Lower crust-mantle interactions in the massif-type anorthosite formation: New evidence from zircon U-Pb-Hf-O isotopes of the Neoproterozoic Kadavur Complex, southern India
Lower crust-mantle interactions in the massif-type anorthosite formation: New evidence from zircon U-Pb-Hf-O isotopes of the Neoproterozoic Kadavur Complex, southern India
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地块型斜长岩形成中的下地壳-地幔相互作用：来自印度南部新元古代 Kadavur 杂岩的锆石 U-Pb-Hf-O 同位素的新证据
DOI：
10.1016/j.lithos.2020.105836
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发表时间：
2020-10
期刊：
影响因子：
3.5
通讯作者：
Hu Yu-Hua
中科院分区：
文献类型：
--
作者：
He Hai-Long;Zhai Ming-Guo;Lu Jun-Sheng;Zhao Yan;Zhang Cheng-Li;George P. M.;Sajeev K.;Rajkumar P.;Gou Long-Long;Ao Wen-Hao;Hu Yu-Hua
侵入印度南部马杜赖地块基底中的Kadavur-100型斜长岩由斜长岩、浅色辉长岩和（长英质）辉长岩组成，含少量铁钛氧化物矿石。锆石U-Pb西姆斯定年表明岩浆作用发生在新元古代（Tonian），闪长质辉长岩（790.4 ± 5.1 Ma）、辉长岩（793.0 ± 4.1 Ma）、浅红色辉长岩（784.9 ± 4.1 Ma）和斜长岩（790.7 ± 4.3 Ma）。结合已发表的同时代紫苏花岗岩和A型花岗岩的年龄数据，我们认为斜长岩-紫苏花岗岩-环斑花岗岩套的侵位时代为约1000年。785-805 Ma。Kadavur辉长岩和斜长岩的原位锆石Hf-O同位素数据提供了对Kadavur型斜长岩的母岩浆来源和演化的见解。斜长岩中的锆石具有古地壳εHf（T）值（−11.4 ~ −6.5）和较高的δ 18 O值（5.92 ~ 6.4‰）。相比之下，粗粒辉长岩中的锆石具有相对原始的εHf（T）值（−6.3至−2.3）和类似地幔的δ 18 O值（4.86-5.73‰）。此外，闪长质辉长岩和浅色辉长岩中锆石的εHf（T）值（−11.1 ~ −3.7）和δ 18 O值（5.35 ~ 6.77‰）介于斜长岩和粗晶辉长岩之间。新的锆石Hf-O数据表明，母体熔体的斜长岩受到地壳污染的早期演化阶段，产生了演化的岩浆与地壳同位素和微量元素的签名。辉长岩受地壳影响较小，似代表Kadavur杂岩的原始岩浆源。从原始辉长岩到更演化的斜长岩的锆石Hf-O同位素组成阵列表明，母岩浆来源于上地幔的部分熔融，并伴随着不同的地壳输入，斜长岩形成时的地壳输入可达30-40%。长英质地壳对玄武质岩浆的污染可以有效地增加岩浆中SiO2、Al 2 O3、Na 2 O和Sr的含量，这可能是造成基性岩型斜长岩中巨大斜长石分馏的必要条件。
The Kadavur massif-type anorthosite, which intruded the basement of the Madurai Block in southern India, comprises anorthosite, leucogabbro, and (noritic) gabbro with minor Fe-Ti oxide ores. The U-Pb zircon SIMS dating indicates that the magmatism occurred during the Neoproterozoic period (Tonian), i.e., noritic gabbro (790.4 ± 5.1 Ma), gabbro (793.0 ± 4.1 Ma), leucogabbro (784.9 ± 4.1 Ma), and anorthosite (790.7 ± 4.3 Ma). Combined with the published age data from the coeval charnockite and A-type granite, we conclude that the anorthosite-charnockite-rapakivi granite suite was emplaced during ca. 785–805 Ma. In-situ zircon Hf-O isotopic data of the Kadavur gabbros and anorthosite provide insights on the source and evolution of the parental magmas of the massif-type anorthosites. Zircons from the anorthosite are characterized by ancient crustal εHf(T) values (−11.4 to −6.5) and higher δ18O values (5.92 to 6.4‰). In contrast, zircons from the coarse-grained gabbro have relatively primitive εHf(T) values (−6.3 to −2.3) and mantle-like δ18O values (4.86–5.73‰). Moreover, zircons from the noritic gabbro and leucogabbro have εHf(T) values (−11.1 to −3.7) and δ18O values (5.35 to 6.77‰) distributed between those of the anorthosite and coarse-grained gabbro. The new zircon Hf-O data demonstrate that the parental melt of the anorthosite was subjected to crustal contamination during the early evolution stages, producing an evolved magma with crustal isotope and trace element signatures. In contrast, the gabbros show less crustal influence and like to represent original magma source of the Kadavur Complex. The zircon Hf-O isotope compositional array from the primitive gabbros to the more-evolved anorthosite demonstrates that the parental magmas were derived from partial melting of the upper mantle with varying crustal input, which can be up to 30–40% for the anorthosite formation. Contamination of the ponded basaltic magmas by the felsic crust can effectively increase the SiO2, Al2O3, Na2O, and Sr contents in the magmas, which was likely essential for enormous plagioclase fractionation in the massif-type anorthosites.
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