Anchimetamorphose im Anis und Ladin (Trias) der Nördlichen Kalkalpen zwischen Arlberg und Kaisergebirge — ihre Verbreitung und deren baugeschichtliche Bedeutung

Anisian to Ladinian sedimentary rocks of the Northern Calcareous Alps from the area between the Arlberg pass and the Kaisergebirge mountains have been sampled (more than 2500 samples) in about 50 stratigraphic profiles, recorded in great detail. The (silicate) mineral residue, fraction below 2 micron, resulting from solution in formic acid, has been investigated mineralogically. Its sheet silicate content proved to be markedly homogeneous, containing mainly di-octahedral illite minerals, their crystallinity as most prominent result found to increase in a twofold way:

1. The (Upper Austro-Alpine) Lechtal-Nappe is in its southern part characterized by increasing illite crystallinity from hanging to basal strata within the Ladinian to Anisian stratigraphic column. The source of this effect is found to be older than folding was.
2. The whole area of sedimentary rocks investigated here presents an increase in illite crystallinity data from north to south (i. e. towards the Central Alpine metamorphic units), irrespective of the presently existing tectonic structures (folding or nappe units within the Upper Austro-Alpine of the Northern Calcareous Alps). Hence the source of this effect must be younger than these events were. With this also a broad margin of “anchimetamorphic” influence has been detected within the southern part of the Northern Calcareous Alps, in the area of the Mieminger and Wetterstein mountains showing even a strong extension towards the north (reaching the location of Garmisch-Partenkirchen)

. These effects can by no means be attributed simply to sedimentary mineral distribution. Contradictionary to such an interpretation are the non-conformity of the illite crystallinity distribution within the existing tectonic setting to the original sedimentary position as well as general sedimentary data (paleo-morphology within the sedimentation area compared to homogeneous mineral distribution). Also (former or recent) sedimentary overburden cannot be quoted for as explanation, with no indication for this influence found so far in the stratigraphie profiles investigated at the thick Triassic sedimentary rock sequence in the steep descent of the Southern Karwendel mountains as well as in more than 6400 m of sedimentary rock sequence investigated in the ultradeep exploration borehole Vorderriß 1. The effects described here are attributed to very low grade metamorphic (“anchimetamorphic”) influences detected by these investigations within the Northern Calcareous Alps. A much higher influence due to increase in temperature compared to increase of pressure is indicated by experimental work done by the author. Even with a cautious attempt to incorporate these newly found temperature effects on Triassic sedimentary rocks into the geologic development of the Northern Calcareous Alps and the Alpine Orogeny, at least for the older effect the conception of “transported” metamorphism is implied, perhaps also for the younger one. This idea is furthermore supported by K/Ar — age determinations of well ordered illite minerals gained from the Schwaz Triassic occurrence, yielding data of about 110–120 mio. y. This age for the older temperature effect can be explained in terms of (starting?) subduction of Penninic units below Austro-Alpine units, long before Austro-Alpine nappes reached their present position within the Northern Calcareous Alps.     

Thermal history of the evaporitic Haselgebirge mélange in the Northern Calcareous Alps (Austria)

In the central and eastern part of the Northern Calcareous Alps, Upper Permian evaporitic rocks form a tectonic mélange whose distribution is restricted largely to the topmost thrust unit (Juvavicum). Mudrock and dolostone samples associated with the evaporites in ten major outcrops (mostly mines) were examined in order to constrain the paleothermal conditions of the mélange. Measurements of illite "crystallinity" reveal a regionally variable pattern of metamorphic grade ranging from diagenesis to the high anchizone and possibly epizone. Most samples contained very little organic matter and vitrinite particles were rare. Samples containing vitrinite show consistent minimum reflectance values of ～1.3–1.7% R_o, whereas maximum reflectance values are more variable (up to 4.9%). The former data constrain the minimum burial temperatures to ～160–180°C. The observed variability in illite "crystallinity" and organic maturity both between and within individual outcrops is consistent with the mélange architecture of this unit and is in good agreement with the regional thermal pattern recognized in Middle to Upper Triassic carbonate formations within the Juvavicum by conodont color alteration studies. Mélange formation and heating of the evaporites is suggested to be linked to the Upper Jurassic closure of the Meliata-Hallstatt Ocean and subsequent thrusting of obducted terranes (Juvavicum) into the depositional realm of the Northern Calcareous Alps.     

Präorogene Versenkungstiefe und Orogenese als Diagenesefaktoren für altpaläozoische Kontinentalrandbildungen der Nördlichen Appalachen in Quebec,Kanada

This paper presents data and preliminary interpretations on the diagenesis of Early Paleozoic continental margin deposits along a traverse of the Quebec Appalachians near Quebec City, Canada. Regional variations in diagenesis were studied using the thermal maturation of organic matter in shales (reflectance measured on asphaltic bitumen, 105 samples) and illite crystallinity (330 samples). These revealed a regional southeastward increase in grade from the late middle and late stage of diagenesis to epimetamorphism, which is reflected in the distinction of four zones: Zone I representing the late middle diagenetic stage has a mean reflectance in oil (R₀) between 1.0 and 1.5% and illite crystallinity between 5.5 and 8.0 mm. Zone II (late diagenetic stage) is characterized by R₀=1.5–2.6% and illite crystallinity between 3.5 and 5.5 mm. Anomalously poor illite crystallinities in Zone II (i. e. 5.5 to 8.0 mm) were obtained for black shales, in which improvement of crystallinity lags behind red and green shales. Zone II is subdivided into subzones IIA and IIB. In the former, reflectance and illite crystallinity increase, within individual nappes, as a function of age or depth of burial. In the latter no such dependence is observed, instead diagenetic grade increases regionally in a southeastward direction as it does in zones III and IV. Zone III represents the anchizone in which observed reflectance values R₀ range from 2.6 to 4.0% and illite crystallinities from 2.0 to 3.1 mm. In Zone IV (epizone) illite crystallinity is less than 2.0 mm (In terms of reflectance the anchi-zone/epizone boundary was not defined). Zones I and IIA are anomalous in that lower tectonic units are diagenetically less altered than higher tectonic units: R₀ varies from 1.71 to 2.30% for the highest tectonic unit (Cambrian Chaudière Nappe), 1.53 to 1.90% (Cambro-Ordovician Bacchus Nappe) and 1.08 to 1.46% (Lower Ordovician Pointe-de-Lévy Nappe) for the middle tectonic units, and 1.01 to 1.15% for the lowest tectonic unit (Middle Ordovician Quebec Promotory Nappe). Thermal maturation and mineral diagenesis in zone IIA are probably due solely to sedimentary burial at the original site of deposition (by an estimated 6 to 7 km of younger sediments) because in this zone the highest diagenetic grade occurs in the highest tectonic unit. Diagenesis in the nappes of zone I probably required additional tectonic burial by the higher nappes because original sedimentary thicknesses that once overlay these Lower and Middle Ordovician rocks appear insufficient to have caused the observed degree of diagenesis. Diagenesis in zone IIA, therefore, was most likely formed entirely before orogenesis; in zone I it is probably partly pre-orogenic in origin and has been transported during nappe-movement. In contrast, diagenesis and metamorphism in zones IIB to IV are interpreted as related to regional synorogenic heating in conjunction with the Taconic orogeny. Thermal maturation levels in zone I indicate that the rocks have not yet passed the “oil window” which is of interest for petroleum exploration in Quebec. An extended English version of this paper is in preparation for the Bulletin of Canadian Petroleum Geology (Ogunyomi et al., ms.).     

川北阿坝地区三叠系粘土矿物特征及地质意义

分析了川北阿坝地区三叠系泥质岩的岩石矿物组合、粘土矿物类型、伊利石结晶度和镜质体反射率特征,并以此划分成岩演化阶段及变质程度。以成岩作用—极低级变质作用的研究方法,明确了阿坝地区成岩作用及极低级变质作用的上、下界限及区域分布规律:以唐克为中心的地区处于成岩作用晚期阶段,成岩作用温度200～212℃,伊利石结晶度IC≥0.42;周围地区处于极低级变质作用阶段,成岩作用温度212～222℃,伊利石结晶度IC<0.42。镜质体反射率(Ro)也具有同样的演化规律。对该地区域上成岩演化的差异及原因作如下解释:由于构造活动的远近程效应存在差异,该地区的周缘明显受到构造作用的影响,因叠加动力变质而达到极低级变质作用阶段;唐克位于阿坝地块中心,受构造作用的影响相对较小,因而处于成岩作用晚期阶段。     

划分成岩作用与埋藏变质作用的指标及其界线

本文是对“陕北鄂尔多斯盆地埋藏变质作用研究”一文的讨论,它综述并讨论了划分成岩作用和埋藏变质作用的指标,界线及其在鄂尔多斯盆地中的应用。伊利石结晶度、粘土矿物、浊沸石胶结物,石油形成,镜质体反射率,煤阶和地温等指标一致表明,鄂尔多斯盆地中生代地层处于中期成岩作用阶段,从而否定了本区为埋藏变质地区的结论。     

The change from rifting to thrusting in the Northern Calcareous Alps as recorded in Jurassic sediments

Facies analysis, fossil dating, and the study of the metamorphism in the Late Triassic to Early Cretaceous sedimentary successions in the central part of the Northern Calcareous Alps allow to reconstruct the tectonic evolution in the area between the South Penninic Ocean in the northwest and the Tethys Ocean with the Hallstatt Zone in the southeast. The Triassic as well as the Early and Middle Jurassic sediments were deposited in a rifted, transtensive continental margin setting. Around the Middle/Late Jurassic boundary two trenches in front of advancing nappes formed in sequence in the central part of the Northern Calcareous Alps. The southern trench (Late Callovian to Early Oxfordian) accumulated a thick succession of gravitatively redeposited sediments derived from the sedimentary sequences of the accreted Triassic–Liassic Hallstatt Zone deposited on the outer shelf and the margin of the Late Triassic carbonate platform. During a previous stage these sediments derived from sequences deposited on the more distal shelf (Salzberg facies zone of Hallstatt unit, Meliaticum), and in a later stage from more proximal parts (Zlambach facies zone of Hallstatt unit, Late Triassic reef belt). Low temperature–high pressure metamorphism of some Hallstatt limestones before redeposition is explained by the closure of parts of the Tethys Ocean in Middle to Late Jurassic times and associated subduction. In the northern trench (Late Oxfordian to Kimmeridgian) several hundred meters of sediment accumulated including redeposited material from a nearby topographic rise. This rise is interpreted as an advancing nappe front as a result of the subduction process. The sedimentary sealing by Tithonian sediments, documented by uniform deep-water sedimentation (Oberalm Formation), gives an upper time constraint for the tectonic events. In contrast to current models, which propose an extensional regime for the central and eastern Northern Calcareous Alps in the Late Jurassic, we propose a geodynamic model with a compressional regime related to the Kimmerian orogeny.     

Late Cretaceous to Early Tertiary palaeogeography of the Western Carpathians (Slovakia) and the Eastern Alps (Austria): implications from heavy mineral data

The Late Cretaceous Brezová and Myjava Groups of the Western Carpathians in Slovakia and formations of the Gosau Group of the Northern Calcareous Alps in Lower Austria comprise similar successions of alluvial/shallow marine deposits overlain by deep water hemipelagic sediments and turbidites. In both areas the heavy mineral spectra of Late Cretaceous sediments contain significant amounts of detrital chrome spinel. In the Early Tertiary the amount of garnet increases. Cluster analysis and correspondence analysis of Coniacian/Santonian and Campanian/Early Maastrichtian heavy mineral data indicate strong similarities between the Gosau deposits of the Lunz Nappe of the north-eastern part of the Northern Calcareous Alps and the Brezova Group of the Western Carpathians. Similar source areas and a similar palaeogeographical position at the northern active margin of the Adriatic/Austroalpine plate are therefore suggested for the two tectonic units.Basin subsidence mechanisms within the Late Cretaceous of the Northern Calcareous Alps are correlated with the Western Carpathians. Subsidence during the Campanian-Maastrichtian is interpreted as a consequence of subduction tectonic erosion along the active northern margin of the Adriatic/Austroalpine plate. Analogous facies and heavy mineral associations from deep water sandstones of the Manin Unit and the Klape Unit indicate accretion of parts of the Pieniny Klippen Belt during the Late Cretaceous along the Adriatic/Austroalpine margin.     

Chlorite crystallinity: an empirical approach and correlation with illite crystallinity, coal rank and mineral facies as exemplified by Palaeozoic and Mesozoic rocks of northeast Hungary

Abstract Fairly strong (r= 0.75–0.85) positive linear correlations were found between crystallinity indices (peak widths) measured on the first two basal reflections of chlorite and those of illite–muscovite in <2-μm fractions of a representative shale–slate–phyllite series from Palaeozoic and Mesozoic formations of northeast Hungary. The metamorphic grade ranges from late or deep diagenesis through anchizone to epizone conditions. Chlorite crystallinity values measured on air-dried and ethylene-glycol-solvated samples suggest that the effects of expandable interlayers are negligable, especially in the higher grade (～temperature) part of the series. However, the greater scattering of crystallinity values for the chlorite 001 reflection compared to those of the 002 reflection may be related to the effects of minor amounts of interlayered and/or discrete smectite and/or vermiculite. With increasing metamorphic grade and advancing equilibrium recrystallization, the chlorite compositions in different samples become more homogenous. No correlation exists between crystallinity and changes in chlorite composition as estimated from the intensity ratios of basal reflections. Hence an increase of domain size and a decrease of lattice distortion with increasing grade (～temperature) may be decisive factors affecting chlorite crystallinity. Chlorite crystallinity can be applied as a reliable regional, statistical technique complementary with, or instead of, the illite crystallinity method. The illite and chlorite crystallinity scales used here are related to Kübler's epi-, anchi- and diagenetic zones and correlated with coal rank, conodont colour alteration and mineral facies data. As the effects of the detrital white mica can be observed even in the <2-μm fractions of anchizonal metapelites, the anchizone boundaries determined solely on the base of ‘fixed’illite crystallinity values may vary with amounts of detrital and newly formed muscovite–illite. Hence a complex approach utilizing more than one method for determination of grade is preferred for petrogenetic purposes, even if relationships between crystallinity scales, coal rank and mineral facies also vary strongly in different tectonic settings and lithologies.     

Late Cretaceous extension overprinting a steep belt in the Northern Calcareous Alps (Schesaplana, R?tikon, Switzerland and Austria)

The Triassic to Cretaceous sediment succession of the Lechtal Nappe in the western part of the Northern Calcareous Alps (NCA) has been deformed into large-scale folds and crosscut by thrust and extensional faults during Late Cretaceous (Eoalpine) and Tertiary orogenic processes. The following sequence of deformation is developed from overprinting relations in the field: (D1) NW-vergent folds related to thrusting; (D2) N–S shortening leading to east–west-trending folds and to the formation of a steep belt (Arlberg Steep Zone) along the southern border of the NCA; (D3) E–W to NE–SW extension and vertical shortening, leading to low-angle normal faulting and recumbent “collapse folds” like the Wildberg Syncline. D1 and D2 are Cretaceous in age and predate the Eocene emplacement of the Austroalpine on the Penninic Nappes along the Austroalpine basal thrust; the same is probably true for D3. Finally, the basal thrust was deformed by folds related to out-of-sequence thrusting. These results suggest that the NCA were at least partly in a state of extension during the sedimentation of the Gosau Group in the Late Cretaceous.     

Berriasian drowning of the Plassen carbonate platform at the type-locality and its bearing on the early Eoalpine orogenic dynamics in the Northern Calcareous Alps (Austria)

The Plassen carbonate platform (Kimmeridgian to Early Berriasian) developed above the Callovian to Tithonian carbonate clastic radiolaritic flysch basins of the Northern Calcareous Alps during a tectonically active period in a convergent regime. Remnants of the drowning sequence of the Plassen Formation have been discovered at Mount Plassen in the Austrian Salzkammergut. It is represented by calpionellid-radiolaria wacke- to packstones that, due to the occurrence of Calpionellopsis oblonga (Cadisch), are of Late Berriasian age (oblonga Subzone). Thus, the Plassen Formation at its type-locality shows the most complete profile presently known, documenting the carbonate platform evolution from the initial shallowing upward evolution in the Kimmeridgian until the final Berriasian drowning. The shift from neritic to pelagic sedimentation took place during Berriasian times. A siliciclastic-influenced drowning sequence sealed the highly differentiated Plassen carbonate platform. The former interpretation of a Late Jurassic carbonate platform formed under conditions of tectonic quiescence cannot be confirmed. The onset, evolution and drowning of the Plassen carbonate platform took place at an active continental margin. The tectonic evolution of the Northern Calcareous Alps during the Kimmeridgian to Berriasian time span and the reasons for the final drowning of the Plassen carbonate platform are to be seen in connection with further tectonic shortening after the closure of the Tethys Ocean.     

Escape models of the Alpine-Carpathian-Pannonian region in the light of palaeomagnetic observations

Recent tectonic models of the Alpine-Carpatho-Pannonian region (ALCAPA) assume a large eastward shift of the Transdanubian Range domain, in the Cenozoic. Since palaeomagnetism is one of the most powerful tools in solving geodynamic processes, the authors present an approach to the escape problem by using all available and relevant palaeomagnetic data. This data set demonstrates consistency with models put forward by geologists for Jurassic and older ages. From the mid-Jurassic on the Northern Calcareous Alps (NCA) did not share the rotations of the Transdanubian Range domain and of the Southern Alps. After individual movements from Neocomian to Miocene, the Transdanubian Range domain must have drifted northward in the mid-Miocene up to the Southern margin of the Northern Calcareous Alps, before starting the escape in the geologists' definition.     

内蒙古东北地区上古生界伊利石研究

内蒙古东北地区上古生界主要是一套泥质岩石,其详细深入的矿物学工作尚不多见.本文利用JSM-6700F场发射电镜及INCA能谱仪,探讨了伊利石在成岩.极低级变质作用过程中的行为.采用D/max-2500 X-射线衍射仪,研究了伊利石的结晶度、多型和b0值.伊利石结晶度变化于0.28～0.77,除去构造应力对伊利石结晶度指数值的影响,研究区伊利石结晶度指数应>0.34,反映晚古生代地层主体属于晚期成岩带和低级近变质带.伊利石(白云母)多型分三种类型,分别是1Md型、1Md+2M1混合型和2M1型,是晚期成岩带和低级近变质带的产物.伊利石(白云母)b0值变化于8.9892 ～9.0404 之间,b0平均值9.0196 ,属中压相.     

Late Jurassic tectonics and sedimentation: breccias in the Unken syncline,central Northern Calcareous Alps

This study analyses and discusses well preserved examples of Late Jurassic structures in the Northern Calcareous Alps, located at the Loferer Alm, about 35 km southwest of Salzburg. A detailed sedimentary and structural study of the area was carried out for a better understanding of the local Late Jurassic evolution. The Grubhörndl and Schwarzenbergklamm breccias are chaotic, coarse-grained and locally sourced breccias with mountain-sized and hotel-sized clasts, respectively. Both breccias belong to one single body of breccias, the Grubhörndl breccia representing its more proximal and the Schwarzenbergklamm breccia its more distal part, respectively. Breccia deposition occurred during the time of deposition of the Ruhpolding Radiolarite since the Schwarzenbergklamm breccia is underlain and overlain by these radiolarites. Formation of the breccias was related to a major, presumably north-south trending normal fault scarp. It was accompanied and post-dated by west-directed gravitational sliding of the Upper Triassic limestone (“Oberrhätkalk”), which was extended by about 6% on top of a glide plane in underlying marls. The breccia and slide-related structures are sealed and blanketed by Upper Jurassic and Lower Cretaceous sediments. The normal fault scarp, along which the breccia formed, was probably part of a pull-apart basin associated with strike slip movements. On a regional scale, however, we consider this Late Jurassic strike-slip activity in the western part of the Northern Calcareous Alps to be synchronous with gravitational emplacement of “exotic” slides and breccias (Hallstatt mélange), triggered by Late Jurassic shortening in the eastern part of the Northern Calcareous Alps. Hence, two competing processes affected one and the same continental margin.     

Palynomorphe und organisches Material aus den Raibler Schichten einer oberostalpinen Schuppe der Iberger Klippen (Kanton Schwyz, Schweiz)

A palynology and organic matter study has been carried out on samples of the Upper Triassic Raibl beds from an Upper Austroalpine thrust sheet, preserved in the area of the Iberg Klippen (Laucherenst?ckli). The palynological assemblages indicate an early Carnian (Julian) age. Comparison with well calibrated successions from the Southern Alps suggests a correlation with the Late Julian ammonoid zone Austrotrachyceras austriacum. The lithofacies of the studied sections suggests a substantial similarity to Raibl beds of the Upper Austroalpine of the Northern Calcareous Alps and those of the Silvretta- and the S-charl nappe of the Grisons. The minute Upper Austroalpine thrust sheet represents the westward extension of series with similar facies, which are still preserved in the Northern Calcareous Alps of Liechtenstein and western Austria (Vorarlberg). According to the Thermal Alteration Scale (TAS) of Batten (1996) the observed medium brown colors of the pollen grains correspond to a value of 4/5, which is equivalent to vitrinite reflectance (VR) values of 0.7–0.9 %R_o. In comparison with other sites in Liechtenstein, Vorarlberg and the Upper Austroalpine of Central Grisons (Silvretta and S-charl nappe) with measured VR values of > 2%R_o the organic matter of the studied samples shows only minor thermal alteration, indicating that the Upper Austroalpine thrust sheets of Iberg represent the highest part of the nappe stack in Central Switzerland, formerly covered by a comparatively thin overburden.      

Growing folds and sedimentation of the Gosau Group, Muttekopf, Northern Calcareous Alps, Austria

Analysis of the three-dimensional geometry of Upper Cretaceous clastics in the Muttekopf area (Northern Calcareous Alps, Austria) indicate fold and fault structures active during deposition. Coniacian continental to neritic sedimentation (Lower Gosau Subgroup) was contemporaneous with displacements on NW-trending faults and minor folding along NE-trending axes. From the Santonian onwards (sedimentation of the deep-marine Upper Gosau Subgroup) the NW-trending faults were sealed and large folds with WSW-trending axes developed. The direction of contraction changed to N-S after the end of Gosau deposition in the Danian (Paleocene). Synorogenic sedimentation patterns indicate continuous contraction from the Coniacian to the Late Maastrichtian/?Danian. Therefore, large-scale extension as observed in the central part of the Eastern Alps cannot be documented in the western parts of the Northern Calcareous Alps. A combination of subduction tectonic erosion for the frontal parts and gravitational adjustment of an unstable orogen after nappe stacking for the internal parts possibly accounts for the different development of Gosau basins in the frontal and trailing regions of the Austroalpine wedge.     

Kaeveria fluegeli (Zaninetti, Altiner, Dager et Ducret, 1982) (Foraminifera) from Upper Triassic of the South-East Pamirs

Foraminifers representing species Kaeveria fluegeli have been found in the Zorkaradjilga Formation (Sagenites quinquepunctatus Zone) of the upper Norian (or lower Rhaetian) in the central structural-facies zone of the South-East Pamirs. Their occurrence here is an additional criterion substantiating age and correlation of host deposits and an evidence in favor of fauna migration from the southern Tethys during the respective time span not only in northwestern areas of that ocean (Northern Calcareous Alps), but also in its central part (the South-East Pamirs).     

SUR LA CRISTALLINITÉ DE L'ILLITE DANS LA DIAGENÈSE ET L'ANCHIMÉTAMORPHISME

On the crystallinity of illite in diagenesis and anchimetamorphism A simple method to estimate the degree of “crystallinity” of illite has been used for several years in three French laboratories. Many results, which are unpublished, were obtained; three examples are presented in this paper. They show the sensibility of the method, which allows one to appreciate, above all other methods, burial diagenesis, the front of metamorphism, or some regional areas of very weak metamorphism.     

内蒙古林西地区晚二叠世林西组碎屑岩成岩作用及其对储层物性的影响

通过薄片鉴定、扫描电镜以及岩石物性分析等方法,对内蒙古林西地区晚二叠世林西组碎屑岩成岩作用及其对储层物性的影响进行了系统研究,结果表明该地区林西组地层碎屑岩成岩作用主要为压实作用、胶结作用、交代作用及溶蚀作用。砂岩胶结物主要为黏土矿物、硅质矿物及碳酸盐矿物3种,其中黏土胶结物出现最多,以伊利石为主,绿泥石次之;碳酸盐胶结物以方解石为主;硅质胶结主要表现为石英次生加大和自生微晶石英。有机质镜质体反射率(Ro)、泥岩伊利石/蒙皂石(I/S)中的S(%)含量、石英次生加大级别、颗粒接触类型、伊利石结晶度等多项数据指标显示林西地区林西组碎屑岩处于晚成岩阶段。储层物性与成岩作用密切相关,压实作用、胶结作用使储层孔隙度和渗透率降低;溶蚀作用使储层孔隙度提高。     

Deformation and metamorphism in the Fenes Nappe (southern Apuseni Mountains,Romania)Déformation et métamorphisme dans la nappe de Fenes (monts Apuseni méridionaux,Roumanie)

The Fenes Nappe belongs to the stack of tectonic units cropping out in the southern Apuseni Mts (Romania). It is characterised by a structural history consisting of two folding phases that developed during the time spanning from Early Aptian to Late Maastrichtian. The D1 phase produced west-northwest-verging, isoclinal to very tight folds, associated to a slaty cleavage. The main metamorphic imprint of the Fenes Nappe is linked to this deformation phase; illite and chlorite ‘crystallinity’ values indicate metamorphic conditions of the late diagenesis, close to the diagenetic zone/anchizone boundary. The subsequent D2 phase produced north-northwest-verging, parallel folds, not associated with synkinematic recrystallisation. These phases are interpreted as developed during a structural path, which includes burial at a depth of 8–10 km, followed by exhumation at shallower structural levels. To cite this article: A. Ellero et al., C. R. Geoscience 334 (2002) 347–354.     

Paleomagnetic evidence for large en-bloc rotations in the Eastern Alps during Neogene orogeny

We present new paleomagnetic data from the Northern Calcareous Alps and the Central Alps of Austria. All new data are overprint magnetizations and can be subdivided into two groups: In rocks older than earliest Rupelian, two remagnetizations reflecting both clockwise and counter-clockwise rotation were detected. In rocks of late Rupelian and younger ages, only a counter-clockwise rotated remagnetization was found. Our results together with results from previous paleomagnetic studies from the Eastern and Southern Alps suggest two main phases of vertical axis rotation. The first, clockwise rotation affecting the Northern Calcareous Alps was active between earliest to Late Rupelian. We propose a model where the Northern Calcareous Alps are segmented into individual blocks. Within a dextral shear corridor these blocks rotated clockwise due to the counter-clockwise rotation of the Southern Alps and Central Alps. The second, counter-clockwise rotation occurred in the Late Oligocene to Middle Miocene, affecting Eastern and Southern Alps. In this stage of orogeny, the internal massifs of the Western Alps were already accreted to the upper plate and therefore included in counter-clockwise rotation. This rotation is contemporaneous with counter-clockwise rotation in the Apennines and opening of the Balearic basin, and a genetic relationship is suggested. A second step of counter-clockwise rotation, reconstructed from published data, is observed in the sedimentary basins at the southeastern margin of the Eastern Alps, where counter-clockwise rotated Miocene and Pliocene sedimentary rocks are present. This rotation is seen in connection to a young counter-clockwise rotation of the Adriatic plate.