Pleistocene (Valmont) ages. The Tortonian-Messinian thanatocœnosis contained in the Fécamp Crag shows the presence of a former bryozoan-rich platform on the floor of the Channel that was reworked during the Lower Pliocene transgression. Tortonian-Messinian and Lower Pliocene deposits have been found in Belgium, England, Brittany, and at Fécamp, but are absent in Cotentin (North-West Normandy), which was uplifted at this period. The Lower Pleistocene tidal sands and crags described in Cotentin, Upper Normandy and the southern North Sea Basin indicate a marine passage between the Channel and the North Sea.     

Cenozoic collisional tectonics and origin of Pb-Zn-F mineralization in the Bitlis Massif,SE Turkey

Hasbey Pb-Zn-F mineralization in the Bitlis Massif, south of Lake Van, lies within the Neotethyan suture of the Alpine orogenic belt. Mineralization occurs in two different lithologies and locations: Type-I is present in dolostone fractures and faults as veins and veinlets, whereas Type-II occupies a fault zone between black marbles and calc-schists. Sphalerite and argentiferous galena are the main ore minerals in both types. The dominant gangue minerals are quartz and dolomite in Type-I ore and calcite, quartz, and green-white fluorite in Type-II. Analysed fluid inclusion data from sphalerite, fluorite, and quartz indicate that high-temperature (>500°C) mineralization was initiated from low-salinity fluids (4.3 wt.% NaCl equiv.). As temperatures dropped from 400°C to 160°C, the salinity of solutions increased and appreciable CO₂ was contributed to the fluid system. In the absence of immiscibility, assemblages of fluid inclusions containing CO₂ indicate that the solutions were homogeneous during entrapment and that mineralization took place under pressure conditions between 5 and 2 kb.

Analysed δ³⁴S _CDT (‰) values (?1.5 and??3.8, n?=?15) of sphalerite and galena indicate that the source of the sulphur is consistent with a magmatic origin for Hasbey Pb-Zn-F mineralization. The stable isotopic compositions and fluid inclusions in fluorite are also suggestive of an origin related to high-temperature, high-salinity magmatic fluids. In the region, volcanic rocks are abundant, and they document the magmatic events associated with the closure of the neo-Tethys.

The timing of mineralization is restricted to post-early Oligocene, inasmuch as mineralization occurs in faults that cut post-Eocene–Oligocene thrust faults and because of the relationship between mineralization and wall-rock deformation.     

Stratigraphy and tectonic evolution of the Kazdağı Massif (NW Anatolia) based on field studies and radiometric ages

The Kazda?? Massif was previously considered as the metamorphic basement of the Sakarya Zone, a microcontinental fragment in NW Anatolia. Our new field mapping, geochemical investigations, and radiometric dating lead to a re-evaluation of previous suggested models of the massif. The Kazda?? metamorphic succession is subdivided into two major units separated by a pronounced unconformity. The lower unit (the Tozlu metaophiolite) is a typical oceanic crust assemblage consisting of ultramafic rocks and cumulate gabbros. It is unconformably overlain by a thick platform sequence of the upper group (the Sar?k?z unit). The basement ophiolites and overlying platform strata were subjected to a single stage of high-temperature metamorphism under progressive compression during the Alpine orogeny, accompanied by migmatitic metagranite emplacement. Radiometric age data obtained from the Kazda?? metamorphic succession reveal a wide range of ages. Metagranites of the Kazda?? metamorphic succession define a U–Pb discordia upper intercept age of ca. 230 Ma and a lower intercept age of 24.8 ± 4.6 Ma. This younger age agrees with ²⁰⁷Pb/²⁰⁶Pb single-zircon evaporation ages of 28.2 ± 4.1 to 26 ± 5.6 Ma. Moreover, a lower intercept age of 28 ± 10 Ma from a leucocratic metagranite supports the Alpine ages of the massif within error limits. Reconnaissance detrital zircon ages constrain a wide range of possible transport and deposition ages of the metasediments in the Sar?k?z unit from ca. 120 to 420 Ma. Following high-temperature metamorphism and metagranite emplacement, the Kazda?? sequence was internally imbricated by Alpine compression, and the lowermost Tozlu ophiolite thrust southward onto the Sar?k?z unit. Field mapping, internal stratigraphy, and new radiometric age data show that the Sar?k?z unit is the metamorphic equivalent of the Mesozoic platform succession of the Sakarya Zone. The underlying metaophiolites are remnants of the Palaeo tethys Ocean, which closed during the early Alpine orogeny. After strong deformation attending nappe emplacement, the unmetamorphosed Miocene Evciler and Kavlaklar granites intruded the tectonic packages of the Kazda?? Massif. During Pleistocene time, the Kazda?? Massif was elevated by EW trending high-angle normal faults dipping to Edremit Gulf, and attained its present structural and topographic position. Tectonic imbrication, erosion and younger E–W-trending faulting were the main cause of the exhumation of the massif.     

Ping Jian (1964–2015)

ABSTRACT

Metasedimentary rocks from the El Triunfo Complex (Jocote Unit) in the southern Chiapas Massif (SE México) are constituted mainly by sillimanite-rich micaschist, locally intercalated with marble and calc-silicate rocks. Mafic rocks (now amphibolite) intruded the sequence prior to deformation and folding. Peak metamorphic conditions are estimated by geothermobaromerty at ~6.0 kbar and ~650ºC. The timing of the metamorphic event is dated by LA-MC-ICPMS analysis on zircon rims at 438⁺²³/_–12 Ma. Furthermore, detrital zircon grains yield mainly Stenian–Tonian and minor early Mesoproterozoic ages, indicating provenance from Grenville-type orogens (such as Oaxaquia) and some older cratonic sources. The ⁸⁷Sr/⁸⁶Sr values of 0.70775–0.70777 and the δ¹³C values from +1.9‰ to +2.7‰ in associated calcite marble define the time of deposition between 600 and 580 Ma. Geochemical markers from metapelite samples (such as La/Th > 3.94, La/Sc > 3.72, Th/U > 8.19, Th/Co > 0.42 and CIA = 74 to 83), as well as Sm–Nd isotope data (εNd_i = ?8.1 to ?4.0, TDM_(Nd) = 1.65–1.32 Ga) suggest weathering of Mesoproterozoic felsic rocks during temperate to warm climate. Furthermore, Zr/Sc values (9.1–21.0), chondrite-normalized REE patterns [La/Yb]_N = 10.3–23.3, Eu/Eu* < 0.64), and ΔHf values (1.98–10.02) are indicative of pelagic and zircon-depleted sediments of a passive margin. The results suggest that the Jocote Unit was deposited during the opening of the Eastern Iapetus Ocean in the Ediacaran Period. This is the first evidence for Rodinia breakup in southern México. Besides that, the Ordovician tectonothermal event is probably related to compression during subduction and accretion along the western margin of Gondwana.     

Middle Jurassic subduction-related ophiolite fragment in Triassic accretionary complex (Mamu Dağı ophiolite,Northern Turkey)

ABSTRACT

The Mamu Da?? ophiolite, ca. 13 km long and 5 km across (Tokat, Sakarya Zone), consists of peridotites, pyroxenites, gabbros, and basalts, which are crosscut by dolerite dykes. These rocks show variable degrees of serpentinization and alteration. Gabbroic rocks consisting of plagioclase + clinopyroxene ± orthopyroxene ± olivine ± amphibole ± sphene ± opaque minerals have commonly the ophitic and the cumulate textures. Similar mineral paragenesis is observed in the basalts and the dolerites, which are commonly characterized by the sub-ophitic and the microlitic porphyric textures.

Primitive mantle-normalized rare earth and trace element diagrams of gabbros and basalts display subduction-related geochemical characteristics such as high Th concentrations, negative Nb, Zr, and Ti anomalies. Some of the gabbros are interpreted to be the cumulate rocks. They have mostly positive europium anomaly (Eu/Eu* 1.77–0.83) and relatively low SiO₂ and incompatible element (e.g. Zr, Ti) contents. The initial ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd values of gabbro/dolerite and basalt samples vary between 0.7036 and 0.7049, between 0.51259 and 0.51278, respectively. The isotope data and the whole rock geochemistry suggest that the Mamu Da?? ophiolite was derived from a mantle source that was affected by the subduction component rather than MORB or depleted mantle source.

Hornblendes from a gabbro sample of the Mamu Da?? ophiolite yielded ⁴⁰Ar/³⁹Ar plateau age of 159 ± 1 Ma. This age data is similar to those of many ophiolites located along the ?zmir-Ankara-Erzincan suture zone but is different from the ages reported for the Tokat Massif.     

Le Léon : un domaine exotique au Nord-Ouest de la chaine varisque armoricaine (France)

Résumé

La synthèse des données structurales, pétrologiques, géochimiques et radiochronologiques permet d’avoir une vision nouvelle du Léon et de proposer un modèle d’évolution géodynamique dans cette région. Cette évolution, entièrement paléozoïque, débute par la mise en place de granitoïdes d’affinité calco-alcaline (orthogneiss de Brest), témoins probables d’une subduction ordovicienne corroborée par la présence de reliques d’un métamorphisme HP-HT (éclogites de Lesne-ven). Toutes les séries lithologiques seront ensuite soumises à une déformation tangentielle associée à un métamorphisme de type intermédiaire pouvant aller localement jusqu’à l’anatexie. Cet événement tec-tono-métamorphique correspond à une collision continentale dvonienne qui achève la période de convergence précédente. La suite de 1 évolution au cours du Carbonifère est intracontinentale. Elle est marquée par une succession d’événements plutono-tectoniques : mise en place vers 340 Ma de granitoîdes crustaux (St Renan-Kersaint) associés au cisaillement dextre nord-armoricain; mise en place vers 300 Ma d’ un ensemble granitique d’origine plus profonde (Aber - Mut) immédiatement suivi par des venues crustales (Ploudalmézeau-Kernil.s) associée au fonctionnement d’une nouvelle zone de cisaillement (zone senestre de Porspoder-Guisseny); mise en place enfin, vers 290 Ma, d’un dernier complexe granitique crustal (Brignogan-Plouescat) terminant avec les mierogranites du Bas-Léon l’évolution hercynienne de cette

La période antécarbonifère de l’évolution du Léon pose un problème lié à sa position géographique actuelle dans le prolongement du Domaine cadomien nord-armoricain peu affecté par les événements varisques. En réalité le Léon par sa structure et son histoire précoce (éohercynienne) possède plus d’affinités avec le Domaine sud-armoncain. L hypothèse d’une probable origine exotique du Léon est discutée.     

Les dépôts détritiques plioc è nes du contact Massif Armoricain - Bassin Parisien entre Angers et Laval (France).

Résumé

Les dépôts détritiques pliocenes du contact Massif Armoricain - Bassin Parisien, entre Laval et Angers.

Dans les régions de contact Massif Armoricain - Bassin Parisien, les dépôts détritiques pliocènes restent assez mal connus malgré de nombreux travaux tant géologiques que géographiques. Les granulométries fines, la spectrométrie Mössbauer et la détermination des argiles permettent de séparer ces dépôts des sables éocènes plus anciens et des alluvions quaternaires, mais aussi d’identifier deux nappes d’âge légèrement différent en leur sein. Ainsi, les sables rouges, d’origine marine, qui se mettent en place lors de la régression prétiglienne sur une topographie irrégulière, apparaîssent toujours plus altérés (plus forte concentration d’hydroxydes de fer, prédominance de la kaolinite, plagioclases altérés) que les cailloutis supérieurs mal classés, qui correspondent à une nappe d’épandage continentale plus récente. Au cours du Quaternaire et du Pliocène, les hydroxydes de fer sont d’autant plus abondants que le matériel est plus anciennement mis en place et exposé aux oxydations.     

Karst et évolution des rivières : le cas de l’Ardenne

Résumé

Dans les régions karstiques comprenant des vallées épigénétiques, les phénomènes tectoniques ont deux influences majeures : a) la surrection donne de l’énergie potentielle en créant des différences d’altitude, générant à la fois le creusement des vallées et celui du karst ; b) une tectonique est nécessaire pour que le processus de karstification débute. L’opposition entre le développement privilégié soit des vallées, soit des réseaux karstiques dépend ainsi du type dissipée. Les réseaux karstiques de l’Ardenne se situent surtout entre 5 et 15 m au-dessus de la surface piézométrique pour les réseaux secs, et dans la zone saturée pour les parties actives. La structuration de ces réseaux karstiques est favorisée par un ralentissement de la surrection et une activité tectonique. Cette période se situe dans le Pléistocène moyen et récent, d apres les datations U/Th de spéléothèmes. © Elsevier, Paris     

Erratum

The Monts de Lacaune belong to the south-eastern (external) part of the French Massif Central. They constitute the lowermost unit in the Albigeois Nappe Pile, which is juxtaposed to the S against the gneiss dome (“Zone Axiale”) of the Montagne Noire. The Monts de Lacaune are composed of Cambrian to Silurian sediments, which show very low-grade metamorphic conditions. A multi-method investigation of phyllosilicates (illite and chlorite crystallinity, b cell dimension, K-Ar dating of fine fractions and electron microprobe analysis) permits to distinguish three metamorphic events: M1 (acquired during early folding and nappe stacking, 342-333 Ma), M2 (caused by the rise of the hot Zone Axiale) and M3 (probably caused by post-Variscan intrusions, Permian). The age range obtained for the nappe stacking is intermediate between deformation ages dated in the northern part of the Albigeois Nappe Pile and in the Southern Palaeozoic Nappes (southern Montagne Noire). This conforms to the classical concept of S-ward propagating tectonic accretion in the French Massif Central with a rate of shortening of c. 1.5 cm/year.