Clay mineral formation and fluid-rock interaction in fractured crystalline rocks of the Rhine rift system : case studies from the Soultz-sous-Forêts granite (France) and the Schauenburg Fault (Germany)

The following study deals with the fluid-alteration history of fractured and faulted crystalline granitic basement in the Rhine rift system, based on the analytical investigation of clay mineral assemblages. It evaluates the argillite mineralizations along faults and fracture zones at key tectonic positions in relation to the upper Rhine graben rift structure and assesses the timing and episodic nature of clay mineral formation that occurred within both the buried basement rocks and similar exhumed units exposed in the uplifted rift shoulders. The rock alteration history is established largely on the basis of combined X-ray diffraction, X-ray textural goniometry, electron microscopy (SEM, HRTEM) and isotopic (K-Ar) techniques. One chapter presents results from the granitic basement rocks of the 2230m deep EPS-1 drilling site at Soultz-sous-Forêts, situated in the western part of the Upper Rhine graben basin (France). Pure illite without any sign of mixed-layerings could be distinguished in the different hydrothermal altered and fractured granite and argillite veins. The morphology of these illites varies clearly in the different rock types, with pseudo-hexagonal, platy 2M1 illite polytypes dominating the veins and thin and fibrous to lath shaped 1M trans-vacant illite polytypes common in pores of the granite matrix. The separated grain size fractions (> 63µm, 10-63µm, 4-10µm, 2-4µm, 1-2µm, 0.4-1µm, 0.2-0.4µm, < 0.2µm) indicate mixtures of both illite shapes and polytypes to characterize all samples, which based on K-Ar isotope results, occurred during three main crystallization episodes spanning over 200 Ma in time. The oldest illite crystallization recognized is of Permian age, which is most evident in the argillite veins (2176m) and samples of hydrothermally altered granite (e.g. 1570m). In contrast, a mixture of Jurassic and Cretaceous (or younger) illite was recorded in fractured rocks at 2167m, but Tertiary K-Ar values were not encounted in the limited amount of sample studied here. Younger Tertiary ages have, however, been reported in other studies. The multiple episodes of local illite crystallizations are suggested to reflect the range of fluid events documented from quartz fluid inclusions. The Permian vein mineralization probably relates to the high temperature CO2-rich fluids and the Mesozoic and Cenozoic illite to the younger, lower temperature saline brines. On the basis of the mineral characteristics presented, it is also suggested that the 2M to 1M transition was favored by lowering of the rock permeability and the related increase in the state of fluid saturation, which occurred during successive episodic crystallization and progressive sealing of the granite. The next chapter presents the results from the uplifted shoulder locality of the Schauenburg Fault, near Heidelberg. These fault rocks occur along a E-W trending dextral oblique-slip fault (displacement ca. 100m), which separates the Variscan Heidelberg granite from younger Permian volcanics. In comparison to the Soultz-granite, the alteration assemblages of the Schauenburg indicate a retrograde sequence of fluid-controlled, low-temperature clay mineral reactions, ranging from Jurassic times to more recent activity during uplift of the rift shoulder. The progressive decrease in fluid temperatures caused a back-reaction of 2M1 illite to 1Md (R3) illite-smectite, as well as smectite and kaolinite. The enhanced rock permeability and fluid movement along the cataclastic fault zone is evident from the illite texture and rock fabric. The last chapter synthesizes and discusses the different alteration histories of both studied localities of the Rhine Graben rift structure and evaluates the nature of clay mineral reactions and the timing and mechanisms of crystal growth in relation to the history of fluid-rock interaction. Despite the petrological similarities of both Variscan granites, there are notable differences in mineral alteration history. The hydrothermal alteration of the buried Soultz-sous-Forêts granite shows a number of episodic pure illite crystallization events with repeated transition from 2M to 1M polytypes occuring during Permian, Jurassic and Cretaceous (to younger) time. In contrast, the exhumed Schauenburg Fault rocks document a similar hydrothermal illite crystallization event during the Jurassic, but was subsequently flushed by more dilute meteoric waters attributed to rift shoulder uplift

Strain Partitioning and Frictional Behavior of Opalinus Clay During Fault Reactivation

The Opalinus Clay (OPA) formation is considered a suitable host rock candidate for nuclear waste storage. However, the sealing integrity and long-term safety of OPA are potentially compromised by pre-existing natural or artificially induced faults. Therefore, characterizing the mechanical behavior and microscale deformation mechanisms of faults and the surrounding rock is relevant for predicting repository damage evolution. In this study, we performed triaxial tests using saw-cut samples of the shaly and sandy facies of OPA to investigate the influence of pressure and mineral composition on the deformation behavior during fault reactivation. Dried samples were hydrostatically pre-compacted at 50 MPa and then deformed at constant strain rate, drained conditions and confining pressures (pc) of 5–35 MPa. Mechanical data from triaxial tests was complemented by local strain measurements to determine the relative contribution of bulk deformation and fault slip, as well as by acoustic emission (AE) monitoring, and elastic P-wave velocity measurements using ultrasonic transmissions. With increasing pc, we observe a transition from brittle deformation behavior with highly localized fault slip to semi-brittle behavior characterized by non-linear strain hardening with increasing delocalization of deformation. We find that brittle localization behavior is limited by pc at which fault strength exceeds matrix yield strength. AEs were only detected in tests performed on sandy facies samples, and activity decreased with increasing pc. Microstructural analysis of deformed samples revealed a positive correlation between increasing pc and gouge layer thickness. This goes along with a change from brittle fragmentation and frictional sliding to the development of shear zones with a higher contribution of cataclastic and granular flow. Friction coefficient at fault reactivation is only slightly higher for the sandy (µ ~ 0.48) compared to the shaly facies (µ ~ 0.4). Slide-hold-slide tests performed after ~ 6 mm axial shortening suggest stable creeping and long-term weakness of faults at the applied conditions. Our results demonstrate that the mode of fault reactivation highly depends on the present stress field and burial history

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The mineralogical and lithogeochemical footprint of the George Fisher Zn-Pb-Ag massive sulphide deposit in the Proterozoic Urquhart Shale Formation, Queensland, Australia

The Proterozoic Carpentaria Province (McArthur basin and Mount Isa Inlier) in northern Australia comprises a number of world class clastic dominated (CD-type) Zn-Pb massive sulphide deposits, formally known as SEDEX deposits. In order to identify the geochemical footprint of any mineralizing system it is necessary to characterize compositional variability of the host rock to mineralization. In the southern Carpentaria, establishing the baseline composition of the host rock is complicated by varying degrees of tectonic overprint, a lack of metamorphic indicator minerals, and the overall size of the ore forming systems. In this study, samples from drill-holes intersecting the main ore bodies at the world class George Fisher CD-type massive sulphide deposit have been compared to samples from a drill-hole intersecting barren, correlative lithologies of the Urquhart Shale Formation (ca. 1654 Ma). Bulk rock lithogeochemical (X-ray fluorescence, inductively coupled plasma mass spectrometry and LECO) and mineralogical (X-ray diffraction) analyses have been combined with petrographic observations to (1) establish the baseline composition of the Urquhart Shale Formation and (2) determine the geochemical and mineralogical footprint of the CD-type system at George Fisher. The absence of metamorphic indicator minerals, combined with the preservation of illite in un-mineralized Urquhart Shale, suggests that in this part of the Mount Isa area, the host rocks did not reach greenschist facies conditions (>300 degrees C). Chlorite in the un-mineralized Urquhart Shale is very fine grained (<= 10 mu m) within interstitial pore spaces with other phyllosilicates (e.g., illite), and is interpreted to be diagenetic in origin. Relative to the un-mineralized Urquhart Shale, the first stage of sulphide mineralization (Zn-dominated, stratabound) at George Fisher is associated with decreased abundances of albite, chlorite, and calcite, and higher abundances of dolomite and phyllosilicates (muscovite and phlogopite). These mineralogical transformations are associated with strong minor and trace element depletion (Sr and Na) and enrichment (Tl and Mn). An element index based on this suite of elements (GF index = 10(400Tl+Mn/10Sr+Na)) is highly effective in differentiating between the background Urquhart Shale Formation and the alteration footprint at George Fisher and may provide an additional tool for geochemical exploration programmes in the Mount Isa area. This study affirms the benefit of combining lithogeochemical, mineralogical, and petrographic data in order to understand the host rock baseline composition and the alteration footprint of Carpentaria CD-type massive sulphide systems

Late diagenesis of illite-smectite in the Podhale Basin, southern Poland: Chemistry, morphology, and preferred orientation

Well-characterized samples from the Podhale Basin, southern Poland, formed the basis for exploring and illuminating subtle diagenetic changes to a mudstone toward the upper end of the diagenetic window, prior to metamorphism.Transmission electron microscopy (TEM) performed on dispersed grains and ion-beam thinned preparations, selected area diffraction patterns,and chemistry by TEM-EDS (energy dispersive spectra) augmented mineralogy and fabric data. The deepest samples show no change in their percent illite in illite-smectite (I-S), yet I-S–phase octahedral Fe3+ and Al3+ are statistically different between samples. A decrease in the Fe3+ concentration in the octahedral sheet correlates with an increase in I-S fabric intensity and apparent crystallinity. The D-statistic from the Kolmogorov-Smirnov test on TEM- EDS data describes statistical differences in the I-S chemistry. Previous work on these samples showed a significant increase in the preferred orientation of the I-S phase across the smectite to illite transition and a significant slowdown in the rate of development of preferred orientation beyond the termination of smectite illitization. Lattice fringe images describe an I-S morphology that coalesces into larger and tighter packets with increasing burial temperature and a decrease in I-S packet contact angle, yet some evidence for smectite collapse structures is retained. The deepest sample shows the thickest, most coherent I-S packets. We propose that the deepest samples in the Podhale Basin describe the precursor stage in phyllosilicate fabric preferred orientation increase from diagenesis into metamorphism, where continued evolution of crystallite packets and associated crystallinity create higher I-S fabric intensities as the structural formulae of I-S approach an end-member composition

Entrepreneurship Education Monitor 2018: für MINT-Studiengänge in Ostdeutschland

In Deutschland ist in Sachen Entrepreneurship an Hochschulen in den vergangenen 20 Jahren viel geschehen. Seit 1998 befördert das EXIST-Programm Gründungsgeist an Hochschulen. Laut der Forschungsgemeinschaft Gründungsforschung e.V. existieren insgesamt 134 Entrepreneurship-Professuren, davon 32 in Ostdeutschland. Es gibt eine Vielzahl an Wettbewerben und Förderprogrammen für Gründerinnen und Gründer. Für alle an den Hochschulen, die sich schon für das Thema Unternehmertum interessieren und mit dem Gedanken einer eigenen Gründung spielen, ist gut gesorgt. Es gibt hinreichend viele Anlaufstellen und Fördermöglichkeiten an und im Umfeld der Hochschulen. Doch eine Herausforderung ist es bis heute, potenzielle Gründerinnen und Gründer und weitere Akteure an Hochschulen überhaupt für unternehmerisches Denken und Handeln zu sensibilisieren. Vorhandene Angebote erreichen die, die interessiert sind und nicht jene, die noch nicht darüber nachgedacht haben. Eine weitere Herausforderung gibt es. Sensibilisierung für unternehmerisches Denken und Handeln geschieht im Rahmen des Studiums, jedoch leider nicht für alle Studierenden. Ein Blick auf die Hochschulebene zeigt, dass noch vor fünf Jahren vor allem Studierende der Wirtschaftswissenschaften von Angeboten rund um das Thema Entrepreneurship profitierten (Gründungsradar, 2013; Kulicke et al., 2012). Die „Interdisziplinarität in der Gründungsförderung und die Ausschöpfung des Potenzials in nicht wirtschaftswissenschaftlichen Fächern sind also noch ausbaufähig“ (Gründungsradar, 2013: 12). Gerade im Kontext der technischen und naturwissenschaftlichen Disziplinen, der sogenannten MINT-Fächer, liegen Potenziale für zukünftige technologische und ggf. auch unternehmerische Innovationen. Die Zielgruppe dieser Studierenden wird jedoch bislang kaum erreicht. Ein sicherer Weg, Studierende zu erreichen, ist die universitäre Lehre entlang des Studiencurriculums. Es gibt verschiedene Argumente, die für eine breite curriculare Verankerung von Entrepreneurship Education an Hochschulen sprechen. So wird dies im wissenschaftlichen Diskurs diskutiert (Nelson & Byers, 2008; Semrau, Fischbach & Schober, 2011) und im politischen Diskurs klar unterstützt; so versteht sich die Europäische Kommission als Katalysator, um Entrepreneurship Education zu einem Basiselement im Bildungssystem zu machen (Europäische Kommission, 2018). Hier liegen Ursprung und Idee dieser Studie. Es war bisher nicht klar, wie die Chancen für Studierende der MINT-Fächer stehen, während ihres Studiums mit Entrepreneurship in Kontakt zu kommen. Es gibt eine Vielzahl von Studien, die sich mit der Umsetzung von Maßnahmen zur Sensibilisierung unternehmerischen Denkens und Handelns auf Hochschulebene beschäftigen. Umfassende Analysen, welche auf Studiengangebene analysieren, ob und inwiefern dort Inhalte mit Bezug zu Entrepreneurship verankert sind, sind kaum vorhanden (Gossel & Kalka, 2015). An dieser Stelle setzt die vorliegende Studie an. Für das wichtige Segment der MINT-Studiengänge wird im Rahmen einer Vollerhebung in sechs ostdeutschen Bundesländern ermittelt, ob und inwiefern dort Inhalte mit Bezug zu Entrepreneurship curricular verankert sind. Ziel der Studie ist es, so breit und so tief wie möglich zu erfassen, wie es um den Erwerb unternehmerischer Kompetenzen in den MINT-Studiengängen steht. Von der Verbreitung der Ergebnisse der Studie erhoffen wir uns eine Belebung der Diskussion rund um Entrepreneurship Education an Hochschulen in Deutschland. Gründungssensibilisierung ist und bleibt eine Daueraufgabe in der Hochschulbildung. Denjenigen Akteuren, die sich für eine nachhaltige Gründungssensibilisierung in der Hochschullehre einsetzen, jenen, die Studiengänge überarbeiten und Curricula modernisieren, und denjenigen, die darüber entscheiden, ob es Mittel und Personal an Hochschulen für Aufgaben der Entrepreneurship Education in der Hochschullehre gibt, soll diese Studie als Argumentations- und Diskussionsgrundlage dienen

Constraints on mineralization, fluid‐rock interaction, and mass transfer during faulting at 2–3 km depth from the SAFOD drill hole

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94888/1/jgrb15975.pd