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

这项研究的目的是量化岩浆分异的数量，这种分异发生在缓慢冷却的侵入玄武岩岩浆片上，是由于晶体糊状压实作用的结果。这种差异以前只是根据薄片的化学变化来假设的。然而，最近发现，在缓慢冷却的玄武岩岩浆结晶的早期，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。这种网络最初形成时，具有随机结构，但在压实过程中它会变形。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，然后将其淬火成玻璃。网络的形状是通过连续切片或CT x射线扫描来测量的。在康涅狄格州厚的霍利奥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，这种模式与通过这种流动的化学变化所显示的模式完全吻合。在目前的研究中，这些相同的技术将应用于一个典型的分异侵入火成岩，即新泽西州的帕利塞斯岩。许多化学研究指出，压实作用是这一阶段重要的分化过程。测量斜长石网络在垂直剖面上的变形程度，将直接表明在其凝固过程中发生了多少压实。如果这些技术能成功应用于帕利塞斯岩，将在大型侵入火成岩分异研究中具有广泛的应用前景。

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.