Geochronology, geochemistry and petrogenesis of two periods of intermediate-acid intrusive rocks from Hongshan area in Zhongdian arc
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摘要:
青藏高原东部中甸岛弧红山地区发育有印支期和燕山晚期两期中酸性岩浆侵入活动，主要集中在~216Ma和~76Ma两个时期。印支期中酸性岩浆的侵入活动形成于甘孜-理塘洋西向俯冲背景下，与矽卡岩型铜多金属成矿作用密切相关。形成于印支期的红山石英闪长玢岩具有埃达克质岩的部分地球化学特征，如高Sr (平均为938×10-6)、低Y (平均为18.6×10-6)、Yb (平均为1.7×10-6) 含量，轻重稀土分异明显((La/Yb)N平均为20.1)，同时也有着较高的Mg#(平均为51)、Cr (平均为103×10-6)、Ni (平均为22×10-6) 含量，指示印支期红山中酸性岩与普朗-雪鸡坪成矿岩体有着相似的地球化学特征，二者可能有着相似的物质源区和成岩模式。而形成于燕山晚期的红山花岗斑岩具有低Sr含量(平均为149×10-6) 和更低的Y (平均为10.8×10-6)、Yb (平均为0.9×10-6) 含量，轻重稀土强烈分异((La/Yb)N平均为56.0)，明显区别于义敦岛弧弧后区的高贡-措莫隆A型花岗岩，前者很可能是红山中下地壳部分熔融的产物。结合中甸岛弧发育于燕山晚期的斑岩型矿床，我们认为该地区发育于燕山晚期的中酸性岩浆作用以及与之相联系的斑岩型矿床形成于造山后伸展环境下。
Abstract:Two periods of intermediate-acid magmatic activities occur in Hongshan area, Zhongdian arc, which were mainly emplaced at~216Ma and~76Ma, respectively. The 216Ma magmatism, which is associated with the porphyric Cu-Mo mineralization, was produced during the westward subduction of Ganzi-Litang ocean plate in Late Triassic. It is composed of quartz dioritic porphyrites, and shows some geochemical characteristics of an adakite, such as high Sr (938×10-6 in average), but low Y (18.6×10-6 in average), Yb (1.7×10-6 in average) contents, and strongly fractionation between LREE and HREE ((La/Yb)N=20.1 in average). Meanwhile, it has relatively high Mg# (51 in average), Cr (103×10-6 in average) and Ni (22×10-6 in average) concentrations. These quartz dioritic porphyrites show geochemical characteristics same as or similar to those of the ore-bearing rocks in Pulang-Xuejiping, hinting that the both had a similar composition in source and/or were formed by a tectonic event. On the other hand, 76Ma granitic porphyries in Hongshan area have low Sr (149×10-6 in average), Y (10.8×10-6 in average) and Yb (0.9×10-6 in average) concentrations, and strongly fractionation between LREE and HREE ((La/Yb)N=56.0 in average), which is obviously different from the A-type granite of Gaogong-Cuomolong in Yidun island arc. It is likely the result of partial melting of the middle-lower crust of Hongshan area. Combined with other porphyric rocks and deposits in Zhongdian arc, the 76Ma intermediate-acid magmatism in Hongshan area, which is associated with porphyric mineralization, were generated in a post-orogenic extensional setting in Late Cretaceous.
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Key words:
- Porphyric deposit /
- Geochemistry /
- Intermediate-acid rock /
- Hongshan /
- Zhongdian arc
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图 1
中甸岛弧大地构造位置(a) 和地质简图(b)(据任江波等，2011a) 及研究区地质简图(c，据徐兴旺等，2006修改)
Figure 1.
Simplified geological map of Zhongdian island arc (a, b, after Ren et al., 2011a) and geological map of the studied area (c, after Xu et al., 2006)
图 2
红山石英闪长玢岩(a、b) 和红山花岗斑岩(c、d) 镜下特征
Figure 2.
Microphoto of quartz diorite porphyrite (a, b) and granite porphyry (c, d) in Hongshan
图 3
红山石英闪长玢岩(HS-763) 和花岗斑岩(HS-800) 的锆石阴极发光图片(a, b) 和U-Pb年龄谐和图(c, d)
Figure 3.
The CL images of zircon (a, b) and LA-ICPMS U-Pb concordant curves (c, d) of quartz diorite porphyrite (HS-763) and granitic porphyry (HS-800) in Hongshan
图 4
中甸岛弧红山印支期与燕山晚期岩浆岩SiO2-K2O图(a，据Peccerillo and Taylor, 1976) 和LOI-K2O图(b)
Figure 4.
SiO2 vs. K2O diagram (a, after Peccerillo and Taylor, 1976) and LOI vs. K2O diagram (b) for Indosinian and Late Yanshanian lavas in Zhongdian arc
图 5
中甸岛弧印支期与燕山晚期岩浆岩TAS图(据Le Bas, 1986)
Figure 5.
TAS diagram for Indosinian and Late Yanshanian lavas in Zhongdian arc (after Le Bas, 1986)
图 6
中甸岛弧印支期与燕山晚期岩浆岩Harker图
Figure 6.
Harker diagram for Indosinian and Late Yanshanian lavas in Zhongdian arc
图 7
球粒陨石标准化配分REE图(a, c) 和微量元素原始地幔标准化蛛网图(b, d)(标准化数据为Sun and McDonough, 1989)
Figure 7.
Chondrite-normalized REE distribution patterns (a) and primitive mantle-normalized trace element spider diagram (b)(normalized values after Sun and McDonough, 1989)
图 8
中甸岛弧印支期中酸性侵入岩年龄分布图(a) 和义敦岛弧燕山晚期中酸性侵入岩年龄分布图(b)
Figure 8.
Cumulative age spectra of Indosinian intermediate-acid intrusive rocks in Zhongdian arc (a) and Late Yanshanian intermediate-acid intrusive rocks in Yidun Island arc (b)
图 9
中甸岛弧印支期与燕山晚期岩浆岩Sr/Y vs. Y (a，据Defant et al., 2002) 和(La/Yb)N vs.(Yb)N图(b，据Defant and Drummond, 1990; Petford and Atherton, 1996)
Figure 9.
Sr/Y vs. Y (a, after Defant, 2002) and (La/Yb)N vs.(Yb)N(b, after Defant and Drummond, 1990; Petford and Atherton, 1996) diagrams for Indosinian and Late Yanshanian lavas in Zhongdian arc
图 10
中甸岛弧印支期与燕山晚期岩浆岩SiO2 vs. MgO图(a，据Huang et al., 2009)、SiO2 vs. Mg#图(b，据Wang et al., 2006)、SiO2 vs. Cr图(c，据Huang et al., 2009) 和SiO2 vs. Ni图(d，据Huang et al., 2009)
Figure 10.
SiO2 vs. MgO (a, after Huang et al., 2009), SiO2 vs. Mg#(b, after Wang et al., 2006), SiO2 vs. Cr (c, after Huang et al., 2009) and SiO2 vs. Ni (d, after Huang et al., 2009) diagrams for Indosinian and Late Yanshanian lavas in Zhongdian arc
图 11
中甸岛弧印支期与燕山晚期岩浆岩La/Yb vs. La图(a，据Chung et al., 2009) 和La/Sm vs. La图(b)
Figure 11.
La/Yb vs. La diagram (a, after Chung et al., 2009) and La/Sm vs. La diagram (b) for Indosinian and Late Yanshanian lavas in Zhongdian arc
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