雷琼第四纪火山活动的新认识

A NEW APPROACH TO THE QUATERNARY VOLCANICITY IN THE LEIQIONG AREA

本文根据７６个岩石样品的年龄和１０７个钻孔剖面的对比，认为本区第四纪火山活动可分为６期，并具有以喷溢为主、多旋回、从海相向陆相转变的特点。文中以较多的岩石学证据论证了岩浆源地和火山构造环境，同时从板块构造观点论述了雷琼裂谷的发育阶段和火山活动兴衰过程。

The Leiqiong area including Leizhou peninsula and northern pet of Hainan island is all of Quaterany volcanic rocks with an area of 7295. 79 km2 except some outerops of Tertiary. Its area of volcanic rocks is the largest and the number of 177 volcanic cones ranks second among the 9 volcano groups in China. It is also one of the 4 volcano groups which were activated through the Quaternary.Based on the ages of 76 samples of rocks and the comparison of 107 drill hole sections, the volcanicity can be divided into 6 periods as follows; Q￣1(1) (2. 3±0. 72-0. 99 ±0. 49Ma),Q￣2(1) (0. 904±0. 054-0. 76±0. 07Ma), Q￣1(1)(0. 73±0. 312Ma), Q￣2(2) (0. 29±0. 02-0. 133±0. 006Ma), Q￣1(3)(0. 127±0. 02-0. 098Ma) and Q￣3(3)-Q￣1(4)(0. 013±0. 009Ma). The forms of vol-calilcity were both crevice spill and central eruption while the former was common. From 33 sections, total 136 eruption cycles are distinguished, in which the weatherinS and depeitional unconformable boundaries of cycle account for 71 %. It is obvious that the volcanism was intermittsnt.The eruption environment was marine before Q1 and terrestrial after Q2, res respectively. About 71 % of the samples are thoce of tholeiite, and alkaline olivine basalt the next. It shows the tensile tectonic environment and the same resource of magma from upper mantle. The mechanism of volcanicity of rift valley in the Plat6 margin is associated with the relative movement of the threePlates and the spseding of the South China sa. The QUate￣ vol￣ was the continuationOf the Tertiary. There was little vol￣ during Cretaceous and greene in Leiqiong rift valleyfoamal sinal Crabs￣us ￣use of the Pness tectoaic enwtorunent. Since NeoSene the intensivevol￣c eruption co￣ due to the tensile and depression environment related with the spreadingof the South C￣ sa in a farce aam aam the vol￣m reached a magnificent staSe during QZbut gradually ￣e weaker since Qs. Voldricity in iniqiong area i$of a pet of the Mediterranean volCano zone but not the Pacific rim volCano zone.