G. Wörner - Profile on Academia.edu (original) (raw)

Papers by G. Wörner

Research paper thumbnail of 6. The Johnnie Walker Formation: A Pre-Granite Harbour Subvolcanic Unit in the Wilson Terrane, Lower Mawson Glacier, Victoria Land, Antarctica

Research paper thumbnail of 3. Volcanic observations on Scott Island in the Antarctic Ocean

Polarforschung, 1992

Scott Island is a small rocky oceanic island in the Southem Ocean located at 67°23' S, 179°05' W ... more Scott Island is a small rocky oceanic island in the Southem Ocean located at 67°23' S, 179°05' W (REITMAYR & REDFIELD pers. comm.). WRIGHT & KYLE (1990) list it in their compilation .Volcanoes of the Antarctic Plate and Southem Oceans" (LEMASURIER & THOMPSON 1990) and noted "apart from a single phonoIite sampIe, no geological investigations have been carried out on Scott Island". However, reconnaissance sampling had been undertaken early during GANOVEX II in 1982. Sampies and records were later lost after the expedition ship Gorland had sunk. For that reason, Scott Island had been visited by GANOVEX VI in order to provide more volcanological, petrographical and geochemical information on this small oceanic island. WRIGHT & KYLE (1990) summarized earlier work (PRIOR 1907, JOHNSON et al. 1982, CAMPSIE et al. 1983) including five geochemical analyses of one phonolite and nepheline-mugearites from the island and its surrounding oceanic plateau, respectively.

Research paper thumbnail of Geochemical and thermochronological signals in Tertiary to Recent sediments from the Western Andes (15-19°S): proxies for sediment provenance and Andean uplift

During the Cenozoic the landscape at the western margin of South America changed dramatically due... more During the Cenozoic the landscape at the western margin of South America changed dramatically due to the tectonic evolution of the Andes (Isacks 1988, J Geophysical Res 93) and significant variations in climate (Gregory-Wodzicki 2000, GSA Bulletin 112). At present day the climate in the western Central Andes (N-Chile, S-Peru) is arid (rainfall average is less than 100-200 mm/y) Climate

Research paper thumbnail of Chemical, petrologic and experimental constraints on the pre-eruptive conditions of Lascar volcano, Central Andean magma systems

Research paper thumbnail of Compositional and petrological variability in central Andean magmas explained by three uniform and ubiquitous magmatic components

Research paper thumbnail of Distinct regimes of differentiation in Central Andean magma systems

Research paper thumbnail of Tracing Crustal Evolution in the Southern Central Andes from Late Precambrian to Permian with Geochemical and Nd and Pb Isotope Data

Tracing Crustal Evolution in the Southern Central Andes from Late Precambrian to Permian with Geochemical and Nd and Pb Isotope Data

The Journal of Geology, 2000

... B. Bock,1 H. Bahlburg,2 G. Wörner, and U. Zimmermann3 ... Figure thumbnail (110 KB). Figure 1... more ... B. Bock,1 H. Bahlburg,2 G. Wörner, and U. Zimmermann3 ... Figure thumbnail (110 KB). Figure 10. A, 206 Pb/ 204 Pb versus 207 Pb/ 204 Pb with northern hemisphere reference line (NHRL; Hart 1984), Stacey and Kramers evolution curve, and 450 Ma reference line. ...

Research paper thumbnail of Lithospheric dynamics and mantle sources of alkaline magmatism of the Cenozoic West Antarctic Rift System

Global and Planetary Change, 1999

Lithospheric extension in the West Antarctic Rift System and the Ross Sea embayment is related to... more Lithospheric extension in the West Antarctic Rift System and the Ross Sea embayment is related to Cenozoic alkaline volcanism. Basanites and alkali basalts define the two endmembers of primary magmas with distinct petrographic, chemical and isotopic compositions. Basanites are generally more primitive and significantly more enriched in incompatible trace elements than alkali basalts. Parallel incompatible trace-element distribution patterns in both rock types but slightly different isotopic compositions suggest a derivation by different degrees of partial melting from different mantle sources. Sr-, Nd-and Pb-isotopes allow the identification of distinct magma sources: asthenospheric mantle, enriched lithospheric mantle and a HIMU plume component which is widespread beneath the entire area. Spatial and temporal variations in isotopic compositions suggest a relationship between the dynamics of lithospheric extension and changing mantle sources of related magmas. Geothermobarometry on mantle xenoliths documents a pressure-temperature-time evolution of the mantle lithosphere which is related to rifting, uplift and cooling of mantle below the Ross Sea Rift-Transantarctic Mountain transition. This paper reviews existing data and ideas but is biased towards the author's own working area, the Western Ross Sea.

Research paper thumbnail of Erosion rates and erosion patterns of Neogene to Quaternary stratovolcanoes in the Western Cordillera of the Central Andes: An SRTM DEM based analysis

Geomorphology, 2012

Erosion patterns and rates of 33 stratovolcanoes in the arid to hyperarid Central Andean Volcanic... more Erosion patterns and rates of 33 stratovolcanoes in the arid to hyperarid Central Andean Volcanic Zone (14°S to 27°S) have been constrained by morphometric modelling. All selected volcanoes belong to the short-lived, symmetrical, circular andesitic stratocone type, with ages spanning 14 Ma to recent. Starting from the initial, youthful volcano morphology of this type, represented in our study by Parinacota volcano, and comparing reconstructed volumes of progressively eroded volcanoes, such a time span allows us to infer long-term erosion rates. Typical erosion rates of b 10 to 20 m/Ma have been obtained for the Altiplano-Puna Plateau. Lowest erosion rates typify the hyperarid Puna plateau (7-9 m/Ma), while somewhat higher values (13-22 m/Ma) are recorded for volcanoes in the more humid South Peru, suggesting climatic control on differences in erosion rates. By contrast, much higher short-term erosion rates of 112 to 66 m/Ma, decreasing with age, are found for young (Late Quaternary) volcanoes, which indicates that juvenile volcanoes erode more rapidly due to their unconsolidated cover and steeper slopes; surface denudation slows down to approximately one tenth of this after a few Ma. An inverse correlation is observed between the degree of denudation (defined as volume removed by erosion/original volume) and edifice height from base to top after erosion. This relationship is independent of climate and original edifice elevation. The degree of denudation vs. volcano age provides a rough morphometric tool to constrain the time elapsed since the extinction of volcanic activity. This method can, however, only be applied to the volcanoes of the Altiplano (i.e. under uniform, long-term arid climate) with an uncertainty of ~1 Ma. Finally, an erosional pathway is suggested for volcanoes of the Altiplano-Puna preserving a peculiar "edelweiss" valley pattern related to glaciations. This pattern may have overprinted previous drainages and resulted in a discontinuous height reduction of the degrading stratovolcanoes.

Research paper thumbnail of Shallow and deep crustal control on differentiation of calc-alkaline and tholeiitic magma

Shallow and deep crustal control on differentiation of calc-alkaline and tholeiitic magma

Earth and Planetary Science Letters, 2009

The role of changing crustal interaction and plumbing geometry in modulating calc-alkaline vs. th... more The role of changing crustal interaction and plumbing geometry in modulating calc-alkaline vs. tholeiitic magma affinity is well illustrated by the influence of 70 km thick crust beneath Volcán Parinacota. Changes in petrologic affinity correlate with periods of cone-building, sector collapse, and rebuilding of the volcano over the last 52 ka, and are well explained by changes in magma recharge regime. With

Research paper thumbnail of Geochronologic and stratigraphic constraints on canyon incision and Miocene uplift of the Central Andes in Peru

Earth and Planetary Science Letters, 2007

The deepest valleys of the Andes have been cut in southern Peru by the Ríos Cotahuasi Ocoña and C... more The deepest valleys of the Andes have been cut in southern Peru by the Ríos Cotahuasi Ocoña and Colca-Majes. These canyons are Late Miocene landforms based on a new ignimbrite stratigraphy supported by 42 new 40 Ar/ 39 Ar age determinations obtained on plateau-forming and valley-filling ignimbrites. Between 19 and 13 Ma, a gently sloping surface bevelling the clastic wedge southeast of the developing mountain front was mantled by widespread ignimbrites. After 13 Ma, this paleosurface was tilted up from 2.2 km a.s.l. at the mountain front to 4.3 km a.s.l. at the base of the Pliocene and Pleistocene volcanoes that crown the southwestern edge of the Altiplano. The canyons incised this topography after 9 Ma, while the dated base of younger ignimbrite valley fills suggests that these canyons had been cut down to near their present depths as early as 3.8 Ma. By 1.4 Ma, however, the canyons had been almost completely refilled by 1.3 km-thick unwelded pyroclastic deposits, which were subsequently eroded. Valley incision since 9 Ma at an average rate of 0.2 mm yr -1 is the response to topographic uplift after 13 Ma combined with increasing runoff due to a wetter climate recorded after 7 Ma. Although long-term aridity generated an imbalance between high long-term uplift rates and low plateau denudation rates, the combination of aridity and volcanism still promoted canyon incision because episodic volcanic fills maintained a cycle of catastrophic debris avalanches and subsequent dam breakouts.

Research paper thumbnail of Os, Sr, Nd, Pb, O isotope and trace element data from the Ferrar flood basalts, antarctica: evidence for an enriched subcontinental lithospheric source

Earth and Planetary Science Letters, 1996

OS, Sr, Nd, Pb and 0 isotopes and trace element data are reported for basaltic andesite and andes... more OS, Sr, Nd, Pb and 0 isotopes and trace element data are reported for basaltic andesite and andesite whole rocks and, in part, for selected mineral separates from the Jurassic Ferrar flood basalt province. Radiogenic Sr ( > 0.709), unradiogenic Nd (e Nd = -3 to -5), and radiogenic Pb isotopes, as well as low Nb/La ratios of 0.4-0.6 and Nb/La ratios between 0.45 and 0.6 are found for all rocks including our most primitive sample (Mg# = 7 1.9). This indicates involvement of either continental crust or enriched lithospheric mantle in magma genesis. 's'Re/ '*sOs correlates strongly with '*'OS/ 'ssOs, with an age of 172 + 5 Ma, in agreement with published Ar-Ar data. Initial '*'OS/ '**OS of 0.194 + 0.023 is close to the range of typical mantle values for MORB, OIB and lithospheric mantle and much lower than that of continental crust. 6 "0 values between 5%a and 7%~ were obtained on fresh bulk samples, separated plagioclases and clinopyroxenes. Sr-0 and Sr-0s isotope mixing calculations between depleted mantle peridotite or mantle melts and crustal material rule out assimilation involving basalts with low OS concentrations, and simple binary mixing or pure AFC processes involving pi&es. AFC processes, combined with continuous replenishment of picritic magmas, can explain the isotopic data, provided the crustal end-member has high s'Sr/ 86Sr and low S'*O values. However, lower crustal samples displaying these characteristics are absent in the Ferrar region, and are also unlikely to impart the sediment-like trace element patterns observed in the Ferrar data. A more likely explanation is a lithospheric source enriched by subducted sediments. A contribution to Ferrar magmatism from a plume cannot be distinguished.

Research paper thumbnail of Isotopic constraints on open system evolution of the Laacher See magma chamber (Eifel, West Germany)

Isotopic constraints on open system evolution of the Laacher See magma chamber (Eifel, West Germany)

Earth and Planetary Science Letters, 1985

... Polybaric differentiation of alkali basaltic magma: evidence from gree core clinopyrox-enes (... more ... Polybaric differentiation of alkali basaltic magma: evidence from gree core clinopyrox-enes (Eifel, W-Germany), Contrib. Mineral. Petrol. (in press). 37 J. Frechen, Vorg~nge der Sanidinitbildung im l.aacher-See-Gebiet, Fortschr. Mineral. 26, 147-166, 1947. 38 AJ Kilinc and ...

Research paper thumbnail of Sr, Nd, and Pb isotope geochemistry of Tertiary and Quaternary alkaline volcanics from West Germany

Sr, Nd, and Pb isotope geochemistry of Tertiary and Quaternary alkaline volcanics from West Germany

Earth and Planetary Science Letters, 1986

Mantle-derived alkaline magmas from the Quaternary East and West Eifel volcanic fields (West Germ... more Mantle-derived alkaline magmas from the Quaternary East and West Eifel volcanic fields (West Germany) and a range of basalts from various Tertiary Provinces in West Germany show considerable variation in their Nd and Sr isotopic compositions. East Eifel mafic magmas (basanites, ...

Research paper thumbnail of Geochemical evolution of rift magmas by progressive tapping of a stratified mantle source beneath the Ross Sea Rift, Northern Victoria Land, Antarctica

Geochemical evolution of rift magmas by progressive tapping of a stratified mantle source beneath the Ross Sea Rift, Northern Victoria Land, Antarctica

Earth and Planetary Science Letters, 1995

Source compositions of Neogene-Quaternary volcanic rocks from the McMurdo Volcanic Group of the R... more Source compositions of Neogene-Quaternary volcanic rocks from the McMurdo Volcanic Group of the Ross Sea Rift in Northern Victoria Land, Antarctica are constrained by NdSrPb isotopes and trace element ratios in near-primary basalts. The rocks erupted along the western rift margin (Victoria Land Basin) and the western rift shoulder (Transantarctic Mountains). Near-primary basalts show no evidence of crustal contamination, suggesting

Research paper thumbnail of U-series evidence for crustal involvement and magma residence times in the petrogenesis of Parinacota volcano, Chile

Contributions to Mineralogy and Petrology, 2000

In this study, we present Th±U disequilibria as well as radiogenic and trace element data for rec... more In this study, we present Th±U disequilibria as well as radiogenic and trace element data for recent volcanic rocks from the Nevados de Payachata volcano which erupted through $70 km of continental crust in the Central Volcanic Zone of the Andes (18°S, 69°W). Both lavas and mineral separates were analyzed by mass spectrometry for 238 U± 230 Th disequilibria. The lavas are characterized either by 230 Th enrichment or depletion relative to its parent nuclide 238 U. Mineral separates are used to derive U±Th isochron ages and these ages compare favorably with inferred stratigraphic ages or K±Ar ages, although in one case the U±Th age is signi®cantly older than the stratigraphic age. Despite relatively constant Sr, Nd, and Pb isotope ratios, the lavas display inverse trends in 230 Th/ 238 U versus Ce/Yb or Ba/Hf diagrams. These trends cannot be interpreted by simple two-component mixing. Rather, there must be three (and perhaps four components) involved in the genesis of the Parinacota lavas. A mantle wedge, a slab ¯uid, and a lower crustal component can be identi®ed. A sediment component is more dicult to detect as it is dicult to decipher its signature because of the strong crustal in¯uence. The existence of binary arrays can be explained by variable amounts of crustal material. The process of crust±mantle interaction must have been short enough to preserve U±Th disequilibrium (<300 ka).

Research paper thumbnail of Magma chamber evolution prior to the Campanian Ignimbrite and Neapolitan Yellow Tuff eruptions (Campi Flegrei, Italy)

Bulletin of Volcanology, 2007

The Campi Flegrei (Campanian Region, Italy) experienced two cataclysmic caldera-forming eruptions... more The Campi Flegrei (Campanian Region, Italy) experienced two cataclysmic caldera-forming eruptions which produced the Campanian Ignimbrite (39 ka, CI) and the Neapolitan Yellow Tuff (15 ka, NYT). We studied the minor eruptions before both these large events to understand magma chamber evolution leading towards such catastrophic eruptions. Major, trace element, and Sr and Nd isotope compositions of pre-Campanian Ignimbrite and pre-Neapolitan Yellow Tuff products define distinct geochemical groups, which are here interpreted as distinct magma batches. These batches do not show any transitional trend towards the CI and NYT eruptions. The CI and NYT systems are decoupled geochemically and isotopically. At least one of the pre-CI and one of the pre-NYT erupted magma batches qualifies as mixing endmembers for the large CI and NYT eruptions, and thus, must have been stored in reservoirs for some time to remain available for the CI and NYT eruptions. The least evolved, isotopically distinct magma compositions that are typical of the last phases of the NYT and CI eruptions did not occur before caldera-forming events. Based on the new data, we propose the following scenario: Multiple magma chambers with distinct compositions existed below the Campi Flegrei before the CI and NYT eruptions and remained generally separated for some time unless new magma was recharged. In each case, one of the residing magma reservoirs was recharged by a new large-volume magma input of intermediate composition from a deeper differentiating magma reservoir. This may have triggered the coalescence of the previously separated reservoirs into one large chamber which fed the cataclysmic caldera-forming eruption. Large magma chambers in the Campi Flegrei may therefore be ephemeral features, interrupted by periods of evolution in individual, separated magma reservoirs.

Research paper thumbnail of The potential of stalagmites from the Patagonian Andes as sub-annually-resolved paleoclimate records

… 2010, held 2-7 May …, 2010

Research paper thumbnail of Sector collapse and rapid rebuilding of Parinacota Volcano: extending 40Ar/39Ar dating of lava flows into the Holocene

Sector collapse and rapid rebuilding of Parinacota Volcano: extending 40Ar/39Ar dating of lava flows into the Holocene

ABSTRACT Catastrophic debris avalanches have been recognized as a relatively common occurrence in... more ABSTRACT Catastrophic debris avalanches have been recognized as a relatively common occurrence in the life cycle of arc stratovolcanoes. In many cases, for instance at Mt. St. Helens, debris avalanches reflect major changes or additions of new magma into the subvolcanic reservoir. In only a few cases, however, are we able to compare the state of the magmatic system that preceded a catastrophic cone collapse with magmatic processes accompanying the complete re-growth of the volcano. Parinacota is a 46 km3 stratovolcano in the Andean Central Volcanic zone that collapsed to produce a 6 km3 debris avalanche (3 times the size of the collapse at St. Helens), yet has regrown a post-collapse cone of 18 km3. This entire complex is extraordinarily well-preserved owing to the hyper-arid climate and low erosion rates. Parinacota has erupted a variety of high-K calc-alkaline basaltic andesite through rhyolite and is therefore an Ideal candidate to study changes in the magmatic system both before and after a major debris avalanche. We have combined field mapping and stratigraphy with a quantitative and comprehensive geochronology effort in order to understand the pre- and post-collapse history of the magmatic system. New 40Ar/39Ar ages from groundmass and whole-rock samples of 16 lava flows representing the most recent parts of cone-regrowth extend the useful range of this technique well into the Holocene. Previously, precise 40Ar/39Ar dating had been obtained only from sanidine in this age range. Since the greatest source of uncertainty in dating young samples with ~2-3 wt% K2O is low radiogenic 40Ar yield, analytical blanks and instrumental mass fractionation must be well-constrained to obtain precise and accurate ages. Immediately preceding the debris avalanche, andesitic and dacitic (58-64% SiO2) lava flows include abundant petrographic and geochemical evidence for a dynamic magma system, which was likely intermittently compartmentalized, and experienced periodic mixing. The youngest pre-collapse sample is a 20.0 ± 4.0 ka andesite (59% SiO2), constraining the upper limit of debris avalanche timing. Since only the outermost part of the modern cone is accessible by sampling, and these dates range from 8.1 ± 1.8 to 3.6 ± 1.1 ka, the majority of cone re-building must have occurred prior to about 8 ka. This indicates post-collapse eruption rates that averaged in excess of 1.2 km3/ky that were twice the rate of cone growth prior to the collapse, but comparable to peak eruption rates of other large stratovolcanoes studied in similar detail.

Research paper thumbnail of Valley Evolution, Uplift, Volcanism, and related Hazards on the western Slope of the Central Andes

Valley Evolution, Uplift, Volcanism, and related Hazards on the western Slope of the Central Andes

ABSTRACT

Research paper thumbnail of 6. The Johnnie Walker Formation: A Pre-Granite Harbour Subvolcanic Unit in the Wilson Terrane, Lower Mawson Glacier, Victoria Land, Antarctica

Research paper thumbnail of 3. Volcanic observations on Scott Island in the Antarctic Ocean

Polarforschung, 1992

Scott Island is a small rocky oceanic island in the Southem Ocean located at 67°23' S, 179°05' W ... more Scott Island is a small rocky oceanic island in the Southem Ocean located at 67°23' S, 179°05' W (REITMAYR & REDFIELD pers. comm.). WRIGHT & KYLE (1990) list it in their compilation .Volcanoes of the Antarctic Plate and Southem Oceans" (LEMASURIER & THOMPSON 1990) and noted "apart from a single phonoIite sampIe, no geological investigations have been carried out on Scott Island". However, reconnaissance sampling had been undertaken early during GANOVEX II in 1982. Sampies and records were later lost after the expedition ship Gorland had sunk. For that reason, Scott Island had been visited by GANOVEX VI in order to provide more volcanological, petrographical and geochemical information on this small oceanic island. WRIGHT & KYLE (1990) summarized earlier work (PRIOR 1907, JOHNSON et al. 1982, CAMPSIE et al. 1983) including five geochemical analyses of one phonolite and nepheline-mugearites from the island and its surrounding oceanic plateau, respectively.

Research paper thumbnail of Geochemical and thermochronological signals in Tertiary to Recent sediments from the Western Andes (15-19°S): proxies for sediment provenance and Andean uplift

During the Cenozoic the landscape at the western margin of South America changed dramatically due... more During the Cenozoic the landscape at the western margin of South America changed dramatically due to the tectonic evolution of the Andes (Isacks 1988, J Geophysical Res 93) and significant variations in climate (Gregory-Wodzicki 2000, GSA Bulletin 112). At present day the climate in the western Central Andes (N-Chile, S-Peru) is arid (rainfall average is less than 100-200 mm/y) Climate

Research paper thumbnail of Chemical, petrologic and experimental constraints on the pre-eruptive conditions of Lascar volcano, Central Andean magma systems

Research paper thumbnail of Compositional and petrological variability in central Andean magmas explained by three uniform and ubiquitous magmatic components

Research paper thumbnail of Distinct regimes of differentiation in Central Andean magma systems

Research paper thumbnail of Tracing Crustal Evolution in the Southern Central Andes from Late Precambrian to Permian with Geochemical and Nd and Pb Isotope Data

Tracing Crustal Evolution in the Southern Central Andes from Late Precambrian to Permian with Geochemical and Nd and Pb Isotope Data

The Journal of Geology, 2000

... B. Bock,1 H. Bahlburg,2 G. Wörner, and U. Zimmermann3 ... Figure thumbnail (110 KB). Figure 1... more ... B. Bock,1 H. Bahlburg,2 G. Wörner, and U. Zimmermann3 ... Figure thumbnail (110 KB). Figure 10. A, 206 Pb/ 204 Pb versus 207 Pb/ 204 Pb with northern hemisphere reference line (NHRL; Hart 1984), Stacey and Kramers evolution curve, and 450 Ma reference line. ...

Research paper thumbnail of Lithospheric dynamics and mantle sources of alkaline magmatism of the Cenozoic West Antarctic Rift System

Global and Planetary Change, 1999

Lithospheric extension in the West Antarctic Rift System and the Ross Sea embayment is related to... more Lithospheric extension in the West Antarctic Rift System and the Ross Sea embayment is related to Cenozoic alkaline volcanism. Basanites and alkali basalts define the two endmembers of primary magmas with distinct petrographic, chemical and isotopic compositions. Basanites are generally more primitive and significantly more enriched in incompatible trace elements than alkali basalts. Parallel incompatible trace-element distribution patterns in both rock types but slightly different isotopic compositions suggest a derivation by different degrees of partial melting from different mantle sources. Sr-, Nd-and Pb-isotopes allow the identification of distinct magma sources: asthenospheric mantle, enriched lithospheric mantle and a HIMU plume component which is widespread beneath the entire area. Spatial and temporal variations in isotopic compositions suggest a relationship between the dynamics of lithospheric extension and changing mantle sources of related magmas. Geothermobarometry on mantle xenoliths documents a pressure-temperature-time evolution of the mantle lithosphere which is related to rifting, uplift and cooling of mantle below the Ross Sea Rift-Transantarctic Mountain transition. This paper reviews existing data and ideas but is biased towards the author's own working area, the Western Ross Sea.

Research paper thumbnail of Erosion rates and erosion patterns of Neogene to Quaternary stratovolcanoes in the Western Cordillera of the Central Andes: An SRTM DEM based analysis

Geomorphology, 2012

Erosion patterns and rates of 33 stratovolcanoes in the arid to hyperarid Central Andean Volcanic... more Erosion patterns and rates of 33 stratovolcanoes in the arid to hyperarid Central Andean Volcanic Zone (14°S to 27°S) have been constrained by morphometric modelling. All selected volcanoes belong to the short-lived, symmetrical, circular andesitic stratocone type, with ages spanning 14 Ma to recent. Starting from the initial, youthful volcano morphology of this type, represented in our study by Parinacota volcano, and comparing reconstructed volumes of progressively eroded volcanoes, such a time span allows us to infer long-term erosion rates. Typical erosion rates of b 10 to 20 m/Ma have been obtained for the Altiplano-Puna Plateau. Lowest erosion rates typify the hyperarid Puna plateau (7-9 m/Ma), while somewhat higher values (13-22 m/Ma) are recorded for volcanoes in the more humid South Peru, suggesting climatic control on differences in erosion rates. By contrast, much higher short-term erosion rates of 112 to 66 m/Ma, decreasing with age, are found for young (Late Quaternary) volcanoes, which indicates that juvenile volcanoes erode more rapidly due to their unconsolidated cover and steeper slopes; surface denudation slows down to approximately one tenth of this after a few Ma. An inverse correlation is observed between the degree of denudation (defined as volume removed by erosion/original volume) and edifice height from base to top after erosion. This relationship is independent of climate and original edifice elevation. The degree of denudation vs. volcano age provides a rough morphometric tool to constrain the time elapsed since the extinction of volcanic activity. This method can, however, only be applied to the volcanoes of the Altiplano (i.e. under uniform, long-term arid climate) with an uncertainty of ~1 Ma. Finally, an erosional pathway is suggested for volcanoes of the Altiplano-Puna preserving a peculiar "edelweiss" valley pattern related to glaciations. This pattern may have overprinted previous drainages and resulted in a discontinuous height reduction of the degrading stratovolcanoes.

Research paper thumbnail of Shallow and deep crustal control on differentiation of calc-alkaline and tholeiitic magma

Shallow and deep crustal control on differentiation of calc-alkaline and tholeiitic magma

Earth and Planetary Science Letters, 2009

The role of changing crustal interaction and plumbing geometry in modulating calc-alkaline vs. th... more The role of changing crustal interaction and plumbing geometry in modulating calc-alkaline vs. tholeiitic magma affinity is well illustrated by the influence of 70 km thick crust beneath Volcán Parinacota. Changes in petrologic affinity correlate with periods of cone-building, sector collapse, and rebuilding of the volcano over the last 52 ka, and are well explained by changes in magma recharge regime. With

Research paper thumbnail of Geochronologic and stratigraphic constraints on canyon incision and Miocene uplift of the Central Andes in Peru

Earth and Planetary Science Letters, 2007

The deepest valleys of the Andes have been cut in southern Peru by the Ríos Cotahuasi Ocoña and C... more The deepest valleys of the Andes have been cut in southern Peru by the Ríos Cotahuasi Ocoña and Colca-Majes. These canyons are Late Miocene landforms based on a new ignimbrite stratigraphy supported by 42 new 40 Ar/ 39 Ar age determinations obtained on plateau-forming and valley-filling ignimbrites. Between 19 and 13 Ma, a gently sloping surface bevelling the clastic wedge southeast of the developing mountain front was mantled by widespread ignimbrites. After 13 Ma, this paleosurface was tilted up from 2.2 km a.s.l. at the mountain front to 4.3 km a.s.l. at the base of the Pliocene and Pleistocene volcanoes that crown the southwestern edge of the Altiplano. The canyons incised this topography after 9 Ma, while the dated base of younger ignimbrite valley fills suggests that these canyons had been cut down to near their present depths as early as 3.8 Ma. By 1.4 Ma, however, the canyons had been almost completely refilled by 1.3 km-thick unwelded pyroclastic deposits, which were subsequently eroded. Valley incision since 9 Ma at an average rate of 0.2 mm yr -1 is the response to topographic uplift after 13 Ma combined with increasing runoff due to a wetter climate recorded after 7 Ma. Although long-term aridity generated an imbalance between high long-term uplift rates and low plateau denudation rates, the combination of aridity and volcanism still promoted canyon incision because episodic volcanic fills maintained a cycle of catastrophic debris avalanches and subsequent dam breakouts.

Research paper thumbnail of Os, Sr, Nd, Pb, O isotope and trace element data from the Ferrar flood basalts, antarctica: evidence for an enriched subcontinental lithospheric source

Earth and Planetary Science Letters, 1996

OS, Sr, Nd, Pb and 0 isotopes and trace element data are reported for basaltic andesite and andes... more OS, Sr, Nd, Pb and 0 isotopes and trace element data are reported for basaltic andesite and andesite whole rocks and, in part, for selected mineral separates from the Jurassic Ferrar flood basalt province. Radiogenic Sr ( > 0.709), unradiogenic Nd (e Nd = -3 to -5), and radiogenic Pb isotopes, as well as low Nb/La ratios of 0.4-0.6 and Nb/La ratios between 0.45 and 0.6 are found for all rocks including our most primitive sample (Mg# = 7 1.9). This indicates involvement of either continental crust or enriched lithospheric mantle in magma genesis. 's'Re/ '*sOs correlates strongly with '*'OS/ 'ssOs, with an age of 172 + 5 Ma, in agreement with published Ar-Ar data. Initial '*'OS/ '**OS of 0.194 + 0.023 is close to the range of typical mantle values for MORB, OIB and lithospheric mantle and much lower than that of continental crust. 6 "0 values between 5%a and 7%~ were obtained on fresh bulk samples, separated plagioclases and clinopyroxenes. Sr-0 and Sr-0s isotope mixing calculations between depleted mantle peridotite or mantle melts and crustal material rule out assimilation involving basalts with low OS concentrations, and simple binary mixing or pure AFC processes involving pi&es. AFC processes, combined with continuous replenishment of picritic magmas, can explain the isotopic data, provided the crustal end-member has high s'Sr/ 86Sr and low S'*O values. However, lower crustal samples displaying these characteristics are absent in the Ferrar region, and are also unlikely to impart the sediment-like trace element patterns observed in the Ferrar data. A more likely explanation is a lithospheric source enriched by subducted sediments. A contribution to Ferrar magmatism from a plume cannot be distinguished.

Research paper thumbnail of Isotopic constraints on open system evolution of the Laacher See magma chamber (Eifel, West Germany)

Isotopic constraints on open system evolution of the Laacher See magma chamber (Eifel, West Germany)

Earth and Planetary Science Letters, 1985

... Polybaric differentiation of alkali basaltic magma: evidence from gree core clinopyrox-enes (... more ... Polybaric differentiation of alkali basaltic magma: evidence from gree core clinopyrox-enes (Eifel, W-Germany), Contrib. Mineral. Petrol. (in press). 37 J. Frechen, Vorg~nge der Sanidinitbildung im l.aacher-See-Gebiet, Fortschr. Mineral. 26, 147-166, 1947. 38 AJ Kilinc and ...

Research paper thumbnail of Sr, Nd, and Pb isotope geochemistry of Tertiary and Quaternary alkaline volcanics from West Germany

Sr, Nd, and Pb isotope geochemistry of Tertiary and Quaternary alkaline volcanics from West Germany

Earth and Planetary Science Letters, 1986

Mantle-derived alkaline magmas from the Quaternary East and West Eifel volcanic fields (West Germ... more Mantle-derived alkaline magmas from the Quaternary East and West Eifel volcanic fields (West Germany) and a range of basalts from various Tertiary Provinces in West Germany show considerable variation in their Nd and Sr isotopic compositions. East Eifel mafic magmas (basanites, ...

Research paper thumbnail of Geochemical evolution of rift magmas by progressive tapping of a stratified mantle source beneath the Ross Sea Rift, Northern Victoria Land, Antarctica

Geochemical evolution of rift magmas by progressive tapping of a stratified mantle source beneath the Ross Sea Rift, Northern Victoria Land, Antarctica

Earth and Planetary Science Letters, 1995

Source compositions of Neogene-Quaternary volcanic rocks from the McMurdo Volcanic Group of the R... more Source compositions of Neogene-Quaternary volcanic rocks from the McMurdo Volcanic Group of the Ross Sea Rift in Northern Victoria Land, Antarctica are constrained by NdSrPb isotopes and trace element ratios in near-primary basalts. The rocks erupted along the western rift margin (Victoria Land Basin) and the western rift shoulder (Transantarctic Mountains). Near-primary basalts show no evidence of crustal contamination, suggesting

Research paper thumbnail of U-series evidence for crustal involvement and magma residence times in the petrogenesis of Parinacota volcano, Chile

Contributions to Mineralogy and Petrology, 2000

In this study, we present Th±U disequilibria as well as radiogenic and trace element data for rec... more In this study, we present Th±U disequilibria as well as radiogenic and trace element data for recent volcanic rocks from the Nevados de Payachata volcano which erupted through $70 km of continental crust in the Central Volcanic Zone of the Andes (18°S, 69°W). Both lavas and mineral separates were analyzed by mass spectrometry for 238 U± 230 Th disequilibria. The lavas are characterized either by 230 Th enrichment or depletion relative to its parent nuclide 238 U. Mineral separates are used to derive U±Th isochron ages and these ages compare favorably with inferred stratigraphic ages or K±Ar ages, although in one case the U±Th age is signi®cantly older than the stratigraphic age. Despite relatively constant Sr, Nd, and Pb isotope ratios, the lavas display inverse trends in 230 Th/ 238 U versus Ce/Yb or Ba/Hf diagrams. These trends cannot be interpreted by simple two-component mixing. Rather, there must be three (and perhaps four components) involved in the genesis of the Parinacota lavas. A mantle wedge, a slab ¯uid, and a lower crustal component can be identi®ed. A sediment component is more dicult to detect as it is dicult to decipher its signature because of the strong crustal in¯uence. The existence of binary arrays can be explained by variable amounts of crustal material. The process of crust±mantle interaction must have been short enough to preserve U±Th disequilibrium (<300 ka).

Research paper thumbnail of Magma chamber evolution prior to the Campanian Ignimbrite and Neapolitan Yellow Tuff eruptions (Campi Flegrei, Italy)

Bulletin of Volcanology, 2007

The Campi Flegrei (Campanian Region, Italy) experienced two cataclysmic caldera-forming eruptions... more The Campi Flegrei (Campanian Region, Italy) experienced two cataclysmic caldera-forming eruptions which produced the Campanian Ignimbrite (39 ka, CI) and the Neapolitan Yellow Tuff (15 ka, NYT). We studied the minor eruptions before both these large events to understand magma chamber evolution leading towards such catastrophic eruptions. Major, trace element, and Sr and Nd isotope compositions of pre-Campanian Ignimbrite and pre-Neapolitan Yellow Tuff products define distinct geochemical groups, which are here interpreted as distinct magma batches. These batches do not show any transitional trend towards the CI and NYT eruptions. The CI and NYT systems are decoupled geochemically and isotopically. At least one of the pre-CI and one of the pre-NYT erupted magma batches qualifies as mixing endmembers for the large CI and NYT eruptions, and thus, must have been stored in reservoirs for some time to remain available for the CI and NYT eruptions. The least evolved, isotopically distinct magma compositions that are typical of the last phases of the NYT and CI eruptions did not occur before caldera-forming events. Based on the new data, we propose the following scenario: Multiple magma chambers with distinct compositions existed below the Campi Flegrei before the CI and NYT eruptions and remained generally separated for some time unless new magma was recharged. In each case, one of the residing magma reservoirs was recharged by a new large-volume magma input of intermediate composition from a deeper differentiating magma reservoir. This may have triggered the coalescence of the previously separated reservoirs into one large chamber which fed the cataclysmic caldera-forming eruption. Large magma chambers in the Campi Flegrei may therefore be ephemeral features, interrupted by periods of evolution in individual, separated magma reservoirs.

Research paper thumbnail of The potential of stalagmites from the Patagonian Andes as sub-annually-resolved paleoclimate records

… 2010, held 2-7 May …, 2010

Research paper thumbnail of Sector collapse and rapid rebuilding of Parinacota Volcano: extending 40Ar/39Ar dating of lava flows into the Holocene

Sector collapse and rapid rebuilding of Parinacota Volcano: extending 40Ar/39Ar dating of lava flows into the Holocene

ABSTRACT Catastrophic debris avalanches have been recognized as a relatively common occurrence in... more ABSTRACT Catastrophic debris avalanches have been recognized as a relatively common occurrence in the life cycle of arc stratovolcanoes. In many cases, for instance at Mt. St. Helens, debris avalanches reflect major changes or additions of new magma into the subvolcanic reservoir. In only a few cases, however, are we able to compare the state of the magmatic system that preceded a catastrophic cone collapse with magmatic processes accompanying the complete re-growth of the volcano. Parinacota is a 46 km3 stratovolcano in the Andean Central Volcanic zone that collapsed to produce a 6 km3 debris avalanche (3 times the size of the collapse at St. Helens), yet has regrown a post-collapse cone of 18 km3. This entire complex is extraordinarily well-preserved owing to the hyper-arid climate and low erosion rates. Parinacota has erupted a variety of high-K calc-alkaline basaltic andesite through rhyolite and is therefore an Ideal candidate to study changes in the magmatic system both before and after a major debris avalanche. We have combined field mapping and stratigraphy with a quantitative and comprehensive geochronology effort in order to understand the pre- and post-collapse history of the magmatic system. New 40Ar/39Ar ages from groundmass and whole-rock samples of 16 lava flows representing the most recent parts of cone-regrowth extend the useful range of this technique well into the Holocene. Previously, precise 40Ar/39Ar dating had been obtained only from sanidine in this age range. Since the greatest source of uncertainty in dating young samples with ~2-3 wt% K2O is low radiogenic 40Ar yield, analytical blanks and instrumental mass fractionation must be well-constrained to obtain precise and accurate ages. Immediately preceding the debris avalanche, andesitic and dacitic (58-64% SiO2) lava flows include abundant petrographic and geochemical evidence for a dynamic magma system, which was likely intermittently compartmentalized, and experienced periodic mixing. The youngest pre-collapse sample is a 20.0 ± 4.0 ka andesite (59% SiO2), constraining the upper limit of debris avalanche timing. Since only the outermost part of the modern cone is accessible by sampling, and these dates range from 8.1 ± 1.8 to 3.6 ± 1.1 ka, the majority of cone re-building must have occurred prior to about 8 ka. This indicates post-collapse eruption rates that averaged in excess of 1.2 km3/ky that were twice the rate of cone growth prior to the collapse, but comparable to peak eruption rates of other large stratovolcanoes studied in similar detail.

Research paper thumbnail of Valley Evolution, Uplift, Volcanism, and related Hazards on the western Slope of the Central Andes

Valley Evolution, Uplift, Volcanism, and related Hazards on the western Slope of the Central Andes

ABSTRACT