F. Ryerson - Academia.edu (original) (raw)
Papers by F. Ryerson
Geophysical Research Letters, 2002
Using 36 Cl cosmic ray exposure dating we obtained continuous exposure histories for 7-12 m-high ... more Using 36 Cl cosmic ray exposure dating we obtained continuous exposure histories for 7-12 m-high limestone surfaces at two sites (10 km apart) on the Sparta normal fault scarp. As each major earthquake adds new surface to the cumulative scarp exposing new material to cosmic-ray bombardment these exposure histories allow the slip history to be constrained. The results show that an earthquake occurred on this fault 2800 ± 300 yr ago. We infer that this is the seismic event that destroyed ancient Sparta in 464 B.C. Four earlier earthquakes ruptured the Sparta fault in the last 13 ka with similar slip amplitudes of about 2 m and with time intervals ranging from 500 yr to 4500 yr. The observations also confirm that the Sparta scarp is post-glacial, supporting the hypothesis that similar scarps elsewhere in the Mediterranean region have a comparable age. The absence of any event since 464 B.C. could suggest a future event is imminent. However, the irregularity of earthquake time intervals could also be due to changes of loading with important consequences for the mechanics of continental deformation.
The high retentivity of monazite for Pb, its high U and Th concentrations, and its emergence in s... more The high retentivity of monazite for Pb, its high U and Th concentrations, and its emergence in staurolite-zone metapelites suggests its use as a prograde thermochronometer. However, the monazite-producing reactions in pelites are as yet incompletely understood. We have investigated by experiment the suggestion that rhabdophane (LREEPO4-nH20) should be considered as an important reactant in monazite-producing reactions in pelitic compositions. Results of our combined hydrothermal and 1-bar heating experiments preclude rhabdophane from being the immediate precursor to neoformed monazite in lower amphibolite-facies metamorphic sequences and restrict rhabdophane occurrence to the uppermost portion of the crust. Dehydration of rhabdophane to form monazite appears to occur in a manner that may be analogous to the dehydration equilibria of zeolite minerals. Dry, 1-bar heating experiments indicate that La-rhabdophane persists (metastably?) to temperatures approaching 500 ° C. XRD and visible-near-infrared spectroscopy examination of La-rhabdophane heated isothermally in air at temperatures ranging from 200* to 700°C indicate that structural water is largely retained up to 500 °C over heating intervals of up to 24 hr. Structural modifications involving H20 appear to take place between 300 ° and 500 ° C. Partial decomposition of La-rhabdophane to La-monazite is observed at 600 o C while rapid and complete reaction to La-monazite occurs at 700 ° C. Experiments conducted under elevated water pressure (0.5-2 kbar) at temperatures between 200 ° and 600 ° C have not encountered conditions under which rhabdophane is stable relative to La-monazite + H20. The low rhabdophane dehydration temperatures relative to the temperatures inferred for monazite formation in metapelites indicate that rhabdophane does not convert directly to monazite during pelite metamorphism. Rather, the "monazite LREE component" produced by rhabdophane breakdown must be incorporated in intermediate phases such as allanite and, perhaps more likely, LREE-oxides prior to monazite formation.
Journal of Geophysical Research, 1988
The relationship between the rheology and phase equilibria of a picritic basalt from Kilauea Iki ... more The relationship between the rheology and phase equilibria of a picritic basalt from Kilauea Iki has been investigated at 1 atm along the QFM buffer. Between 1270° and 1180°C olivine and minor spinel are the only liquidus phases, and the melt volume decreases from 85 to 74 ...
Long-term slip rates for the Denali Fault in southern Alaska are derived using 10 Be cosmogenic r... more Long-term slip rates for the Denali Fault in southern Alaska are derived using 10 Be cosmogenic radionuclide (CRN) dating of offset glacial moraines at two sites. Correction of 10 Be CRN model ages for the effect of snow shielding uses historical, regional snow cover data scaled to the site altitudes. To integrate the time variation of snow cover, we included the relative changes in effective wetness over the last 11 ka, derived from lake-level records and d 18 O variations from Alaskan lakes. The moraine CRN model ages are normally distributed around an average of 12.1 ± 1.0 ka (n = 22, ± 1s). The slip rate decreases westward from �13 mm/a at 144°49 0 W to about 7 mm/a at 149°26 0 W. The data are consistent with a kinematic model in which southern Alaska translates northwestward at a rate of �14 mm/a relative to a stable northern Alaska with no rotation. This suggests progressive slip partitioning between the Denali Fault and the active fold and thrust belt at the northern front of the Alaska range, with convergence rates increasing westward from �4 mm/a to 11 mm/a between 149°W and 145°W. As the two moraines sampled for this study were emplaced synchronously � , our suggestion of a westward decrease in the slip rate of the Denali Fault relies largely upon the measured offsets at both sites, regardless of any potential systematic uncertainty in the CRN model ages.
Geology, 1998
Cosmogenic dating, using in-situ 26 Al and 10 Be in quartz pebbles from alluvial terrace surfaces... more Cosmogenic dating, using in-situ 26 Al and 10 Be in quartz pebbles from alluvial terrace surfaces, constrains the late Holocene slip rate on the Xidatan segment of the Kunlun fault in northeastern Tibet. Two terrace risers offset by 24 ± 3 and 33 ± 4 m, having respective ages of 1788 ± 388 and 2914 ± 471 yr, imply a slip rate of 12.1 ± 2.6 mm/yr. The full range of ages obtained (≤22.8 k.y., most of them between 6.7 and 1.4 k.y.) confirm that terrace deposition and incision, hence landform evolution, are modulated by post-glacial climate change. Coupled with minimum offsets of 9-12 m, this slip rate implies that great earthquakes (M ~8) with a recurrence time of 800-1000 yr, rupture the Kunlun fault near 94°E.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1990
Ion implantation is used to introduce lead into the mineral apatite. Diffusion profiles are obtai... more Ion implantation is used to introduce lead into the mineral apatite. Diffusion profiles are obtained using Rutherford backscat~~~g (RBS) and the results fit with a model to dete~e I). Results for apatite over the temperature range 600-900 o C show agreement with earlier results obtained by traditional geological techniques. This suggests that radiation damage induced by ion implantation has little eFfect on diffusion in this case. This approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times.
Geophysical Research Letters, 2002
Using 36 Cl cosmic ray exposure dating we obtained continuous exposure histories for 7-12 m-high ... more Using 36 Cl cosmic ray exposure dating we obtained continuous exposure histories for 7-12 m-high limestone surfaces at two sites (10 km apart) on the Sparta normal fault scarp. As each major earthquake adds new surface to the cumulative scarp exposing new material to cosmic-ray bombardment these exposure histories allow the slip history to be constrained. The results show that an earthquake occurred on this fault 2800 ± 300 yr ago. We infer that this is the seismic event that destroyed ancient Sparta in 464 B.C. Four earlier earthquakes ruptured the Sparta fault in the last 13 ka with similar slip amplitudes of about 2 m and with time intervals ranging from 500 yr to 4500 yr. The observations also confirm that the Sparta scarp is post-glacial, supporting the hypothesis that similar scarps elsewhere in the Mediterranean region have a comparable age. The absence of any event since 464 B.C. could suggest a future event is imminent. However, the irregularity of earthquake time intervals could also be due to changes of loading with important consequences for the mechanics of continental deformation.
The high retentivity of monazite for Pb, its high U and Th concentrations, and its emergence in s... more The high retentivity of monazite for Pb, its high U and Th concentrations, and its emergence in staurolite-zone metapelites suggests its use as a prograde thermochronometer. However, the monazite-producing reactions in pelites are as yet incompletely understood. We have investigated by experiment the suggestion that rhabdophane (LREEPO4-nH20) should be considered as an important reactant in monazite-producing reactions in pelitic compositions. Results of our combined hydrothermal and 1-bar heating experiments preclude rhabdophane from being the immediate precursor to neoformed monazite in lower amphibolite-facies metamorphic sequences and restrict rhabdophane occurrence to the uppermost portion of the crust. Dehydration of rhabdophane to form monazite appears to occur in a manner that may be analogous to the dehydration equilibria of zeolite minerals. Dry, 1-bar heating experiments indicate that La-rhabdophane persists (metastably?) to temperatures approaching 500 ° C. XRD and visible-near-infrared spectroscopy examination of La-rhabdophane heated isothermally in air at temperatures ranging from 200* to 700°C indicate that structural water is largely retained up to 500 °C over heating intervals of up to 24 hr. Structural modifications involving H20 appear to take place between 300 ° and 500 ° C. Partial decomposition of La-rhabdophane to La-monazite is observed at 600 o C while rapid and complete reaction to La-monazite occurs at 700 ° C. Experiments conducted under elevated water pressure (0.5-2 kbar) at temperatures between 200 ° and 600 ° C have not encountered conditions under which rhabdophane is stable relative to La-monazite + H20. The low rhabdophane dehydration temperatures relative to the temperatures inferred for monazite formation in metapelites indicate that rhabdophane does not convert directly to monazite during pelite metamorphism. Rather, the "monazite LREE component" produced by rhabdophane breakdown must be incorporated in intermediate phases such as allanite and, perhaps more likely, LREE-oxides prior to monazite formation.
Journal of Geophysical Research, 1988
The relationship between the rheology and phase equilibria of a picritic basalt from Kilauea Iki ... more The relationship between the rheology and phase equilibria of a picritic basalt from Kilauea Iki has been investigated at 1 atm along the QFM buffer. Between 1270° and 1180°C olivine and minor spinel are the only liquidus phases, and the melt volume decreases from 85 to 74 ...
Long-term slip rates for the Denali Fault in southern Alaska are derived using 10 Be cosmogenic r... more Long-term slip rates for the Denali Fault in southern Alaska are derived using 10 Be cosmogenic radionuclide (CRN) dating of offset glacial moraines at two sites. Correction of 10 Be CRN model ages for the effect of snow shielding uses historical, regional snow cover data scaled to the site altitudes. To integrate the time variation of snow cover, we included the relative changes in effective wetness over the last 11 ka, derived from lake-level records and d 18 O variations from Alaskan lakes. The moraine CRN model ages are normally distributed around an average of 12.1 ± 1.0 ka (n = 22, ± 1s). The slip rate decreases westward from �13 mm/a at 144°49 0 W to about 7 mm/a at 149°26 0 W. The data are consistent with a kinematic model in which southern Alaska translates northwestward at a rate of �14 mm/a relative to a stable northern Alaska with no rotation. This suggests progressive slip partitioning between the Denali Fault and the active fold and thrust belt at the northern front of the Alaska range, with convergence rates increasing westward from �4 mm/a to 11 mm/a between 149°W and 145°W. As the two moraines sampled for this study were emplaced synchronously � , our suggestion of a westward decrease in the slip rate of the Denali Fault relies largely upon the measured offsets at both sites, regardless of any potential systematic uncertainty in the CRN model ages.
Geology, 1998
Cosmogenic dating, using in-situ 26 Al and 10 Be in quartz pebbles from alluvial terrace surfaces... more Cosmogenic dating, using in-situ 26 Al and 10 Be in quartz pebbles from alluvial terrace surfaces, constrains the late Holocene slip rate on the Xidatan segment of the Kunlun fault in northeastern Tibet. Two terrace risers offset by 24 ± 3 and 33 ± 4 m, having respective ages of 1788 ± 388 and 2914 ± 471 yr, imply a slip rate of 12.1 ± 2.6 mm/yr. The full range of ages obtained (≤22.8 k.y., most of them between 6.7 and 1.4 k.y.) confirm that terrace deposition and incision, hence landform evolution, are modulated by post-glacial climate change. Coupled with minimum offsets of 9-12 m, this slip rate implies that great earthquakes (M ~8) with a recurrence time of 800-1000 yr, rupture the Kunlun fault near 94°E.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1990
Ion implantation is used to introduce lead into the mineral apatite. Diffusion profiles are obtai... more Ion implantation is used to introduce lead into the mineral apatite. Diffusion profiles are obtained using Rutherford backscat~~~g (RBS) and the results fit with a model to dete~e I). Results for apatite over the temperature range 600-900 o C show agreement with earlier results obtained by traditional geological techniques. This suggests that radiation damage induced by ion implantation has little eFfect on diffusion in this case. This approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times.