西藏班公湖-怒江缝合带美日切错组中酸性火山岩锆石U-Pb年龄、Sr-Nd-Hf同位素、岩石成因及其构造意义
发布时间：2019-02-27 18:53
【摘要】：西藏班公湖-怒江缝合带是我国重要的斑岩铜金矿成矿带,成矿地质条件极为优越。多龙矿集区是班公湖-怒江缝合带西段典型斑岩-浅成低温热液型铜(金)超大型矿床,区内广泛分布着美日切错组喷溢相火山岩,但其岩石成因、源区属性、形成年代及地球化学动力学背景尚不明确。本文对美日切错组安山岩及流纹岩进行锆石U-Pb测年,获得结晶年龄分别为108.2±2.6Ma(MSWD=0.39)和109.3±2.2Ma(MSWD=1.70)。矿区安山岩及流纹岩具高硅(SiO2=60.89%~72.00%)、富钾(K2O=3.08%~5.53%)、富碱(K2O+Na2O=6.88%~8.96%)、准铝质-过铝质(A/CNK=0.92~1.28)特征,属于高钾钙碱性及钾玄岩系列岩石。其明显均富集轻稀土(LREE)及大离子亲石元素(LILE:Th、U、K、Pb及Rb),亏损重稀土(HREE)及高场强元素(HFSE:Ta、Nb、Ti及Zr),稀土总量(ΣREE)为141.52×10-6~236.05×10-6之间,LaN/YbN为10.42~11.05,δEu为0.65~0.80,具有中等负铕异常,显示出典型岛弧岩浆岩的特征。(87 Sr/86 Sr)i值为0.7050~0.7053,(143 Nd/144 Nd)i为0.5124~0.5126,εNd(t)值为-1.51~1.29,具有高Sr低Nd的特征。锆石Hf同位素分析结果表明,流纹岩εHf(t)为+11.6~+15.5,平均值为+13.8,两阶段模式年龄平均值为288.0Ma;安山岩εHf(t)为+3.4~+8.0,平均值为+4.8,两阶段模式年龄平均值为813.1Ma;表现出明显的幔源特征。综合研究表明,美日切错组火山岩为班公湖-怒江新特斯洋洋壳向北的俯冲背景下,由俯冲板片脱水产生流体交代地幔楔发生部分熔融形成原始玄武质岩浆,并在上升后,滞留在壳幔边界形成新生下地壳,新生下地壳与持续底侵幔源玄武质岩浆混合而部分熔融形成。其形成于典型岛弧的构造背景下,暗示班公湖-怒江洋在早白垩世晚期(108~109Ma)仍正在向北俯冲于羌塘地块之下,可能尚未关闭。
[Abstract]:The Bangong Lake-Nujiang suture belt in Tibet is an important porphyry copper-gold deposit belt in China, and the ore-forming geological conditions are extremely superior. The Duolong ore concentration area is a typical porphyry-shallow hydrothermal copper (gold) superlarge deposit in the western part of the Bangongghu-Nujiang suture belt. The volcanic rocks of the spilled facies of the United States-Japan cut-off formation are widely distributed in the area, but their petrogenesis and source area attribute. The age of formation and the background of geochemical dynamics are not clear. In this paper, zircon U-Pb dating of andesite and rhyolite of the American-Japanese shear fault group has been carried out. The crystallization ages are 108.2 卤2.6Ma (MSWD=0.39) and 109.3 卤2.2Ma (MSWD=1.70), respectively. The andesite and rhyolite in the ore area are characterized by high silicon (SiO2=60.89%~72.00%), rich potassium (K 2O + 3.08%), alkali rich (K 2O Na2O=6.88%~8.96%) and quasi aluminous peraluminite (A/CNK=0.92~1.28). It belongs to the rocks of high potassium calc-alkaline and potassium basaltic series. They are obviously enriched in light rare earth (LREE) and large ion lithophile elements (LILE:Th,U,K,Pb and Rb), heavy rare earth (HREE) and high field strength elements (HFSE:Ta,Nb,Ti and Zr),). The total amount of rare earths (危 REE) is between 141.52 脳 10 脳 10 ~ 6 and 236.05 脳 10 ~ (6), the LaN/YbN is 10.42 ~ 11.05, and the 未 Eu is 0.65 ~ 0.80, showing the characteristics of typical island arc magmatic rocks. (87 Sr/86 Sr) I = 0.7050 ~ 0.7053, (143 Nd/144 Nd) i is 0.5124 脳 0.5126, 蔚 Nd (t) is-1.51? 1.29), which has the characteristics of high Sr and low Nd. Zircon Hf isotopic analysis shows that the 蔚 HF (t) of rhyolite is 11.6 ~ 15.5, the average value is 13.8, and the average age of two-stage model is 288.0 Ma. The 蔚 Hf (t) of the andesite is 3.4 ~ 8.0, with an average value of 4.8, and the average age of the two-stage model is 813.1Ma, showing obvious mantle-derived characteristics. The comprehensive study shows that under the background of the northward subduction of the Bangong Lake-Nujiang Xintesian Ocean crust, the volcanic rocks of the United States-Japan shear fault formation are partially melted to form primitive basaltic magma by dewatering the subduction plate to produce the fluid metasomatism mantle wedge, and after rising, the volcanic rocks of the United States and Japan formed the primitive basaltic magma. The Neo-lower crust is formed at the boundary of crust-mantle, which is partly melted by mixing with the basaltic magma of continuous underplating mantle-derived basaltic magma. It was formed in the tectonic setting of the typical island arc suggesting that the Bangong Lake-Nujiang Ocean was still subducting northward under the Qiangtang block in the late early Cretaceous (108~109Ma) and may not have been closed.
【作者单位】： 中国地质大学(北京)地球科学与资源学院;中国地质科学院矿产资源研究所;成都理工大学;中铝西藏金龙矿业股份有限公司;
【基金】：国土资源部公益性行业专项“斑岩-浅成低温热液成矿系统研究及勘查评价示范-以西藏多龙整装勘查区为例”(编号:201511017) 国家自然科学青年基金“西藏羌塘地体南缘铁格龙南超大型浅成低温热液型铜(金)矿床保存条件研究”(编号:41402178) 科技基础性工作专项(项目编号:2014FY121000)共同资助
【分类号】：P597.3;P588.14
本文编号：2431495
[Abstract]:The Bangong Lake-Nujiang suture belt in Tibet is an important porphyry copper-gold deposit belt in China, and the ore-forming geological conditions are extremely superior. The Duolong ore concentration area is a typical porphyry-shallow hydrothermal copper (gold) superlarge deposit in the western part of the Bangongghu-Nujiang suture belt. The volcanic rocks of the spilled facies of the United States-Japan cut-off formation are widely distributed in the area, but their petrogenesis and source area attribute. The age of formation and the background of geochemical dynamics are not clear. In this paper, zircon U-Pb dating of andesite and rhyolite of the American-Japanese shear fault group has been carried out. The crystallization ages are 108.2 卤2.6Ma (MSWD=0.39) and 109.3 卤2.2Ma (MSWD=1.70), respectively. The andesite and rhyolite in the ore area are characterized by high silicon (SiO2=60.89%~72.00%), rich potassium (K 2O + 3.08%), alkali rich (K 2O Na2O=6.88%~8.96%) and quasi aluminous peraluminite (A/CNK=0.92~1.28). It belongs to the rocks of high potassium calc-alkaline and potassium basaltic series. They are obviously enriched in light rare earth (LREE) and large ion lithophile elements (LILE:Th,U,K,Pb and Rb), heavy rare earth (HREE) and high field strength elements (HFSE:Ta,Nb,Ti and Zr),). The total amount of rare earths (危 REE) is between 141.52 脳 10 脳 10 ~ 6 and 236.05 脳 10 ~ (6), the LaN/YbN is 10.42 ~ 11.05, and the 未 Eu is 0.65 ~ 0.80, showing the characteristics of typical island arc magmatic rocks. (87 Sr/86 Sr) I = 0.7050 ~ 0.7053, (143 Nd/144 Nd) i is 0.5124 脳 0.5126, 蔚 Nd (t) is-1.51? 1.29), which has the characteristics of high Sr and low Nd. Zircon Hf isotopic analysis shows that the 蔚 HF (t) of rhyolite is 11.6 ~ 15.5, the average value is 13.8, and the average age of two-stage model is 288.0 Ma. The 蔚 Hf (t) of the andesite is 3.4 ~ 8.0, with an average value of 4.8, and the average age of the two-stage model is 813.1Ma, showing obvious mantle-derived characteristics. The comprehensive study shows that under the background of the northward subduction of the Bangong Lake-Nujiang Xintesian Ocean crust, the volcanic rocks of the United States-Japan shear fault formation are partially melted to form primitive basaltic magma by dewatering the subduction plate to produce the fluid metasomatism mantle wedge, and after rising, the volcanic rocks of the United States and Japan formed the primitive basaltic magma. The Neo-lower crust is formed at the boundary of crust-mantle, which is partly melted by mixing with the basaltic magma of continuous underplating mantle-derived basaltic magma. It was formed in the tectonic setting of the typical island arc suggesting that the Bangong Lake-Nujiang Ocean was still subducting northward under the Qiangtang block in the late early Cretaceous (108~109Ma) and may not have been closed.
【作者单位】： 中国地质大学(北京)地球科学与资源学院;中国地质科学院矿产资源研究所;成都理工大学;中铝西藏金龙矿业股份有限公司;
【基金】：国土资源部公益性行业专项“斑岩-浅成低温热液成矿系统研究及勘查评价示范-以西藏多龙整装勘查区为例”(编号:201511017) 国家自然科学青年基金“西藏羌塘地体南缘铁格龙南超大型浅成低温热液型铜(金)矿床保存条件研究”(编号:41402178) 科技基础性工作专项(项目编号:2014FY121000)共同资助
【分类号】：P597.3;P588.14
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