59 research outputs found
Feminist perspectives on times and spaces in distance learning
This study draws on a feminist perspective on time and space, or a feminist time and space literacy, in order to better understand the times and spaces in distance learning. I seek to respond to some of the key gaps in the literature by considering the multiplicity of times and spaces in distance learning, and the underpinning power relations, within respondents' stories of being a distance learner. This research makes a substantial contribution to the research on time, space and distance learning. This is not only in terms of bringing a feminist time and space literacy to the area of distance learning but, by doing so in conjunction with data collected over time and space, it also adds many new layers to the stories about the multiplicity of times and spaces in distance learners' lives, and the ways in which gendered and other power relations shape these. Moreover, this study has contributed to the wider body of feminist knowledge in seeking to explore a multiplicity of times and spaces in women and men's lives- as opposed to a binary of women's time and space and men's time and space - and in seeking to focus on time and space simultaneously
Feminist perspectives on times and spaces in distance learning
This study draws on a feminist perspective on time and space, or a feminist time and space literacy, in order to better understand the times and spaces in distance learning. I seek to respond to some of the key gaps in the literature by considering the multiplicity of times and spaces in distance learning, and the underpinning power relations, within respondents' stories of being a distance learner. This research makes a substantial contribution to the research on time, space and distance learning. This is not only in terms of bringing a feminist time and space literacy to the area of distance learning but, by doing so in conjunction with data collected over time and space, it also adds many new layers to the stories about the multiplicity of times and spaces in distance learners' lives, and the ways in which gendered and other power relations shape these. Moreover, this study has contributed to the wider body of feminist knowledge in seeking to explore a multiplicity of times and spaces in women and men's lives- as opposed to a binary of women's time and space and men's time and space - and in seeking to focus on time and space simultaneously.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Slow Cenozoic uplift of the western Andean Cordillera indicated by cosmogenic 3He in alluvial boulders from the Pacific Planation Surface
This material is based upon work supported by NERC grant (NER/S/A/2003/11945) and BHP Billiton. Data used in this study are provided from Evenstar et al. [2009] and from modelling detailed in the supporting information. We are grateful to Philip G. Roxby, Steve Sparks and Shasta Marrero for their help with preparation of the manuscript.Peer reviewedPublisher PD
Using spatial patterns of fluvial incision to constrain continental-scale uplift in the Andes
This study was funded by BHP and the University of Brighton Rising Stars. The authors are grateful to Marit Van Zalinge and Masie Mather for discussions on the manuscript.Peer reviewedPostprin
Orogenic-orographic feedback and the rise of the Central Andes
The rise of large mountain ranges is considered to be driven by tectonics potentially coupled with climate driven-erosion, although the role of this coupling remains uncertain. The arid climate of the Central Andes allows us to strengthen our understanding of the relative roles of these processes in mountain range development globally. Here we compile estimates of exhumation, sedimentation, aridity and surface uplift across the Central Andes for the last 50 Ma. We aim to place constraints on the relative timing of rock uplift (displacement of rocks with respect to the geoid), exhumation (displacement of rocks with respect to the surface) and surface uplift (displacement of the earth's surface with respect to the geoid). We show that initial rock uplift of the Andes extends back at least 50 Myr. This rock uplift generated orographically driven precipitation on windward slopes leading to increased exhumation but limited preservation of surface uplift. Eastward propagation of the mountain range resulted in increasingly extreme orographic effects on the leeward side amplifying aridity, reducing exhumation and increasing preservation of surface uplift. Essentially, surface uplift shows a ∼5-10 Myr lag behind initial rock uplift as the Andes grow asymmetrically through time. We suggest that an eastward propagating pattern of exhumation, aridity and surface uplift with time, reconciles previous contradictory models of Andean uplift. One Sentence Summary: Uplift of the Central Andes is reconstructed over the last 50 Myr and the precise relationship between roles of tectonics and climate established
A rusty record of weathering and groundwater movement in the hyperarid Central Andes
The Atacama Desert, on the western margin of the Central Andes, hosts some of the world's largest porphyry copper deposits (PCDs). Despite a hyperarid climate, many of these PCDs have undergone secondary “supergene” enrichment, whereby copper has been concentrated via groundwater-driven leaching and reprecipitation, yielding supergene profiles containing valuable records of weathering and landscape evolution. We combine hematite (U-Th-Sm)/He geochronology and oxygen isotope analysis to compare the weathering histories of two Andean PCDs and test the relative importance of climate and tectonics in controlling both enrichment and water table movement. At Cerro Colorado, in the Precordillera, hematite precipitation records prolonged weathering from ∼31 to ∼2 Ma, tracking water table descent following aridity-induced canyon incision from the late Miocene onward. By contrast, hematite at Spence, within the Central Depression, is mostly younger than ∼10.5 Ma, suggesting exhumation ended much later. A heavy oxygen isotopic signature for Spence hematite suggests that upwelling formation water has been an important source of groundwater, accounting for a high modern water table despite persistent hyperaridity, whereas isotopically light hematite at Cerro Colorado formed in the presence of meteoric water. Compared with published paleo-environmental and sedimentological records, our data show that weathering can persist beneath appreciable post-exhumation cover, under hyperarid conditions unconducive to enrichment. The susceptibility of each deposit to aridity-induced water table descent, canyon incision and deep weathering has been controlled by recharge characteristics and morphotectonic setting. Erosional exhumation, rather than aridity-induced water table decay, appears to be more important for the development of supergene enrichment
Geomorphology on geologic timescales: Evolution of the late Cenozoic Pacific paleosurface in Northern Chile and Southern Peru
publisher: Elsevier articletitle: Geomorphology on geologic timescales: Evolution of the late Cenozoic Pacific paleosurface in Northern Chile and Southern Peru journaltitle: Earth-Science Reviews articlelink: http://dx.doi.org/10.1016/j.earscirev.2017.04.004 content_type: article copyright: © 2017 Elsevier B.V. All rights reserved
Using ignimbrites to quantify structural relief growth and understand deformation processes: implications for the development of the Western Andean Slope, northernmost Chile
Large-volume ignimbrites are excellent spatial and temporal markers for local deformation and structural relief growth because they completely inundate and bury the underlying paleotopography and leave planar surfaces with relatively uniform, low-gradient slopes dipping less than 2°. Using one of these planar surfaces as a reference frame, we employed a line-balanced technique to reconstruct the original morphology of an ignimbrite that has undergone postemplacement deformation. This method allowed us to constrain both the amount of posteruptive deformation and the topography of the pre-eruptive paleolandscape. Our test case was the unwelded surface of the 21.9 Ma Cardones ignimbrite, located on the western slope of the Central Andes in northernmost Chile (18°20′S). By reconstructing the original surface slope of this ignimbrite, we demonstrate that the pre–21.9 Ma topography of the Western Andean Slope was characterized by structural relief growth and erosion in the east, and the creation of accommodation space and sedimentation in the west. The paleoslope at that time was dissected by river valleys of up to 450 ± 150 m deep that accumulated great thicknesses (>1000 m) of the Cardones ignimbrite, and likely controlled the location of the present-day Lluta Quebrada as a result of differential welding compaction of the ignimbrite. Our reconstruction suggests that growth of the Western Andean Slope had already started by ca. 23 Ma, consistent with slow and steady models for uplift of the Central Andes. Subsequent deformation in the Miocene generated up to 1725 ± 165 m of structural relief, of which more than 90% can be attributed to fault-related folding of the ∼40-km-wide Huaylillas anticline. Uplift related to regional forearc tilting is less than 10% and could have been zero. The main phase of folding likely occurred in the mid- to late Miocene and had ceased by ca. 6 Ma
Pluton Exhumation in the Precordillera of Northern Chile (17.8°–24.2°S): implications for the Formation, Enrichment, and Preservation of Porphyry Copper Deposits
Hypogene mineralization in porphyry Cu deposits is typically associated with crustal thickening and rapid exhumation, whereas supergene enrichment requires slow exhumation to allow sufficient time for leaching and downward transport of Cu before it is lost to surface erosion. Therefore, spatial and temporal patterns of exhumation within a metallogenic belt can highlight favorable locations for hypogene mineralization, supergene enrichment, and preservation. Here, we determine average pluton exhumation rates along an ~730-km segment of the middle Eocene-early Oligocene metallogenic belt in northern Chile (17.8°–24.2°S). By combining zircon U-Pb geochronology with Al-in-hornblende geobarometry, we pinpoint the time and depth at which each pluton was emplaced and use the age of overlying cover units or supergene minerals to date its arrival at the surface (or near-surface) environment.
Uranium-lead zircon ages for 49 samples from plutons and porphyries range from Carboniferous to Eocene (~314–35 Ma). Al-in-hornblende emplacement depths for 19 plutons are ~4–7 km, with one Carboniferous pluton emplaced at ~12 km. Two phases of net exhumation are identified: early Permian-Middle Triassic and middle Eocene-late Oligocene, with an intervening period of net burial. The highest exhumation rates (>0.30 km/m.y.) derive from the second phase, coeval with the Incaic orogeny and the main phase of hypogene mineralization. Present-day preservation of plutons and porphyry Cu deposits required low post-Oligocene average exhumation rates of <~0.01 km/m.y.—favorable for the development of many world-class supergene blankets. However, spatial variability in exhumation and burial across the belt led to poor conditions for supergene development locally: enrichment was hampered in some places by rapid exhumation after hypogene mineralization (e.g., ≥~4 km at El Abra), by burial beneath significant cover (e.g., Ministro Hales, Queen Elizabeth), or, in the Inti region of northernmost Chile, by a combination of the two
Origin and development of theater-headed valleys in the Atacama Desert, northern Chile: Morphological analogs to martian valley networks
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