ALBERT

Description: The Grande Aula, or Great Hall, of the Markets of Trajan is an intact example of the sophisticated, domed, concrete architecture of imperial Rome, which records the expertise of Roman builders in formulating extraordinarily durable pozzolanic concretes between about AD 96 and 115. Petrographic, chemical, X-ray diffraction analyses and SEM images demonstrate that the pozzolanic mortars of the conglomeratic wall concretes contain strätlingite, a complex calcium aluminate cement hydrate (C2 ASH8) that gives modern cements high durability and compressive strength. It has not been previously recognized in ancient pozzolanic mortars. New methods of assessing bulk specific gravity of the porous concretes suggest unit weights of 1495 kg/m³ for the conglomeratic wall cores and 1200-1300 kg/m³ for the pumice-bearing vaulted ceiling mortar.Innovative point load tensile strength testing methods provide a means of evaluating the strengths of small samples of ancient, conglomeratic cementitious materials. Tests of coarse aggregate clasts, pozzolanic mortar, and the adhesive interfacial surfaces of coarse aggregate clasts (caementa) in contact with the mortar, suggest tensile strengths (ft) of 2.7 MPa for brick clasts, 1.2 MPa for Tufo Lionato tuff clasts, and 0.9 MPa for Tufo Giallo della Via Tiberina tuff clasts based on a tentative, approximate correlation with splitting (Brazilian) tests on these materials. The pozzolanic mortar and interfacial zones appear to have lower ft, in the range of 0.8 MPa to 0.5 MPa. The relatively low tensile strengths of the mortar and its somewhat tenuous adhesion to coarse aggregate clasts suggests that the caementa may have had a role in arresting the propagation of tensile microcracks that formed in the mortar, thereby increasing the composite tensile strength of the concrete. Roman builders evidently selected the complex aggregate mixes to optimize the performance and durability of the wall and vault masonry.

Description: Published

Description: 2481-2492

Description: 3.10. Storia ed archeologia applicate alle Scienze della Terra

Description: JCR Journal

Description: open

Description: Laboratory experiments suggest that fault zones form in porous rocks through the extension and coalescence of fractures of predictable geometries. These fractures form in an array of Riedel fractures in R1, R2, P and Y orientations. Displacement along closely spaced fractures leads to the formation of comminuted fault gouge. Localization of displacement within the fault gouge progresses from distributed shearing to comminution and compaction of the fault rock material culminating in fractures in the Riedel orientations. Colour boundaries within the simulated gouge zones show the change in accommodation of displacement to fractures in the Y orientation as shear strain progresses. Clayquartz mixtures demonstrate that the clay inhibits localization and the achievement of steady-state sliding as well as stick-slip. A reduction in the coefficient of friction does not occur until about 30% of the clay is present and continues to decrease until about 70% is reached. Localization of slip appears as a necessary condition for steady-state sliding as well as unstable behaviour. Field studies show the implication of grain-size reduction in the localization process by porosity decrease inhibiting fluid flow normal to the fault zone. The pervasive Y fractures, however, facilitate fluid migration parallel to some faults.

Description: To investigate the role of texture on the brittle deformation of dolomite, 23 triaxial deformation experiments were performed at confining pressures of 25, 50, and 100 MPa, dry, at room temperature, on dolomite from three texturally distinct sample suites. The variations in the mechanical response of these mineralogically and chemically similar dolomites, and the ensuing microstructures, indicate that grain boundary textures promote or inhibit the ability of grains to shear and rotate with respect to one another, whereas the presence of intragranular flaws, such as cleavage, that act as weaknesses, promote intragranular deformation. In samples with porosities greater than c. 7%, inelastic pore collapse controls the transition from brittle faulting to extensive intragranular deformation and cataclastic flow. This porosity is much higher than has been observed at the onset of pore collapse in calcite, as a consequence of the inability of dolomite to deform by crystal plastic processes at room temperature. Combined, these textural features may dictate the transition from brittle faulting to cataclastic flow in brittle rocks in the upper crust.

Description: Paired belts of alkalic and calc-alkalic porphyry deposits are genetically linked to early Mesozoic volcanic arcs preserved as the Quesnel and Stikine terranes in western Canada. These parallel arc terranes extend for 2,000 km along the axis of the Canadian Cordillera. They are joined at their northern ends, but are otherwise separated by relics of Tethyan ocean basin and oceanic arc rocks collectively referred to as the Cache Creek terrane. Porphyry Cu ± Au-Mo-Ag deposits are concentrated within the Stikine-Quesnel arc terranes, with most of their economic metal endowment a consequence of a 15-m.y. mineralizing epoch. A particularly prolific period within the mineralizing epoch is a 6-m.y. pulse centered on 205 Ma when more than 90% of the known copper endowment was acquired. Distinct trends of Cu-Au ± Ag-Mo mineralization within both arc terranes coincide in time and space with events that are attributed to effects of slab subduction. Stratigraphy within both Stikine and Quesnel arc terranes is equivalent, with greater variation along the arcs than between them. Magmatism within both arcs began in the Late Devonian, following initiation of subduction near eastern Panthalassa and formation of the back-arc Slide Mountain ocean basin margin adjacent to Laurentia. Both terranes record further arc development in the lower Carboniferous and cessation in the Permian. Between the Late Permian and Middle Triassic, both arcs foundered, and then recorded a cryptic Early Triassic deformational event, coincident with closing of the Slide Mountain ocean. Permo-Triassic subduction and arc magmatism are recorded in the Sitlika-Kutcho-Venables arc, but this occurred far to the west, within the Tethyan realm. Early in the Late Triassic (early Carnian), both the Stikine and Quesnel arcs reignited. Later, near the end of the Triassic (late Norian), the arcs were uplifted, picrites were erupted locally, and magmatism was dominantly strongly alkaline. Monzonitic plutons hosting alkalic Cu porphyry deposits were emplaced along the arcs, followed by a widespread erosional hiatus that extends throughout much of the latest Triassic (Rhaetian). Late Triassic events culminating in generation of Cu porphyry deposits are attributed to a model wherein delivery of the Permo-Triassic Sitlika-Kutcho-Venables arc to the Stikine-Quesnel arc trench led to stalled subduction and arc-parallel tearing of the slab. Ingress of hot subslab mantle into the tear resulted in high-degree partial melts, as recorded by picrite within the arc circa 210 Ma. Widening of the tear and decay of the initial thermal spike raised temperatures across broad regions of the metasomatized mantle wedge, with low-degree partial melts generated from the most hydrated, metal-enriched portions circa 203 Ma. These melts produced the well-defined belt of alkalic Cu-Au-Ag porphyries. Parts of the slab tear may have nucleated near the forearc to generate Mo-rich Cu porphyries, such as the Gibraltar deposit, which partly cuts the accreted Cache Creek terrane. Metal-rich hydrous melts may have traveled along preexisting intrusive pathways to invade batholithic bodies along the arc axis, such as at Highland Valley, where 204 Ma mineralization is hosted within a larger ~210 Ma plutonic complex. Migration of the locus of mineralized porphyry intrusions toward the backarc may track the leading edge of the slab gap, with the formation of Cu-Au and younger Au-rich porphyries until ~195 Ma. Late alkalic porphyry formation, following emplacement of the Quesnel arc onto the ancestral North American margin at ~186 Ma, may have been produced through cannibalism of mineralized intrusions emplaced at deeper crustal levels during the ~203 Ma Cu porphyry event. Two calc-alkalic porphyry deposits that predate Sitlika-Kutcho-Venables arc collision—Fin and Schaft Creek (~220 Ma)—are temporally related to arc uplift and erosion across the northern Stikine arc, but little is known about the extent and cause of this event and how it relates to porphyry Cu genesis. Slab tears may play a dominant role in the formation of porphyry deposits globally. Previous workers have linked episodes of porphyry formation with subduction of ocean plateaus, changes in subduction polarity, or termination of subduction. In each case, slab tears are the likely underlying cause of porphyry formation. We believe them to be fundamental to mineralization in the early Mesozoic arc terranes of Stikine and Quesnel.

Description: Snakes are limbless predators, and many species use venom to help overpower relatively large, agile prey. Snake venoms are complex protein mixtures encoded by several multilocus gene families that function synergistically to cause incapacitation. To examine venom evolution, we sequenced and interrogated the genome of a venomous snake, the king...