Solutions of one‐dimensional transport equations indicate that the time‐space evolution of oxygen isotope exchange between rock and infiltrating fluid is dependent on 1)the rate of fluid infiltration, 2)the dispersive properties of the rock matrix, 3)the rate of isotopic exchange, and 4)the mass oxygen ratio. The geometry of isotopic exchange fronts developed in a rock sequence depends on the interplay between these first three parameters. The change in isotopic ratio in a rock depends on its position in the flowpath and the rate of isotopic exchange with the fluid in addition to the cumulative fluid flux. Thus conventional water/rock (W/R) ratios will also depend on position in flow paths. Absence of significant 18 O depletions in rock sequences does not require low W/R ratios, but may only mean that the rock is in a rock‐dominated segment of a flowpath or alternatively that fluid infiltration was characterized by nonequilibrium exchange.
This dataset is supplemented to Wang, Y., Willett, S., Wu, D., Haghipour, N., & Christl, M. (2021). Retreat of the Great Escarpment of Madagascar from Geomorphic Analysis and Cosmogenic 10Be Concentrations. https://doi.org/10.1002/essoar.10507366.1. (in revision and under consideration at G-Cubed).
Research Article| October 01, 2003 Mantle flow, dynamic topography, and rift-flank uplift of Arabia Amy Daradich; Amy Daradich 1Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada Search for other works by this author on: GSW Google Scholar Jerry X. Mitrovica; Jerry X. Mitrovica 1Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada Search for other works by this author on: GSW Google Scholar Russell N. Pysklywec; Russell N. Pysklywec 2Department of Geology, University of Toronto, Toronto, Ontario M5S 3B1, Canada Search for other works by this author on: GSW Google Scholar Sean D. Willett; Sean D. Willett 3Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Alessandro M. Forte Alessandro M. Forte 4Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information Amy Daradich 1Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada Jerry X. Mitrovica 1Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada Russell N. Pysklywec 2Department of Geology, University of Toronto, Toronto, Ontario M5S 3B1, Canada Sean D. Willett 3Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA Alessandro M. Forte 4Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada Publisher: Geological Society of America Received: 17 Mar 2003 Revision Received: 18 Jun 2003 Accepted: 08 Jul 2003 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2003) 31 (10): 901–904. https://doi.org/10.1130/G19661.1 Article history Received: 17 Mar 2003 Revision Received: 18 Jun 2003 Accepted: 08 Jul 2003 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Amy Daradich, Jerry X. Mitrovica, Russell N. Pysklywec, Sean D. Willett, Alessandro M. Forte; Mantle flow, dynamic topography, and rift-flank uplift of Arabia. Geology 2003;; 31 (10): 901–904. doi: https://doi.org/10.1130/G19661.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Rift-flank uplift adjacent to the Red Sea is asymmetric, i.e., a broad tilt of the entire Arabian plate along an axis parallel to the rift and more localized uplift on the African shoulder. A suite of models has been proposed to explain this pattern, but no model has considered the dynamic effects of large-scale mantle flow. Recent high-resolution images from seismic tomography show a massive, anomalously slow shear velocity structure that emerges from the core-mantle boundary beneath South Africa and that reaches close to the surface at the Red Sea. This buoyant megaplume has been identified as the driving mechanism for anomalously high topography in southern Africa and rifting in East Africa; in this paper we investigate its role in present-day African-Arabian topography. In particular, we present predictions of dynamic topography based on viscous-flow simulations initiated using seismically inferred mantle heterogeneity. These predictions demonstrate that viscous stresses associated with mantle flow are responsible for the long-wavelength signal in African-Arabian flank uplift. Our results do not preclude localized topographic contributions from other processes, particularly within the near field of the Red Sea. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Abstract. We present a formal inverse procedure to extract exhumation rates from spatially distributed low temperature thermochronometric data. Our method is based on a Gaussian linear inversion approach in which we define a linear problem relating exhumation rate to thermochronometric age with rates being parameterized as variable in both space and time. The basis of our linear forward model is the fact that the depth to the "closure isotherm" can be described as the integral of exhumation rate, ..., from the cooling age to the present day. For each age, a one-dimensional thermal model is used to calculate a characteristic closure temperature, and is combined with a spectral method to estimate the conductive effects of topography on the underlying isotherms. This approximation to the four-dimensional thermal problem allows us to calculate closure depths for data sets that span large spatial regions. By discretizing the integral expressions into time intervals we express the problem as a single linear system of equations. In addition, we assume that exhumation rates vary smoothly in space, and so can be described through a spatial correlation function. Therefore, exhumation rate history is discretized over a set of time intervals, but is spatially correlated over each time interval. We use an a priori estimate of the model parameters in order to invert this linear system and obtain the maximum likelihood solution for the exhumation rate history. An estimate of the resolving power of the data is also obtained by computing the a posteriori variance of the parameters and by analyzing the resolution matrix. The method is applicable when data from multiple thermochronometers and elevations/depths are available. However, it is not applicable when there has been burial and reheating. We illustrate our inversion procedure using examples from the literature.
One of the important developments in Earth science over the past decade has been recognition of the significance of linking deep Earth dynamic processes with surface and near‐surface geologic processes [e.g., Braun , 2010]. Deep Earth research, encompassing fields such as seismology and mantle geodynamics, has traditionally operated distinctly from fields focusing on dynamics of the Earth's surface, such as sedimentology and geomorphology. However, these endeavors have in common the study of Earth's topography and the prediction of changes in its surface. Observables from surface studies, such as basin stratigraphy, geomorphology of landscapes, changes in surface elevation, and changes in sea level, provide some of the principal constraints on geodynamic and tectonic models. Conversely, deep geodynamic processes give rise to the topography, erosion, and sediment generation that are the basis of surface geology. Surface manifestations of deep geodynamic processes have significant societal impact by creating natural hazards, such as earthquakes and mass movements, and controlling the distribution of natural resources such as fossil fuels or geothermal energy. The relevance of research conducted in both the deep Earth and surface regimes is thus enhanced through a focus on their interaction.
Critical wedge theory provides a direct link between the form of an orogen, the rate of orogen evolution, and the accretionary and erosional fluxes that promote orogen growth and decay, respectively. We explore several fundamental characteristics of an eroding critical orogen: (1) the sensitivity of steady-state orogen size to tectonic and climatic forcing, (2) the response time of a critical orogen to perturbations in forcing, and (3) the behavior of surface topography and the rock uplift field in a system in which they are not prescribed. To do this, we develop a numerical model that couples a two-dimensional, planform surface erosion model with a two-dimensional, plane-strain finite element model of deformation. We first present a base model in which a critical orogen evolves to a steady-state under boundary conditions similar to those of analog sandbox experiments. We find that mean topography and tectonic uplift reach steady states, whereas planform topography remains dynamic throughout the simulation. From a suite of simulations, we determine the steady-state scaling relationship between orogen size and tectonic and climatic forcing and find good agreement with predictions from one-dimensional models. In addition, we examine the response of the steady-state orogen to climatic and tectonic perturbation with four simulations in which changes in tectonic and climatic conditions lead to either growth or contraction of the orogen to a new steady state. We show that the response time to perturbation agrees well with predictions from a one-dimensional semi-analytical model. We find that the transient evolution of erosion rate and erosional flux is potentially useful for distinguishing between tectonic and climatic forcing mechanisms.
Reconstructing paleo-denudation rates over Holocene timescales in an Alpine catchment provides a unique opportunity to isolate the climatic forcing of denudation from other tectonic or anthropogenic effects. Cosmogenic 10 Be on two sediment cores from Lake Stappitz (Austrian Alps) were measured yielding a 15-kyr-long catchment-averaged denudation record of the upstream Seebach Valley. The persistence of a lake at the outlet of the valley fixed the baselevel, and the high mean elevation minimizes anthropogenic impacts. The 10 Be record indicates a decrease in the proportion of paraglacial sediments from 15 to 7 kyr cal. BP after which the 10 Be concentrations are considered to reflect hillslope erosion and thus can be converted to denudation rates. These ones significantly fluctuated over this time period: lower hillslope erosion rates of ca. 0.4 mm/year dated between 5 and 7 kyr cal. BP correlate with a stable climate, sparse flooding events and elevated temperatures that favoured the widespread growth of stabilizing soils and vegetation. Higher hillslope erosion rates of ca. 0.8 mm/year over the last ~4 kyr correlate with a variable, cooler climate where frequent flooding events enhance denudation of less protected hillslopes. Overall, our results suggest a tight coupling of climate and hillslope erosion in alpine landscapes as it has been observed in other parts of the Alps.
The lateral movement of Earth’s crust through tectonic advection plays an important role in shaping topography in many active orogens worldwide. Numerical modelling and select field studies have shown that tectonic advection can alter topography and thereby create asymmetric drainage divides. Divide migration typically occurs opposite to the direction of tectonic advection, however, in many mountain belts, the wedge-tip propagation towards the foreland outpaces the rate of convergence, in which case the direction of topographic asymmetry should be reversed. We combine geomorphic and geodetic analyses with numerical models to test whether topographic asymmetry in the Longmenshan region of Southeast Tibet is dominated by advection of the crust from the ongoing India-Eurasia collision, movement of river base-level with the propagation of the thrust front into the Sichuan Basin, or other tectonic and climatic factors. We measure the magnitude and direction of drainage divide asymmetry using geomorphic metrics and compare these to horizontal GNSS velocities, which measure tectonic advection and shortening relative to the stable Sichuan Basin block. Geologic studies estimate that wedge-tip propagation toward the Sichuan Basin has been negligible since ~5-10 Ma.Our results show that drainage divide asymmetries in the Longmenshan and Bayankala tectonic blocks indicate a dominantly northwest divide migration direction relative to the underlying rock. This is opposite to the dominantly southeast-pointing GNSS rates and suggests that within-wedge shortening and southward surface advection are more important than wedge-tip propagation. These findings also indicate that topography in the Longmenshan and Bayankala blocks has already adjusted to the current kinematics. Inconsistencies in the signal can be explained by localized deformation and uplift from faulting and other small-scale transient adjustments in the river network, such as those caused by stream captures. We compare these results to a series of numerical model scenarios with varying advection and wedge-tip propagation velocities to discern the relative influence of tectonic advection and thrust-front dynamics on the region’s topography. Our study highlights the critical role tectonic advection plays in shaping topography on the Southeast Tibetan Plateau and it provides a comparative framework for distinguishing the relative rates of advection and wedge-tip propagation.
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