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Isoline map of the AMS ellipsoid's shape factor T for the entire FIC. Light grey shades indicate prolate and dark grey shades oblate AMS ellipsoids, respectively. Oblate ellipsoids are concentrated along the SE' shear zone and along the SW' and E' rim of the pluton, while prolate ellipsoids dominate the Eberhardsreuth granite. The mainly oblate AMS fabric in the Saldenburg granite indicates flattening strains during the intrusion of the main magma pulse. For sampling sites, see Fig. 5.
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![Fig. 11: Simplified geological map (redrawn from [23]) of the FIC...](profile/Helga-De-Wall/publication/236233552/figure/fig5/AS:393599079469060@1470852741356/Simplified-geological-map-redrawn-from-23-of-the-FIC-showing-a-the-orientation-of_Q320.jpg)
Models consisting of a thick overburden resting on a buoyant layer were sheared and centrifruged in order to study the relationship between strike-slip shear zones and intrusions of buoyant material. Three experiments were carried out: In model 1, where the overburden consisted of a viscous material, no diapirs formed even after shearing for 40 mm...
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... FIC's grani- toid with the lowest values of bulk suscep- tibility ranging from 3*10 -5 to 1.5*10 -4 SI (southern part of the FIC in Fig. 7) clearly within the realm of paramagnetism. The MS carriers are biotite and muscovite (Tab. 3). The shape of the AMS ellipsoids varies from prolate (T = -0.34) to oblate ( = 0.59; southern part of the FIC in Fig. 9) with a degree of anisotropy quite high for magmatic fabrics in paramagnetic granites (southern part of the FIC in Fig. 8): 7 of the 9 samples exhibit P' values ≥ 1.05, 4 even P' values > 1.10 (Tab. 2). The lowest eccentricity measured is 3%. The magnetic lineation plunges in average gently towards the ESE and the magnetic foliation ...
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... SI (eastern rim of the FIC in Fig. 7) indicating the contribution of paramagnatic biotite and ferrimagnetic magnetite (± pyrrothite as proven by thermo- magnetic measurements) to the MS (Tab. 3). In 4 of the 6 samples oblate AMS ellipsoid were determined, 1 is triaxial and 1 prolate (Tab. 2): T ranges from -0.29 to 0.48 (eastern rim of the FIC in Fig. 9). P' scatters from 1.02 to 1.16 (eastern rim of the FIC in Fig. 8). The magnetic lineation plunges in average gently to the SE and the magnetic foliation dips generally steeply to the ESE (Figs. 10 and 11). Isoline map of the degree of anisotropy (P') of the AMS ellipsoid for the entire FIC. Light shades stand for low eccentricity, ...
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... -4 to 1.3*10 -4 SI (northern rim of the FIC in Fig. 7). Biotite and probably ilmenite are responsible for the paramagnetic MS (Tab. 3). The AMS ellipsoids of the 3 investigated samples are moderately prolate (T = -0.45) to weakly oblate (T = 0.19). The average AMS ellipsoid can, therefore, be regarded as triaxial (northern rim of the FIC in Fig. 9). The ellipsoides' anisotropy is low and is around 2 % (northern rim of the FIC in Fig. 8). The magnetic lineation lies almost horizontally, plunging slightly to the E or W. Consequently, the magnetic foliation strikes E-W and dips steeply to the N or S (Figs. 10 and ...
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... (center of the FIC in Fig. 7) and the intrusion is paramagnetic with biotite, muscovite and ilmenite as MS carriers. One sample yielded a κ of 5*10 -4 SI (Tab. 2) and a minor contribution of magnetite could be inferred from tempe- rature dependent MS measurements (Tab. 3). AMS ellipsoids in the center of the Saldenburg granite are of oblate shape (Fig. 9). 11 of the 23 samples are prolate; T varies from -0.5 to 0.85 (Tab. 2). The anisotropy factor P' ranges from 1.01 to 1.09 corresponding to ellipticities < 10 % (center of the FIC in Fig. 8). The average magnetic lineation plunges gently to the NE parallel to the long axes of the K-feldspar megacrysts [23]. The average magnetic ...
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... dynamic recrystallisation of quartz and a subsolidus foliation parallel to the BPSZ (Fig. 6 b). This conclusion is in good agreement with observations of Hrouda [28] who interpreted AMS ellipsoids of granites with a P' > 1.10 as the result of subsolidus deformation. The prevailing oblate shape of the AMS ellipsoids from the two-mica granite ( Fig. 9) suggests the presence of a strong flattening component during formation of the subsolidus ...
Citations
... Diorites to granodiorites have been emplaced along deep reaching lineaments in the continental crust, e.g. the palites (granodiorites with mafic enclaves) along the Bavarian Shear Zone (332 Ma, Siebel et al. 2005). In contrast, diorites of the Fürstenstein Massif (334-332 Ma, Chen and Siebel 2004) are considered to be emplaced in tension gashes as an early magmatic phase (Dietl et al. 2006). Regional high-temperature metamorphism associated with migmatization of Moldanubian rock in the Bavarian Forest is constrained between 326 and 322 Ma (Kalt et al. 2000;Siebel et al. 2012). ...
... The 753 ± 9 Ma age of the Mirpur Granite pre- sented in this study further substantiates such interpretation. Analogue models have shown that buoyant melts cannot pierce through the overburdened rigid upper crust but preexisting frac- tures can facilitate their uprise (Roman-Berdiel, 1999;Dietl et al., 2006). Extensional faults are the suitable pathways for ascending plutons since they can provide the space for pluton emplacement and weaken the overburden units (e.g. ...
The Neoproterozoic Malani Igneous Suite (MIS) in NW India, along with analogous magmatic rocks from the adjoining Nagarparkar region in SE Pakistan can be collectively classified as a Silicic-dominated Large Igneous Province (SLIP). This magmatic event includes bimodal (predominantly felsic) volcanism, granite emplacement and felsic and mafic dyke intrusions. Felsic rocks have typical A-type affinity as indicated by high abundance of silica, alkali, high field strength and large ion lithophile element concentrations and low CaO and MgO contents. Their Nb negative anomalies and Zr-saturation parameters indicate significant crustal input and high temperature melting. Mafic volcanics and dykes show geochemical homogeneity and derivation from a depleted continental mantle source without any significant crustal contamination (low U and Th contents and no visible Nb anomaly). The region extending from the Mount Abu batholith in the east to Jaswantpura in the west (2700 km²), representing a transition from the metamorphic Sirohi terrane to the undeformed MIS, was evaluated through an integrated structural (including satellite image analysis), geochemical and geochronological study. During the initial stage (prior to 760 Ma) the granitic basement (Erinpura granites) and overlying Sirohi metasediments behaved in a brittle manner that led to development of linear fractures and NNE trending rift structures, and bimodal volcanic activity. Emplacement of voluminous granitic bodies in response to progressive extension of the crust is inferred during the more evolved second stage (younger than 760 Ma). Mirpur Granite, a representative of this younger granitic suite (Jalor type pink granite) has yielded 753 ± 9 Ma zircon, U-Pb, crystallization age. Granitic plutons mark regions of crustal extension, as seen in parallel alignment of plutonic bodies (Jaswantpura granitic belt) and parallel mafic dyke swarms (340°) transecting the granites. Structural analysis further identified an episode of crustal convergence which is documented in folding and faulting of the Sindreth Basin sequence and in tectonic overprint of early stage mafic rocks. Rifting and bimodal magmatic activity in MIS is coeval with similar rock types in Nagarparkar in SE Pakistan, further traceable into the Seychelles microplate and Central Madagascar. Considering the Neoproterozoic paleogeography and our observations, an extensional setting and an active continental margin position for MIS is inferred.
... Our new models also complement previous studies by offering insights into the patterns of lithospheric thinning, in addition to the brittle deformation in the upper crust. Although a few previous studies investigated specific aspects of strike-slip deformation in the centrifuge (e.g., pluton emplacement in shear zones, Dietl et al., 2006; reactivation of pre-existing structures, Koyi et al., 2008), to our knowledge this is the first application of centrifuge modelling to a systematic analysis of pull-apart basins. ...
Abstract We present here the results of the first lithospheric-scale centrifuge models of pull-apart basins. The experiments simulate relative displacement of two lithospheric blocks along two offset master faults, with the presence of a weak zone in the offset area localising deformation during strike–slip displacement. Reproducing the entire lithosphere–asthenosphere system provides boundary conditions that are more realistic than the horizontal detachment in traditional 1 g experiments and thus provide a better approximation of the dynamic evolution of natural pull-apart basins. Model results show that local extension in the pull-apart basins is accommodated through development of oblique–slip faulting at the basin margins and cross-basin faults obliquely cutting the rift depression. As observed in previous modelling studies, our centrifuge experiments suggest that the angle of offset between the master fault segments is one of the most important parameters controlling the architecture of pull-apart basins: the basins are lozenge shaped in the case of underlapping master faults, lazy-Z shaped in case of neutral offset and rhomboidal shaped for overlapping master faults. Model cross sections show significant along-strike variations in basin morphology, with transition from narrow V- and U-shaped grabens to a more symmetric, boxlike geometry passing from the basin terminations to the basin centre; a flip in the dominance of the sidewall faults from one end of the basin to the other is observed in all models. These geometries are also typical of 1 g models and characterise several pull-apart basins worldwide. Our models show that the complex faulting in the upper brittle layer corresponds at depth to strong thinning of the ductile layer in the weak zone; a rise of the base of the lithosphere occurs beneath the basin, and maximum lithospheric thinning roughly corresponds to the areas of maximum surface subsidence (i.e., the basin depocentre).
... During cooling, this crystal framework within the intrusion leads to coupling with their surrounding host rocks, and further fabric evolution in the intrusion is in response to tectonic stresses acting in the host rocks (e.g. D' Lemos et al., 1992;Barros et al., 2001;Dietl et al., 2006). As a consequence, the deformation seen at the microscopic scale (Fig. 6a-c) indicates that the plutons show an imprint of a regional stress field. ...
... There is now a wealth of literature which documents the successful application of AMS for establishing emplacement mechanisms and the relationships of granitoid intrusion to tectonic settings (e.g. Bouchez et al., 1999;Mamtani and Greiling, 2005;Dietl et al., 2006;Mamtani et al., 2012). The significance and nature of granitoid fabrics (e.g. ...
Field investigations, microstructural observations, and magnetic fabric analyses revealed a polyphase, late Pan-African deformational evolution in the Um Sheqila-Um Had (595 Ma) composite pluton and in the Hammamat and Atalla areas of the Central Eastern Desert of Egypt in Ediacaran times. Major stages are early shortening (NNW-SSE), subsequent strike-slip (NW-SE shear zones), and late shortening (NW-SE). Strain studies on pebbles and xenoliths together with AMS data show a predominance of shallow, NW-SE trending X axes or magnetic lineations, associated with steep, NW-SE striking magnetic foliations. Magnetic fabrics and microstructures indicate a tectonic fabric in the Um Sheqila-Um Had granitoid plutons, which is dominated by steep NW-SE striking foliations and shallow NW-SE trending lineations, similar to those in the high-angle Atalla Shear Zone. There is a change of lineation directions from ESE-WNW at Um Sheqila (oldest) to NW-SE to Um Had II (youngest). This pattern may indicate an influence of strike-slip and is also consistent with NE-SW compression. This holds also true for the asymmetry of the contact aureole, which is extended towards NW, parallel with the trend of the magnetic lineation. The character and orientation of the deformation pattern in the Um Sheqila-Um Had plutons and the Atalla Shear Zone is thus similar to the pattern of the late shortening phase. The intrusion of the Um Sheqila-Um Had granitoid rocks, therefore, took place before the late shortening stage, but postdates early deformation, which, according to published data, was associated with lithospheric thinning in the Central Eastern Desert. Therefore, these Pan-African plutons do not represent the earliest post-deformational intrusions but a late stage of syn-deformational magmatic activity. At a regional scale, this deformation with steep foliations and shallow lineations may also be related with lateral escape tectonics. The pluton emplacement, the importance of transcurrent shear zones, and the low lithospheric thickness in the area are not consistent with tectonic elements at the Pan-African orogenic margin but imply a more internal position for the Wadi Hammamat area.
... The Fürstenstein Intrusive Complex (FIC) is a composite granitoid pluton in the Moldanubian basement of the Bohemian Massif (Fig. 1). It covers an area of roughly 140 km 2 and consists of four magma pulses of dioritic, granodioritic and granitic composition with distinct intrusion ages (Chen and Siebel, 2004) and distinct fabrics (Dietl et al., 2006). ...
... The oldest intrusive phase is represented by xenoliths and stoped blocks of dark, medium-grained, biotite ± hornblende ± sphene bearing diorites, which form an E-W trending girdle within the center of the FIC (Fig. 2). Also the magmatic foliation within the diorite blocks follows an E-W trend (Dietl et al., 2006). Chen and Siebel (2004) reported U/Pb and 207 Pb/ 206 Pb zircon ages of ca. ...
... A fine to medium-grained, yet undated two-mica granite occupies a NW-SE-trending shear zone at the south-eastern rim of the FIC. From cross-cutting relationships with the diorites and the so-called Tittling and Saldenburg granites (to the north) we infer that this granite is the second intrusion phase (Dietl et al., 2006). It has a steep, NW-SE-trending magmatic to solid-state foliation (Fig. 2). ...
Tube-like schlieren structures occur at the boundary between two units of the Fürstenstein Intrusive Complex, the Tittling and the Saldenburg granites. We have analysed the magnetic fabrics, petrographic variation and geochemistry of key examples of these structures in order to test the hypothesis that they originated as granitic microdiapirs. The rims of the schlieren structures have high magnetic susceptibility compared to their interiors and surrounding granite due to the enrichment of biotite±opaques. The low anisotropy that characterizes the AMS fabric is probably caused by magmatic flow. Hypersolidus microfabrics support this interpretation. Magnetic fabric orientation within the schlieren structures differs significantly from the NE–SW-trending magnetic foliation generally observed within the hosting Tittling granite. A steeply plunging magnetic lineation and a NNE–SSW girdle distribution of the magnetic foliation poles within the schlieren structures are consistent with the conical geometry of the schlieren structures evolved during the rise of the magma. Based on geochemistry, granite in the schlieren structures is interpreted to be differentiated melt expelled from the Tittling granite mush that formed after early crystallization of plagioclase. We suggest that the schlieren structures are pockets of residual melt of the Tittling granite that were mobilized buoyantly due to a thermal input from the neighbouring Saldenburg granite. The mafic rims of the schlieren structures formed as a result of early crystallization and subsequent accumulation due of the Bagnold effect. The results of the magnetic and geochemical investigations allow us to interpret the schlieren structures as diapiric in nature and consequently as “within-chamber diapirs” (sensu Weinberg et al., 2001).
... Many of these granitoid bodies consist of several magma batches. Good examples come from the Fürstenstein Intrusive Complex (Fig. 1) whose MS distribution has been documented by DIETL et al. (2006) and from the Hauzenberg granite, the aim of the present study. Due to extensive quarrying, numerous fresh outcrops are available in the Hauzen-berg granite body, but they only provide a discontinuous sampling. ...
In the Hauzenberger pluton of East Bavaria two granites, (Hauz I and II) and a granodiorite are distinguished. Their magnetic susceptibility, measured in the field using a portable susceptometer, is low, but clear differences appear between the granodiorite (84 × 10−6 SI) and both granite types (52 × 10−6 SI). These differences are related to the variable content in biotite and muscovite. Based on systematic magnetic susceptibility measurement at 372 sites, a susceptibility contour map of the Hauzenberg pluton was drawn. There is a good agreement between the spatial distribution of the different lithotypes of the pluton and the areas of iso-susceptibility values. Susceptibility measurements on rock-floats can be considered as reliable in the frame of the contoured susceptibility map, thus allowing the implementation of float data sets into the magnetic susceptibility mapping routine.
Im Intrusivkomplex von Fürstenstein treffen wir auf eine besonders große Vielfalt magmatischer Gesteine. Sie begegnen sich in enger Nachbarschaft, mitunter sind sie vor allen an den Rändern auch miteinander vermischt. Ihre Umgebung wird durchweg von Migmatiten mit fortgeschrittener Anatexis bestimmt. Offenbar sind die Magmen nicht in die kühle obere Kruste aufgestiegen, sondern in größerer Tiefe, noch nahe an ihrem Bildungsbereich, kristallisiert.
The magmatic history of batholiths formed as the result of tectonic accretion mirrors the evolution of the underlying crust from island arcs to accretion and collapse. Chemical composition, age and structure give information about the magma source and emplacement depths. The target of this study is the Central Finland batholith (CFGC) that provides a magmatic record after terrane accretion during the Svecofennian orogeny followed by orogenic collapse. The crustal source of partial melting has changed during the crustal evolution and differentiation after the terrane accretion, and when the stress regime has changed from contraction to extension.
We carried out a centrifuge experiment to model the diapiric rise of a stratified PDMS layer from three perturbations through a non-Newtonian, ductile overburden. The experiment carried out at 700 g resulted in three composite diapirs fed by different PDMS layers. The three resulting diapirs represent two different stages of diapirism. One of the diapirs (diapir 1), which reached its level of neutral buoyancy and extruded at the surface of the model, was tabular in profile and copied by an internal intrusive body. The other two diapirs (diapirs 2 and 3) were still in the ascending stage when centrifuging was stopped and thus did not extrude at the surface. They displayed a typical balloon-on-string geometry, which develops at a high viscosity contrast between a highly viscous overburden and a less viscous buoyant material. The internal geometry of these last two diapirs, fed by the lower impure PDMS, however, did not copy the shape of their precursors. Instead, they had a finger-like shape. The finger geometry of the internal part of the diapirs might be the result of the higher viscosity of the impure lower PDMS intruding a less viscous clean PDMS. Compared to nature, diapir 1 represents a fully developed concentrically expanded pluton or nested diapir, while diapirs 2 and 3 resemble composite plutons which host magma batches of dyke-like geometry. Based on the results of our experiment we suggest that truly concentrically expanded plutons develop from the latter.
