CAJ | 학술논문

山东临朐-昌乐地区新生代岩浆活动强烈,以形成含大量地幔包体的玄武岩为特征.作者在考察与研究昌乐北岩古火山口玄武岩中地幔包体的过程中,发现一些包体中发育有地幔钾交代成因的金云母细脉.鉴于金云母的封闭温度远低于玄武岩浆喷发时的温度以及金云母可以记录喷发的玄武岩浆冷却通过金云母封闭温度的时间,本文尝试通过金云母所记录的~(40)Ar/~(39)Ar年龄来推断玄武岩浆喷溢的结束时间.该火山口玄武岩不同部位的三个地幔岩包体其金云母的~(40)Ar/~(39)Ar坪年龄分别为18.42±0.21Ma、18.65±0.27Ma和18.39±0.36Ma,年龄结果具有很好的一致性,充分说明了该定年手段的有效性.因此可以确定该火山口玄武岩浆喷溢活动约在18.5Ma前结束.由此推测山旺盆地中不整合发育在源于该火山口喷溢的玄武岩之上的化石群的形成时代下限约为18.5Ma.用玄武岩地幔包体金云母的~(40)Ar/~(39)Ar年龄来确定玄武岩年龄是玄武岩定年一个有效的新方法.
산동림구-창악지구신생대암장활동강렬,이형성함대량지만포체적현무암위특정.작자재고찰여연구창악북암고화산구현무암중지만포체적과정중,발현일사포체중발육유지만갑교대성인적금운모세맥.감우금운모적봉폐온도원저우현무암장분발시적온도이급금운모가이기록분발적현무암장냉각통과금운모봉폐온도적시간,본문상시통과금운모소기록적~(40)Ar/~(39)Ar년령래추단현무암장분일적결속시간.해화산구현무암불동부위적삼개지만암포체기금운모적~(40)Ar/~(39)Ar평년령분별위18.42±0.21Ma、18.65±0.27Ma화18.39±0.36Ma,년령결과구유흔호적일치성,충분설명료해정년수단적유효성.인차가이학정해화산구현무암장분일활동약재18.5Ma전결속.유차추측산왕분지중불정합발육재원우해화산구분일적현무암지상적화석군적형성시대하한약위18.5Ma.용현무암지만포체금운모적~(40)Ar/~(39)Ar년령래학정현무암년령시현무암정년일개유효적신방법.
Cenozoic basalts in the Linqu-Changle area, Shandong Province, are characterized by abundant mantle-derived xenoliths. Recently, we discovered that some xenoliths in the Beiyan paleovolcanic crater contain some fine phlogopite veins related to mantle K-metasomatism. Since the closure temperature of phlogopite is much lower than the eruptive temperature of basaltic magma and the phlogopite has potential to record the time when hot magma cool down through the closure temperature of phlogopite, here we try to use the ~(40)Ar/~(39)Ar age of phlogopites to determine the ending time of eruption of basaltic magmas and age of basalt in the Beiyan paleovolcanic crater. Three phlogopite samples from three mantle-derived xenoliths from different positions in the Beiyan paleovocanic crater yielded identical ~(40)Ar/~(39)Ar plateau ages of 18.42±0.21Ma, 18.65±0.27Ma and 18.03±0.63Ma respectively. It is concluded that the basaltic volcanic activities in the Beiyan paleovolcanic crater ended before about 18.5Ma. It further suggests that the lacustrine sedimentary rocks containing abundant fossils in the Shanwang Basin unconformably overlying the basaltic rocks from the Beiyan paleovolcanic crater formed later after 18.5Ma. ~(40)Ar/~(39)Ar dating of phlogopites is a new effective method for the dating of basalts containing phlogopite-bearing xenoliths.