Petrogenesis of the concealed Daqiling intrusion in Guangxi and its tectonic significance: Constraints from geochemistry, zircon U-Pb dating and Nd-Hf isotopic compositions
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The late Eocene high-K to shoshonitic Zajkan intrusion, situated in the Tarom-Hashtjin magmatic belt (THMB), NW Iran, ranges in composition from gabbro to pyroxene quartz monzodiorite, pyroxene quartz monzonite and monzogranite, and is classified as an I-type metaluminous granitoid. On the primitive mantle-normalised spider diagram, these rocks demonstrate negative high field strength element (HFSE) anomalies, large-ion lithophile element (LILE) enrichment, and positive Pb anomaly, indicating a subduction-related signature. Furthermore, the granitoids are characterised by coherent chondrite-normalised rare earth element patterns with high light rare earth elements/heavy rare earth elements (LREE/HREE) and moderate to weakly negative Eu anomalies (Eu/Eu* = 0.6–0.86). LA-ICP-MS zircon U–Pb dating demonstrates that the Zajkan intrusion crystallised at ca 36.5 Ma. Relatively low to moderate 87Sr/86Sr ratios (0.7046–0.7061) and positive εNd(t) values (1.52–1.88) of the Zajkan samples are consistent with an enriched lithospheric mantle source that was metasomatised by an earlier subducted slab. Geochemical features show that the parental magma of the Zajkan intrusion likely resulted from a partial melting of metasomatised amphibole-bearing mantle source. Sr–Nd isotope modelling is consistent with the Zajkan intrusion formed from a mix of ∼80% of a mantle-derived magma and ∼20% of a juvenile lower crustal-derived magma. Partial melting of the metasomatised mantle may have resulted from late Eocene lithospheric thinning and hot asthenospheric upwelling through slab roll-back or lithospheric delamination. KEY POINTSThe late Eocene high-K to shoshonitic Zajkan intrusion is located within the Tarom-Hashtjin magmatic belt, NW Iran.U–Pb zircon dating revealed an age of ca 36.5 Ma for emplacement of the Zajkan intrusion.Sr–Nd isotope modelling is consistent with the Zajkan intrusion formed from a mix of ∼80% of mantle-derived magma and ∼20% of juvenile lower crustal-derived magma.
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Lile
Quartz monzonite
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The Gazu Cu deposit is located at the boundary between the Lut and Tabas Blocks in Central Iranian Microcontinent. The intrusions in the Gazu area are characterized by SiO2 contents ranging from 52.6 to 66.4 wt.%, K2O from 1.98 to 3.64 wt.%, and Na2O from 2.5 to 5.2 wt.%. The intrusions have features typical of high-K calc-alkaline rocks, are metaluminous to weakly peraluminous, and formed in a volcanic arc setting. Zircon U–Pb age data for hornblende monzonite porphyry, hornblende monzodiorite porphyry, pyroxene monzonite, hornblende granite, hornblende quartz monzonite porphyry, and hornblende diorite porphyry are 68.1 ± 1.7 Ma, 67.74 ± 0.72 Ma, 67.41 ± 0.94 Ma, 65.9 ± 3.7 Ma, 65.1 ± 1.2 Ma, and 60.2 ± 1.2 Ma, respectively. Copper mineralization is related to the hornblende granite and hornblende quartz monzonite porphyry. Field observations and the U–Pb dating indicated three stages for intrusive rock emplacement: pre-mineralization intrusions (hornblende monzonite porphyry, hornblende monzodiorite porphyry, and pyroxene monzonite), syn-mineralization intrusions (hornblende granite and hornblende quartz monzonite porphyry), and post-mineralization intrusions (hornblende diorite porphyry). Mantle-normalized, trace-element spider diagrams display enrichment in large ion lithophile elements, such as Rb, Ba, K, and Cs, and depletion in high field strength elements, e.g., Nb, Ti, Zr, Y, and heavy rare earth elements, with light rare earth element enrichment ((La/Yb)N = 6.4–13.4) and a weak negative Eu anomaly (Eu/Eu* = 0.87–1.01). Zircon Hf isotope data indicate that the Gazu intrusive rocks are characterized by low positive εHf(t) values, with an average of 4.23, and show young Hf model ages (789–188 Ma), indicating derivation from juvenile crust. Relatively low positive εHf(t) values, the wide range for εHf(t), and the presence of zircon xenocrysts can be explained by involvement of a mantle component that mixed with older continental crust (Cadomian).
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滇西剑川富碱岩浆岩位于青藏高原东南缘的三江南段，是金沙江-红河富碱岩浆岩带的重要组成部分。剑川富碱岩浆岩包括花岗岩和正长岩两类岩石，前者主要有花岗斑岩和石英二长斑岩，后者主要是正长斑岩和粗面岩。本文对剑川富碱岩浆岩进行了主微量元素、锆石U-Pb年代学和Sr-Nd-Hf同位素特征研究。锆石U-Pb测年结果显示，剑川花岗岩结晶年龄为35.1~36.1Ma，正长岩结晶年龄为35.7~35.8Ma，均形成于始新世。花岗斑岩和石英二长斑岩的SiO2含量为67.92%~69.93%，K2O/Na2O比值介于0.86~1.22，具有高钾钙碱性特征；正长斑岩和粗面岩的SiO2含量为53.94%~63.51%，K2O/Na2O比值介于1.30~2.68，属于钾玄质岩石系列。两类岩石都富集轻稀土元素（LREE）和大离子亲石元素（LILE），相对亏损高场强元素（HFSE）。其中，花岗斑岩和石英二长斑岩有着较高的Sr、Sr/Y、La/Yb值和低的Y、Yb含量，具有埃达克质岩浆属性。结合Sr-Nd-Hf同位素研究认为，滇西剑川地区花岗岩起源于增厚的镁铁质新生下地壳部分熔融，正长岩是由交代富集的岩石圈地幔熔融产生的基性岩浆演化而来的产物。滇西剑川新生代富碱岩浆活动是对印度与欧亚板块晚碰撞阶段，岩石圈地幔发生对流减薄和软流圈物质上涌过程的响应。
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(t) 价值(到 1.96 的 -5.04 ) 和外壳的模型 1.16-1.5 Ga 变老的 Hf 同位素。锆石 Hf 同位素和锆石浸透温度整个岩石(801 °C-823°C ) 证明导出披风的材料也许在 Kejie pluton 的产生起了一个重要作用。Kejie pluton 很可能在，与 neo-Tethys 海洋的东方 subduction 联系的一个背景被产生在外壳中的玄武岩的岩浆引起了后者的 anatexis 的披风楔的侵入，形成混血儿融化，它随后经历了高度的部分结晶化。
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Abstract: Paleoproterozoic potassic granitoids in the southern Sushui Complex from the Zhongtiao Mountains yielded SHRIMP zircon U‐Pb ages of 1968‐1944 Ma. Lithologically, the potassic granitoid series consists chiefly of monzodiorite, quartz monzonite and syenogranite. Their trace elements and Sm‐Nd isotope characteristics indicate that they were derived from partial melting of Archean TTG rocks in an overthickened continental crust. Petrogenesis of this potassic granitoid series implies a collisional environment within the Trans‐North China Orogen in the Paleoproterozoic, which supports a tectonic model of Eastern and Western Continental Blocks being amalgamated in the Paleoproterozoic.
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