The possible contribution of circumferential fault intrusion to caldera resurgence
The possible contribution of circumferential fault intrusion to caldera resurgence
复制标题
环向断层侵入对火山口复苏的可能贡献
DOI：
10.1007/s00445-004-0360-z
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发表时间：
2004
影响因子：
3.5
通讯作者：
S. Saunders
中科院分区：
文献类型：
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作者：
S. Saunders
在地质记录中，经常观察到大量岩浆侵入环向断层和环形断裂。有限元建模在这里被用来调查应变场，可能是预期从这样的侵入事件。两个简单的垂直场景进行了探讨，一个是一个破火山口的中心块的厚度与直径比为1：1（类似拉包尔），一个比远小于1：1（类似于“山谷型”）。在这两种情况下的表面变形是类似的中央隆起，护城河（或槽）一样的功能的发展外的交叉点的方位角的侵入环断层和自由表面，和更广泛的规模膨胀在规模上几倍于破火山口的半径。然而，两种情况下块体和次破火山口岩浆房的反应是不同的。这些块体实际上受到挤压;高纵横比的块体在表面向上变形，在底部向下变形，而低纵横比的块体则在破火山口块体的中心部分向上变形（或弯曲）。当环形断裂系统或环向断层只有一个短弧侵入时，仍会发生中央隆起。在这两种模型中，单环形岩墙侵入造成的破火山口中心的膨胀只能解释分米到米的表面抬升。然而，数十万年到数十万年的反复入侵可能会导致火山口块逐渐隆起，从而导致更大规模的复兴特征。由于挤压高纵横比块体而可能产生的上提量是有限的。然而，有人建议，在弯曲的板状块体发生以上的减压和/或韧性岩浆体，环断层侵入可能是一个重要的贡献者复苏。在这里显示的简单概念模型中，环形岩墙引起的中央隆起量将大于环形复合体宽度的40 - 50%。在地质记录中，侵入到一些环形断裂中的侵入物的积累导致了数百米至数千米厚的环形或弧形岩体。在某些破火山口，这种侵入体可能控制着由破火山口断层限定的限制区域内明显集中的隆起。与入侵的环形和弧形岩墙的水平位移的复杂性也进行了探讨。侵入环形断裂带往往发生在环形带的那些垂直于最小压应力矢量的扇区。这可能是一个因素，在拉伸和挤压地区的破火山口演化观察到的差异。在几个现代破火山口的动荡是暂时有关的环断层侵入。
In the geological record, the intrusion of substantial amounts of magma into circumferential faults and ring fractures is commonly observed. Finite element modelling is used here to investigate the strain field that may be expected from such intrusive events. Two simple vertical scenarios are explored, one for a caldera with a central block of thickness to diameter ratio of ~1:1 (similar to Rabaul) and one with a ratio much less than 1:1 (similar to the ‘Valles type’). Surface deformation in both cases is similar with central uplift, the development of a moat (or trough) like feature just outside of the intersection of the azimuth of the intruded ring fault and the free surface, and broader scale tumescence at a scale several times larger than the caldera’s radius. The response of the block and sub-caldera magma chamber for the two scenarios, however, is different. The blocks are in effect squeezed; the high aspect ratio one deforms upwards at the surface and downwards at its base, whereas the low aspect ration one experiences up arching (or bending) of the central part of the caldera block. Central uplift still occurs when only a short arc of a ring fracture system or a circumferential fault is intruded. In both models, tumescence in the centre of the caldera from single ring dyke intrusion can only account for decimetres to metres of surface uplift. Repeated intrusions over tens to hundreds of thousands of years, however, may cause incremental up doming of the caldera block leading to larger scale resurgent features. The amount of uplift possible due to squeezing of a high aspect ratio block is limited. It is proposed, however, that where bending of plate-like blocks occur above a decompressible and/or malleable magma body, ring fault intrusion may be a significant contributor to resurgence. In the simple conceptual models shown here, the amount of ring dyke-induced central uplift will be >40–50% of the width of the ring complex. In the geological record the accumulation of intrusions into some ring fractures has led to annular or arcuate plutons of hundreds of meters to several kilometres in thickness. At certain calderas such intrusions may be a control on the marked concentration of uplift within the restricted area defined by the caldera faults. The complex nature of the horizontal displacements associated with the intrusion of ring and arcuate dykes is also explored. Intrusion into ring fracture zones will tend to take place into those sectors of the annular zone which are perpendicular to the least compressive stress vector. This may be a factor in the observed difference for caldera evolution in extensional and compressional areas. The unrest at several modern calderas is tentatively related to circumferential fault intrusion.