The Wild Bight Group, Newfoundland Appalachians : a composite Early to Middle-Ordovician ensimatic arc and continental margin arc-arc rift basin

• Main Author: MacLachlan, Kate
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1998
• Subjects: Wild Bight; Newfoundland
• Online Access: https://research.library.mun.ca/7191/; https://research.library.mun.ca/7191/1/MacLachlan_Kate.pdf; https://research.library.mun.ca/7191/3/MacLachlan_Kate.pdf

The Wild Bight Group (WBG) and South Lake Igneous Complex (SLIC) represent a peri-Gondwanan Ordovician accreted oceanic terrane of the central Newfoundland Appalachians. The Wild Bight Group is a sequence of volcanic and volcaniclastic rocks, and the South Lake igneous complex is comprised of layered gabbro and sheeted dykes intruded by hornblende diorite and tonalite plutons. -- This study involves detailed mapping (~ 1:12,500) in the South Lake igneous complex and adjacent rocks of the eastern Wild Bight Group, combined with petrography, geochemical, and Sm-Nd isotopic studies, and U-Pb geochronology. It shows that there are two temporally and genetically distinct sequences of volcanic, volcaniclastic and sedimentary rocks in the WBG, separated by up to 10 Ma. The older sequence is genetically related to plutonic rocks of the South Lake igneous complex, and these older rock packages have been structurally interleaved with the younger sequence during subsequent deformation. The younger sequence has also been structurally imbricated and does not represent a simple conformable sequence in its present configuration. -- Magmatic rocks related to the older sequence of the WBG formed predominantly between 486 +/-4 and 489 +/-3 Ma (Tremadoc to early Arenig), and range in composition from normal island arc tholeiitic basalt (IATs), to incompatible element-depleted low-Ti, high-Mg IATs and boninites, and high-Si, low-K rhyolite/tonalite. They are interpreted to represent the initiation and stabilization of a primitive ensimatic oceanic arc. Sm-Nd isotope systematics in the depleted IATs and boninites, show an apparent decoupling of isotopic and geochemical characteristics, which require a complex source or melt generation process for these rocks. The geochemical, isotopic and field relationships in the older volcanic sequence and SLIC provide some insight into tectonomagmatic processes in volcanic arcs in general. -- The younger sequence of the Wild Bight Group comprises two volcanic successions which are ...