Electron microprobe technique for U-Th-Pb and REE chemistry of monazite, and its implications for pre-, peak- and post- metamorphic events of the Lutzow-Holm Complex and the Napier Complex, East Antarctica-猫眼课题宝

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发表时间：

2006-10

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Polar geoscience

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其他

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作者：

T. Hokada;Y. Motoyoshi

用电子探针对l<s:1> zow- holm配合物和Napier配合物中高品位变长岩中的单氮石进行了U、Th、Pb和稀土元素（REE）化学分析。研究样品包括来自<s:1> tzoholm杂岩的Skallen的4块麻粒岩相石榴石-黑云母变质长岩，以及来自Napier杂岩UHT带的Mt. riise - larsen地区的一块再水合石榴石-硅线石片麻岩。Skallen的4个含石榴石的变质长岩样品中，有2个样品给出了简单的/0* /** Ma独居石U-Th-Pb年龄，而另外2个样品给出了/0* /** Ma和0/* /2* Ma两个年龄群。较年轻年龄组与SHRIMP报告的//* /、* Ma变质年龄一致。较老的/2* Ma独居石与较年轻的/0* /** Ma独居石相比，Nd、Sm、Gd、Dy （MREE）相对富集，Si （Ca、Th）相对缺乏。这些古老的独居石可能是在富含m - ree的条件下形成的，如无石榴石条件，表明这些独居石的生长早于变质峰期。来自Mt. Riiser-Larsen地区的石榴石-硅线石片麻岩显示出各种post - ht再水化结构，如黑云母-硅线石聚集体和细粒黑云母薄片，围绕石榴石斑岩母细胞或晶体内裂缝。石榴石芯内的独居石有；2 * . .* Ma U-Th-Pb年龄与报道的锆石和独居石SHRIMP年龄一致。另一方面，与再水合带相关的那些给出波动的，** 1** Ma。这些较年轻的年龄被认为反映了uht后不完全的化学紊乱

Monazites in high-grade metapelites from the Lützow-Holm Complex and Napier Complex have been examined in terms of U, Th, Pb and rare earth element (REE) chemistry using an electron microprobe. The studied samples include four granulite-facies garnet-biotite-bearing metapelites from Skallen within the LützowHolm Complex, and a re-hydrated garnet-sillimanite gneiss from the Mt. Riiser-Larsen area within the UHT zone of the Napier Complex. Two out of four garnet-bearing metapelitic samples from Skallen gave simple /0* /** Ma monazite U-Th-Pb ages, whereas the other two samples yielded two age populations, i.e., /0* /** Ma and 0/* /2* Ma. The younger age group is consistent with the //* /,* Ma metamorphic ages reported by SHRIMP. The older /2* Ma monazites are relatively enriched in Nd, Sm, Gd, Dy (MREE) and depleted in Si (Ca and Th) compared with the younger (/0* /** Ma) ones. These older monazites possibly formed through M-HREE-enriched conditions such as garnet-free conditions, suggesting that the growth of these monazites pre-dated the peak metamorphism. Garnet-sillimanite gneiss from the Mt. Riiser-Larsen area shows various postUHT re-hydration textures such as biotite-sillimanite aggregates, and fine-grained biotite flakes around or intracrystalline fractures within garnet porphyroblasts. Monazites enclosed within garnet cores have ,.2* ,..* Ma U-Th-Pb ages consistent with the reported zircon and monazite SHRIMP dates. On the other hand, those associated with re-hydrated zones gave fluctuating ,,** 1** Ma ages. These younger ages are thought to reflect the incomplete chemical disturbance during the post-UHT

Electron microprobe technique for U-Th-Pb and REE chemistry of monazite, and its implications for pre-, peak- and post- metamorphic events of the Lutzow-Holm Complex and the Napier Complex, East Antarctica

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