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cycles in Hawaii. ( 英 文 ). Sheldon N D.
Journal of Geology, 2006, 114(3): 367-
376
The upper kilometer of the Hawaiian
Scientific Drilling Program core consists
of lavas that were emplaced subaerially,
burying paleosols. These paleosols were
preserved with minimal alteration and
are used to construct a similar to 330-kyr
Quaternary climate record. Within the
temporal resolution of this record, there
appears to be a similar to 100-kyr climate
oscillation between cool-dry and
warm-wet conditions, indicating that
tropical regions such as Hawaii have responded
to the same global climate forcings
as have higher-latitude areas during
at least the past three glacial-interglacial
cycles. It is also suggested that Hawaiian
climate may have become progressively
warmer and wetter over the same period.
2010010592
墨 西 哥 Guanajuato 地 区 San Miguel
de Allende 地 堑 中 新 世 - 上 新 世 火 山 灰
沉 积 中 硅 酸 岩 浆 的 对 比 = Contrasting
silicic magma series in Miocene-
Pliocene ash deposits in the San Miguel
de Allende Graben, Guanajuato, Mexico.
( 英 文 ). Adams A J; Christiansen E H;
Kowallis B J; Carranza-Castaneda O;
Miller W E. Journal of Geology, 2006,
114(2): 247-266
The San Miguel de Allende graben,
Guanajuato, Mexico, contains numerous
rhyolitic volcanic ash beds. Electron microprobe
and x-ray fluorescence analyses
of glass shards from 14 localities,
combined with mineralogic, stratigraphic,
radiometric, and paleomagnetic
data, allow us to correlate the ash beds
( and the intervening sedimentary strata
and fossils), understand the timing of
volcanism, date the age of extension,
and better understand the tectonic and
volcanic evolution of central Mexico.
Our analyses reveal that at least six
separate eruptions of rhyolitic ash occurred
during the Late Miocene and
Pliocene (5-3 Ma) while the San Miguel
Allende basin was subsiding. The fallout
ash beds can be distinguished by
phenocryst mineralogy, inferred eruption
temperatures, and differences in
major and trace element compositions.
Two magma series ( medium K and high
K) are represented in the rhyolitic tephra
deposits. The high-K series is marginally
peralkaline, reduced ( indicated by
high Fe/Mg ratios), dry ( paucity of hydrous
silicates), hot (