扬子西缘陆内构造转换系统与构造-岩浆-成矿效应

doi:10.13745/j.esf.sf.2020.3.16

摘要/Abstract

摘要：

横跨欧亚呈东西延伸的特提斯构造域是全球最重要的有色贵金属成矿带之一,该带向东到达扬子陆块后转向东南,位于转折部位的扬子西缘近年发现系列大型-超大型Cu-Au矿床。以往认为,扬子西缘金沙江—红河大型走滑断裂切穿岩石圈,诱发岩浆上侵,形成富碱斑岩带。本文通过对扬子西缘剑川老君山、鹤庆北衙、姚安老街子—干沟、大姚吁支拉和永仁直苴等多个富碱岩体进行调查和构造应力分析,表明富碱斑岩在沿金沙江—红河断裂两侧分布的同时,也有大量岩体(脉)进入扬子板块内部,沿EW向断裂展布,其成岩成矿年龄为36.87~30.70 Ma,与富碱斑岩带一致,同时岩浆活动表现出由西向东时代变新,碱质增加等自西向东运移的特征;对近EW向岩体(脉)及节理的野外观测和统计分析表明,控岩构造具有东西挤压南北伸展的应力特征,与北西向大型走滑构造配套。由此提出,扬子陆块西缘新生代发育大规模陆内构造转化系统,陆块内部系列富碱岩浆,其形成与深切的NW向大型走滑构造有关,自西而东就位于派生的SN向、EW向次级构造,发育斑岩Cu-Au等成矿作用,成岩成矿与陆内构造转化系统耦合。

关键词: 扬子西缘, 新生代, 陆内构造转换系统, 富碱斑岩, 成矿效应

Abstract:

The Tethys tectonic domain, which extends from east to west across Eurasia, contains one of the most important precious/base metallogenic belts. The belt turns toward the southeast after reaching the Yangtze Block and series of large to giant Cu-Au deposits have recently been discovered at this hinge zone. It has previously been determined that the large-scale Jinshajiang-Honghe strike-slip fault along the western Yangtze margin cut through the lithosphere, inducing magmatic intrusions and forming an alkali-rich porphyry belt. In this study, several alkali-rich intrusions (including Laojunshan in Jianchuan, Beiya in Heqing, Laojiezi-Gangou in Yao’an, Yuzhila in Dayao, and Zhiju in Yongren) were analysed for tectonic stress. The results show that in addition to the distribution of alkali-rich porphyries along both sides of the Jinshajiang-Honghe Fault, there are also many dykes along the E-W-trending structures within the interior of the Yangtze Block. These intrusions have magmatic and mineralization ages ranging from 36.87-30.70 Ma, coeval with the formation of the porphyry belt. It was found that the magmatic ages become younger and alkalinity increases from west to east, defining an eastward magmatic migration. Field observations and statistical analyses of these nearly E-W-trending dykes and joints revealed that the structures controlling magmatism have undergone E-W compression and N-S extension, which is compatible with the large NW-trending strike-slip structures observed. Based on these lines of evidence, the formation of a series of alkali-rich intrusions within the Yangtze Block is likely related to the large-scale NW-trending strike-slip structures. The alkali-rich intrusions and related Cu-Au porphyry mineralization are distributed in the N-S- and E-W-trending secondary structures from west to east, and magmatism and mineralization were coupled with intracontinental structural transformations.

Key words: western margin of Yangtze Block, Cenozoic, intracontinental tectonic transformation system, alkali-rich porphyry, metallogenic effect

中图分类号:

李文昌, 江小均. 扬子西缘陆内构造转换系统与构造-岩浆-成矿效应[J]. 地学前缘, 2020, 27(2): 151-164.

LI Wenchang, JIANG Xiaojun. The Cenozoic tectono-magmatism-mineralization effect of the intracontinental tectonic transformation system in the western margin of Yangtze Block[J]. Earth Science Frontiers, 2020, 27(2): 151-164.

图/表 11

图1 金沙江—红河走滑断裂富碱斑岩带(矿床)及年龄(据文献[18]修改)

Fig.1 Alkali-rich porphyry belt(deposit)and age of Jinshajiang-Honghe strike-slip fault. Modified from [18].

表1 扬子西缘新生代近EW向富碱斑岩脉锆石U-Pb年龄及采样位置

Table 1 Zircon U-Pb age and sampling location of Cenozoic alkali-rich porphyry dike near EW direction in western margin of Yangtze Block

图2 扬子西缘新生代EW向富碱斑岩脉锆石LA-ICP-MS U-Pb谐和图

Fig.2 LA-ICP-MS U-Pb concordia diagram for zircon of Cenozoic alkaline-rich porphyry dike along EW direction from western margin of Yangtze Block

图3 扬子西缘姚安老街子Pb-Ag和干沟Au矿床地区地质简图(a)及新生代EW向富碱斑岩脉(b)

Fig.3 Geological sketch of Pb-Ag deposit in Laojiezi and Au deposit in Gangou(a) and Cenozoic alkali-rich porphyry dike along EW direction(b) in Yao’an in the western margin of Yangtze Block

图4 扬子西缘永仁直苴Cu-Mo矿地质简图(a)及新生代EW向富碱斑岩脉(b)

Fig.4 Geological sketch of Zhiju Cu-Mo deposits in Yongren(a) and Cenozoic alkali-rich porphyry dike along EW direction(b) in western margin of Yangtze Block

图5 扬子西缘地区新生代近EW向富碱斑岩脉素描图 a,b—剑川县老君山岩体东部和园村西公路旁;c,d,e—南华县沙桥镇石冠山地区;f—姚安至南华公路旁扁担酒馆旁。

Fig.5 Sketch of Cenozoic alkali-rich porphyry dike near EW direction in western margin of Yangtze Block

图6 扬子西缘新生代陆内构造转换系统EW向富碱斑岩脉及各种破裂构造等密度图(a)和构造应力场解析(b) 1~9—扬子西缘EW富碱斑岩脉及同期石英脉产状;10—姚安老街子Pb-Ag矿区含矿节理脉;11—姚安老街子Pb-Ag矿区断裂构造

Fig.6 Iso-intensity diagram(a)and tectonic stress field analysis(b)for alkali-rich porphyry dike along EW direction and various fracture structures of Cenozoic intracontinental tectonic transformation system in western margin of Yangtze Block

图7 扬子西缘新生代陆内构造转换系统NW向与EW向富碱斑岩及相关矿床分布图

Fig.7 Distribution diagram of NW and EW direction alkali-rich porphyry and related deposits for Cenozoic intracontinental tectonic transformation system in western margin of Yangtze Block

图8 扬子西缘新生代陆内构造转换系统NW向与EW向富碱斑岩成岩-成矿年龄对比直方图

Fig.8 Contrast histogram of magmatism and mineralization age on NW and EW direction alkali-rich porphyry dike of Cenozoic intracontinental tectonic transformation system in western margin of Yangtze Block

图9 扬子西缘新生代陆内构造转换系统构造-岩浆-成矿概念模型(据文献[18, 65]修改) 走滑断层:JARSSZ—金沙江-红河左行韧性剪切断裂带;LZJSSZ—绿枝江左行剪切断裂带;XJSSZ—小江左行剪切断裂带。

Fig.9 Tectono-magmatism-mineralization conceptual model of Cenozoic intracontinental tectonic transformation system in western margin of Yangtze Block. Modified from [18,65].

图10 扬子西缘新生代陆内构造转换系统及其岩浆成矿效应模式图 JARSSZ—金沙江—红河左行韧性剪切断裂带;LZJSSZ—绿枝江左行剪切断裂带;XJSSZ—小江左行剪切断裂带。1—造山型Au矿床;2—“构造-贯入”热液改造Zn-Pb矿床;3—斑岩型Cu-Au多金属矿床;4—斑岩型Cu-Mo矿床;5—碳酸岩-碱性岩REE矿床;6—岩浆上侵方向;7—成矿流体运移方向;8—NEE-SWW向拉张EW展布的富碱岩浆;9—拉分盆地。

Fig.10 Model map of Cenozoic intracontinental tectonic transformation system and its magmatic metallogenetic effect in western margin of Yangtze Block

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