| Abstract: | Geologic and geophysical data from Laguna de Ayarza, a figure-8-shaped doublecaldera lake in the Guatemalan highlands, show no evidence of postcaldera eruptive tectonic activity. The bathymetry of the lake has evolved as a result of sedimentary infilling. The western caldera is steep-sided and contains a large flat-floored central basin 240 m deep. The smaller, older, eastern caldera is mostly filled by coalescing delta fans and is connected with the larger caldera by means of a deep channel. Seismicreflection data indicate that at least 170 m of flat-lying unfaulted sediments partly fill the central basin and that the strata of the pre-eruption edifice have collapsed partly along inward-dipping ring faults and partly by more chaotic collapses. These sediments have accumulated in the last 23,000 years at a minimum average sedimentation rate of 7 m/103 yr. The upper 9 m of these sediments is composed of > 50% turbidites, interbedded with laminated clayey silts containing separate diatom and ash layers. The bottom sediments have >1% organic material, an average of 4% pyrite, and abundant biogenic gas, all of which demonstrate that the bottom sediments are anoxic. Although thin (<0.5 cm) ash horizons are common, only one thick (7-16 cm) primary ash horizon could be identified in piston cores. Alterations in the mineralogy and variations in the diatom assemblage suggest magnesium-rich hydrothermal activity. ?? 1985. |
| Genre: | Article |
| ProdID: | 70012718 |
| Citation Author: | Poppe, L. J.; Paull, C. K.; Newhall, C. G.; Bradbury, J. P.; Ziagos, J. |
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| Citation End Page: | 144 |
| Citation Issue: | 1-2 |
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| Citation Language: | English |
| Citation Larger Work Title: | Journal of Volcanology and Geothermal Research |
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| Citation Number Of Pages: | 20 |
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| Citation Search Results Text: | A geophysical and geological study of Laguna de Ayarza, a Guatemalan caldera lake; 1985; Article; Journal; Journal of Volcanology and Geothermal Research; Poppe, L. J.; Paull, C. K.; Newhall, C. G.; Bradbury, J. P.; Ziagos, J. |
| Citation Start Page: | 125 |
| Citation Volume: | 25 |
| Citation Year: | 1985 |
| Type: | citation/reference |
| Text: | A geophysical and geological study of Laguna de Ayarza, a Guatemalan caldera lake; 1985; Article; Journal; Journal of Volcanology and Geothermal Research; Poppe, L. J.; Paull, C. K.; Newhall, C. G.; Bradbury, J. P.; Ziagos, J. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Tue, 1 Jan 1985 00:00 -0600 |
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