地质科学
地質科學
지질과학
SCIENTIA GEOLOGICA SINICA
2010年
1期
80-91
,共12页
基性岩墙群%弧形展布%Poly3D软件%应力场扰动
基性巖牆群%弧形展佈%Poly3D軟件%應力場擾動
기성암장군%호형전포%Poly3D연건%응력장우동
Maric dike swarm%Curved distribution%Poly3D software%Stress perturbation
在甘肃北山一个东西向展布、椭圆状的晚古生代花岗岩体内主要发育着3期岩墙群,其中中期基性岩墙群最密集,呈现出弧形展布的特征,在该侵入体北部呈北北东向趋势,向南逐渐偏转为北北西向.关于中期岩墙群弧形展布的原因有两种可能的解释,即:纵弯褶皱和应力场扰动野外观察不支持第一种解释,因为在岩墙或围岩内都没有观察到与褶皱有关的变形构造.本文利用Poly3D软件模拟了近东西向隐伏断层活动对上覆应力场的扰动.计算结果表明,当北北西-南南东向的区域性拉张叠加上沿着隐伏断层发生不协调的右行走滑时,水平大主压应力迹线在隐伏断层上方出现类似的弧形展布.这意味着稍早的花岗岩侵入体冷凝冷却并没有完全焊接地壳内一些大尺度断层,地壳断块的相对独立活动可以造成沿着这些断层发生与区域变形场不协调的右行走向滑动,进而形成岩墙群弧形展布所需要的地应力场.
在甘肅北山一箇東西嚮展佈、橢圓狀的晚古生代花崗巖體內主要髮育著3期巖牆群,其中中期基性巖牆群最密集,呈現齣弧形展佈的特徵,在該侵入體北部呈北北東嚮趨勢,嚮南逐漸偏轉為北北西嚮.關于中期巖牆群弧形展佈的原因有兩種可能的解釋,即:縱彎褶皺和應力場擾動野外觀察不支持第一種解釋,因為在巖牆或圍巖內都沒有觀察到與褶皺有關的變形構造.本文利用Poly3D軟件模擬瞭近東西嚮隱伏斷層活動對上覆應力場的擾動.計算結果錶明,噹北北西-南南東嚮的區域性拉張疊加上沿著隱伏斷層髮生不協調的右行走滑時,水平大主壓應力跡線在隱伏斷層上方齣現類似的弧形展佈.這意味著稍早的花崗巖侵入體冷凝冷卻併沒有完全銲接地殼內一些大呎度斷層,地殼斷塊的相對獨立活動可以造成沿著這些斷層髮生與區域變形場不協調的右行走嚮滑動,進而形成巖牆群弧形展佈所需要的地應力場.
재감숙북산일개동서향전포、타원상적만고생대화강암체내주요발육착3기암장군,기중중기기성암장군최밀집,정현출호형전포적특정,재해침입체북부정북북동향추세,향남축점편전위북북서향.관우중기암장군호형전포적원인유량충가능적해석,즉:종만습추화응력장우동야외관찰불지지제일충해석,인위재암장혹위암내도몰유관찰도여습추유관적변형구조.본문이용Poly3D연건모의료근동서향은복단층활동대상복응력장적우동.계산결과표명,당북북서-남남동향적구역성랍장첩가상연착은복단층발생불협조적우행주활시,수평대주압응력적선재은복단층상방출현유사적호형전포.저의미착초조적화강암침입체냉응냉각병몰유완전한접지각내일사대척도단층,지각단괴적상대독립활동가이조성연착저사단층발생여구역변형장불협조적우행주향활동,진이형성암장군호형전포소수요적지응력장.
Within an elliptical,W-E trending Hercynian granitoid in the Northern Mountain,northwestern Gansu Province three main sets of dike swarms were recognized.The second set has a majority of dikes throughout the granitoid.It is mafic in composition,and distributed in a curved pattern.The dike swarm in the set changes the strike gradually from the north-northeast in the north to the north-northwest in the south.This curved pattern may be ascribed to two possible mechanisms,multi-layer buckling and local stress-field perturbation.The former mechanism seems inappropriate,depending upon the fact that no or almost a few deformational structures related to buckling were observed either in the dikes or their contacts at outcrops.For the latter mechanism,Poly3D numerical software was used in this paper to study the influence in the local stress-field perturbation of a presumably hidden,reactivated fault beneath the granitoid.Numerical results show that,under the NNW to SSE extension in the region,a large amount of discordant dextral strike slip along the hidden fault is required to produce a similar map of the curved trajectory of the larger horizontal stress above.This suggests the incomplete welding of the sides of the fault by the granitic intrusion along it,which afterwards permitted the reactivation of the fault,probably due to the relatively independent movement of the faulted blocks,as a dextral transcurrent fault.
