SilMush: A procedure for modeling of the geochemical evolution of silicic magmas and granitic rocks

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• 作者：Jan Hertogen ; ^{jan.hertogen@kuleuven.be" class="auth_mail" title="E-mail the corresponding author} ; Joyce Mareels¹ ; ^{joyce.mareels@redco.be" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Silicic magma ; Crystallization modeling ; Granite geochemistry ; Lanthanides ; Vosges Massif
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2016
• 出版时间：15 July 2016
• 年：2016
• 卷：185
• 期：Complete
• 页码：498-527
• 全文大小：4039 K

文摘

A boundary layer crystallization modeling program is presented that specifically addresses the chemical fractionation in silicic magma systems and the solidification of plutonic bodies. The model is a Langmuir (1989) type approach and does not invoke crystal settling in high-viscosity silicic melts. The primary aim is to model a granitic rock as a congealed crystal-liquid mush, and to integrate major element and trace element modeling. The procedure allows for some exploratory investigation of the exsolution of H₂O-fluids and of the fluid/melt partitioning of trace elements. The procedure is implemented as a collection of subroutines for the MS Excel spreadsheet environment and is coded in the Visual Basic for Applications (VBA) language. To increase the flexibility of the modeling, the procedure is based on discrete numeric process simulation rather than on solution of continuous differential equations. The program is applied to a study of the geochemical variation within and among three granitic units (Senones, Natzwiller, Kagenfels) from the Variscan Northern Vosges Massif, France. The three units cover the compositional range from monzogranite, over syenogranite to alkali-feldspar granite. An extensive set of new major element and trace element data is presented. Special attention is paid to the essential role of accessory minerals in the fractionation of the Rare Earth Elements. The crystallization model is able to reproduce the essential major and trace element variation trends in the data sets of the three separate granitic plutons. The Kagenfels alkali-feldspar leucogranite couples very limited variation in major element composition to a considerable and complex variation of trace elements. The modeling results can serve as a guide for the reconstruction of the emplacement sequence of petrographically distinct units. Although the modeling procedure essentially deals with geochemical fractionation within a single pluton, the modeling results bring up a number of questions about the petrogenetic relationships among parental magmas of nearly coeval granitic units emplaced in close proximity.