兰州大学机构库 >土木工程与力学学院
北祁连造山带东段早古生代构造岩浆作用及成矿的研究
Alternative TitleEarly Paleaozoic Tectono-magmatism and Mineralization of the Eastern Section in the North Qilian Orogenic Belt
王金荣
Thesis Advisor汤中立
2006-11-08
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword板块构造 岩浆作用 成矿作用 白银陆缘弧 老虎山弧后盆地 埃达克(质)岩 早古生代 北祁连东段
Abstract

北祁连构造带是世界上典型的造山带之一,是研究板块构造演化及其地球动力学过程的理想场所。在早古生代时期,北祁连东段壳幔相互作用活跃,岩石圈层圈物质及能量交换强烈,岩浆成矿作用显著,为国内外地质学家所关注。综合地质研究结果表明,北祁连东段由北至南可分为阿拉善古陆缘、老虎山弧后盆地残留体、白银陆缘弧、北祁连俯冲杂岩带、中祁连地块等构造岩石单元;在新元古代晚期-早古生代早期,北祁连造山带东段发生了裂解裂谷作用,以发育大陆拉班玄武岩到碱性玄武岩为特征,到早中寒武世-早中奥陶世,北祁连东段经历了古大洋扩张、俯冲消减、碰撞造山的重要构造事件,形成了白银陆缘弧和老虎山弧后盆地。

岩石学、地球化学研究结果首次揭示并证实: 1) 位于阿拉善古陆缘、 老虎山弧后盆地残留体北侧的屈吴山银硐梁早古生代花岗闪长岩是埃达克岩, 它们具有富 Na 贫 K, SiO2>56 w%, Al2O3>15 w%, Na2O>4.0 w% (4.51% ~ 4.92w%), K2O ( 1.96~2.77 w%), Na2O/K2O = 1.63~ 2.40, 属钙碱性侵入岩;高 Sr(599~691×10-6)低 Y(6.3~8.1×10-6), Sr/Y>40(81~94), Y/Yb>10(Yb<1.9×10-6), La/Yb>20 (22~45), 富集轻稀土元素(LREE), 亏损重稀土元素(HREE),(La/Yb)N > 10(16~32), 轻微负 Eu 异常(Eu/Eu﹡平均为 0.94), ∑REE ~ 85~ 112×10-6, 与典型的环太平洋埃达克岩比较,它们具有更高的 Mg# (58 ~ 64,平均59)和相容元素 Ni(31~38×10-6 )和 Cr(35~43×10-6)含量,因此被归入高镁埃达克岩,其形成于年轻而热的老虎山弧后盆地俯冲板片在消减过程中发生部分熔融,并与地幔橄榄岩发生明显交代作用; 2)侵入于白银陆缘弧火山岩中的早古生代晚期-晚古生代早期黑石山斜长花岗岩、花岗斑岩为埃达克质岩,其具有高 Sr 低 Y 型(Sr/Y>40),富集 LREE,亏损 HREE(La/Yb>20),无 Eu 负异常或轻微正异常(Eu/Eu﹡= 1.0-1.19),其成因是在北祁连东段进入后造山伸展构造阶段,由加厚的下地壳中基性岩石在地幔底侵作用下发生部分熔融的产物,但其富 Na 贫 K 而有别于中国东部燕山期由非板片熔融形成的富 K 贫 Na 的埃达克质岩。本文确定了白银厂矿田火山岩是早古生代北祁连古大洋俯冲产生的陆缘弧岩浆作用的结果,玄武岩主要源自岩石圈地幔部分熔融,而含矿岩系-流纹岩则来源于镁铁质下地壳部分熔融与地幔物质混合作用的产物。

研究结果表明,研究区内岩浆成矿作用显著且成矿类型多样。白银厂矿田早期成矿与陆缘弧酸性火山沉积作用有关,形成了不具规模的层状硫化物矿体,并为后期成矿作用提供矿质来源;晚期成矿作用发生在加里东晚期,成矿机理主要通过发生在酸性火山岩中韧性剪切作用及其释放出的流体活化、萃取岩石中的成矿金属,迁移到构造扩容带堆积成矿。屈吴山银洞粱早古生代岩浆 Au-Cu 成矿带,成矿作用与高 Mg 埃达克岩浆作用密切相关,具有高 fO2 的俯冲板片熔体萃取地幔中 Au、 Cu 等有益金属以及熔体快速上升侵位到地壳浅部是成矿作用重要地质条件;与银洞粱 Au-Cu 成矿带不同,黑石山 Au(Cu)矿床是加厚下地壳基性-中基性岩石部分熔融形成的埃达克质岩浆作用的结果,利于 Au-Cu 成矿的地质条件主要是高温高压下角闪岩相向榴辉岩相转变时角闪石的脱水作用, 其产生的流体利于金属元素的萃取和迁移。本文进一步指出,在米家山-屈吴山构造岩浆岩带和黑石山及其邻区寻找与埃达克(质)岩有关的斑岩型 Au-Cu 矿床可能是一个有希望的找矿方向。

Other Abstract

The North Qilian Orogenic Belt, as one of the typical orogenic zones in the world, is a key region for studying plate tectonic evolution and geodynamic processes. In the development of geosciences, geologists have been always paying close attention to the very mobile interaction between crust and mantle, intensive interchange processes of the lithospheric materials and energy, and remarkable magmatic mineralization in the eastern section of the North Qilian during early Paleaozoic period. The study results of comprehensive geology show that the eastern section of North Qilian may been divided into the Alaxa Paleo-continental margin, Laohushan back-arc basin remnant, Baiyin continental marginal arc, subducted complex zone of the North Qilian, and the Central Qilian Block from north to south, and that the eastern section of the North Qilian was obviously characterized by the tectonic processes of rifting with continental tholeiite to alkaline basalts from late period of Neoproterozoic to early period of Early Paleaozoic, and by tectonic evolution of the spreading, subduction of the paleo-Qilian ocean, forming Baiyin continental marginal arc and Laohushan back-arc basin, to finally plate collision and orogeny.

The study results of petrology and geochemistry are to originally reveal and demonstrate: 1) the early Paleozoic granodiorites from Yindongliang in Quwushang, located in the Alaxa Paleo-continental margin, north of Laohushan back-arc basin remnant, are adakites, similar to the typical adakites from circum-Pacific region. They have high Al2O3 (>15%(w %) ), Na2O (>4.0% (4.51% ~ 4.92%(w %) ), Na2O/K2O = 1.63~ 2.40, and SiO2>56%(w %), and low K2O contents ( 1.96~2.77 %(w %) ), belonging to calc-alkaline series; and high Sr (599~691×10-6) low Y (6.3~8.1 ×10-6)and Yb (Yb<1.9×10-6)contents, Sr/Y>40(81~94), Y/Yb>10, La/Yb>20 (22~45), and but with higher Mg# (58 ~ 64) , Ni(31~38×10-6) and Cr(35~43 ×10-6) contents compared with the typical adakites, so called as high-Mg adakite, indicating the slab melts interacted obviously with the mantle peridotite. It is evidently indicated that they were generated from the partial melting of the young and hot subducted oceanic slab of the Laohushan back-arc basin; 2) intruding into the volcanic rocks of Baiyin continental marginal arc, the Heishishan plagiogranite and granite-porphyry of late period of early Paleozoic to early time of late Paleozoic, with high Sr and low Y contents(Sr/Y > 40)and enrichment in LREE, Na (Na2O/K2O > 2 ) and SiO2, but depletion in HREE (La/Yb > 20) , and no negative Eu anomalies (Eu/Eu﹡ = 1.0-1.19), were originated from the partial melting of the thickened lower crust of intermediate-basic rocks, so called as adakitic rocks. They have higher Na contents (Na2O>4 w%), obviously different from the high-K calc-alkaline adakitic rocks of the Yanshanian period in eastern China, but similar to Cordilera Blanca granitoid (non-slab-melting generated adakites). It is evidently showed that the volcanic rocks from Baiyinchang ore field were formed by early Paleozoic magmatism in the continental marginal arc because of northward subduction of the North Qilian ocean, and that the basalts stemmed from enriched sub-continental lithospheric mantle and the mantle-derived magma was strongly contaminated by continental crust, but the ore-bearing rhyolitic rocks were resulted from mixing of mafic lower crust generated from partial melting of depleted mantle wedge and subduction-related mantle-derived underplating magmas.

The study results further show that the magmatic mineralization was very intensive and had many types in the eastern section of the North Qilian. The mineralizing processes of Baiyinchang ore field can be divided into two episodes, the first was related to the acid volcanic rocks in the continental marginal arc, forming some small layered sulfide ore bodies (deposits), and provided important metal materials for the coming mineralization; the second was due to the ductile shearing taking place in the Cu-Pb-Zn-bearing rhyolitic rocks during late Caledonian period and the related fluids released by the ductile shearing mobilizing, extracting and then transporting the metals to tectonic dilation zones to deposit. The Paleozoic magmatic Au-Cu metallogenetic processes of Yindongliang in Quwushan were closely related to high-Mg adakites, and the high fo2 melts extracting the Au, Cu elements from the mantle and Au-Cu-bearing melts rapidly intruding upwards shallow level of crust may be important geological conditions for the mineralization. Different from Yindongliang Au-Cu metallogenetic belt, the Heishishan Au (Cu) deposit was obviously resulted from the adakitic magmatism generated from the partial melting of the thickened mafic lower crust, and the geological conditions favoring Au-Cu mineralization were mainly the dehydration of amphibole from amphibolite changed into eclogite facies under high temperature and pressure. The fluids produced by the dehydration could extract a lot of the metals from the rocks of lower crust and transport them upward to deposit. It is further pointed out that the Cu-Au ore deposits related to adakites and adakitic rocks in Mijiashan-Quwushan tectono-magmatic belt and Heishishan and its adjacent region can be new ore-prospecting strategy in the eastern section of the North Qilian Mountains.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/226712
Collection土木工程与力学学院
Recommended Citation
GB/T 7714
王金荣. 北祁连造山带东段早古生代构造岩浆作用及成矿的研究[D]. 兰州. 兰州大学,2006.
Files in This Item:
There are no files associated with this item.
Related Services
Recommend this item
Bookmark
Usage statistics
Export to Endnote
Altmetrics Score
Google Scholar
Similar articles in Google Scholar
[王金荣]'s Articles
Baidu academic
Similar articles in Baidu academic
[王金荣]'s Articles
Bing Scholar
Similar articles in Bing Scholar
[王金荣]'s Articles
Terms of Use
No data!
Social Bookmark/Share
No comment.
Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.