Structural geology of Torlesse rocks, Otaki Forks, Tararua Range, New Zealand

Abstract

Complexly deformed Torlesse terrane lithologies of Otaki Forks, North Island, New Zealand, are dominated by very thick bedded sandstone, thinly alternating sandstone and argillite, very thick bedded argillite, with locally important green argillite, rare limestone, and intraformational conglomerate, some of which are Upper Triassic. The strata generally strike north-east-southwest, dipping steeply, but there are significant variations from this trend. The area has been subdivided into geographically bounded structural domains characterised by combinations of the following types of structures: isoclinal folding; “ductile” and “brittle” broken formations; melange; chevron-like folding; pressure solution and veining; striation faulting; open, moderate plunge folding; sinistral and dextral verging, asymmetric, steep plunge folding; and fault brecciation. The structural succession established is: early isoclinal folding, ductile broken formation, chevron-like folding/thrusting, brittle broken formation, veining, striation faulting/folding, sinistral folding, dextral folding, and recent fault brecciation. The Monotis locality at Pukehinau Stream is not within a melange — the structural complexity of this area is largely due to two interfering fold phases.

Keywords:

• structural analysis
• folding
• broken formation
• melange
• striations
• faulting
• Torlesse
• Tararua Range