摘要
一、本区新生代火山岩的地质概述 沿郯庐断裂带及其两侧地区,是我国新生代火山岩广泛出露的地区之一,也是环太平洋带西岸中、新生代火山岩带的重要组成部分。区内新生代火山岩,较集中出露于胶辽断块南段的蓬莱—栖霞一带(称蓬莱火山群)、鲁西河淮块隆北部的临朐—潍坊和沂水—安丘(称昌乐—沂水火山群)以及苏北盆地西部的加山—仪征一带(称加山—六合火山群)。
In the province the Cenozoic volcanic activities can be divided into three stages:Miocene,Pliocene and Pleistocene,and two types:central eruption and fissure eruption.This paper mainly deals with the petrological characteristics and their genesis.According to rock types and main rock-forming minerals,the Cenozoic volcanic rocks mainly are basaltic rocks.Based on A.Streckeisen’s classification(1979)which was refined by Prof.Wu Liren,they include:olivine tholeiite,alkali basalt,alkali olivine basalt,phonolitic tephrite-basanite,phonolitic foidite-foidite.Among these rocks the alkali olivine basalt is most common.Phonolitic tephrite-basanite and phonolitic-foidite are developed in the third stage of volcanic activity,while olivine tholeiite only occur in part of volcanic rocks of Jiashan region.Some of alkalic basaltic rocks contain mantle-derived xenolith(spinel peridotite etc.)and megacrysts(augite,anorthoclase and garnet).Based on CIPW calculated results,these rocks mainly belong to ordinary series.In olivine tholeiite and alkali basalt norm Ol and Cpx are more,norm Q and Opx are rare,F is absent or rare.They belong to magmatic type of SiO_(2)-weakly saturated or weakly undersaturated.In olivine basalt they contain norm Ol,F<10%,Cpx is absent.They belongto magmatic type of SiO_(2)-undersaturated;Phonolitic tephrite-basanite contain norm Ol,F>10%.They belong to magmatic trpe of SiO_(2)-extremely undersaturated.In phonolitic foidite-foidite F>60%,Pl is absent.They belong to SiO_(2)-extremely undersaturated andalkali oversaturated.In the province petrochemical components(main element)of the Cenozoic volcanic rocks are furnished with distinct variation regularities represented by a gradual decrease of the content of SiO_(2) and a gradual in crease of K_(2)O+Na_(2)O from Miocene to Pleistocene.Comparing with the same type of rocks in the world,they have a lower content of Al_(2)O_(3),and a higher alkalinity.Diagrams(SiO_(2)-K_(2)O+Na_(2)O,OL’-Ne’-Q,and An-Ab’-Or)show that only part volcanic rocks from Jiangsu and Anhui Province are extended along the boundary between alkali and sub-alkali series,and the rest completely fall within the alkalic series.Their geographical distribution shows that alkalinity increases from south to north.From Tacheng-Lujiang fault belt to their both sides the volcanic rocks have a evolutionary trend of K-to Na-series.From the above-mentioned features and the geophysical data and the caluclated quencing temperature of basaltic rocks and the calculated data on pressure and temperature for the formation of the spinels and lherzolite xenolith occurring within the andesite lavas,it can be seen that tholeiitic magmas were formed at the depth of about 40km or more,while xenolith-bearing basaltic rocks were formed at the depth of about 70-100 Km.These results indicate that the primary basaltic magma may have resulted from partial melting of the upper mantle materials.
作者
赵大升
肖增岳
王艺芬
Zhao Dasheng;Xiao Zhengyue;Wang Yiten(Institute of Geology,Academia Sinica)
出处
《地质学报》
1983年第2期128-141,共14页
Acta Geologica Sinica
