Geochemistry of Cretaceous Magmatism in Eastern Cuba: Recycling of North American Continental Sediments and Implications for Subduction Polarity in the Greater Antilles Paleo-arc

We present whole-rock major- and trace-element and Nd–Sr–Pbradiogenic isotope data for Cretaceous igneous suites from easternCuba. These rocks are related to the Greater Antilles paleo-islandarc magmatism and have three different igneous styles. Group1 consists of tholeiitic basalts and rare basaltic andesitesthat have normal mid-ocean ridge basalt (N-MORB)-like compositionssimilar to those found in back-arc basin basalts (TiO₂ = 1·2–2·9wt%; La/Yb_(N) = 0·7–0·9, Th/Nb = 0·06–0·08,and initial ²⁰⁸Pb/ ²⁰⁴Pb = 37·65–37·74).Group 2 comprises basaltic and rare basaltic andesitic subvolcanicdykes with major- and trace-element and isotopic compositionssimilar to those of island arc tholeiites (TiO₂ = 0·7–1·4wt%; La/Yb_(N) = 0·6–0·9, Th/Nb = 0·06–0·68,and initial ²⁰⁸Pb/ ²⁰⁴Pb = 37·74–38·25).Group 3 is composed of low-Ti (TiO₂ = 0·3–0·9wt%) calcalkaline igneous rocks that have an unambiguous subduction-relatedcharacter (La/Yb_(N) = 1·1–5·0, Th/Nb = 0·35–1·55,and initial ²⁰⁸Pb/ ²⁰⁴Pb = 37·94–38·39).The parental magmas of the three groups formed by variable meltingdegrees (< 5–25%) of spinel lherzolite, with more depletedmantle sources for Groups 2 and 3 than Group 1. The trace-elementand radiogenic isotope compositions of primitive Group 3 samplesare strongly bimodal. One subgroup of samples is characterizedby low Ta/Yb (0·02–0·03) and Th/La (0·10–0·13),slightly subchondritic Nb/Ta (13·3–17·3),and relatively high initial ²⁰⁶Pb/²⁰⁴Pb (18·57–18·62)and _Nd (7·6–9·4). The remaining primitiveGroup 3 samples have higher Ta/Yb (0·06–0·11)and Th/La (0·24–0·32), and highly subchondriticNb/Ta (7·6–9·1), coupled with lower initial²⁰⁶Pb/²⁰⁴Pb (18·24–18·29) and _Nd (3·4–5·5).These signatures were induced by two distinct slab componentsthat mainly reflect the contributions of Cretaceous Atlanticmarine and North American continental sediments, respectively.Nb/Ta in the first subgroup was influenced by melting of rutile-bearingsubducted crust, whereas in the second it was inherited fromrecycled continental sediments. The involvement of Atlanticand North American sediments in Cuban Cretaceous magmatism indicatesthat the Proto-Caribbean (North American-Proto Atlantic) lithospheresubducted beneath the Greater Antilles arc during the Late Cretaceous(pre-Campanian), consistent with geotectonic models involvingonset of SW-dipping subduction beneath the Greater Antillespaleo-arc during the Aptian. The variable mantle source depletionand magnitude of the subduction component probably reflect differentsettings across the arc, from the arc front to a back-arc spreadingridge. KEY WORDS: eastern Cuba; Greater Antilles paleo-island arc; mantle source depletion; Nb/Ta fractionation; slab component     

Directional response of a reconstituted fine‐grained soil—Part II: performance of different constitutive models

In this paper, the performance of different advanced constitutive models for soils is evaluated with respect to the experimentally observed behaviour of a soft reconstituted clay subject to a wide range of loading directions, see (presented in the companion paper). The models considered include a three‐surface kinematic hardening elastoplastic model; the CLoE hypoplastic model; a recently proposed K‐hypoplastic model for clays, and an enhanced version of the same model incorporating the concept of intergranular strain. A clear qualitative picture of the relative performance of the different models as a function of the loading direction is obtained by means of the incremental strain response envelopes. The definition of suitable error measures allows to obtain further quantitative information in this respect. For the particular initial conditions and loading programme considered in this study, the kinematic hardening and the enhanced K‐hypoplastic models appear to provide the best performance overall. Copyright © 2006 John Wiley & Sons, Ltd.     

Platform margin collapses and sequence stratigraphic organization of carbonate slopes: Cretaceous–Eocene,Gargano Promontory,southern Italy

We describe the sequence stratigraphic organization and the associated sedimentological characteristics of Cretaceous to Eocene slope and base-of-slope carbonate successions. The study area is located in the Gargano Promontory which belongs to the stable foreland of southern Italy. The succession consists of three superimposed depositional sequences separated by major unconformities. The upper two sequences are clear examples of sequence stratigraphic organization; in fact, they both start with huge megabreccia wedges (LST) followed upward by thin pelagic units (TST) and a thick package of calciturbidites and debrites that alternate with pelagic mudstone (HST). The Cretaceous highstand systems tract is clearly arranged in a number of coarsening-upward cycles while the Eocene one which also comprises a toplap shallow water unit, is not. The Gargano stratigraphic palimpsest and the entire margin of the Apulia Platform show remarkable similarities with present-day carbonate platform margins and slopes where irregular, convex-bankward embayments suggest large-scale failures. It is clear that classic sequence stratigraphic organization can result from simple platform dismantling, having no or little time relation with global sea-level fluctuations. In fact, as the margin failure (LST) interrupts the carbonate production, a period of starvation (TST) along the entire slope and base-of-slope follows necessarily. Finally, when the margin once again becomes active and productive, sediment exportation starts again and the system begins to prograde (HST).     

Plasticity with generalized hardening: constitutive modeling and computational aspects

In this work, an extended theory of plasticity with generalized hardening is proposed to describe the response of geomaterials under both mechanical and environmental processes, which include as special cases several elastoplastic constitutive equations proposed in the literature to model such processes as desaturation or suction hardening, thermal softening, chemo-mechanical coupling effects in fine-grained soils, as well as weathering of soft rocks. In the formulation of the theory, the coupling between mechanical and environmental processes takes place at two levels: first, as an additional direct contribution to the constitutive stress changes, taking place in both elastic and elastoplastic processes; and second, as a result of the evolution of the internal state variables induced by changes in the environmental process variables. This last effect is incorporated through a set of generalized hardening rules. As an example of application, the general formulation is specialized to the particular case of weak calcarenite rocks undergoing degradation processes due to plastic deformations, changes in degree of saturation (short-term debonding) and chemical dissolution of the bond material and the solid grains (long-term debonding). The resulting model is implemented in a FE code by means of an implicit generalized backward Euler algorithm, suitably modified to incorporate the full formalism of plasticity with generalized hardening. Results of numerical simulations carried out at the element level show the accuracy and efficiency properties of the proposed stress-point algorithm. The simulation of a representative initial-boundary value problem demonstrates the practical relevance of environmental degradation effects in practical applications, over periods of time comparable with the life cycle of most geotechnical structures.     

Analytical formulation of impulsive collision avoidance dynamics

The paper deals with the problem of impulsive collision avoidance between two colliding objects in three dimensions and assuming elliptical Keplerian orbits. Closed-form analytical expressions are provided that accurately predict the relative dynamics of the two bodies in the encounter b-plane following an impulsive delta-V manoeuvre performed by one object at a given orbit location prior to the impact and with a generic three-dimensional orientation. After verifying the accuracy of the analytical expressions for different orbital eccentricities and encounter geometries the manoeuvre direction that maximises the miss distance is obtained numerically as a function of the arc length separation between the manoeuvre point and the predicted collision point. The provided formulas can be used for high-accuracy instantaneous estimation of the outcome of a generic impulsive collision avoidance manoeuvre and its optimisation.     

Discussing the definition of the second‐order work for unsaturated soils

The volumetric compaction due to wetting processes is a phenomenon observed quite often in unsaturated soils. Under certain circumstances, saturation events can result into a sudden and unexpected collapse of the system. These phenomena are usually referred to as wetting‐induced collapses, without providing any detailed theoretical justification for this terminology. In order to predict in a general fashion the occurrence of coupled instabilities induced by saturation processes, a generalization of the theoretical approaches usually employed for saturated geomaterials is here provided. More specifically, this paper addresses the problem of hydro‐mechanical instability in unsaturated soils from an energy standpoint. For this purpose, an extension of the definition of the second‐order work is here suggested for the case of unsaturated porous media. On the basis of some examples of numerical simulations of laboratory tests, coupled hydro‐mechanical instabilities are then interpreted in the light of this second‐order energy measure. Finally, the implications of the theoretical results here presented are commented from a constitutive modelling perspective. Two possible alternative approaches to formulate incremental coupled constitutive relations are indeed discussed, showing how the onset of hydro‐mechanical instabilities can be predicted using an extended form of Hill's stability criterion. Copyright © 2010 John Wiley & Sons, Ltd.     

Early Holocene climate change and human occupation along the semiarid coast of north‐central Chile

The brief, terminal Pleistocene archaeological site at Santa Julia (SJ, 31° 50′ S; 71° 45′ W) is the only one with fluted projectile preforms and megafauna consumption known from the Chilean semiarid coastline. Here, we present the climatic history at SJ during the early Holocene reconstructed from pollen and charcoal analyses spanning 13.2–8.6 ka (=10³ calibrated ¹⁴C yr BP). Elevated charcoal concentrations confirm human activity by 13.2 ka. Human occupation decreased in intensity and charcoal practically disappears from the record after 10.6 ka, followed by wetland expansion at SJ between 10.5 and 9.5 ka. Local dominance of coastal shrubland reveals that dry phases occurred between >11.2–10.5 and 9.5–9.0 ka. Overall, these findings imply that by modulating available resources at both local and landscape levels climate change may have played an important role in explaining the peopling of semiarid coastal Chile. Copyright © 2010 John Wiley & Sons, Ltd.     

Climate change and human occupation in the northernmost Chilean Altiplano over the last ca. 11 500 cal. a BP

This interdisciplinary study represents an approximation towards understanding how regional human cultural systems may have been affected by climate change in the northernmost Chilean Altiplano (>3600 m) over the last ca. 11 500 cal a BP. We compare the archaeological record from Hakenasa cave with the lake record from Lago Chungará sediment cores, located 50 km to the south. By integrating both of these archives in conjunction with regional palaeoclimate and archaeological data, we provide new evidence for the role of changing environmental and climatic conditions in human settlement patterns. The first human occupation of the entire Altiplano occurs at Hakenasa and is dated to 9980 ± 40 ¹⁴C a BP (11 265–11 619 cal. a BP), and took place under wetter regional climate conditions. An archaeologically sterile deposit occurs at Hakenasa between 7870 and 6890 cal. a BP. Constituted by sands and gravels, these sediments are interpreted as a flood event. This time period is synchronous with alternating short dry and wet events recorded in the Lake Chungará sedimentary sequence. Human activity resumes and increases in importance at Hakenasa by ca. 6000 cal. a BP. This corresponds to wetter conditions indicated by the Chungará record. Even though the lake record indicates intense volcanic activity over the last 6000 cal. a BP, this had little or no impact on the human population present at Hakenasa. This study shows that even in this extreme environment human settlement patterns do not always respond in a linear fashion to environmental change. Copyright © 2008 John Wiley & Sons, Ltd.     

Local effects of redundant terrestrial and GPS-based tie vectors in ITRF-like combinations

Tie vectors (TVs) between co-located space geodetic instruments are essential for combining terrestrial reference frames (TRFs) realised using different techniques. They provide relative positioning between instrumental reference points (RPs) which are part of a global geodetic network such as the international terrestrial reference frame (ITRF). This paper gathers the set of very long baseline interferometry (VLBI)–global positioning system (GPS) local ties performed at the observatory of Medicina (Northern Italy) during the years 2001–2006 and discusses some important aspects related to the usage of co-location ties in the combinations of TRFs. Two measurement approaches of local survey are considered here: a GPS-based approach and a classical approach based on terrestrial observations (i.e. angles, distances and height differences). The behaviour of terrestrial local ties, which routinely join combinations of space geodetic solutions, is compared to that of GPS-based local ties. In particular, we have performed and analysed different combinations of satellite laser ranging (SLR), VLBI and GPS long term solutions in order to (i) evaluate the local effects of the insertion of the series of TVs computed at Medicina, (ii) investigate the consistency of GPS-based TVs with respect to space geodetic solutions, (iii) discuss the effects of an imprecise alignment of TVs from a local to a global reference frame. Results of ITRF-like combinations show that terrestrial TVs originate the smallest residuals in all the three components. In most cases, GPS-based TVs fit space geodetic solutions very well, especially in the horizontal components (N, E). On the contrary, the estimation of the VLBI RP Up component through GPS technique appears to be awkward, since the corresponding post fit residuals are considerably larger. Besides, combination tests including multi-temporal TVs display local effects of residual redistribution, when compared to those solutions where Medicina TVs are added one at a time. Finally, the combination of TRFs turns out to be sensitive to the orientation of the local tie into the global frame.