Petrological Characteristics and Emplacement Mechanism of the Gaoqiaogou Granitic Porphyry in the Hannan Complex: A Geochemistry Approach
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摘要:
高桥沟花岗斑岩体位于扬子板块北缘，属于汉南杂岩的一部分。锆石LA−MCP−MS U−Pb定年结果显示其形成时代为（794.4±5.7）Ma，为南华纪早期。岩石地球化学特征为高Si（75.78%～76.51%）、富碱(K2O＋Na2O=7.78%～7.84%)、富K（K2O/Na2O=1.07～1.10)，属高钾钙碱性系列。稀土总量∑REE为272.57×10–6，轻重稀土元素组之间分馏明显。二长花岗斑岩形成于岩浆演化中晚期阶段，岩浆上侵过程中部分熔融沉积岩、火山岩物质。高桥沟花岗斑岩体形成于后造山构造环境，强力就位的侵位机制。
Abstract:Gaoqiaogou granite porphyry is a part of Hannan Complex, which is located in the northern margin of the Yangtze plate. LA−MCP−MS U−Pb dating of Zircon indicates that the Zircon was formed at (794.4±5.7) Ma in the early South China epoch. The Rock Geochemistry is characterized by high silicon (75.78%～76.51%) , high alkali (K2O＋Na2O=7.78%～7.84%) , high potassium (K2O/Na2O=1.07～1.10) , high potassium calcium alkaline series, total rare earth elements ∑REE=272.57×10–6, and obvious fractionation between light and heavy rare earth elements. The monzonitic granite porphyry was formed in the middle and late stage of magmatic evolution. The material of partial melting sedimentary rock and volcanic rock in the process of magma intrusion. The Gaoqiaogou granite porphyry was formed in the post-orogenic tectonic environment and emplaced strongly.
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Key words:
- Hannan complex /
- granitic porphyry /
- early Nanhua period /
- geochemistry features /
- emplacement mechanism
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图 1 扬子板块北缘大地构造略图（a）南郑区黄官镇一带地质简图（b）据陕西省地质调查院，2008修改）及高桥沟一带地质简图（c）（据陕西省地质调查院，2013修改）
Figure 1.
表 1 高桥沟二长花岗斑岩LA–ICP–MS锆石U–Pb测年数据表
Table 1. LA–ICP–MS U–Pb dating of the Gaoqiaogou adamellite porphyry
测点 U Th Th/U 同位素比值 同位素年龄（Ma） （10−6） 206Pb*/238U 1σ 207Pb*/206Pb* 1σ 207Pb*/235U 1σ 206Pb/238U 207Pb/206Pb 1 114.11 94.86 0.83 0.13118 0.00221 0.06109 0.00186 1.10488 0.02105 794.6 642.3 2 104.65 70.17 0.67 0.13184 0.00223 0.06354 0.00193 1.1547 0.02093 798.4 726.3 3 66.59 51.83 0.78 0.12985 0.00217 0.06377 0.00191 1.14182 0.02101 787.0 734.0 4 35.33 25.03 0.71 0.1314 0.00226 0.06485 0.0021 1.17456 0.02537 795.9 769.3 5 73.62 44.19 0.60 0.13018 0.00217 0.06587 0.00194 1.18231 0.02068 788.9 802.2 6 56.84 41.26 0.73 0.13311 0.00226 0.06649 0.00207 1.2201 0.02445 805.6 821.8 7 57.6 42.84 0.74 0.13125 0.00223 0.06625 0.00205 1.19864 0.02271 795.0 814.4 8 223.3 212.54 0.95 0.13048 0.00218 0.06621 0.00195 1.19094 0.02055 790.6 813.0 9 38.99 27.39 0.70 0.12999 0.00221 0.06658 0.00208 1.19311 0.02414 787.8 824.6 10 18.48 13.36 0.72 0.13208 0.00228 0.06732 0.00222 1.22557 0.02755 799.7 847.7 11 79.25 55.64 0.70 0.1312 0.00221 0.06736 0.00201 1.21817 0.02167 794.7 849.0 12 74.87 43.41 0.58 0.13026 0.00221 0.06733 0.00205 1.20891 0.02214 789.3 848.0 13 54.67 43.17 0.79 0.13166 0.00224 0.07001 0.00217 1.27061 0.0246 797.3 928.8 14 66.17 51.87 0.78 0.12994 0.00218 0.06995 0.00209 1.25327 0.02287 787.5 926.9 15 105.38 109.79 1.04 0.13093 0.0022 0.07055 0.00211 1.27327 0.02237 793.2 944.4 16 73.21 53.57 0.73 0.1313 0.00222 0.07093 0.00215 1.28377 0.02376 795.3 955.4 17 43.44 26.11 0.60 0.13012 0.0022 0.07139 0.00219 1.28045 0.02433 788.5 968.6 18 36.24 20.27 0.56 0.13248 0.00227 0.07227 0.00228 1.31978 0.02659 802.0 993.7 19 47.38 37.24 0.79 0.13311 0.00229 0.07323 0.00234 1.34378 0.02865 805.6 1020.2 注：误差是1σ；Pb*为放射成因铅；应用实测的204Pb进行普通铅校正。 
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