Reply to ‘Comment on “The beginnings of hydrous mantle wedge melting” by Till et al.’ by Green, Rosenthal and Kovacs

The comment of Green et al. debates the interpretation of the temperature of the H₂O-saturated peridotite solidus and presence of silicate melt in the experiments of Till et al. (Contrib Mineral Petrol 163:669–688, 2012) at <1,000?°C. The criticisms presented in their comment do not invalidate any of the most compelling observations of Till et al. (Contrib Mineral Petrol 163:669–688, 2012) as discussed in the following response, including the changing minor element and Mg# composition of the solid phases with increasing temperature in our experiments with 14.5?wt% H₂O at 3.2?GPa, as well as the results of our chlorite peridotite melting experiments with 0.7?wt% H₂O. The point remains that Till et al. (Contrib Mineral Petrol 163:669–688, 2012) present data that call into question the H₂O-saturated peridotite solidus temperature preferred by Green (Tectonophysics 13(1–4):47–71, 1972; Earth Planet Sci Lett 19(1):37–53, 1973; Can Miner 14:255–268, 1976); Millhollen et al. (J Geol 82(5):575–587, 1974); Mengel and Green (Stability of amphibole and phlogopite in metasomatized peridotite under water-saturated and water-undersaturated conditions, Geological Society of Australia Special Publication, Blackwell, pp 571-581, 1989); Wallace and Green (Mineral Petrol 44:1–19, 1991) and Green et al. (Nature 467(7314):448–451, 2010).     

Applicability of different ground-motion prediction models for northern Iran

A total of 163 free-field acceleration time histories recorded at epicentral distances of up to 200 km from 32 earthquakes with moment magnitudes ranging from M _w 4.9 to 7.4 have been used to investigate the predictive capabilities of the local, regional, and next generation attenuation (NGA) ground-motion prediction equations and determine their applicability for northern Iran. Two different statistical approaches, namely the likelihood method (LH) of Scherbaum et al. (Bull Seismol Soc Am 94:341–348, 2004) and the average log-likelihood method (LLH) of Scherbaum et al. (Bull Seismol Soc Am 99:3234–3247, 2009), have been applied for evaluation of these models. The best-fitting models (considering both the LH and LLH results) over the entire frequency range of interest are those of Ghasemi et al. (Seismol 13:499–515, 2009a) and Soghrat et al. (Geophys J Int 188:645–679, 2012) among the local models, Abrahamson and Silva (Earthq Spectra 24:67–97, 2008) and Chiou and Youngs (Earthq Spectra 24:173–215, 2008) among the NGA models, and finally Akkar and Bommer (Seism Res Lett 81:195–206, 2010) among the regional models.     

Paleogeographical restoration and ramp tectonic evidence in Tunisian Tellian domain: Ain El Bey-Bou Awen area

The imbrication’s area in northern Tunisia is the most external segment of Alpine range, where several associated folds types with thrust ramps are recognized within imbricate units beneath Numidian front slope. Their presence help to understand thrusting mechanisms installation through studied area. In fact, this zone was considered as a result of Paleogene gravitary slop (Kujawski (Ann Miner Géol Tunis (24):281, 1969); Caire (Ann Min Géol Tunis 26:87–110, 1973); Rouvier 1977), which is proved to be affected by major deep decollement, given rise to various structures, some are propagation folds, specific of foreland front, limited to this area, and those in more external position: Tunisian Atlas (Creusot et al. (C R Acad Sci Paris 314(Sér II):961–965, 1992); Ouali and Mercier (PII: S0191-8141(97):00048-5, 1997); Ouali 1984; Ahmadi et al. (J Struct Geol 28:721–728, 2006)). Various categories of fold ramps could be identified: frontal folds ramp NE–SW and others as lateral or oblique ramp with NW–SE trend (Aridhi et al. (C R Geosci 343:360–369, 2011)). The relation between various structures has been used as recognition tools of thrusting sequences and to propose a new deformation chronology. Delimited outcropping of these structures between two both parallel faults strikes with regional displacement, leads to interpret these faults as cogenetic tear faults of propagation thrusts; this fault separates two domains with different deformation styles from each other side.     

Comment on “A Comparison of Modified Fuzzy Weights of Evidence,Fuzzy Weights of Evidence,and Logistic Regression for Mapping Mineral Prospectivity” by Daojun Zhang,Frits Agterberg,Qiuming Cheng,and Renguang Zuo Math Geosci DOI 10.1007/s11004-013-9496-8

Despite a missing definition of equivalence of mathematical models or methods by Zhang et al. (Math Geosci, 2013), an “equivalence” (Zhang et al., Math Geosci, 2013, p. 6,7,8,14) of modified weights-of-evidence (Agterberg, Nat Resour Res 20:95–101, 2011) and logistic regression does not generally exist. Its alleged proof is based on a previously conjectured linear relationship between weights of evidence and logistic regression parameters (Deng, Nat Resour Res 18:249–258, 2009), which does not generally exist either (Schaeben and van den Boogaart, Nat Resour Res 20:401–406, 2011). In fact, an extremely simple linear relationship exists only if the predictor variables are conditionally independent given the target variable, in which case the contrasts, i.e., the differences of the weights, are equal to the logistic regression parameters. Thus, weights-of-evidence is the special case of logistic regression if the predictor variables are binary and conditionally independent given the target variable.     

Convergence of iterative coupling for coupled flow and geomechanics

In this paper, we study solving iteratively the coupling of flow and mechanics. We demonstrate the stability and convergence of two widely used schemes: the undrained split method and the fixed stress split method. To our knowledge, this is the first time that such results have been rigorously obtained and published in the scientific literature. In addition, we propose a new stress split method, with faster convergence rate than known schemes. These results are specially important today due to the interest in hydraulic fracturing (Dean and Schmidt SPE J. 14:707–714, 2009; Ji et al. SPE J. 14:423–430, 2009; Samier and De Gennaro 2007; Settari and Maurits SPE J. 3:219–226, 1998), in oil and gas shale reservoirs.     

Oxygen fugacity control in piston-cylinder experiments: a re-evaluation

Jakobsson (Contrib Miner Petrol 164(3):397–407, 2012) investigated a double capsule assembly for use in piston-cylinder experiments that would allow hydrous, high-temperature, and high-pressure experiments to be conducted under controlled oxygen fugacity conditions. Using a platinum outer capsule containing a metal oxide oxygen buffer (Ni–NiO or Co–CoO) and H₂O, with an inner gold–palladium capsule containing hydrous melt, this study was able to compare the oxygen fugacity imposed by the outer capsule oxygen buffer with an oxygen fugacity estimated by the AuPdFe ternary system calibrated by Barr and Grove (Contrib Miner Petrol 160(5):631–643, 2010). H₂O loss or gain, as well as iron loss to the capsule walls and carbon contamination, is often observed in piston-cylinder experiments and often go unexplained. Only a few have attempted to actually quantify various aspects of these changes (Brooker et al. in Am Miner 83(9–10):985–994, 1998; Truckenbrodt and Johannes in Am Miner 84:1333–1335, 1999). It was one of the goals of Jakobsson (Contrib Miner Petrol 164(3):397–407, 2012) to address these issues by using and testing the AuPdFe solution model of Barr and Grove (Contrib Miner Petrol 160(5):631–643, 2010), as well as to constrain the oxygen fugacity of the inner capsule. The oxygen fugacities of the analyzed melts were assumed to be equal to those of the solid Ni–NiO and Co–CoO buffers, which is incorrect since the melts are all undersaturated in H₂O and the oxygen fugacities should therefore be lower than that of the buffer by 2 log $a_{{{\text{H}}_{ 2} {\text{O}}}}$ .     

Chromite alteration processes within Vourinos ophiolite

The renewed interest in chromite ore deposits is directly related to the increase in Cr price ruled by international market trends. Chromite, an accessory mineral in peridotites, is considered to be a petrogenetic indicator because its composition reflects the degree of partial melting that the mantle experienced while producing the chromium spinel-bearing rock (Burkhard in Geochim Cosmochim Acta 57:1297–1306, 1993). However, the understanding of chromite alteration and metamorphic modification is still controversial (e.g. Evans and Frost in Geochim Cosmochim Acta 39:959–972, 1975; Burkhard in Geochim Cosmochim Acta 57:1297–1306, 1993; Oze et al. in Am J Sci 304:67–101, 2004). Metamorphic alteration leads to major changes in chromite chemistry and to the growth of secondary phases such as ferritchromite and chlorite. In this study, we investigate the Vourinos complex chromitites (from the mines of Rizo, Aetoraches, Xerolivado and Potamia) with respect to textural and chemical analyses in order to highlight the most important trend of alteration related to chromite transformation. The present study has been partially funded by the Aliakmon project in collaboration between the Public Power Corporation of Greece and Institute of Geology and Mineral Exploration of Kozani.     

Assessment of Liquefaction Potential of Guwahati City: A Case Study

The liquefaction potential of saturated cohesionless deposits in Guwahati city, Assam, was evaluated. The critical cyclic stress ratio required to cause liquefaction and the cyclic stress ratio induced by an earthquake were obtained using the simplified empirical method developed by Seed and Idriss (J soil Mech Found Eng ASCE 97(SM9):1249–1273, 1971, Ground motions and soil liquefaction during earthquakes. Earthquake Engineering Research Institute, Berkeley, CA, 1982) and Seed et al. (J Geotech Eng ASCE 109(3):458–483, 1983, J Geotech Eng ASCE 111(12):1425–1445, 1985) and the Idriss and Boulanger (2004) method. Critical cyclic stress ratio was based on the empirical relationship between standard penetration resistance and cyclic stress ratio. The liquefaction potential was evaluated by determining factor of safety against liquefaction with depth for areas in the city. A soil database from 200 boreholes covering an area of 262 km² was used for the purpose. A design peak ground acceleration of 0.36 g was used since Guwahati falls in zone V according to the seismic zoning map of India. The results show that 48 sites in Guwahati are vulnerable to liquefaction according to the Seed and Idriss method and 49 sites are vulnerable to liquefaction according to the Idriss and Boulanger method. Results are presented as maps showing zones of levels of risk of liquefaction.     

A phase-by-phase upstream scheme that converges to the vanishing capillarity solution for countercurrent two-phase flow in two-rock media

We discuss the convergence of the upstream phase-by-phase scheme (or upstream mobility scheme) towards the vanishing capillarity solution for immiscible incompressible two-phase flows in porous media made of several rock types. Troubles in the convergence were recently pointed out by Mishra and Jaffré (Comput. Geosci. 14, 105–124, 2010) and Tveit and Aavatsmark (Comput. Geosci. 16, 809–825, 2012). In this paper, we clarify the notion of vanishing capillarity solution, stressing the fact that the physically relevant notion of solution differs from the one inferred from the results of Kaasschieter (Comput. Geosci. 3, 23–48, 1999). In particular, we point out that the vanishing capillarity solution depends on the formally neglected capillary pressure curves, as it was recently proven in by Andreianov and Cancès (Comput. Geosci. 17, 551–572, 2013). Then, we propose a numerical procedure based on the hybridization of the interfaces that converges towards the vanishing capillarity solution. Numerical illustrations are provided.     

Rossberg landslide history and flood chronology as recorded in Lake Lauerz sediments (Central Switzerland)

The southern slopes of Rossberg mountain, Central Switzerland, on which one of the largest historic landslides of the Alpine region was released in 1806 ad (Goldauer Bergsturz), are prone to large-scale mass wasting processes. This has led to numerous sliding events, which are well-recognizable in the modern topography but lack accurate dating. In order to provide new insights into the timing and the processes associated with past landslides as well as into the frequency of exceptional flood events, long sediment cores were retrieved from the subsurface of Lake Lauerz that lies in the pathway of these landslides and that records strong runoff events with typical flood layers. Analyses of the recovered cores display a sedimentologic succession with variable fingerprints of past landslides and flood events, depending on the coring location within the lake. The landslide signature can be calibrated using the 1806 ad event: An organic-rich peaty unit, which is found in two cores located close to the rockmass impact, points towards a sudden, gravity spreading-induced lateral displacement of the swampy plain where parts of the rock mass were accumulating. This rapid lateral mobilization of soft sediments, and not the rock masses, acted as ultimate trigger for the reported ~15 m-high impulse waves on the lake. In the more distal areas, the 1806 ad event led to the deposition of a thick, organic-rich redeposited layer. The 10 m-long core from the distal basin covers a radiocarbon-dated ~2,000 years sedimentation history and contains a highly similar event layer that was deposited in 810 ± 60 ad. This layer is most likely the product of a major historic landslide, known as Röthener Bergsturz, which, based on scarce historical reports, was commonly dated to 1222 ad. In the 2,000 years record, we identify three periods with enhanced occurrence of flood turbidites dated to 580–850 ad, 990–1420 ad, and 1630–1940 ad. Among the 54 detected flood layers, 6 probably mark exceptionally heavy rainfall events that are dated to ~610, ~1160, ~1290, ~1660, ~1850, and ~1876 ad, the latter being associated to one of the most intense rainfall events ever recorded instrumentally in the region.     

The Use of Rock Mass Classification Systems to Estimate the Modulus and Strength of Jointed Rock

Three-dimensional, elastic and elasto-plastic finite element (FE) programs have permitted calculation of the displacements and the factor of safety (FOS) for the excavation for a tower, 132.70 m high (above foundation) on the island of Tenerife. The tower is supported by a 2 m thick reinforced concrete slab on jointed, vesicular and weathered basalt and scoria. The installation of rod extensometers at different depths below the slab has permitted comparison between measured and calculated displacements and the estimation of in situ deformation modulus. The moduli deduced from the simple empirical equations proposed by Hoek et al. (In: NARMS-TAC, 2002) and Gokceoglu et al. (Int J Rock Mech Min Sci 40:701–710, 2003) as a function of GSI, and Nicholson and Bieniawski (Int J Min Geol Eng 8:181–202, 1990) as a function of RMR, provide an acceptable fit with the measured settlements in this type of rock. Good correlation is also obtained with the empirical equation presented by Verman et al. (Rock Mech Rock Eng 30(3):121–127, 1997) that incorporates the influence of confining stress in the deformation modulus. The FOS obtained from different correlations with geomechanical classifications is within a relatively narrow range. These results increase our confidence in the use of classification schemes to estimate the deformation and stability in jointed rock.     

Melting phase relations of a mica–clinopyroxenite from the Milk River area, southern Alberta, Canada

Melting experiments were conducted on a mica–clinopyroxenite xenolith brought up in a minette dyke in southern Alberta, Canada, near Milk River. Both the minettes and mica–clinopyroxenite xenoliths were studied by Buhlmann et al. (Can J Earth Sci 37:1629–1650, 2000), who hypothesized that the minettes formed by partial melting of a mantle source containing clinopyroxene + phlogopite ± olivine, at pressures ≥1.7 GPa. In liquidus experiments performed on the most primitive minette in our previous study (Funk and Luth in Contrib Mineral Petrol 164:999–1009, 2012), we found a multiple saturation point where olivine and orthopyroxene coexisted with liquid at 1.77 GPa and 1,350 °C. We argued that the minette originally formed by partial melting of clinopyroxene + phlogopite, but had re-equilibrated with a harzburgite during ascent. In the current study, we wanted to test both the source region hypothesis of Buhlmann et al. and our re-equilibration hypothesis by studying the near-solidus phase equilibria of a mica + clinopyroxene assemblage. We found the solidus for our xenolith has a steep slope in P–T space and lies at temperatures above those of a normal cratonic geotherm, implying that this mica–clinopyroxenite is stable in the cratonic mantle. Melting could occur at greater depths, where the solidus is extrapolated to cross the geotherm or must be induced either by raising the temperatures of the surrounding rocks or by introducing hydrous fluids into the source. Our melts are in equilibrium with clinopyroxene and olivine. The compositions of the liquids derived from melting this xenolith are similar to madupitic lamproites from the Leucite Hills, Wyoming, studied by Carmichael (Contrib Mineral Petrol 15:24–66, 1967) and Barton and Hamilton (Contrib Mineral Petrol 66:41–49, 1978; Contrib Mineral Petrol 69:133–142, 1979). Barton and Hamilton (Contrib Mineral Petrol 69:133–142, 1979) proposed that the madupitic lamproites may have come from a source containing mica and pyroxene. This study supports their hypothesis. The composition of the most primitive minette from southern Alberta lies between our experimental melt and a population of representative mantle orthopyroxenes. We conclude from our study that the Milk River minettes were likely derived from a source containing phlogopite, clinopyroxene and trace amounts of apatite, which formed olivine upon melting. During ascent, the melts changed composition by reacting with orthopyroxene.     

Investigation of the variability of strong ground motions from Vrancea earthquakes

A systematic investigation of the applicability of several ground motion prediction models for Vrancea intermediate-depth seismic source is conducted in this research. Two ground motion prediction models recommended by previous evaluations (Vacareanu et al. in Bull Earthq Eng 11(6):1867–1884, 2013a; Pavel et al. in Earthq Struct 6(1):1–18, 2014), as well as two new state-of-the-art ground motion prediction equations (Vacareanu et al. in J Earthq Eng, 2013b; Earthq Struct 6(2):141–161, 2014) are tested using an increased strong ground motion database consisting of 150 recordings from Vrancea subcrustal earthquakes. The evaluation is performed by using several goodness-of-fit parameters from the literature. Moreover, the applicability of the single-station sigma method is also investigated by using the same strong ground motion database recorded in 30 seismic stations from southern and eastern Romania. The influence of the soil conditions on the numerical results obtained in this study is investigated and discussed using the results provided by the analysis of variance method. The impact of the single-station standard deviation on the levels of seismic hazard is also assessed in this study, and the results show, in the analyzed cases, significant reductions of the hazard levels.     

Discussion of “The Bushveld Complex,South Africa: formation of platinum–palladium,chrome- and vanadium-rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large,relatively slowly cooling,subsiding magma chamber” by Maier et al. (2013) Miner Deposita 48:1–56

We believe the hypothesis presented by Maier et al. (Miner Deposita 48:1–56, 2012) for the formation of the various ore bodies in the Bushveld Complex to be overly simplistic, and we raise concerns that some of our work, used in support of this hypothesis, has been misrepresented. The formation of both diverse metalliferous layers (platinum-group element (PGE) reefs and Ti-magnetite layers) and some discordant (pipe) ore deposits has been ascribed by Maier et al. to the single unifying process of hydrodynamic sorting. The problem faced by authors of universal hypotheses for the Bushveld Complex is the sheer size and complexity of the intrusion. We disagree with many aspects of the overall Maier et al. model and have also identified several minor errors on maps and photographs, although some of these do not have a material effect on the model. The nature and origin of the layering is, however, too complex a topic to deal with in the context of this commentary, and we restrict ourselves to noting that our preferred hypothesis, namely the incremental buildup of layering from numerous episodes of replenishment, by different magma lineages, is consistent with field relationships. Our hypothesis for the origin of the ultramafic-hosted PGE-rich reefs, i.e., lateral mixing, is applicable to economically mineralized reefs (Mitchell and Scoon, Econ Geol 102:971–1009, 2007) and poorly mineralized layers such as the Pseudoreef harzburgite (Scoon and De Klerk, Canad Mineral 25:51–77, 1987) and the chromitite layers below the UG2 (Scoon and Teigler, Econ Geol 89:1094–1121, 1994).     

The Varnes classification of landslide types,an update

The goal of this article is to revise several aspects of the well-known classification of landslides, developed by Varnes (1978). The primary recommendation is to modify the definition of landslide-forming materials, to provide compatibility with accepted geotechnical and geological terminology of rocks and soils. Other, less important modifications of the classification system are suggested, resulting from recent developments of the landslide science. The modified Varnes classification of landslides has 32 landslide types, each of which is backed by a formal definition. The definitions should facilitate backward compatibility of the system as well as possible translation to other languages. Complex landslides are not included as a separate category type, but composite types can be constructed by the user of the classification by combining two or more type names, if advantageous.     

Assessment of social vulnerability to natural disasters: a comparative study

The purpose of this study is to examine and compare the methodologies being developed in assessing social vulnerability to natural disasters. Existing vulnerability literature shows that two methods have been used in developing social vulnerability indexes: (1) a deductive approach based on a theoretical understanding of relationships and (2) an inductive approach based on statistical relationships (Adger et al. in New indicators of vulnerability and adaptive capacity. Tyndall Centre for Climate Change Research, Norwich, 2004). Two techniques were also utilized in aggregating social vulnerability indicators: (1) a deductive approach using standardization techniques such as z scores or linear scaling (Wu et al. in Clim Res 22:255?C270, 2002; Chakraborty et al. in Nat Hazards Rev 6(1):23?C33, 2005) and (2) an inductive approach using data-reduction techniques such as factor analysis (Clark et al. in Mitig Adapt Strateg Glob Change 3(1):59?C82, 1998; Cutter et al. Soc Sci Quart 84(2):242?C261, 2003). This study empirically compares deductive and inductive index development and indicator aggregation methods in assessing social vulnerability to natural disasters in the Gulf of Mexico and Atlantic coastal areas. The aggregated social vulnerability index is used to examine a relationship with disaster losses in the Gulf of Mexico and Atlantic coastal areas. The results show that coastal counties with more vulnerability in terms of social achieved status are positively associated with disaster damages, while variations in the development of the index using deductive and inductive measurement approaches produce different outcomes.     

Flow rule in a high-cycle accumulation model backed by cyclic test data of 22 sands

The flow rule used in the high-cycle accumulation (HCA) model proposed by Niemunis et al. (Comput Geotech 32: 245, 2005) is examined on the basis of the data from approximately 350 drained long-term cyclic triaxial tests (N = 10⁵ cycles) performed on 22 different grain-size distribution curves of a clean quartz sand. In accordance with (Wichtmann et al. in Acta Geotechnica 1: 59, 2006), for all tested materials, the “high-cyclic flow rule (HCFR)”, i.e., the ratio of the volumetric and deviatoric strain accumulation rates \(\dot{\varepsilon}_{\rm{v}}^{{\rm acc}}/\dot{\varepsilon}_{\rm{q}}^{{\rm acc}}\) , was found dependent primarily on the average stress ratio η ^av = q ^av/p ^av and independent of amplitude, soil density and average mean pressure. The experimental HCFR can be fairly well approximated by the flow rule of the modified Cam-clay (MCC) model. Instead of the critical friction angle \(\varphi_{\rm{c}}\) which enters the flow rule for monotonic loading, the HCA model uses the MCC flow rule expression with a slightly different parameter \(\varphi_{\rm{cc}}\) . It should be determined from cyclic tests. \(\varphi_{\rm{cc}}\) and \(\varphi_{\rm{c}}\) are of similar magnitude but not always identical, because they are calibrated from different types of tests. For a simplified calibration in the absence of cyclic test data, \(\varphi_{\rm{cc}}\) may be estimated from the angle of repose \(\varphi_{\rm{r}}\) determined from a pluviated cone of sand (Wichtmann et al. in Acta Geotechnica 1: 59, 2006). However, the paper demonstrates that the MCC flow rule with \(\varphi_{\rm{r}}\) does not fit well the experimentally observed HCFR in the case of coarse or well-graded sands. For an improved simplified calibration procedure, correlations between \(\varphi_{\rm{cc}}\) and parameters of the grain-size distribution curve (d ₅₀,   C _u) have been developed on the basis of the present data set. The approximation of the experimental HCFR by the generalized flow rule equations proposed in (Wichtmann et al. in J Geotech Geoenviron Eng ASCE 136: 728, 2010), considering anisotropy, is also discussed in the paper.     

Crystal reaming during the assembly, maturation, and waning of an eleven-million-year crustal magma cycle: thermobarometry of the Aucanquilcha Volcanic Cluster

Phenocryst assemblages of lavas from the long-lived Aucanquilcha Volcanic Cluster (AVC) have been probed to assess pressure and temperature conditions of pre-eruptive arc magmas. Andesite to dacite lavas of the AVC erupted throughout an 11-million-year, arc magmatic cycle in the central Andes in northern Chile. Phases targeted for thermobarometry include amphibole, plagioclase, pyroxenes, and Fe–Ti oxides. Overall, crystallization is documented over 1–7.5 kbar (~25 km) of pressure and ~680–1,110 °C of temperature. Pressure estimates range from ~1 to 5 kbar for amphiboles and from ~3 to 7.5 kbar for pyroxenes. Pyroxene temperatures are tightly clustered from ~1,000–1,100 °C, Fe–Ti oxide temperatures range from ~750–1,000 °C, and amphibole temperatures range from ~780–1,050 °C. Although slightly higher, these temperatures correspond well with previously published zircon temperatures ranging from ~670–900 °C. Two different Fe–Ti oxide thermometers (Andersen and Lindsley 1985; Ghiorso and Evans 2008) are compared and agree well. We also compare amphibole and amphibole–plagioclase thermobarometers (Ridolfi et al. 2010; Holland and Blundy 1994; Anderson and Smith 1995), the solutions from which do not agree well. In samples where we employ multiple thermometers, pyroxene temperature estimates are always highest, zircon temperature estimates are lowest, and Fe–Ti oxide and amphibole temperature estimates fall in between. Maximum Fe–Ti oxide and zircon temperatures are observed during the middle stage of AVC activity (~5–3 Ma), a time associated with increased eruption rates. Amphibole temperatures during this time are relatively restricted (~850–1,000 °C). The crystal record presented here offers a time-transgressive view of an evolving, multi-tiered subvolcanic reservoir. Some crystals in AVC lavas are likely to be true phenocrysts, but the diversity of crystallization temperatures and pressures recorded by phases in individual AVC lavas suggests erupting magma extensively reams and accumulates crystals from disparate levels of the middle to upper crust.     

Reworking and resisting globalising influences: Cape Town hip-hop

Global cultural flows have emerged as key influences in driving changes in local consumer behaviour, identities and social relations. These flows are negotiated and contested in the local context. This article considers how local hip-hop artists in Cape Town, South Africa, challenge and disrupt the dominant images of success linked to consumerism and individualism in popular American music imports. Drawing on Katz’s (Signs 26(4):1213–1234, 2001a, Antipode 33(4):709–728, 2001b) thinking around topographies and counter-topographies, this article suggests that local political hip-hop can be used to develop powerful critiques of the outcomes of globalisation.