TY - JOUR
T1 - The shallow depth emplacement of mafic intrusions on a magma-poor rifted margin
T2 - An example from the Bight Basin, Southern Australia
AU - Reynolds, P.
AU - Holford, S.
AU - Schofield, N.
AU - Ross, A.
N1 - This work comprises a part of the Great Australian Bight Deepwater Marine Program (GABDMP) for funding this project. The GABDMP is a CSIRO research program, sponsored by Chevron Australia the results of which will be made publically available. 3D seismic data was gratefully provided by TGS. Dougal Jerram and Craig Magee are thanked for constructive reviews; Adam Bumby is thanked for editorial handling.
PY - 2017/12
Y1 - 2017/12
N2 - Abstract Three-dimensional (3D) seismic data has provided important insights into how magma is transported and stored in sedimentary basins. Much of our understanding is based on volcanic-rifted margins. In contrast, the magma plumbing systems of magma-poor rifted margins are less well studied. This study uses 3D seismic data to describe the magma plumbing system of the Bight Basin Igneous Complex; a volcanic province located along the magma-poor southern Australian margin. Here, magma emplacement occurred in the Mid Eocene, some 40 million years after the onset of seafloor spreading. Our data images a variety of 30–270 m thick, 2–23 km diameter mafic intrusions that are confined to within 1200 m of the paleoseabed. Intrusions emplaced at ≤200 m depth formed hybrid and compound sills and are typified by elongate, lava flow-like morphologies. Intrusions emplaced at depths of 200–1200 m formed saucer-shaped and compound sills, as well as laccoliths. Approximately 60% of the intrusions have lava flows and volcanogenic vents above their shallowest tips, as shown from previous studies. This suggests that the intrusions played a crucial role in transporting magma to the paleoseabed. Furthermore, many of the intrusions are overlain by forced folds, highlighting the role of magma emplacement in inducing overburden deformation. Contrary to observations from volcanic rifted margins, the sills and laccoliths rarely form interlinked complexes. Instead, they most commonly occur as isolated bodies. This suggests that the sills and laccoliths were fed by dykes. We infer that high rates of magma ascent in the dykes prevented their transition into sills within sediments at >1.2 km depth. Our study highlights that the magma plumbing system of the Bight Basin Igneous Complex contains a diversity of magmatic intrusions, the morphology of which is linked to their emplacement depth, host sediment rheology and the physical properties of the magma. This plumbing system contrasts markedly with those found along better-studied volcanic rifted margins.
AB - Abstract Three-dimensional (3D) seismic data has provided important insights into how magma is transported and stored in sedimentary basins. Much of our understanding is based on volcanic-rifted margins. In contrast, the magma plumbing systems of magma-poor rifted margins are less well studied. This study uses 3D seismic data to describe the magma plumbing system of the Bight Basin Igneous Complex; a volcanic province located along the magma-poor southern Australian margin. Here, magma emplacement occurred in the Mid Eocene, some 40 million years after the onset of seafloor spreading. Our data images a variety of 30–270 m thick, 2–23 km diameter mafic intrusions that are confined to within 1200 m of the paleoseabed. Intrusions emplaced at ≤200 m depth formed hybrid and compound sills and are typified by elongate, lava flow-like morphologies. Intrusions emplaced at depths of 200–1200 m formed saucer-shaped and compound sills, as well as laccoliths. Approximately 60% of the intrusions have lava flows and volcanogenic vents above their shallowest tips, as shown from previous studies. This suggests that the intrusions played a crucial role in transporting magma to the paleoseabed. Furthermore, many of the intrusions are overlain by forced folds, highlighting the role of magma emplacement in inducing overburden deformation. Contrary to observations from volcanic rifted margins, the sills and laccoliths rarely form interlinked complexes. Instead, they most commonly occur as isolated bodies. This suggests that the sills and laccoliths were fed by dykes. We infer that high rates of magma ascent in the dykes prevented their transition into sills within sediments at >1.2 km depth. Our study highlights that the magma plumbing system of the Bight Basin Igneous Complex contains a diversity of magmatic intrusions, the morphology of which is linked to their emplacement depth, host sediment rheology and the physical properties of the magma. This plumbing system contrasts markedly with those found along better-studied volcanic rifted margins.
KW - sill
KW - dyke
KW - laccolith
KW - seismic
KW - Australia
U2 - 10.1016/j.marpetgeo.2017.09.008
DO - 10.1016/j.marpetgeo.2017.09.008
M3 - Article
VL - 88
SP - 605
EP - 616
JO - Marine and Petroleum Geology
JF - Marine and Petroleum Geology
SN - 0264-8172
ER -