Petrology of the composite mafic-felsic plutonic rocks of the Fogo Island Batholith: a window to mafic magma chamber processes and the role of mantle in the petrogenesis of the granitoid rocks

• Main Author: Aydin, Nurdan Sebile
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1995
• Subjects: Tilting; Fogo; Fogo Island; Sandy Cove; Newfoundland
• Online Access: https://research.library.mun.ca/6830/; https://research.library.mun.ca/6830/1/NurdanSebileAydin.pdf; https://research.library.mun.ca/6830/3/NurdanSebileAydin.pdf

Field, petrographic, geochemical, geochronologic (U/Pb) and Nd isotopic studies of the diverse plutonic rocks in the Tilting area, Fogo Island, NE Newfoundland, were carried out to elucidate the relative roles of crust and mantle in the petrogenesis of this example of Siluro-Devonian magmatism in the Appalachian-Caledonide orogen. -- The plutonic rocks of the study area are part of the Fogo Island Batholith (FIB) and display a wide range of fabrics, textures, mineralogies and compositions. Based primarily on field and petrographic characteristics they have been divided into three main suites, these are: the Tilting Layered Suite (TLS) composed of layered ultramafic, mafic and intermediate rocks; the Fogo Suite (FS) dominated by monzogranite with minor amounts of granodiorite; and the Wild-Sandy Cove Suite (W-SCS) containing mainly quartz diorite and diorite with minor amounts of leucogabbronorite, hornblendite and granodiorite. -- The TLS is a composite intrusion and contains four main zones (Zones I-IV). Layering features (physical and chemical) of the suite reflect the complex interaction of several magma chamber processes including magma replenishment with or without subsequent mixing of newly introduced and residual magmas, in situ crystallization, current deposition and postcumulus/subsolidus modifications. Effects and consequences of these processes vary from place to place within the suite. Two distinct magma compositions have been recognized in the TLS (quartz-tholeiitic, Zones I-III and olivine-tholeiitic, Zone IV). The interrelationship between silica-saturated and silica-oversaturated magma types is attributed to differences in pressure of partial melting of the same or similar source material(s). Variation in water pressure and silica activity are significant parameters controlling the sequence of crystallization within the suite. -- The TLS shows slight to strong LREE enrichment relative to HREE and significant negative Nb-anomalies. There is significant εNd variation within the suite from -0.1 to ...