山东昌乐新生代碱性玄武岩中的巨晶单斜辉石成因研究
Study on the genesis of clinopyroxene megacrysts in the Cenozoic alkali basalt at Changle, Shandong Province
-
摘要: 山东昌乐新生代碱性玄武岩中除斑晶单斜辉石和基质单斜辉石外，还发育大量巨晶单斜辉石和同源斜方辉石捕掳晶。巨晶单斜辉石与玄武岩间发育复杂和简单两种类型的反应边。复杂反应边往往发育在颗粒较大的巨晶单斜辉石外围。复杂反应边可分为4个带：内部带、过渡带、外部带和边缘带，其中，内部带、过渡带和外部带均由具不同结构特征的单斜辉石＋熔体＋金属氧化物构成，边缘带为不含熔体和金属氧化物的干净的单斜辉石；内部带的单斜辉石具梳状构造，过渡带的单斜辉石具细密筛孔构造，外部带为具似砂钟构造的筛孔状单斜辉石。反应边中单斜辉石、熔体及金属氧化物的成分显示，只有内部带受到单斜辉石巨晶的影响，其余带均受玄武岩浆的制约。简单反应边往往发育在颗粒较小的巨晶单斜辉石外围。简单反应边仅发育不含熔体和金属氧化物的干净的单斜辉石。巨晶单斜辉石的反应边是巨晶与玄武岩浆间温度差造成的。在与玄武岩浆反应的过程中，大颗粒的单斜辉石巨晶需要较长的时间与玄武岩浆达到温度平衡，从而有足够的时间发育包含4个带的复杂反应边；反之，由于缺乏足够的反应时间，小颗粒单斜辉石巨晶的外围只发育不含熔体和金属氧化物的简单反应边。同源斜方辉石捕掳晶的成分与地幔二辉橄榄岩包体中的斜方辉石类似，其边部发育类似于Bowen反应（1956）形成的单斜辉石环边。在单斜辉石AlIV-AlVI图解上，巨晶单斜辉石、二辉橄榄岩包体中的单斜辉石以及部分单斜辉石斑晶的核部，均位于较高压力的“麻粒岩和玄武岩中包体”区域，反应边中单斜辉石、基质单斜辉石以及绝大部分斑晶单斜辉石位于“火成岩”区域，说明部分斑晶单斜辉石核部来源于地幔二辉橄榄岩，属于捕掳晶。结合单斜辉石结晶压力的估算，笔者认为巨晶单斜辉石的成因模式为：来自软流圈的碱质基性熔体上侵到地幔岩石圈下部，结晶形成单斜辉石巨晶，后来该熔体携带巨晶单斜辉石与来自上地幔岩石圈、夹带大量二辉橄榄岩包体以及斜方辉石（和单斜辉石）捕掳晶的玄武岩浆混合，巨晶单斜辉石随混合后的碱性玄武岩浆上升、喷出地表。Abstract: There are four types of pyroxenes in the Cenozoic alkali basalt at Changle, Shandong Province: phenocryst clinopyroxenes, metrix clinopyroxenes, clinopyroxene megacrysts and homologous orthopyroxene xenocrysts. The coronas, between the clinopyroxene megacrysts and alkali basalt, could be divided into complex coronas and simple coronas. The complex coronas appeared in the outside of larger clinopyroxene megacrysts and could be divided into four zones based on their characteristics of textures and components. The zones of interior, transitional and exterior are composed of clinopyroxenes with different textures and a few melts and metal oxides. The edge zone is composed of clean clinopyroxene without melt and metal oxide. The clinopyroxenes at the coronas display comb texture in the interior zone, sieve texture in the transitional zone and both similar sector-zoned and sieve texture in the exterior. The compositions of the clinopyroxenes, melts and metal oxides at the coronas are controled by the clinopyroxene megacrysts only in the interior zone, and by basaltic magma in other zones. The simple coronas appeare in the outside of samller clinopyroxene megacrysts and are composed of whole clinopyroxene without melt and metal oxide. The coronas of clinopyroxene megacrysts are resulted from the temperature difference between clinopyroxene megacrysts and basaltic magma. If the grain of clinopyroxene megacryst is larger, the time taken to adjust the difference of temperature is longer, then the complex coronas with four zones will form; if the grain is smaller, the simple coronas with edge zone will form as a result. The compositions of homologous orthopyroxene xenocrysts are within the range of compositions of the orthopyroxenes in the lherzolite xenoliths. The clinopyroxene rim or reaction rim surrounding the orthopyroxene xenocrysts are the results of the compositional differnece between orthopyroxene and basaltic magma, similar to the reaction rim texture described by Bowen (1956). All clinopyroxene megacrysts, clinopyroxenes in the lherzolite xenoliths and part of the core of clinopyroxene phenocrysts are located in the “granulites and the inclusions in basalts” field of Aoki and Shiba (1973) in the AlIV-AlVI diagram, suggesting a relatively high-pressure crystallization. It suggests that part of the core of clinopyroxene phenocrysts come from mantle lherzolite, and they belong to xenocrysts. Clinopyroxenes in the coronas, metrix clinopyroxenes and a majority of clinopyroxene phenocrysts are plotted in the “igneous rocks” field. Based on the estimated crystallization pressure for clinopyroxene megacrysts and clinopyroxenes in the lherzolite xenoliths, we suggest a formation mechanism for the clinopyroxene megacrysts as following: first, the asthenosphere-derived alkali basaltic melts invaded into the lithospheric mantle near the lithosphere asthenosphere boundary and produced clinopyroxene megacrysts, then the melts with a great lot of clinopyroxene megacrysts mixed with the existing magmatic system from mantle lithosphere entraining an abundance of the xenocrysts of clinopyroxenes and orthopyroxenes and lherzolite xenoliths. The mixed alkali basaltic magmas with clinopyroxene megacrysts, xenocrysts and xenoliths ascended from the crustal magma chambers, and erupted at the surface.
-
Key words:
- Alkali basalt /
- Clinopyroxene megacryst /
- Pyroxene xenocryst /
- Forming model /
- Changle
-
-
[1] Aoki K,Kushim 1,Some clinopyroxenes from ultramafic inclusions in Dreiser Weiher,Eifel Contrib Mineral Petrol,1968.
[2] Aoki K,Shiba I,Pyroxenes from lherzolite inclusions of Itinomegata,Japan,Lithos,1973.
[3] Bowen NL,The Evolution of the Igneous Rocks,New York:Dover Publications,Inc,1956.
[4] Chen DG,Xia QK,Zhi XC,Geochemistry of clinopyroxene megacrysts from Nushan,Anhui,Acta Mineralogica Sinica,1997(03).
[5] Chen DG,Xia QK,Zhi XC,Geochemistry of megacrysts in Cenozoic basalts of eastern China,Acta Geoscientica Sinica,1997(03).
[6] Dobosi G,Jenner GA,Petrologic implications of trace element variation in clinopyroxene megacrysts from the Nograd volcanic province,north Hungary:A study by laser ablation microprobeinductively coupled plasma-mass spectrometry,Lithos,1999(04).
[7] Hyndman DW,Petrology of Igneous and Metamorphic Rocks,New York:McGraw-Hill,1972.
[8] Irving AJ,Flow crystallization:A mechanism for fractionation of primary magmas at mantle pressure,EOS,1978.
[9] Irving AJ,Frey FA,Trace element abundances in megacrysts and their host basalts:Constraints on partition coefficients and megacryst ganesis,Geochimica et Cosmochimica Acta,1984.
[10] Nimis P,Ulmer P,Clinopyroxene geobarometry of magmatic rocks.Part 1:An expanded structural barometer for anhydrous and hydrous basic and ultrabasic rocks,Contributions to Mineralogy & Petrology,1998.
[11] Sutthirat C,Saminpanya S,Droop GTR,Henderson CMB and Manning DAC,Clinopyroxene-corundum assemblages from alkali basalt and alluvium,eastern Thailand:Constraints on the origin of Thai rubies,Mineralogical Magazine,2001(02).
[12] Thompson RN,Some high-pressure pyroxenes,Mineralogical Magazine,1974.
[13] Wass SY,Fractional crystallization in the mantle of late stage kimberlitic liquids:Evidence in xenoliths from Kiama area,N.S.W,Australia,Am.Geophys.Union,Washington,DC,1979.
[14] Woodland AB,Jugo PJ,A complex magmatic system beneath the Deves volcanic field,Massif Central,France:Evidence from clinopyroxene megacrysts,Contributions to Mineralogy & Petrology,2007.
[15] Xia QK,Chen DG,Guo LH,Zhi XC,Structural water in mantle-derived clinopyroxene megacrysts from hannuoba:FTIR investigations,Acta Mineralogica Sinica,1999(02).
[16] Xia QK,Luigi D,Cao H,Chen DG Wu YB and Cheng H,Oxygen isotopic heterogeneity in the mantle:Evidence from clinopyroxene megacrysts of Nushan,eastern China,Chinese Science Bulletin,2002(03).
[17] Xia QK,Pan YJ,Chen DG,Deloule E Zhi XC Chang H and Wu YB,Hydrogen isotopic compositions of mantle-derived clinopyroxene megacrysts from Hannuoba by ion microprobe:Microscale heterogeneity,Acta Petrologica Sinica,2001(01).
[18] Yang YH,Zhang HF,Xie LW,Liu Y Qi CS and Tu Xl,Petrogenensis of typical Mesozoic and Cenozioc volcanic rocks from the North China Craton:New evidence from Hf isotopic studies,Acta Petrologica Sinica,2006(06).
[19] Yu JH,Luo SW,Megacrysts from Cenozoic Yingfengling basalt in Leizhou peninsula,Acta Mineralogica Sinica,2000(02).
[20] Zhi XC,Chen P,Lin CZ,Chen SQ Zhang GL Li YZ and Lin L,Oxidation experiment of natural megacrystal clinopyroxene:Implications for assignment of Mossbaner spectra,Acta Geologica Sinica,2001(01).
[21] Zhu G,Song SZ,Niu ML,Liu GS and Wang YS,Lithospheric textures of the Tanlu fault zong and their genetic analysis,Geological Journal of China Universities,2002(03).
[22] 陈道公,夏群科,支霞臣,安徽女山单斜辉石巨晶的地球化学,矿物学报,1997(03).
[23] 陈道公,夏群科,支霞臣,中国东部新生代玄武岩中巨晶矿物的地球化学,地球学报,1997(03).
[24] 夏群科,陈道公,郭立鹤,支霞臣,汉诺坝幔源单斜辉石巨晶中的结构水:红外光谱观察,矿物学报,1999(02).
[25] 夏群科,潘尤杰,陈道公,DELOULE Etienne 支霞臣 程昊 吴元保,汉诺坝幔源单斜辉石巨晶氢同位素组成的离子探针分析:微尺度不均一性,岩石学报,2001(01).
[26] 杨岳衡,张宏福,谢烈文,刘颖,祁昌实,涂湘林,华北克拉通中、新生代典型火山岩的岩石成因:Hf同位素新证据,岩石学报,2006(06).
[27] 于津海,罗树文,雷州半岛英峰岭新生代玄武岩中的捕虏巨晶,矿物学报,2000(02).
[28] 朱光,送传中,牛漫兰,刘国生,王勇生,郯庐断裂带的岩石圈结构及其成因分析,高校地质学报,2002(03).
[29] 董泽龙,山东、海南新生代玄武岩与刚玉关系研究,南京:南京大学,2005.
-
计量
- 文章访问数:
- PDF下载数:
- 施引文献: 0
下载: