Laser-induced breakdown spectroscopy (LIBS) is a form of optical emission spectroscopy that can b... more Laser-induced breakdown spectroscopy (LIBS) is a form of optical emission spectroscopy that can be used for the rapid analysis of geological materials in the field under ambient environmental conditions. We describe here the innovative use of handheld LIBS for the in situ analysis of rock varnish. This thinly laminated and compositionally complex veneer forms slowly over time on rock surfaces in dryland regions and is particularly abundant across the Mojave Desert climatic region of east-central California (USA). Following the depth profiling examination of a varnished clast from colluvial gravel in Death Valley in the laboratory, our in situ analysis of rock varnish and visually similar coatings on rock surfaces was undertaken in the Owens and Deep Spring valleys in two contexts, element detection/identification and microchemical mapping. Emission peaks were recognized in the LIBS spectra for the nine elements most abundant in rock varnish—Mn, Fe, Si, Al, Na, Mg, K, Ca and Ba, as w...
The availability of both global and regional elevation datasets acquired by modern remote sensing... more The availability of both global and regional elevation datasets acquired by modern remote sensing technologies provides an opportunity to significantly improve the accuracy of stream mapping, especially in remote, hard to reach regions. Stream extraction from digital elevation models (DEMs) is based on computation of flow accumulation, a summary parameter that poses performance and accuracy challenges when applied to large, noisy DEMs generated by remote sensing technologies. Robust handling of DEM depressions is essential for reliable extraction of connected drainage networks from this type of data. The least-cost flow routing method implemented in GRASS GIS as the module r.watershed was redesigned to significantly improve its speed, functionality, and memory requirements and make it an efficient tool for stream mapping and watershed analysis from large DEMs. To evaluate its handling of large depressions, typical for remote sensing derived DEMs, three different methods were compared: traditional sink filling, impact reduction approach, and least-cost path search. The comparison was performed using the Shuttle Radar Topographic Mission (SRTM) and Interferometric Synthetic Aperture Radar for Elevation (IFSARE) datasets covering central Panama at 90 m and 10 m resolutions, respectively. The accuracy assessment was based on ground control points acquired by GPS and reference points digitized from Landsat imagery along segments of selected Panamanian rivers. The results demonstrate that the new implementation of the least-cost path method is significantly faster than the original version, can cope with massive datasets, and provides the most accurate results in terms of stream locations validated against reference points.
Late Tertiary post-orogenic alkaline basalts erupted in the extensional Pannonian Basin following... more Late Tertiary post-orogenic alkaline basalts erupted in the extensional Pannonian Basin following Eocene-Miocene subduction and its related calc-alkaline volcanism. The alkaline volcanic centres, dated between 11-7 and 1-4 Ma, are concentrated in several regions of the Pannonian Basin. Some are near the western (Graz Basin, Burgenland), northern (Nograd), and eastern (Transylvania) margins of the basin, but the majority are concentrated near the Central Range (Balaton area and Little Hungarian Plain). Fresh samples from 31 volcanic centres of the extension-related lavas range from slightly hy-normative transitional basalts through alkali basalts and basanites to olivine nephelinites. No highly evolved compositions have been encountered. The presence of peridotite xenoliths, mantle xenocrysts, and high-pressure megacrysts, even in the slightly more evolved rocks, indicates that differentiation took place within the upper mantle. Rare earth elements (REE) and 87Sr/*6Sr, 143Nd/14*Nd, c...
A bibliography of published articles and reports on mineral-separation techniques, processes, and... more A bibliography of published articles and reports on mineral-separation techniques, processes, and applications is presented along with an author and subject index. This information is intended for use in the mineral-separation facility of the Lunar Receiving Laboratory at the NASA Manned Spacecraft Center and as an aid and reference to persons involved or interested in mineral separation.
... (1979) and Thirlwall and Graham (1984). Overall, Gre nada lavas have lower 143Nd 144Nd and su... more ... (1979) and Thirlwall and Graham (1984). Overall, Gre nada lavas have lower 143Nd 144Nd and substantially higher 87Sr Srsr than Atlantic MORB, forming a data array on Fig. 4 offset to higher 87Sr S6Sr than ocean islands. ...
Public reporting burden for this collection of information is estimated to average 1 hour per res... more Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to
Mat% to intermediate composition gmnulite xenoliths (plagioclase + clinopyroxene f orthopyroxene ... more Mat% to intermediate composition gmnulite xenoliths (plagioclase + clinopyroxene f orthopyroxene + K-feldspar * amphibole) occur in Pliocene to Recent alkali basalts from the Geronimo Volcanic Field (GVF), southeastern Arizona, USA. The range of compositions and mineral assemblages observed suggests that the ultimate derivation of these rocks is from a variety of protoliths and that more than one mechanism has operated during the geologic evolution of the lower crust in this area. Oxygenisotope values ofwhole-rock samples range from +5.9 to +8.4%0 SMOW and are consistent with igneous protoliths for the GVF granulites. The predominance of 6'*0 values greater than +6.0% suggests that a component of older crust or meta-sediment is involved in the petrogenesis of most granulites in the suite. Two-pyroxene, two-feldspar granulites (meta-diorites) have major and trace element characteristics similar to estimates of post-Archaen lower crust (WEAVER and TARNEY, 1984). Low '43Nd/'44Nd values and Proterozoic Nd-depleted-mantle model ages (1.2-1.4 Ga) for these rocks require that Precambrian material exists in the lower crust of southeastern Arizona, either as the metadiotites themselves or as older crust available for melting during production of the meta-diorite protoliths. K-feldspar-free gram&es have more mafic compositions and their trace element characteristics are consistent with a cumulate origin (positive Eu anomaly, low Rb/Sr ratios, and high Sr concentrations). A negative correlation of 20*Pb/204Pb vs. *06Pb/*04Pb suggests that the meta-cumulate granulites represent mixing between Basin and Range age lavas with older meta-diorite crust and is, thus, evidence for Cenozoic underplating of the lower crust beneath the Basin and Range. A summary of granulite xenolith compositions worldwide demonstrates that the lower crust is heterogeneous and more mafic than current estimates of its average composition.
Mat% to intermediate composition gmnulite xenoliths (plagioclase + clinopyroxene f orthopyroxene ... more Mat% to intermediate composition gmnulite xenoliths (plagioclase + clinopyroxene f orthopyroxene + K-feldspar * amphibole) occur in Pliocene to Recent alkali basalts from the Geronimo Volcanic Field (GVF), southeastern Arizona, USA. The range of compositions and mineral assemblages observed suggests that the ultimate derivation of these rocks is from a variety of protoliths and that more than one mechanism has operated during the geologic evolution of the lower crust in this area. Oxygenisotope values ofwhole-rock samples range from +5.9 to +8.4%0 SMOW and are consistent with igneous protoliths for the GVF granulites. The predominance of 6'*0 values greater than +6.0% suggests that a component of older crust or meta-sediment is involved in the petrogenesis of most granulites in the suite. Two-pyroxene, two-feldspar granulites (meta-diorites) have major and trace element characteristics similar to estimates of post-Archaen lower crust (WEAVER and TARNEY, 1984). Low '43Nd/'44Nd values and Proterozoic Nd-depleted-mantle model ages (1.2-1.4 Ga) for these rocks require that Precambrian material exists in the lower crust of southeastern Arizona, either as the metadiotites themselves or as older crust available for melting during production of the meta-diorite protoliths. K-feldspar-free gram&es have more mafic compositions and their trace element characteristics are consistent with a cumulate origin (positive Eu anomaly, low Rb/Sr ratios, and high Sr concentrations). A negative correlation of 20*Pb/204Pb vs. *06Pb/*04Pb suggests that the meta-cumulate granulites represent mixing between Basin and Range age lavas with older meta-diorite crust and is, thus, evidence for Cenozoic underplating of the lower crust beneath the Basin and Range. A summary of granulite xenolith compositions worldwide demonstrates that the lower crust is heterogeneous and more mafic than current estimates of its average composition.
Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences, 1984
Chemical and O-, Sr-, Nd-, and Pb-isotope relations for the British Caledonian granitoids exhibit... more Chemical and O-, Sr-, Nd-, and Pb-isotope relations for the British Caledonian granitoids exhibit systematic variations that are attributed to derivation from both mantle and crustal sources. The ‘older’ (more than ca . 470 Ma) pre- and syn-tectonic granites were the product of local anatectic melting of Late Proterozoic metasedimentary upper crust (8 18 O æ 8 to 14% 0 , 87 S r/ 86 Sr > 0.710, 206 Pb / 204 Pb « 18.1-19.2) during the peak thermal conditions of the Grampian Orogeny. The ‘younger’ (less than ca . 440 Ma) post-tectonic granitoids have a complex origin which, in individual cases, involved at least four different source regions: (i) the upper mantle or subducted oceanic crust (8 18 O « 5.7 to 7.0%o, 87 Sr/ 86 Sr « 0.7035-0.7040, 206 Pb/ 204 Pb = 17.9 to 18.1) and (ii) Lower Palaeozoic geosynclinal sedimentary upper crust (8 18 O « 11 to 14% 0 , 87 Sr/ 86 Sr « 705-0.711, 206 Pb/ 204 Pb « 18.4) within the paratectonic Caledonides in the Scottish Midland Valley and Southe...
A combination of hydrogen and oxygen isotope analyses and fluid inclusion studies has defined the... more A combination of hydrogen and oxygen isotope analyses and fluid inclusion studies has defined the composition of fluids involved in the metamorphism of Lower Palaeozoic rocks in the English Lake District. Three fluid fields have been defined from secondary phases: 1, syn-burial metamorphic D-enriched fluids from epidote and chlorite at a temperature between 250 and 350°C; D-depleted fluid measured from groundmass and quartz inclusions; 3, a mixed magmatic-meteoric fluid with an intermediate H-isotopic composition estimated from W/R granite data and calculated from illite.
ABSTRACT. A combination of hydrogen and oxygen isotope analyses and fluid inclusion studies has d... more ABSTRACT. A combination of hydrogen and oxygen isotope analyses and fluid inclusion studies has defined the composition of fluids involved in the metamorphism of Lower Palaeozoic rocks in the English Lake District. Three fluid fields have been defined from secondary phases: 1, syn-burial metamorphic D-enriched fluids from epidote and chlorite at a temperature b tween 250 and 350 ~ 2, D-depleted fluid measured from groundmass and quartz inclusions; 3, a mixed magmatic-meteoric fluid with an intermediate H-isotopic omposition esti-mated from W/R granite data and calculated from illite.
The major element chemistry was determined for surface waters from four watersheds in Central Pan... more The major element chemistry was determined for surface waters from four watersheds in Central Panama during the 2005 dry season to ascertain geochemical patterns resulting from differing geology and human influences as well to estimate chemical denudation rates for this montane region of tropical rain forest. The Upper Rio Chagres (580 km 2), Rio Pequini (281 km 2) and Rio Cuango (175 km 2) watersheds are formed on a geologically mixed terrain that consists of strongly hydrothermally altered andesite and volumetrically subordinate mafic-intermediate volcanic rocks and felsic intrusive lithologies, whereas the Rio Pacora watershed (374 km 2) is developed largely on gabbroic and dioritic lithologies. The headwater areas of all four river basins lie in pristine tropical rainforest, with the Rio Cuango, Rio Pequini and Rio Pacora subject to varying degrees of different land uses in their middle to lower reaches. Values of pH for the four watersheds are near neutral to slightly alkaline (7.0-8.5), DO saturation is high (typically >90%) and dissolved solute contents of the rivers and tributary streams are low (SPC = 130 ± 31 lS/cm), documenting the overall pristine quality of the waters in all four basins. Cluster analysis, supported by a comparison of elemental variations, indicates a broad geochemical similarity of rivers and streams in the four watersheds, but also reveals subtle differences that can be attributed to lithologic control rather than anthropogenic influences. Low-order streams in the Pacora watershed have distinctly higher TDS values plus silica and Ca 2+ concentrations than those forming in the mixed lithology terrain. Streams and rivers developed on mafic terrain are also slightly more enriched in total dissolved cations (TZ +) and HCO À 3 , relative to silica, than streams and rivers developed in the mixed lithology terrain. Potassium concentrations are uniformly low, and like Mg 2+ and Na + , are similar in both terrains. Calcium/Mg ratios for all watersheds are lower than the world river average, indicating the importance of the weathering of Mg-rich minerals. The Ca/Na, HCO 3 /Na and Mg/Na ratios for the Rio Pacora streams and rivers fall within the mid-range of what has been observed globally for other streams/rivers draining mafic rocks. The chemical weathering rate calculated is 108 tons/km 2 /a, which is about 40% of the physical denudation rate for the Upper Rio Chagres watershed of 275-289 tons/km 2 /a. The results of this study document that both chemical and physical erosion rates within tropical montane watersheds in central Panama are significant in a global context.
Oxygen isotope data are presented for 37 samples of subduction-related lavas from the Aeolian Isl... more Oxygen isotope data are presented for 37 samples of subduction-related lavas from the Aeolian Islands, southern Italy, that were characterised for radiogenic isotopes (Sr, Nd, Pb) and major- and trace-element abundances in previous studies. The samples, which were all erupted within the past 500,000 years, span the full compositional range of Aeolian magmatism from the calc-alkaline basalt-dacite sequence of Salina to the shoshonites of Stromboli and the potassic leucite-bearing basalt to rhyolite series of Vulcano, Whole-rock δ18O values range from +6.3‰ to +8.5‰, but in some cases (14 samples) 18O enrichment by post-crystallization hydration and low-temperature alteration is suspected, and an empirical correction for excess water yields a primary magmatic δ18O range of +6.1‰ to +8.5‰. Variations in δ18O exhibit a compositional dependence, increased δ18O values characterize the evolved samples of the various magmatic series, and δ18O-SiO2 trends are steeper than those predicted for...
Laser-induced breakdown spectroscopy (LIBS) is a form of optical emission spectroscopy that can b... more Laser-induced breakdown spectroscopy (LIBS) is a form of optical emission spectroscopy that can be used for the rapid analysis of geological materials in the field under ambient environmental conditions. We describe here the innovative use of handheld LIBS for the in situ analysis of rock varnish. This thinly laminated and compositionally complex veneer forms slowly over time on rock surfaces in dryland regions and is particularly abundant across the Mojave Desert climatic region of east-central California (USA). Following the depth profiling examination of a varnished clast from colluvial gravel in Death Valley in the laboratory, our in situ analysis of rock varnish and visually similar coatings on rock surfaces was undertaken in the Owens and Deep Spring valleys in two contexts, element detection/identification and microchemical mapping. Emission peaks were recognized in the LIBS spectra for the nine elements most abundant in rock varnish—Mn, Fe, Si, Al, Na, Mg, K, Ca and Ba, as w...
The availability of both global and regional elevation datasets acquired by modern remote sensing... more The availability of both global and regional elevation datasets acquired by modern remote sensing technologies provides an opportunity to significantly improve the accuracy of stream mapping, especially in remote, hard to reach regions. Stream extraction from digital elevation models (DEMs) is based on computation of flow accumulation, a summary parameter that poses performance and accuracy challenges when applied to large, noisy DEMs generated by remote sensing technologies. Robust handling of DEM depressions is essential for reliable extraction of connected drainage networks from this type of data. The least-cost flow routing method implemented in GRASS GIS as the module r.watershed was redesigned to significantly improve its speed, functionality, and memory requirements and make it an efficient tool for stream mapping and watershed analysis from large DEMs. To evaluate its handling of large depressions, typical for remote sensing derived DEMs, three different methods were compared: traditional sink filling, impact reduction approach, and least-cost path search. The comparison was performed using the Shuttle Radar Topographic Mission (SRTM) and Interferometric Synthetic Aperture Radar for Elevation (IFSARE) datasets covering central Panama at 90 m and 10 m resolutions, respectively. The accuracy assessment was based on ground control points acquired by GPS and reference points digitized from Landsat imagery along segments of selected Panamanian rivers. The results demonstrate that the new implementation of the least-cost path method is significantly faster than the original version, can cope with massive datasets, and provides the most accurate results in terms of stream locations validated against reference points.
Late Tertiary post-orogenic alkaline basalts erupted in the extensional Pannonian Basin following... more Late Tertiary post-orogenic alkaline basalts erupted in the extensional Pannonian Basin following Eocene-Miocene subduction and its related calc-alkaline volcanism. The alkaline volcanic centres, dated between 11-7 and 1-4 Ma, are concentrated in several regions of the Pannonian Basin. Some are near the western (Graz Basin, Burgenland), northern (Nograd), and eastern (Transylvania) margins of the basin, but the majority are concentrated near the Central Range (Balaton area and Little Hungarian Plain). Fresh samples from 31 volcanic centres of the extension-related lavas range from slightly hy-normative transitional basalts through alkali basalts and basanites to olivine nephelinites. No highly evolved compositions have been encountered. The presence of peridotite xenoliths, mantle xenocrysts, and high-pressure megacrysts, even in the slightly more evolved rocks, indicates that differentiation took place within the upper mantle. Rare earth elements (REE) and 87Sr/*6Sr, 143Nd/14*Nd, c...
A bibliography of published articles and reports on mineral-separation techniques, processes, and... more A bibliography of published articles and reports on mineral-separation techniques, processes, and applications is presented along with an author and subject index. This information is intended for use in the mineral-separation facility of the Lunar Receiving Laboratory at the NASA Manned Spacecraft Center and as an aid and reference to persons involved or interested in mineral separation.
... (1979) and Thirlwall and Graham (1984). Overall, Gre nada lavas have lower 143Nd 144Nd and su... more ... (1979) and Thirlwall and Graham (1984). Overall, Gre nada lavas have lower 143Nd 144Nd and substantially higher 87Sr Srsr than Atlantic MORB, forming a data array on Fig. 4 offset to higher 87Sr S6Sr than ocean islands. ...
Public reporting burden for this collection of information is estimated to average 1 hour per res... more Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to
Mat% to intermediate composition gmnulite xenoliths (plagioclase + clinopyroxene f orthopyroxene ... more Mat% to intermediate composition gmnulite xenoliths (plagioclase + clinopyroxene f orthopyroxene + K-feldspar * amphibole) occur in Pliocene to Recent alkali basalts from the Geronimo Volcanic Field (GVF), southeastern Arizona, USA. The range of compositions and mineral assemblages observed suggests that the ultimate derivation of these rocks is from a variety of protoliths and that more than one mechanism has operated during the geologic evolution of the lower crust in this area. Oxygenisotope values ofwhole-rock samples range from +5.9 to +8.4%0 SMOW and are consistent with igneous protoliths for the GVF granulites. The predominance of 6'*0 values greater than +6.0% suggests that a component of older crust or meta-sediment is involved in the petrogenesis of most granulites in the suite. Two-pyroxene, two-feldspar granulites (meta-diorites) have major and trace element characteristics similar to estimates of post-Archaen lower crust (WEAVER and TARNEY, 1984). Low '43Nd/'44Nd values and Proterozoic Nd-depleted-mantle model ages (1.2-1.4 Ga) for these rocks require that Precambrian material exists in the lower crust of southeastern Arizona, either as the metadiotites themselves or as older crust available for melting during production of the meta-diorite protoliths. K-feldspar-free gram&es have more mafic compositions and their trace element characteristics are consistent with a cumulate origin (positive Eu anomaly, low Rb/Sr ratios, and high Sr concentrations). A negative correlation of 20*Pb/204Pb vs. *06Pb/*04Pb suggests that the meta-cumulate granulites represent mixing between Basin and Range age lavas with older meta-diorite crust and is, thus, evidence for Cenozoic underplating of the lower crust beneath the Basin and Range. A summary of granulite xenolith compositions worldwide demonstrates that the lower crust is heterogeneous and more mafic than current estimates of its average composition.
Mat% to intermediate composition gmnulite xenoliths (plagioclase + clinopyroxene f orthopyroxene ... more Mat% to intermediate composition gmnulite xenoliths (plagioclase + clinopyroxene f orthopyroxene + K-feldspar * amphibole) occur in Pliocene to Recent alkali basalts from the Geronimo Volcanic Field (GVF), southeastern Arizona, USA. The range of compositions and mineral assemblages observed suggests that the ultimate derivation of these rocks is from a variety of protoliths and that more than one mechanism has operated during the geologic evolution of the lower crust in this area. Oxygenisotope values ofwhole-rock samples range from +5.9 to +8.4%0 SMOW and are consistent with igneous protoliths for the GVF granulites. The predominance of 6'*0 values greater than +6.0% suggests that a component of older crust or meta-sediment is involved in the petrogenesis of most granulites in the suite. Two-pyroxene, two-feldspar granulites (meta-diorites) have major and trace element characteristics similar to estimates of post-Archaen lower crust (WEAVER and TARNEY, 1984). Low '43Nd/'44Nd values and Proterozoic Nd-depleted-mantle model ages (1.2-1.4 Ga) for these rocks require that Precambrian material exists in the lower crust of southeastern Arizona, either as the metadiotites themselves or as older crust available for melting during production of the meta-diorite protoliths. K-feldspar-free gram&es have more mafic compositions and their trace element characteristics are consistent with a cumulate origin (positive Eu anomaly, low Rb/Sr ratios, and high Sr concentrations). A negative correlation of 20*Pb/204Pb vs. *06Pb/*04Pb suggests that the meta-cumulate granulites represent mixing between Basin and Range age lavas with older meta-diorite crust and is, thus, evidence for Cenozoic underplating of the lower crust beneath the Basin and Range. A summary of granulite xenolith compositions worldwide demonstrates that the lower crust is heterogeneous and more mafic than current estimates of its average composition.
Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences, 1984
Chemical and O-, Sr-, Nd-, and Pb-isotope relations for the British Caledonian granitoids exhibit... more Chemical and O-, Sr-, Nd-, and Pb-isotope relations for the British Caledonian granitoids exhibit systematic variations that are attributed to derivation from both mantle and crustal sources. The ‘older’ (more than ca . 470 Ma) pre- and syn-tectonic granites were the product of local anatectic melting of Late Proterozoic metasedimentary upper crust (8 18 O æ 8 to 14% 0 , 87 S r/ 86 Sr > 0.710, 206 Pb / 204 Pb « 18.1-19.2) during the peak thermal conditions of the Grampian Orogeny. The ‘younger’ (less than ca . 440 Ma) post-tectonic granitoids have a complex origin which, in individual cases, involved at least four different source regions: (i) the upper mantle or subducted oceanic crust (8 18 O « 5.7 to 7.0%o, 87 Sr/ 86 Sr « 0.7035-0.7040, 206 Pb/ 204 Pb = 17.9 to 18.1) and (ii) Lower Palaeozoic geosynclinal sedimentary upper crust (8 18 O « 11 to 14% 0 , 87 Sr/ 86 Sr « 705-0.711, 206 Pb/ 204 Pb « 18.4) within the paratectonic Caledonides in the Scottish Midland Valley and Southe...
A combination of hydrogen and oxygen isotope analyses and fluid inclusion studies has defined the... more A combination of hydrogen and oxygen isotope analyses and fluid inclusion studies has defined the composition of fluids involved in the metamorphism of Lower Palaeozoic rocks in the English Lake District. Three fluid fields have been defined from secondary phases: 1, syn-burial metamorphic D-enriched fluids from epidote and chlorite at a temperature between 250 and 350°C; D-depleted fluid measured from groundmass and quartz inclusions; 3, a mixed magmatic-meteoric fluid with an intermediate H-isotopic composition estimated from W/R granite data and calculated from illite.
ABSTRACT. A combination of hydrogen and oxygen isotope analyses and fluid inclusion studies has d... more ABSTRACT. A combination of hydrogen and oxygen isotope analyses and fluid inclusion studies has defined the composition of fluids involved in the metamorphism of Lower Palaeozoic rocks in the English Lake District. Three fluid fields have been defined from secondary phases: 1, syn-burial metamorphic D-enriched fluids from epidote and chlorite at a temperature b tween 250 and 350 ~ 2, D-depleted fluid measured from groundmass and quartz inclusions; 3, a mixed magmatic-meteoric fluid with an intermediate H-isotopic omposition esti-mated from W/R granite data and calculated from illite.
The major element chemistry was determined for surface waters from four watersheds in Central Pan... more The major element chemistry was determined for surface waters from four watersheds in Central Panama during the 2005 dry season to ascertain geochemical patterns resulting from differing geology and human influences as well to estimate chemical denudation rates for this montane region of tropical rain forest. The Upper Rio Chagres (580 km 2), Rio Pequini (281 km 2) and Rio Cuango (175 km 2) watersheds are formed on a geologically mixed terrain that consists of strongly hydrothermally altered andesite and volumetrically subordinate mafic-intermediate volcanic rocks and felsic intrusive lithologies, whereas the Rio Pacora watershed (374 km 2) is developed largely on gabbroic and dioritic lithologies. The headwater areas of all four river basins lie in pristine tropical rainforest, with the Rio Cuango, Rio Pequini and Rio Pacora subject to varying degrees of different land uses in their middle to lower reaches. Values of pH for the four watersheds are near neutral to slightly alkaline (7.0-8.5), DO saturation is high (typically >90%) and dissolved solute contents of the rivers and tributary streams are low (SPC = 130 ± 31 lS/cm), documenting the overall pristine quality of the waters in all four basins. Cluster analysis, supported by a comparison of elemental variations, indicates a broad geochemical similarity of rivers and streams in the four watersheds, but also reveals subtle differences that can be attributed to lithologic control rather than anthropogenic influences. Low-order streams in the Pacora watershed have distinctly higher TDS values plus silica and Ca 2+ concentrations than those forming in the mixed lithology terrain. Streams and rivers developed on mafic terrain are also slightly more enriched in total dissolved cations (TZ +) and HCO À 3 , relative to silica, than streams and rivers developed in the mixed lithology terrain. Potassium concentrations are uniformly low, and like Mg 2+ and Na + , are similar in both terrains. Calcium/Mg ratios for all watersheds are lower than the world river average, indicating the importance of the weathering of Mg-rich minerals. The Ca/Na, HCO 3 /Na and Mg/Na ratios for the Rio Pacora streams and rivers fall within the mid-range of what has been observed globally for other streams/rivers draining mafic rocks. The chemical weathering rate calculated is 108 tons/km 2 /a, which is about 40% of the physical denudation rate for the Upper Rio Chagres watershed of 275-289 tons/km 2 /a. The results of this study document that both chemical and physical erosion rates within tropical montane watersheds in central Panama are significant in a global context.
Oxygen isotope data are presented for 37 samples of subduction-related lavas from the Aeolian Isl... more Oxygen isotope data are presented for 37 samples of subduction-related lavas from the Aeolian Islands, southern Italy, that were characterised for radiogenic isotopes (Sr, Nd, Pb) and major- and trace-element abundances in previous studies. The samples, which were all erupted within the past 500,000 years, span the full compositional range of Aeolian magmatism from the calc-alkaline basalt-dacite sequence of Salina to the shoshonites of Stromboli and the potassic leucite-bearing basalt to rhyolite series of Vulcano, Whole-rock δ18O values range from +6.3‰ to +8.5‰, but in some cases (14 samples) 18O enrichment by post-crystallization hydration and low-temperature alteration is suspected, and an empirical correction for excess water yields a primary magmatic δ18O range of +6.1‰ to +8.5‰. Variations in δ18O exhibit a compositional dependence, increased δ18O values characterize the evolved samples of the various magmatic series, and δ18O-SiO2 trends are steeper than those predicted for...
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