摘要
长江中下游燕山期中酸性-酸性火山-侵入杂岩大家公认为具有偏碱性到碱性特点，但对富碱原因即碱质来石源则存在不同意见，大多数人认为壳幔亮混源，碱质来源于富集地幔的部分熔融，也受到地壳物质的混染．另一种意见强调富碱是由于岩浆侵位或分异过程中受到蒸发岩（特别是膏盐层）的混染与同化。笔者根据长江中下游有关岩体的大量岩石化学分析数据．分地区、分岩体、也按时代对其K2O、Na2O、CaO、MgO与SiO2的相关性作了直观性对比分析，事实表现出Na2O对SiO2几乎完全没有相关性，Na2O对SiO2可以说是独立变化的；K2O与MgO对SiO2具有不同程度的相关性；而CaO－SiO2则具有明显的直线性相关。据此提出：除了原始岩浆具有的碱质外，在岩浆分导过程中不时地有外来碱质加入，这些外来的碱质主要由中、下三叠统中的膏盐层提供。文中根据岩浆硫的δ34S值偏高、膏盐层主要矿物的自由能在高温下熔融及分解温度与低温下在水中的溶解度、石膏矿山的矿泉水中K＋、Na＋、C1＋、SO32-等的浓度，以及斜长石的环带构造方面作了论证．
The Yanshanian medium-acidic to acidic volcanic-intrusive complexes in the Middle-Lower Yangtze area are thought to be alkaline to sub-alkaline by many geologists' However,the origin of alkali has evoked much controversy. Most geologists who have worked in thisarea hold a view that the alkaline magma was resulted from mantle-crust mixture, alkalis wereoriginated from partial melting of enriched upper mantle with contamination -assimilation ofcrustal material during differentiation processes. Different opinion suggested by another part ofgeologists emphasize the contamination-assimilation of magma during its intruding and evolu-tional process in contact with the Triassic evaporite (especially anhydirte-halide) beds.The prcsent authors, on the basis of abundant data of chemical analyses in this area,lnake a thorough inquiry of the correlationship between K2O, Na2O, CaO MgO vs. SiO2 indifferent fields of ore deposits. individual intrusives in a same ore field and according to theirages in a same orc field. The results show that Na2O vs. SiO2 completely no correlationship ex-ists; Na2O amount (weight percent )changes with increase of SiO2 indepently and sporatically.K2O-MgO vs. SiO2 reveal different degree of correlationship, while CaO vs- SiO2 keeps a tightcorrelationship as indicated on the diagrams. Therefore a consideration that there are a fairamount of Na2O (coming from contamination-assimilation of evaporite(anhydrite and halides )beds besides those originated from primitive magma is suggested. A detail discussion on thehigher magmatic sulphur isotopc δ34S Values; the free energy, melting and resolution tempera-ture, disso1uton in water at lower temperature of the major minerals of evaporite beds; theconcentration of K+, Na+,Cl-, SO23, CO2-3 etc- in ground water of some anhydrite mines;and finally the zonal and anti-zonal structures of plagioclase is given as the basis of this inference.
出处
《火山地质与矿产》
1995年第2期1-20,共20页
Volcanology & Mineral Resources
基金
国家攀登项目!30-12
国家自然科学基金!49272104
关键词
火山
侵入杂岩
长江中下游
岩浆流
同位素
sub-alkaline to alkaline volcanic-intrusive rocks, magmatic δ^(34)S valus, Middle-Lower Yangtze area
