Measurement of Crystal Mush Compaction in the Palisades Sill, NJ, Using Serial Sections and X-Ray CT Scans of Partly Melted Oriented Samples

9902890这项研究的目标是量化由于晶体碎屑压实而在缓慢冷却的侵入玄武岩岩浆片中发生的岩浆分异程度。在此之前，这种区分仅仅是基于薄片之间的化学变化而提出的。然而，最近发现，在缓慢冷却的玄武岩岩浆结晶早期，斜长石晶体聚集在一起形成连续的三维网络，这为直接测量已经发生的压实量提供了一种手段。这种网络在最初形成时具有随机的结构，但在压缩过程中可能会变形。变形网络的形状最容易在先部分熔化的样品中测量，以便将后期结晶的矿物转化为液体，然后液体可以淬火成玻璃。网络的形状是在连续切片或CT X射线扫描中测量的。在康涅狄格州厚厚的霍利约克洪水玄武岩中进行的这种测量揭示了一种压实和膨胀的模式，这种模式与流经该流动的化学变化所指示的模式完全匹配。在目前的研究中，这些相同的技术将被应用于典型的差异化侵入火成岩，新泽西州的Palisade Sill。大量的化学研究表明，压实作用是这个岩床的一个重要的分异过程。通过测量斜长岩网络在垂直剖面中的变形程度，将直接表明在其凝固过程中发生了多少压实作用。如果这些技术能够成功地应用于栅栏地台，它们在大型侵入型火成岩的分异研究中可能会有广泛的应用。

9902890PhilpottsThe goal of this research is to quantify the amount of magmatic differentiation that takes place in a slowly cooled sheet of intrusive basaltic magma as a result of crystal mush compaction. Such differentiation has previously been hypothesized only on the basis of chemical variations through sheets. However, the recent discovery that plagioclase crystals cluster together to form a continuous 3-D network early in the crystallization of slowly cooled basaltic magma provides a means of measuring directly the amount of compaction that has occurred. This network, when initially formed, has a random fabric, but during compaction it can become deformed. The shape of the deformed network is most easily measured in samples that have first been partly melted so as to convert late crystallizing minerals to liquid, which can then be quenched to glass. The shape of the network is measured in serial sections or in CT X-ray scans. Such measurements in the thick Holyoke flood basalt of Connecticut have revealed a pattern of compaction and dilation that matches exactly the pattern indicated by the chemical variation through this flow. In the present research, these same techniques will be applied to a classic differentiated intrusive igneous body, the Palisades Sill of New Jersey. Numerous chemical studies have pointed to compaction having been an important differentiation process in this sill. Measurements of the degree of deformation of the plagioclase network in a vertical section through this sill will indicate directly how much compaction took place during its solidification. If these techniques can be applied successfully to the Palisades Sill, they may have wide application in the study of the differentiation of larger intrusive igneous bodies.