Zircon SHRIMP U-Pb geochronology, geochemistry and petrogenesis of the upper Eocene Shuangmaidi peraluminous granite in Baoshan Block, Western Yunnan Terrain, southwestern China
Zircon SHRIMP U-Pb geochronology, geochemistry and petrogenesis of the upper Eocene Shuangmaidi peraluminous granite in Baoshan Block, Western Yunnan Terrain, southwestern China
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滇西保山地块始新世双麦地过铝质花岗岩的锆石SHRIMP U-Pb年代学、地球化学及岩石成因
DOI：
10.1007/s11430-011-4200-7
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发表时间：
2011-05
期刊：
影响因子：
--
通讯作者：
Cheng ZhiZhong
中科院分区：
文献类型：
--
作者：
Huang JingNing;Chen YongQing;Zhai XiaoMing;Lu YingXiang;Xie YongFu;Cheng ZhiZhong
宝山地块在构造上位于泗马苏板块中段。宝山地块内的花岗质岩浆活动被认为是弱活动，主要是由于喜马拉雅造山期的暴露非常有限。对埋藏双麦地花岗岩的年代学研究证实了宝山地块新生代花岗岩类的存在。研究表明：(1)花岗岩为中~粗粒双云母辉生花岗岩，SiO2含量高（73.55% ~ 77.16%），CaO含量低（0.34% ~ 1.38%），总碱（K2O+Na2O） 5.22% ~ 8.03%， K2O/Na2O比值0.24 ~ 1.79，稀土元素总量（ΣREE）在85 ~ 125 ppb之间。所有样品均富集轻稀土元素，呈现中等负Eu异常；在地幔正一化微量元素图上，Ba、Sr、Ti、Nb呈显著负异常，而K、Rb、U、Th、Pb呈显著正异常，表明典型的过铝-强过铝s型花岗岩。(2) ZK7-1和ZK0-1花岗岩锆石SHRIMP U-Pb年龄分别为36.27±0.48 Ma和35.78±0.49 Ma。两个岩心的锆石含量相近，说明花岗岩样品可能来自同一埋藏岩体。(3)花岗岩206Pb/204Pb值变化范围为20.115 ~ 25.355,207 pb /204Pb值变化范围为15.776 ~ 16.160,208pb /204Pb值变化范围为39.236 ~ 41.285，显示出上地壳放射性铅异常特征。二云母正长石花岗岩（36 Ma）平均年龄的（87Sr/86Sr）值在0.72524 ~ 0.77503之间，Nd(t)值在−10.9 ~−11.7之间。这些数据，连同1.73-1.80 Ga的枯竭地幔Nd模态年龄，表明花岗岩可能是由前寒武纪晶体基底的部分熔融形成的。(4)在Hf-Rb-Ta图上，几乎所有样品都落在碰撞后构造环境场内。CaO/Na2O和Al2O3/ tio2比值表明，花岗岩岩浆可能是由富含粘土的地壳物质部分熔融形成的，熔融温度约为900℃，结晶温度为775 ~ 795℃。(5)喜马拉雅造山带碰撞后，随着印度大陆持续向北挤压进入亚洲，印度支那大陆东南向挤压，作为印度支那大陆西界的高立贡断裂大规模右向走滑运动，引发增厚地壳部分熔融，形成了双麦地二云母正长石花岗岩的过铝花岗岩浆。
The Baoshan Block is tectonically located in the middle segment of the Sibumasu plate. Granitic magmatism within the Baoshan Block has been considered weakly active due mainly to very limited exposures during the Himalaya orogenic episode. The geochronological study on the buried Shuangmaidi granite has confirmed the existence of the Cenozoic granitoids in the Baoshan Block. The present study indicates that: (1) It is medium- to coarse-grained two mica phyric granite, characterized by high SiO2(73.55%–77.16%) and low CaO (0.34%–1.38%) contents, with a total alkalis (K2O+Na2O) of 5.22%–8.03%, K2O/Na2O ratios of 0.24–1.79, and total rare earth elements (ΣREE) of the granite between 85 and 125 ppb. All samples are enriched in light REE and exhibit medium negative Eu anomalies; and they show pronounced negative anomalies in Ba, Sr, Ti, and Nb but significant positive anomalies in K, Rb, U, Th, and Pb on mantle-normalized trace element patterns, indicating typically peraluminous to strongly peraluminous S-type granite. (2) The zircon SHRIMP U-Pb ages of the granite are 36.27±0.48 Ma for the samples from ZK7-1 and 35.78±0.49 Ma for those from ZK0-1, respectively. The similar zircon ages from these two drill cores may suggest that the granite samples come from the same buried pluton. (3)206Pb/204Pb values of the granite vary from 20.115 to 25.359,207Pb/204Pb from 15.776 to 16.160, and208Pb/204Pb from 39.236 to 41.285, showing the characteristics of radioactive lead anomaly of the upper crust. The (87Sr/86Sr)ivalues calculated on the average age of the two-mica orthoclase granite (36 Ma) range from 0.72524 to 0.77503 and ɛNd(t) values vary from −10.9 to −11.7. These data, along with the depleted-mantle Nd modal ages of 1.73–1.80 Ga, imply that the granites might have formed from partial melting of the Precambrian crystal basements. (4) On the Hf-Rb-Ta diagram, almost all the samples fall within the field of post-collision tectonic setting. The CaO/Na2O and Al2O3/TiO2ratios suggest that the granitic magma may have formed from partial melting of clay-rich crustal materials with a possible melting temperature of about 900°C and a possible crystallization temperature of 775–795°C. (5) During the post-collision of the Himalaya orogen, with the southeastward extrusion of the Indochina continent resulting from the continuous northward indentation of the India continent into the Asia, the Gaoligong Fault, as the western boundary of the Indochina continent, moved in the dextral strike-slip on a large scale to trigger partial melting of the thickened crust, and the peraluminous granitic magma from which the Shuangmaidi two-mica orthoclase granite derived was formed.
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