華南中生代雙模式火成活動之成因及其大地構造意義（Ⅰ）
Date Issued
1998
Date
1998
Author(s)
李寄嵎
DOI
872116M002008
Abstract
Among North China Block, Indochina
Block and Pacific plate, the greatest
magmatic belts of Western Pacific are
distributed in Huanan. These belts are formed
after Indochina orogeny and collisions of
North China and South china Blocks. Except
the voluminous intrusives, the Mesozoic
volcanics(or Yanshanian volcanics) are also
widespread in this area. Generally, the basic
parts are only 5% of the total volume, the
others are the mediate and acidic volcanics.
The Jurassic and Cretaceous bimodal
magmatic suites are scatteredly distributed in
Zhejiang, Fujian, Jiangxi, Hunan and
Guangdong provinces.
The Mesozoic volcanism of Zhejiang
Province can be divided into two episodes.
(1)Early episode(lower volcanic sequence, or
Late Jurasic-Early Cretaceous sequence)
consist predominantly of high-K calc-alkaline
series (andesite-dacite-rhyolite);
(2)Late episode (upper volcanic sequence, or
Late Cretaceous sequence) are exposed in
small fault-bounded basins and consist of
bimodal basalt-rhyolite series. According to 40 Ar/39 Ar ages, the Late episode (upper
volcanic sequence) began at 108Ma.
Late Cretaceous bimodal basalt-rhyolite
series mainly crop out in the eastern Zhejiang.
The mafic member consist of basalt/ basaltic
andesite (SiO2@43.6-55.8%), and belong to
the middle K to Shoshonitic suites. Similar to
Cretaceous A-type granites from the nearby
region, the felsic member shows peralkaline
nature [SiO2> 70%, Na2O +K2O@6-9%].
Generally, both members show enrichment in
the incompatible trace elements and
depletion in Nb and Ta. But the felsic
member is characterized by the significant
depletion of Ba, Sr, Eu, P and Ti which
reflect the process of feldspar fractionation.
From a series of studies of the Late
Yanshanian granitoids in Zhejiang-Fujian
areas since three years ago, the geochemical
results show that some rock units have the
characteristics of extension-type granite. This
seems to imply the tectonic style of SE China
has been changed from compression to
extension since late Cretaceous. Therefore
the studies of Mesozoic bimodal volcanism
in the Zhejiang province shows that the
extensional activity of SE China may be
earlier than 110 Ma.
Subjects
bimodal volcanism
40 Ar/39 Ar
ages
ages
extensional activity
Publisher
臺北市：國立臺灣大學地質科學系暨研究所
Type
report
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