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deepest level rocks, Oman mountains:
U/Pb SHRIMP evidence for Late Carboniferous
Neotethys rifting. ( 英 文 ).
Gray D R; Gregory R T; Armstrong R A;
Richards I J; Miller J M. Journal of Geology,
2005, 113(6): 611-626
Igneous zircons in felsic schist, or
metatuff, infolded with mafic schist,
calcschist, and quartz mica schist of the
As Sifah lower plate window, NE Oman,
have yielded a U/Pb SHRIMP crystallization
age of 298 +/- 3 Ma. The metatuff
was previously considered to represent
Permian bimodal volcanism, but these
data indicate that the magmatism is
older and suggest that Neotethys intracontinental
rifting on the Oman part
of the Gondwana northern margin was
initiated in the Late Carboniferous. This,
combined with delta(13)C values of
calcschists indicating a predominantly
pre-Late Permian age for the basal lower
plate metacarbonates, suggests that passive
margin carbonate ramp development
occurred in the Late Carboniferous/Early
Permian during Neotethys
oceanic spreading and not just in the
Late Permian, as previously thought.
The restricted occurrence of the metatuff
to the Saih Hatat lower plate, a unique
lower plate stratigraphy, and the unique
delta(13)C values of the calcschists all
suggest that the lower plate was certainly
distal, and possibly exotic, to the
Arabian Peninsula. The felsic schist
sample was entrained within an eclogite
megaboudin at As Sifah. The age relationships
therefore suggest that the high-
P rocks that reached pressures of up to
20 kbar and are now part of the lower
plate of Gregory and coworkers were
either part of a subducted Florida-style
promontory as part of the attenuated
leading edge of the Arabian platform or
part of a subducted microplate that was
originally caught in the developing
southern Neotethys ocean some 1300
km from the margin.
2010010549
美 国 东 北 部 寒 武 纪 — 奥 陶 纪 沉 积 岩 的
地 球 化 学 特 征 : 康 塔 造 山 作 用 初 始 沉
积 物 源 的 改 变 = Geochemistry of
Cambro-Ordovician sedimentary rocks
of the Northeastern United States:
Changes in sediment sources at the onset
of Taconian orogenesis. ( 英 文 ).
Hurowitz J A; McLennan S M. Journal
of Geology, 2005, 113(5): 571-587
Trace element and Nd isotopic compositions
of Late Cambrian to Middle
Ordovician passive margin metasediments
from the northernmost Taconic
Allochthon of the northeast United
States indicate a provenance consistent
with a two-component mixture of an
evolved Grenville source and a rift
source generated during the Late Proterozoic
opening of the Iapetus Ocean.
Initial epsilon(Nd) values for these preorogenic
deposits range from -11.3 to -
14.6 (average=-13.0). Samples of overlying
mid-Ordovician Taconian sediments
exhibit initial epsilon(Nd) values
between -6.1 and -9.8 (average=-8.5).
The trace element and Nd isotopic compositions
of these synorogenic samples
are consistent with a mixture of a less
evolved Grenville Province source and
recycled preorogenic passive margin deposits.
No mantle-derived (ophiolitic or
andesitic) source is unambiguously recognized
in the synorogenic samples,
consistent with published geochemical
studies of other Taconian foreland sequences
from this region. Sedimentary
rocks from the northern Appalachians
record a clear change in provenance at
ca. 458 Ma, coincident with the onset of
Taconian orogenesis and similar to patterns
observed in other sedimentary sequences
throughout North America.
2010010550
海 平 面 升 降 旋 回 地 层 中 生 物 的 改 变 :
莫 斯 科 Peski 采 石 场 石 炭 系 莫 斯 科 阶
Domodedovo 组 = Biotic changes in a
eustatic cyclothem: Domodedovo For-
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