Zircon and Monazite U–Pb Systems and the Histories of I-Type Magmas, Berridale Batholith, Australia
Zircon and Monazite U–Pb Systems and the Histories of I-Type Magmas, Berridale Batholith, Australia
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DOI：
10.1093/petrology/24.1.76
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发表时间：
1983-02
影响因子：
3.9
通讯作者：
I. Williams;W. Compston;B. Chappell
中科院分区：
文献类型：
--
作者：
I. Williams;W. Compston;B. Chappell
对Berridale岩基四个I型花岗岩类的锆石和独居石进行了U-Pb年龄测定，并与相同深成岩体的其他同位素年龄进行了比较。不同的技术确定的年龄有很大的不同。Rb-Sr云母年龄与野外侵位序列一致，但并非都是侵位年龄。在Maffra二长花岗岩上测定的大多数年龄与∼413 Ma的侵位年龄一致。锆石U-Pb显示有少量遗传或中间子体产物长期丢失的证据。二长花岗岩的∼视年龄范围为：锆石U-铅45 4±15 Ma，全岩Rb-Sr 45 2±13 Ma，独居岩U-Pb 42 6·7±2.4 Ma，黑云母Rb-Sr 4 15 0±2.6 Ma，反映了岩浆的继承性和延展历史。塔拉花岗闪长岩侵位年龄为412.0±1.4 Ma。花岗闪长岩含有至少820 Ma±50 Ma的继承锆石，而闪长岩捕虏体则不含。花岗闪长岩和捕虏体中的锆石均未显示出∼412 Ma事件的证据，而是表明事件∼33 Ma更早。费尼斯特花岗闪长岩的全岩Rb-Sr年龄为497±37 Ma。是遗传的。岩体中黑云母Rb-Sr年龄已部分重置为416.8±3.0 Ma。锆石U-Pb显示了至少539±13 Ma年龄的成分遗传。该岩体的侵位年龄为∼440 Ma。岩基围岩中含有至少1823 Ma±10 Ma的前寒武纪锆石，但塔拉和菲尼斯特花岗闪长岩中继承的锆石可能是源岩。继承的年龄支持通过模拟I型花岗岩体源Rb-Sr而推断的∼1100 Ma源区‘年龄’。某些岩浆的形成和侵位之间可能有一段时间间隔，可以用同位素方法进行分辨。
U–Pb ages of zircon and monazite from four I-type granitoids of the Berridale Batholith have been compared with other isotopic ages for the same plutons. The ages determined by different techniques differ considerably. Rb–Sr mica ages agree with the field intrusive sequence but not all are emplacement ages. Most ages determined on the Maffra Adamellite are consistent with an emplacement age of ∼413 Ma. Zircon U–Pb shows evidence of either minor inheritance or prolonged loss of intermediate daughter products. There is an ∼40 Ma range in apparent ages of the Delegate Adamellite: 454 ± 15 Ma for zircon U–Pb, 452 ± 13 Ma for total-rock Rb–Sr, 426·7 ± 2·4 Ma for monazite U–Pb and 4150·0 ± 2·6 Ma for biotite Rb–Sr. This reflects inheritance and the extended history of the magma. The emplacement age of the Tara Granodiorite is 412·0 ±1·4 Ma. The granodiorite contains inherited zircon at least 820 ± 50 Ma old but a dioritic xenolith does not. Zircon in both the granodiorite and the xenolith shows no evidence of an ∼412 Ma event, but instead suggests an event ∼33 Ma earlier. The total-rock Rb–Sr age of the Finister Granodiorite, 497 ± 37 Ma. is inherited. Biotite Rb–Sr ages in the pluton have been partially reset to 416·8 ± 3·0 Ma. Zircon U–Pb shows inheritance of a component at least 539±13 Ma old. The pluton's emplacement age is inferred to be ∼440 Ma. The country rock to the batholith contains Precambrian zircon at least 1823 ± 10 Ma old, but the inherited zircons in the Tara and Finister Granodiorites are, nevertheless, probably source-derived. The inherited ages support the ∼1100 Ma source ‘ages’ inferred by modelling the I-type granitoids’ source Rb–Sr. There may be a time interval between the formation and emplacement of some of the magmas that can be resolved isotopically.