摘要
滇西北甭哥金矿区赋矿岩石类型主要为黑云辉石正长岩、黑云母正长岩及正长斑岩。锆石LA-ICP-MS定年结果表明黑云辉石正长岩和黑云母正长岩的结晶年龄分别为213.8±2.2Ma和219.1±4.7Ma,形成于印支期甘孜-理塘洋向西俯冲时期。岩石地球化学分析表明三类岩石均高钾富碱,属于钾玄质系列,富集LREE和大离子亲石元素(Sr、K、Rb、Ba、Th),亏损高场强元素(如Nb、Ta、Hf、Ti等),具有高的Mg#、Zr/Nd比值、Cr和Ni含量,黑云辉石正长岩和黑云母正长岩锆石εHf(t)值多集中于-2^+2之间,显示源区为俯冲板片物质交代的富集地幔。二阶段Hf模式年龄(978~1317Ma和998~1611Ma)远大于结晶年龄,结合从黑云母正长岩的部分锆石中获得510~534Ma、598~945Ma和1096~1206三组晚古生代-元古代的年龄信息,显示岩浆在上升侵位的过程中经历了壳源物质的混染。推测此次岩浆活动可能与晚三叠世甘孜-理塘洋向西俯冲,大洋板片断离,形成弧后拉张作用相关。
The host rocks of the Bengge gold deposit include biotite-pyroxene syenite,biotite syenite and porphyry syenite. Zircon LA-ICP-MS U-Pb dating results indicate that the biotite pyroxene syenite and the biotite syenite crystallized at 213. 8 ± 2. 2Ma and219. 1 ± 4. 7Ma,respectively,which is located within the arc-like magmatism period deduced from the Indosinian subduction of the Ganze-Litang oceanic crust. Geochemically,the syenites have very high potassium- and alkaline-contents,and are of shoshonitic series. They are characterized by high Mg#,Zr/Nd ratio,and Ni-,Co-contents,and enriched in LREE and large ion lithophile elements and depleted in the high field strength elements. The εHf（ t） of the biotite pyroxene syenite and biotite syenite mostly range from- 2 to ＋ 2. These features suggest the syenites are derived from partial melting of an enrichment mantle which has been metasomatized by the fluid derived from the dehydration of the subducted oceanic slab. Their corresponding tDM2（ Hf） model ages（ 978~ 1317 Ma and 998 ~ 1611Ma） are older than the crystallization age,combining with the inherited zircon age information of Late Palaeozoic to Proterozoic（ 510 ~ 534 Ma,598 ~ 945 Ma and 1096 ~ 1206Ma）,indicating crustal contamination during magma evolution.This magma then were likely formed in an extensional back-arc setting related with a slab break-off resulting from the westward subduction of the Garze-Litang oceanic crust in the Late Triassic.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第11期3234-3246,共13页
Acta Petrologica Sinica
基金
973项目(2015CB452601)
国家自然科学青年基金项目(U0933605)联合资助
关键词
正长岩
地球化学
年代学
HF同位素
滇西北甭哥
Syenite
Geochemistry
Geochronology
Hf isotopes
Bengge
northwestern Yunnan
