Mechanisms and conditions of deformation in quartzites from the Cantabrian and west Asturian-Leonese zones, north Spain

Deformation mechanisms and conditions have been studied, principally in Ordovician quartzites, from the Cantabrian and West Asturian-leonese zones, north Spain. The quartzites have been strongly deformed at shallow crustal levels during the Variscan orogeny. In the external Cantabrian zone, the dominant mechanism was cataclasis, which occurred both pervasively around large-scale folds by shear on a network of bedding-normal fractures, and as localised deformation along large faults. Solution transfer was confined to grain boundaries. Grain boundary sliding operated in sandstones with porous microstructures, which deformed by small-scale chevron folds. This contrast in deformation modes is shown to be a consequence of different initial microstructures. In the West-Asturian leonese zone ( towards the internal part of the orogen), solution transfer extended along stylolites, and progressively increasing amounts of crystal plasticity became the fold accommodating mechanism. This can be followed by an increase in the intracrystalline extinction angle as grain boundary migration and sub-grain rotation contributed to further dynamic recrystallisation. The late stages of deformation were cataclastic. In all examples of cataclasis, fractures clustered together to form deformation zones of high density fracturing: this is an inherent part of the deformation mechanism, which is interpretted as a localisation phenomenon in response to changed material properties. The changes in mechanisms from the external to internal parts of the orogen correlate with an increase in temperature from 0-2500 to 311 - 411°. Effective confining pressures were from 30 to 7S MPa. and differential stresses from 50 to 300 MPa. These conditions of deformation are linked with the deformation modes to define nine deformation facies; the sequence of facies, the deformation path, is plotted for the four localities studied in detail, and it is suggested that the study area can be subdivided into four sub-areas, each characterised by one path

New age constraints for the Tommy Creek domain of the Mount Isa Inlier, Australia

The Tommy Creek Domain is a complex, yet little studied, terrane in the Eastern Subprovince of the Mount Isa Province, northwest Queensland Australia. In this study, we take advantage of modern low-cost and rapid geochronology techniques to undertake an iterative dating approach integrated with detailed fieldwork to define the ages and extents of numerous lithologies and units of the Tommy Creek Domain. This includes some units not previously identified, lithologies previously grouped together based on field observations but now shown to have multiple distinct ages and dates not commonly represented in Mount Isan time–space plots. We identify an episode of felsic magmatism at ca 1640 Ma, and multimodal intrusions (ca 1615 Ma) immediately preceding the onset of the Isan Orogeny. A major rock package of the Tommy Creek Domain, the Milo beds, are characterised here as the youngest pre-Isan Orogeny sedimentary unit in the Eastern Subprovince (1660–1620 Ma), confirming that sedimentation and possibly rifting continued after deposition of the Soldiers Cap, Mount Albert and Kuridala groups (ca 1690–1650 Ma) before the onset of the Isan Orogeny (ca 1600 Ma). The Milo beds are thus age equivalent to the Mount Isa and McNamara groups of the Western Succession. There is evidence of a compositional shift in sedimentation coincident with the ca 1640 Ma Riversleigh Inversion event, previously only observed in the Western Subprovince in the Lawn Hill Platform. The application of geochronology as part of the mapping workflow can assist with differentiating geological units in terranes where field evidence is ambiguous and can aid in the focusing of objectives for field campaigns to enable the best possible interpretations to be made

Re-evaluating ambiguous age relationships in Archean cratons: implications for the origin of ultramafic-mafic complexes in the Lewisian Gneiss Complex

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Archean ultramafic-mafic complexes have been the focus of important and often contentious geological and geodynamic interpretations. However, their age relative to the other components of Archean cratons are often poorly-constrained, introducing significant ambiguity when interpreting their origin and geodynamic significance. The Lewisian Gneiss Complex (LGC) of the northwest Scottish mainland – a high-grade, tonalite-trondhjemite-granodiorite (TTG) terrane that forms part of the North Atlantic Craton (NAC) – contains a number of ultramafic-mafic complexes whose origin and geodynamic significance have remained enigmatic since they were first described. Previous studies have interpreted these complexes as representing a wide-range of geological environments, from oceanic crust, to the sagducted remnants of Archean greenstone belts. These interpretations, which are often critically dependent upon the ages of the complexes relative to the surrounding rocks, have disparate implications for Archean geodynamic regimes (in the NAC and globally). Most previous authors have inferred that the ultramafic-mafic complexes of the LGC pre-date the TTG magmas. This fundamental age relationship is re-evaluated in this investigation through re-mapping of the Geodh’ nan Sgadan Complex (where tonalitic gneiss reportedly cross-cuts mafic rocks) and new mapping of the 7 km2 Ben Strome Complex (the largest ultramafic-mafic complex in the LGC), alongside detailed petrography and spinel mineral chemistry. This new study reveals that, despite their close proximity in the LGC (12 km), the Ben Strome and Geodh’ nan Sgadan Complexes are petrogenetically unrelated, indicating that the LGC (and thus NAC) records multiple temporally and/or petrogenetically distinct phases of ultramafic-mafic Archean magmatism that has been masked by subsequent high-grade metamorphism. Moreover, field observations and spinel mineral chemistry demonstrate that the Ben Strome Complex represents a layered intrusion that was emplaced into a TTG-dominated crust. Further to representing a significant re-evaluation of the LGC’s magmatic evolution, these findings have important implications for the methodologies utilised in deciphering the origin of Archean ultramafic-mafic complexes globally, where material suitable for dating is often unavailable and field relationships are commonly ambiguous.We thank both the Society of Economic Geologists (Graduate Fellowship Award) and Geological Society (Timothy Jefferson Fund) for extremely generous monetary contributions in 2016 and 2017 respectively, which facilitated the (lead author’s) fieldwork that formed basis for this paper

Pengembangan Agrowisata Di Pulau Nusakambangan(agritoarism Dewlopment of Nusakambangan Isi.and)

Penelitian dalam rangka menyusun rencana induk pengembangan pariwisata telah Dilakukan di Pulau Nusakambangan. Salah satu program yang diusulkan dalam Rencana Induk PengembanganPariwisata Pulau Nusakambangan 2001-2005 adalah pengembangan agrowisata. Lokasi yang diperuntukkan menjadi kawasan agrowisata terletak di sekitar bekas Lapas ( Lembaga Pemasyarakatan) Karanganyar dengan luas area sekitar 100ha. Tulisani ni bertujuan untuk menginformasikan kelayakan investasi dalam pengembangan agrowisata di Karang anyar yang merupakan bagian dari pengembangan pariwisata Pulau Nusakambangan. Hasil analisis dengan menggunakan kriteria investasi terhadap Salak pondoh yang diambil sebagai contoh komoditas yang hendak dikembangkan diperoleh hasil : (1) NPV dengan discount factor ( dt) 30% sebesar 5.906.591,8 dan dengan df 26% sebesar 9.450.546,9 (;2 ) IRR : 36,6%; ( 3) Net B / C : 4,45;( 4) ROI = 345,3%; dan (5) BEP untuk produk 21.895,6 k g dan untuk hargaR p 1.112,219/kg. Berdasarkan hasil analisis tersebut disimpulkan salak pondoh termasuk komoditas yang layak investiasi untuk pengembangan agrowisata.D isarankan, k omoditas lain yang direkomendasikan untuk pengembangan agrowisata yang diminati oleh calon investor hendaknya dilakukan analisis seperti metode di atas untuk menilai kelayakani ivestasinya

The effect of rock particles and D2O replacement on the flow behaviour of ice

Ice–rock mixtures are found in a range of natural terrestrial and planetary environments. To understand how flow processes occur in these environments, laboratory-derived properties can be extrapolated to natural conditions through flow laws. Here, deformation experiments have been carried out on polycrystalline samples of pure ice, ice–rock and D2O-ice–rock mixtures at temperatures of 263, 253 and 233 K, confining pressure of 0 and 48 MPa, rock fraction of 0–50 vol.% and strain-rates of 5 × 10−7 to 5 × 10−5 s−1. Both the presence of rock particles and replacement of H2O by D2O increase bulk strength. Calculated flow law parameters for ice and H2O-ice–rock are similar to literature values at equivalent conditions, except for the value of the rock fraction exponent, here found to be 1. D2O samples are 1.8 times stronger than H2O samples, probably due to the higher mass of deuterons when compared with protons. A gradual transition between dislocation creep and grain-size-sensitive deformation at the lowest strain-rates in ice and ice–rock samples is suggested. These results demonstrate that flow laws can be found to describe ice–rock behaviour, and should be used in modelling of natural processes, but that further work is required to constrain parameters and mechanisms for the observed strength enhancement