Denudation rates and a topography-driven rainfall threshold in northern Chile: Multiple cosmogenic nuclide data and sediment yield budgets

Abstract The quantification of geomorphic process rates on the outcrop- and the orogen-scale is important to describe accurately the interaction between the relative effects of erosion, tectonics and climate on landscape evolution. We report single and paired cosmogenic nuclide ( 10 Be, 26 Al and 21 Ne) derived erosion rates and exposure ages on hillslope interfluves from the tectonically active western central Andes that show a distinct spatial variation. A positive correlation of erosion rates with elevation and present-day rainfall rates is observed. Erosion rates at lower altitudes–the hyperarid Coastal Cordillera and the Western Escarpment with the northern part of the Atacama Desert –are extremely low and of the order of 10–100 cm/My (nominal exposure ages 1–6 My). In contrast, erosion rates at higher altitudes–the semiarid Western Cordillera –range up to 4600 cm/My (nominal exposure ages 0.02–0.1 My). This latter average long-term bedrock erosion rate record, suggested to be coupled to an orographically controlled pattern of rainfall, is also reflected in the pattern of denudation rates derived from a short-term decadal record of limited sediment yield data. Specifically, denudation rates calculated from sediment flux data are of a similar order of magnitude as erosion rates deduced from long-lived cosmogenic nuclides from bedrock hillslope interfluves of the Western Cordillera . Nevertheless, the production and the supply of sediment from the western Andean slope are very limited. Analysis of multiple cosmogenic nuclides allows simultaneous determination of erosion rates and exposure ages but also reveals complex exposure histories of non-bedrock samples, such as boulders or amalgamated clast samples. Notably, this study shows that saturation of nuclides, usually assumed in studies where only a single nuclide is analyzed, is rather the exception than the rule, as revealed by erosion island plots. Constant erosion that started much later than the formation age of the rocks or episodic erosion by spalling can partially explain non-steady-state concentrations and more complicated exposure scenarios. Furthermore, the use of multiple nuclides with different half-lives allowed us to infer that no significant variations in long-term erosion rates have occurred and that at the Western Escarpment erosion rates have been low and constant for most of the late Neogene . Nevertheless, the time intervals necessary to reach steady-state concentrations for cosmogenic nuclides can be quite different from those needed for landscapes to reach steady state.

[1]  O. C. Allkofer.  Introduction to cosmic radiation , 1975 .

[2]  M. Döbeli,et al.  Status report of the PSI/ETH AMS facility , 1997 .

[3]  F. Schlunegger,et al.  The Oxaya anticline (northern Chile): a buckle enhanced by river incision? , 2005 .

[4]  S. Niedermann.  Cosmic-ray-produced noble gases in terrestrial rocks: Dating tools for surface processes , 2002 .

[5]  M. Summerfield.  Geomophology and Global Tectonics , 2000 .

[6]  M. Caffee,et al.  Slow Rates of Rock Surface Erosion and Sediment Production across the Namib Desert and Escarpment, Southern Africa , 2001 .

[7]  P. Kubik,et al.  Minimum 10Be exposure ages of early Pliocene for the Table Mountain plateau and the Sirius Group at Mount Fleming, Dry Valleys, Antarctica , 1995 .

[8]  C. Alpers,et al.  Middle Miocene climatic change in the Atacama desert , 1988 .

[9]  Adrian J. Hartley,et al.  The central Andean west‐slope rainshadow and its potential contribution to the origin of hyper‐aridity in the Atacama Desert , 2003 .

[10]  J. Darrozes,et al.  A geomorphological approach to determining the Neogene to Recent tectonic deformation in the Coastal Cordillera of northern Chile (Atacama) , 2003 .

[11]  R. Anderson,et al.  EROSION RATES OF ALPINE BEDROCK SUMMIT SURFACES DEDUCED FROM IN SITU 10BE AND 26AL , 1997 .

[12]  M. Summerfield,et al.  Geomorphological applications of cosmogenic isotope analysis , 2004 .

[13]  C. Riebe,et al.  Erosional and climatic effects on long-term chemical weathering rates in granitic landscapes spanning diverse climate regimes ☆ , 2004 .

[14]  F. Phillips,et al.  Terrestrial in situ cosmogenic nuclides: theory and application , 2001 .

[15]  P. Kubik,et al.  Production of selected cosmogenic radionuclides by muons 1. Fast muons , 2002 .

[16]  F. Schlunegger,et al.  Assessing the age of relief growth in the Andes of northern Chile: Magneto‐polarity chronologies from Neogene continental sections , 2005 .

[17]  T. P. Ojha,et al.  Decoupling of erosion and precipitation in the Himalayas , 2003, Nature.

[18]  David R. Montgomery,et al.  Climate, tectonics, and the morphology of the Andes , 2001 .

[19]  S. Ivy‐Ochs,et al.  Production of selected cosmogenic radionuclides by muons: 2. Capture of negative muons , 2002 .

[20]  M. Meybeck.  Global chemical weathering of surficial rocks estimated from river dissolved loads , 1987 .

[21]  Cedric Mortimer Santiago,et al.  Cenozoic studies in northernmost Chile , 1975 .

[22]  Paul Davis,et al.  Cenozoic climate change as a possible cause for the rise of the Andes , 2003, Nature.

[23]  M. Grosjean,et al.  From proxy data to paleoclimate interpretation: the mid-Holocene paradox of the Atacama Desert, northern Chile , 2003 .

[24]  N. Hovius,et al.  Paleoerosion Rates from Cosmogenic 10Be in a 1.3 Ma Terrace Sequence: Response of the River Meuse to Changes in Climate and Rock Uplift , 2004, The Journal of Geology.

[25]  K. M. Gregory-Wodzicki,et al.  Uplift history of the Central and Northern Andes: A review , 2000 .

[26]  R. Wieler,et al.  Correction of in situ cosmogenic nuclide production rates for geomagnetic field intensity variations during the past 800,000 years , 2001 .

[27]  Revealing histories of exposure using in situ produced (super 26) Al and (super 10) Be in Libyan Desert glass. , 1986 .

[28]  David R. Montgomery,et al.  Topographic controls on erosion rates in tectonically active mountain ranges , 2002 .

[29]  Marcelo H. García,et al.  Fault-related folding, drainage network evolution and valley incision during the Neogene in the Andean Precordillera of Northern Chile , 2005 .

[30]  Tibor J. Dunai,et al.  Oligocene Miocene age of aridity in the Atacama Desert revealed by exposure dating of erosion-sensitive landforms , 2005 .

[31]  K. Nishiizumi,et al.  Cosmic‐ray produced neon in Antarctic rocks , 1991 .

[32]  J. Stone.  Air pressure and cosmogenic isotope production , 2000 .

[33]  S. Willett,et al.  On steady states in mountain belts , 2002 .

[34]  G. Wörner,et al.  Evolution of the West Andean Escarpment at 18°S (N. Chile) during the last 25 Ma: uplift, erosion and collapse through time , 2002 .

[35]  M. Caffee,et al.  Cosmogenic exposure and erosion history of Australian bedrock landforms , 2002 .

[36]  Rech,et al.  A 22,000-Year Record of Monsoonal Precipitation from Northern Chile's Atacama Desert. , 2000, Science.

[37]  P. Kubik,et al.  Cosmogenic nuclide evidence for low weathering and denudation in the wet, tropical highlands of Sri Lanka , 2004 .

[38]  E. Farrar,et al.  K-Ar ages from Tertiary lavas of the northernmost Chilean Andes , 1974 .

[39]  L. Kulm,et al.  Sedimentation in the Chile Trench; petrofacies and provenance , 1987 .

[40]  Cedrig Mortimer,et al.  The Cenozoic history of the southern Atacama Desert, Chile , 1973, Journal of the Geological Society.

[41]  M. Summerfield,et al.  Quantifying denudation rates on inselbergs in the central Namib Desert using in situ–produced cosmogenic 10Be and 26Al , 1999 .

[42]  R. Tosdal,et al.  Cenozoic polyphase landscape and tectonic evolution of the Cordillera Occidental, southernmost Peru , 1984 .

[43]  D. Montgomery,et al.  Coupled spatial variations in precipitation and long-term erosion rates across the Washington Cascades , 2003, Nature.

[44]  R. Wieler,et al.  Noble Gases : In Geochemistry and Cosmochemistry , 2002 .

[45]  S. Niedermann.  The 21Ne production rate in quartz revisited , 2000 .

[46]  Dimitri Lague,et al.  Links between erosion, runoff variability and seismicity in the Taiwan orogen , 2003, Nature.

[47]  B. Isacks.  Uplift of the Central Andean Plateau and bending of the Bolivian orocline , 1988 .

[48]  P. Kubik,et al.  10BE AND 26AL PRODUCTION RATES DEDUCED FROM AN INSTANTANEOUS EVENT WITHIN THE DENDRO-CALIBRATION CURVE, THE LANDSLIDE OF KOFELS, OTZ VALLEY, AUSTRIA , 1998 .

[49]  C. Ammann,et al.  Late Quaternary Glacier response to humidity changes in the arid Andes of Chile (18–29°S) , 2001 .

[50]  M. Hulme,et al.  A high-resolution data set of surface climate over global land areas , 2002 .

[51]  M. N. Christensen,et al.  Peru-Chile Trench Sediments and Sea-Floor Spreading , 1970 .

[52]  K. Nishiizumi,et al.  Remnants of a fossil alluvial fan landscape of Miocene age in the Atacama Desert of northern Chile using cosmogenic nuclide exposure age dating , 2005 .

[53]  S. Ivy‐Ochs,et al.  The chemical behavior of Be, Al, Fe, Ca and Mg during AMS target preparation from terrestrial silicates modeled with chemical speciation calculations , 1997 .

[54]  D. Lal,et al.  Cosmic ray labeling of erosion surfaces: in situ nuclide production rates and erosion models , 1991 .

[55]  K. Nishiizumi,et al.  Cosmic ray produced 10Be and 26Al in Antarctic rocks: exposure and erosion history , 1991 .

[56]  G. Wörner,et al.  Geochronology (40Ar/39Ar, K-Ar and He-exposure ages) of Cenozoic magmatic rocks from Northern Chile (18-22°S): implications for magmatism and tectonic evolution of the central Andes , 2000 .

[57]  R. Wieler,et al.  In situ cosmogenic 10Be and 21Ne in sanidine and in situ cosmogenic 3He in Fe–Ti-oxide minerals , 2005 .

[58]  A. Hartley.  Andean uplift and climate change , 2003, Journal of the Geological Society.

[59]  L. Kulm,et al.  Surface sediments of the Peru-Chile continental margin and the Nazca plate , 1980 .

[60]  E. Fielding,et al.  Erosion and tectonics at the margins of continental plateaus , 1994 .

[61]  F. Schlunegger,et al.  Surface uplift and climate change: The geomorphic evolution of the Western Escarpment of the Andes of northern Chile between the Miocene and present , 2006 .

[62]  M. Vuille,et al.  Atmospheric circulation over the Bolivian Altiplano during dry and wet periods and extreme phases of the southern oscillation , 1999 .

[63]  K. Nishiizumi,et al.  Chemical isolation of quartz for measurement of in-situ-produced cosmogenic nuclides , 1992 .

[64]  O. Oncken,et al.  Uplift of the western Altiplano plateau: Evidence from the Precordillera between 20° and 21°S (northern Chile) , 2004 .

[65]  R. H. Meade,et al.  World-Wide Delivery of River Sediment to the Oceans , 1983, The Journal of Geology.