阿拉斯加麥金利系列岩體之鋯石定年與地球化學研究

Zircon U-Pb Ages and Geochemical Characteristics of the McKinley Sequence and Associated Plutons, Central Alaska Range

洪千惠(Chien-Hui Hung)

指導教授 ： 鍾孫霖

國立臺灣大學/理學院/地質科學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.01476

摘要

無資料

關鍵字

阿拉斯加山脈 ； 麥金利系列岩體 ； 鋯石鈾鉛定年 ； 鍶釹鉿同位素

並列摘要

Plutonic rocks in the Central Alaska Range were emplaced during important
tectonic events including the end of Late Cretaceous-Paleocene arc magmatism, the
terminal phase of terrane accretion, the Kula ridge subduction, regional strike-slip
faulting, oroclinal rotation of western Alaska, and Eocene resumption of arc
magmatism along the proto-Aleutian arc system. Here we report the first set of
LA-ICPMS and SHRIMP zircon U-Pb ages for granitoids from (1) the McKinley
Sequence, (2) the Composite Plutons and (3) the Foraker Pluton, central Alaska Range.
Two peraluminous granites from the McKinley Sequence yielded 206Pb/238U ages of
62±1 and 60±1 Ma; an A-type granite from the same area gave age of 64±1 Ma. Two
granodiorites from the Composite Plutons and a granite from the Foraker Pluton gave
ages of 69±1, 67±1 and 37±1 Ma, respectively.
The age results indicate that the Composite Plutons and the McKinley Sequence
granites are older than previously reported and that the McKinley granites can be
divided into two magma suites that consist of peraluminous and A-type compositions
occurring at ca. 62-60 and 64 Ma, respectively. Nd and Sr isotope data suggest a
temporal change in the magma’s isotopic compositions, with the Foraker granites
showing higher and more heterogeneous εNd(T) values that range from about +6 to -2
and the Composite and McKinley Sequence granitoids showing lower and less
heterogeneous εNd(T) values from +1 to -3. Besides, zircon Hf isotopic data of the
dated samples show that a granite from the Foraker plutons has the highest zircon
εHf(T) values from +15 to +10, in contrast to the Composite plutons that show
apparently lower zircon εHf(T) values from +4 to -3. Peralumous and A-type granites
from the McKinley Sequence have zircon εHf(T) values from +2 to -5 and +8 to +1,
respectively.
The Composite and McKinley Sequence plutonic rocks are interpreted as products
of the ending phase of Late Cretaceous-Paleocene arc magmatism. The peraluminous
granites from the McKinley sequence may have been sourced from the remnant
mantle wedge, previously responsible for generating the Composite plutons and
earlier arc magmas. Besides, generation of the A-type granites can be attributed to the
v
oroclinal rotation of western Alaska and ridge subduction that started around 64 Ma, a
mechanism that may also have resulted in broadly coeval volcanism in the nearby
Cantwell basin and northern Talkeetna Mountains. The Foraker pluton are interpreted
as the product of renewed magmatism along the proto-Aleutian arc, in response to
north or northwestward subduction of the Pacific plate during 45-30 Ma.

並列關鍵字

Alaska Range ； the McKinley Sequence ； zircon U-Pb dating ； Sr-Nd isotopes ； Hf isotope

參考文獻

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