Genesis of hydrous-oxidized parental magmas for porphyry Cu (Mo, Au) deposits in a postcollisional setting: examples from the Sanjiang region, SW China
Genesis of hydrous-oxidized parental magmas for porphyry Cu (Mo, Au) deposits in a postcollisional setting: examples from the Sanjiang region, SW China
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DOI：
10.1007/s00126-022-01143-x
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发表时间：
2022-10
影响因子：
4.8
通讯作者：
Leiluo Xu;Jing-Jing Zhu-Jing;Mingliang Huang;Lichuan Pan;R. Hu;X. Bi
中科院分区：
文献类型：
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作者：
Leiluo Xu;Jing-Jing Zhu-Jing;Mingliang Huang;Lichuan Pan;R. Hu;X. Bi
后碰撞环境中斑岩矿床的岩浆来源仍有争议。我们利用新近发表的三江地区始新世-渐新世斑岩型Cu ± Mo ± Au矿床的岩石学和地球化学数据来解决这一突出问题。三个矿床的新数据哀牢山-红河斑岩金铜钼带中的马厂箐、铜厂、北崖（三江地区南部）表明成矿斑岩侵位时间约为35 Ma，（87 Sr/86 Sr）i（0.7068-0.7071），εNd（t）为负值（− 6.9 ~ − 5.0），锆石εHf（t）为负值（− 5.3 ~ 4.5），δ 18 O较高（5.9-9.0‰）。岩浆角闪石斑晶成分表明，母岩浆均为相对氧化的（ΔFMQ = 1.7 ± 0.6），富H2O（3.8 ± 0.3wt%H2O）。这些结果分别与根据锆石成分（ΔFMQ = 1.8 ± 0.8）和全岩高Sr/Y比值（75 ± 31）估算的结果一致。本文认为哀牢山-红河斑岩Au-Cu-Mo带的母岩浆来源于新元古代俯冲事件中保存下来的幼年弧下地壳和下伏的交代的陆下岩石圈地幔。玉龙斑岩铜钼带的母岩浆（三江地区北方）起源于二叠-三叠纪幼年弧下地壳和交代的SCLM。此外，这些斑岩矿床的母岩浆都是氧化的和富含H2O的，我们将这些特征归因于继承混合的地幔-地壳来源，以前的大洋板片俯冲修改。
Magmatic sources of porphyry deposits in postcollisional settings remain controversial. We have used new and published petrological and geochemical data for the Eocene–Oligocene porphyry Cu ± Mo ± Au deposits in the Sanjiang region, SW China, to address this outstanding issue. New data for three deposits (Machangqing, Tongchang, and Beiya) in the Ailaoshan–Red River porphyry Au-Cu-Mo belt (southern part of the Sanjiang region) suggest that ore-forming porphyries were emplaced at ~ 35 Ma, have high (87Sr/86Sr)i(0.7068–0.7071) and negative εNd(t) (− 6.9 to − 5.0), low zircon εHf(t) (− 5.3 to 4.5), and relatively high δ18O (5.9–9.0‰). Magmatic amphibole phenocryst compositions indicate that the parental magmas are all relatively oxidized (ΔFMQ = 1.7 ± 0.6), and H2O-rich (3.8 ± 0.3 wt% H2O). These results are consistent with those estimated from zircon compositions (ΔFMQ = 1.8 ± 0.8) and high whole-rock Sr/Y ratios (75 ± 31), respectively. Based on the new and published data, we suggest that the parental magmas for the Ailaoshan–Red River porphyry Au-Cu-Mo belt were derived from a preserved juvenile arc lower-crust and the underlying metasomatized subcontinental lithospheric mantle (SCLM) attributed to a Neoproterozoic subduction event, whereas the parental magmas for the Yulong porphyry Cu-Mo belt (northern part of the Sanjiang region) originated from the Permian–Triassic juvenile arc lower-crust and metasomatized SCLM. Additionally, parental magmas for these porphyry deposits are all oxidized and H2O-rich, and we attribute such characteristics to inheritance from mixed mantle-crust sources that were modified by previous oceanic slab subduction.