Possible orogeny-parallel lower crustal flow and thickening in the Central Andes

Gerbault, Muriel; Martinod, Joseph; Hérail, Gérard

doi:10.1016/j.tecto.2004.12.015

Cited by 50 publications

(35 citation statements)

References 55 publications

(61 reference statements)

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“…Geophysical data acquired in the past two decades have confirmed the extreme crustal thickening of the Central Andes. They also clarified the picture of the crustal structure in the Central Andes and demonstrated the variable nature of the mantle root (Whitman et al 1992(Whitman et al , 1996Giese et al 1999;Beck and Zandt 2002;Gerbault et al 2005).…”

Section: Geodynamic Settingmentioning

confidence: 86%

Magma evolution of Quaternary minor volcanic centres in southern Peru, Central Andes

et al. 2006

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International audienceMinor centres in the Central Volcanic Zone (CVZ) of the Andes occur in different places and are essential indicators of magmatic processes leading to formation of composite volcano. The Andahua–Orcopampa and Huambo monogenetic fields are located in a unique tectonic setting, in and along the margins of a deep valley. This valley, oblique to the NW–SE-trend of the CVZ, is located between two composite volcanoes (Nevado Coropuna to the east and Nevado Sabancaya to the west). Structural analysis of these volcanic fields, based on SPOT satellite images, indicates four main groups of faults. These faults may have controlled magma ascent and the distribution of most centres in this deep valley shaped by en-echelon faulting. Morphometric criteria and 14C age dating attest to four main periods of activity: Late Pleistocene, Early to Middle Holocene, Late Holocene and Historic. The two most interesting features of the cones are the wide compositional range of their lavas (52.1 to 68.1 wt.% SiO2) and the unusual occurrence of mafic lavas (olivine-rich basaltic andesites and basaltic andesites). Occurrence of such minor volcanic centres and mafic magmas in the CVZ may provide clues about the magma source in southern Peru. Such information is otherwise difficult to obtain because lavas produced by composite volcanoes are affected by shallow processes that strongly mask source signatures. Major, trace, and rare earth elements, as well as Sr-, Nd-, Pb- and O-isotope data obtained on high-K calc-alkaline lavas of the Andahua–Orcopampa and Huambo volcanic province characterise their source and their evolution. These lavas display a range comparable to those of the CVZ composite volcanoes for radiogenic and stable isotopes (87Sr/86Sr: 0.70591–0.70694, 143Nd/144Nd: 0.512317–0.512509, 206Pb/204Pb: 18.30–18.63, 207Pb/204Pb: 15.57–15.60, 208Pb/204Pb: 38.49–38.64, and δ 18O: 7.1–10.0‰ SMOW), attesting to involvement of a crustal component. Sediment is absent from the Peru–Chile trench, and hence cannot be the source of such enrichment. Partial melts of the lowermost part of the thick Andean continental crust with a granulitic garnet-bearing residue added to mantle-derived arc magmas in a high-pressure MASH [melting, assimilation, storage and homogenisation] zone may play a major role in magma genesis. This may also explain the chemical characteristics of the Andahua–Orcopampa and Huambo magmas. Fractional crystallisation processes are the main governors of magma evolution for the Andahua–Orcopampa and Huambo volcanic province. An open-system evolution is, however, required to explain some O-isotopes and some major and trace elements values. Modelling of AFC processes suggests the Charcani gneisses and the local Andahua–Orcopampa and Huambo basement may be plausible contaminants

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Section: Geodynamic Settingmentioning

confidence: 86%

Magma evolution of Quaternary minor volcanic centres in southern Peru, Central Andes

et al. 2006

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“…Uplift appears to be a two-stage processes caused primarily by crustal shortening and related lower crustal flow (e.g. Allmendinger et al 2005;Gebault et al 2005;Hindle et al 2005). About 25-30 % of the present elevation of the Altiplano was reached by 20 Ma and no more than half of it by 10 Ma (Gregory-Wodzicki 2000).…”

Section: Geological Overviewmentioning

confidence: 99%

The origin and crust/mantle mass balance of Central Andean ignimbrite magmatism constrained by oxygen and strontium isotopes and erupted volumes

Freymuth

Brandmeier

Wörner³

2015

Contrib Mineral Petrol

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distinctly more radiogenic Sr and heavier O isotopes and thus contrast with older dacitic ignimbrites in northernmost Chile and southern Peru. Results of assimilation and fractional crystallization (AFC) models show that the largest chemical changes occur in the lower crust where magmas acquire a base-level geochemical signature that is later modified by middle to upper crustal AFC. Using geospatial analysis, we estimated the volume of these ignimbrite deposits throughout the Central Andes during the Neogene and examined the spatiotemporal pattern of socalled ignimbrite flare-ups. We observe a N-S migration of maximum ages of the onset of large-volume "ignimbrite pulses" through time: Major pulses occurred at 19-24 Ma (e.g. Oxaya, Nazca Group), 13-14 Ma (e.g. Huaylillas and Altos de Pica ignimbrites) and <10 Ma (Altiplano and Puna ignimbrites). Such "flare-ups" represent magmatic production rates of 25 to >70 km 3 Ma −1 km −1 (assuming plutonic/ volcanic ratios of 1:5) which are additional to, but within the order of, the arc background magmatic flux. Comparing our results to average shortening rates observed in the Andes, we observe a "lag-time" with large-volume eruptions occurring after accelerated shortening. A similar delay exists between the ignimbrite pulses and the subduction of the Juan Fernandez ridge. This is consistent with the idea that large-volume ignimbrite eruptions occurred in the wake of the N-S passage of the ridge after slab steepening has allowed hot asthenospheric mantle to ascend into and cause the melting of the mantle wedge. In our model, the older large-volume dacitic ignimbrites in the northern part of the CVZ have lower (15-37 %) crustal contributions because they were produced at times when the Central Andean crust was thinner and colder, and large-scale melting in the middle crust could not be achieved. Younger ignimbrite flare-ups further south (<10 Ma, >22°S) formed with a significantly higher crustal contribution (22-68 %) Abstract Volcanism during the Neogene in the Central Volcanic Zone (CVZ) of the Andes produced (1) stratovolcanoes, (2) rhyodacitic to rhyolitic ignimbrites which reach volumes of generally less than 300 km 3 and (3) large-volume monotonous dacitic ignimbrites of up to several thousand cubic kilometres. We present models for the origin of these magma types using O and Sr isotopes to constrain crust/mantle proportions for the large-volume ignimbrites and explore the relationship to the evolution of the Andean crust. Oxygen isotope ratios were measured on phenocrysts in order to avoid the effects of secondary alteration. Our results show a complete overlap in the Sr-O isotope compositions of lavas from stratovolcanoes and low-volume rhyolitic ignimbrites as well as older (>9 Ma) large-volume dacitic ignimbrites. This suggests that the mass balance of crustal and mantle components are largely similar. By contrast, younger (<10 Ma) large-volume dacitic ignimbrites from the southern portion of the Central Andes have Communicated by Othmar Müntener. Electronic supple...

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“…This paper reviews the evolution of ideas that has led some geoscientists to believe that mechanical weakening in lower or middle crust explains diverse phenomena observed in many orogenic belts, including the Andes (Gerbault & Martinod 2005), the Appalachian orogenic belt (Merschat et al 2005), the Canadian cordillera (Williams & Jiang 2005) and the Himalayan-Tibet orogen (Grujic et al 2002). Specifically, it examines the quantitative evidence for the hypothesis that flow of a lowviscosity channel is linked to orography and surface precipitation in collisional orogens such as the Himalaya (Beaumont et al 2001).…”

mentioning

confidence: 99%

Channel flow and the Himalayan–Tibetan orogen: a critical review

Harris

2007

JGS

130

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The movement of a low-viscosity crustal layer in response to topographic loading provides a potential mechanism for (1) eastward flow of the Asian lower crust causing the peripheral growth of the Tibetan Plateau and (2) southward flow of the Indian middle crust to be extruded along the Himalayan topographic front. Thermomechanical models for channel flow link such extrusion to focused orographic precipitation at the surface. Isotopic constraints on the timing of fault movement, anatexis and thermobarometric evolution of the exhumed garnet-to sillimanite-grade metasedimentary rocks support mid-crustal channel flow during the Early to Mid-Miocene. Exhumed metamorphic assemblages suggest that the dominant mechanism of the viscosity reduction that is a requirement for channel flow was melt weakening along the upper surface, defined by the South Tibetan Detachment System, and strain softening along the base, bounded by the Main Central Thrust. Neotectonic extrusion, bounded by brittle Quaternary faults south of the Main Central Thrust, is positively correlated with the spatial distribution of precipitation across a north-south transect, suggesting climate-tectonic linkage over a million-year time scale. A proposed orogen-wide eastward increase in extrusion rate over 20 Ma reflects current precipitation patterns but climate-tectonic linkage over this time scale remains equivocal.

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Possible orogeny-parallel lower crustal flow and thickening in the Central Andes

Cited by 50 publications

References 55 publications

Magma evolution of Quaternary minor volcanic centres in southern Peru, Central Andes

Magma evolution of Quaternary minor volcanic centres in southern Peru, Central Andes

The origin and crust/mantle mass balance of Central Andean ignimbrite magmatism constrained by oxygen and strontium isotopes and erupted volumes

Channel flow and the Himalayan–Tibetan orogen: a critical review

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