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首页> 外文期刊>Journal of Asian earth sciences >Early-Cretaceous highly fractionated I-type granites from the northern Tengchong block, western Yunnan, SW China: Petrogenesis and tectonic implications
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Early-Cretaceous highly fractionated I-type granites from the northern Tengchong block, western Yunnan, SW China: Petrogenesis and tectonic implications

机译：中国西南云南腾冲地块北部的早白垩世高度分离的I型花岗岩：成岩作用和构造意义

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Western Yunnan, an important constituent of the southeastern segment of the East Tethyan tectonic domain, lies along a transformed orientation from the NVVW trending Himalayan-Tethyan segment to the northerly trending Southeast Asian segment. However, the geodynamical setting of the Early Cretaceous tectonothermal magmatism along the Bangong-Nujiang-Lushui-Luxi-Ruili belt as the Tethyan branch in western Yunnan (SW China) remains controversial. The Donghe granitoid, which is located between the Gaoligong and Tengliang belts in the northern Tengchong block, reveals its petrogenesis and its tectonics, both of which play a vital role in resolving previous disputes. Our zircon laser ablation inductively coupled plasma mass spectrometry U-Pb dating of granites from the Donghe batholith yields ages of 119.9 +/- 0.9-130.6 +/- 2.5 Ma. These granites display features typical of highly fractionated I-type granites: high SiO2 contents (>71 wt.%), high K contents (K2O = 3.88-5.66 wt.%), calc-alkaline character, slight peraluminosity (A/CNK = 1.02-1.16), and a highly differentiated index ranging from 83.6 to 95.6. In addition, as SiO2 contents increase, the rare earth element (REE) abundances, especially heavy REE abundances, and REE pattern slopes change gradually, but the negative Eu anomalies increase sharply, while the degree of enrichment in Rb, Th, U, and Pb and depletion in Ba, Nb, Sr, P, and Ti are enhanced. These features indicate that K-feldspar, +/- plagioclase, biotite, +/- amphibole, +/- apatite, +/- sphene/garnet, and +/- Fe-Ti oxides such as ilmenite play the major role in the fractional crystallization process. The high initial Sr-87/Sr-86 (0.7067 and 0.7079) and negative epsilon(Nd)(t) values (-8.6 to -10.1), with T-2DM ranging from 1.39 to 1.49 Ga, indicate that the sources were mainly derived from the mature ancient middle to lower crust and minor mantle-derived materials. The initial (206)pb/(204)pb, (207)pb/(204)pb, and F-208/(204) Pb ratios of 18.462-18.646, 15.717-15.735, and 38.699-39.007, respectively, signify that some subduction-related material such as ocean island volcanic rocks and mature arc primitive rocks may be involved as sources. Based on an analysis of similar zircon saturated temperature and geochemical characteristics of typical highly fractionated l-type granites in SE and SW China, and consideration of the regional geological setting, we suggest that the parent magma may be derived from the ancient middle to lower continental crust and mantle-derived basaltic magma. These were generated in the setting of a westward subducted Lushui-Luxi-Ruili (LLR) Tethyan oceanic slab, where mantle-wedge-derived sources provided enough heat and material to melt the middle to lower ancient crust. Taking into account the temporal-spatial distributions of Early Cretaceous magmatic rocks in the region, we further suggest the existence of an Andean-type active continental margin from the Lhasa block to the Tengchong block along the Bangong-Nujiang-LLR Tethys Ocean during the Early Cretaceous. (C) 2015 Elsevier Ltd. All rights reserved.
机译：云南西部是东特提斯构造区东南段的重要组成部分，其方向从NVVW趋势的喜马拉雅-特提斯段向北趋势的东南亚段转变。然而，作为云南西部特提斯支（中国西南部）的班公-怒江-庐水-芦溪-瑞丽一带的早白垩世构造热岩浆的地球动力学背景仍存在争议。位于腾冲地块北部高黎贡带与腾梁带之间的东河花岗岩体，揭示了它的成岩作用和构造特征，两者在解决先前的争端中都起着至关重要的作用。我们的锆石激光烧蚀电感耦合等离子体质谱法从东河岩床中提取花岗岩的U-Pb年代为119.9 +/- 0.9-130.6 +/- 2.5 Ma。这些花岗岩具有典型的高分型I型花岗岩特征：高SiO2含量（> 71 wt。％），高K含量（K2O = 3.88-5.66 wt。％），钙碱特性，轻微的高铝酸度（A / CNK = 1.02-1.16），以及高度分化的索引，范围从83.6到95.6。此外，随着SiO2含量的增加，稀土元素（REE）的丰度，尤其是重稀土元素的丰度和REE图案的斜率逐渐变化，但负Eu异常急剧增加，而Rb，Th，U和Rb的富集程度Ba，Nb，Sr，P和Ti中的Pb和贫化增强。这些特征表明钾长石，+ /-斜长石，黑云母，+ /-闪石，+ /-磷灰石，+ /-蝶粉/石榴石和+/- Fe-Ti氧化物如钛铁矿在分馏中起主要作用结晶过程。高初始Sr-87 / Sr-86（0.7067和0.7079）和负ε（Nd）（t）值（-8.6至-10.1），T-2DM范围为1.39至1.49 Ga，表明来源主要是来源于成熟的古代中下地壳和次要的地幔物质。初始（206）pb /（204）pb，（207）pb /（204）pb和F-208 /（204）Pb之比分别为18.462-18.646、15.717-15.735和38.699-39.007）表示可能与某些与俯冲有关的物质如烃源岩有关。在分析东南部和西南部典型的高分馏l型花岗岩相似的锆石饱和温度和地球化学特征，并考虑到区域地质环境后，我们认为母岩浆可能来自古代中下陆地壳和地幔衍生的玄武岩浆。这些是在向西俯冲的露水-鲁西-瑞丽（LLR）特提斯洋洋板块的环境中产生的，那里的地幔楔源提供了足够的热量和物质，以融化中下部古地壳。考虑到该地区早白垩世岩浆岩的时空分布，我们进一步提出，在早期，从拉萨地块到腾冲地块沿班公-怒江-LLR特提斯海洋存在安第斯型活跃大陆边缘。白垩纪。 （C）2015 Elsevier Ltd.保留所有权利。

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