Abstract

Detailed 3D seismic images of a volcano-plutonic complex offshore northwestern New Zealand indicate the intrusive complex lies in a relay zone between NE-trending en echelon normal faults. A series of high angle normal faults fan out from the margin of the Southern Intrusive Complex and cut the folded strata along the margin. These faults terminate against the margins of the intrusion, extend as much as 1 pluton diameter away from the margin, and then merge with regional faults that are part of the Northern Taranaki Graben. Offset along these faults is on the order of 10s to over 100 meters. Strata on top of the complex are thinned and deformed into a faulted dome with an amplitude of about 0.7 km. Steep dip-slip faults form a semi-radial pattern in the roof rocks, but are strongly controlled by the regional stress field as many of the faults are sub-parallel to those that form the Northern Taranaki Graben. The longest roof faults are about the same length as the diameter of the pluton and cut through approximately 0.7 km of overlying strata. Fault offset gradually diminishes vertically away from the top of the intrusion. The Southern Intrusive Complex is a composite intrusion and formed from multiple steep-sided intrusions as evidenced by the complex margins and multiple apophyses. Small sills are apparent along the margins and near the roof of the Southern complex. Multiple episodes of deformation are also indicated by a series of unconformities in the sedimentary strata around the complex. Two large igneous bodies make up the composite intrusion as evidenced by the GeoAnomaly body detection tool. The Southern Intrusive Complex has a resolvable volume of 277 km3. Room for the complex was made by multiple space-making mechanisms. Roof uplift created ~3% of the space needed. Compaction/porosity loss is estimated to have contributed 20-40% of the space needed. Assimilation may have created ~0-30% space. Extension played a major role in creating the space needed and is estimated to have created a minimum of 33% of the space. Floor subsidence and stoping may have occurred, but are not resolvable in the seismic survey.

Degree

College and Department

Physical and Mathematical Sciences; Geological Sciences

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