GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 266-10
Presentation Time: 9:00 AM-6:30 PM


QUINN, Daven P., Division of Geological and Planetary Sciences, California Institute of Technology, Mail Code 170-23, Pasadena, CA 91125 and GROTZINGER, J.P., Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125,

The Zebra Nappe is the lowest allocthonous tectonic unit of the Naukluft Nappe Complex, an outlier of the 650-540 Ma Damara orogeny that consists of carbonate and clastic strata thrust south- and southwestward over the Nama foreland basin. The tectonic units of the nappe complex are Neoproterozoic in depositional age, while orogenesis and foreland-basin deposition span the Precambrian-Cambrian boundary. While the lithology of the upper nappes is characteristic of Marinoan cap carbonates, the Zebra Nappe has an uncertain age and affinity. Here we present a regional structural map of the southern Naukluft Nappe complex that clarifies the internal structure of the Zebra Nappe and its structural relationship with the upper members of the nappe complex.

Deformation within the Zebra Nappe is dominantly southwest-vergent, in contrast to the southward-verging structural grain of the supradjacent Pavian and Kudu nappes. The nappe exhibits significant internal shortening accommodated by shearing and imbrication at multiple scales. Dolomites at the base of the nappe are imbricated at ~30 m scale, while the middle strata form z-geometry folds and imbrications with a larger amplitude. The upper strata, dominantly platform-facies dolomites, fold gently over a ~5 km baseline. Shale packages separating these layer-bound domains of deformation are heavily strained. The layer-bound modes of deformation within the Zebra Nappe are consistent with varying rheological properties of the strata. This interpretation significantly differs from that of Hartnady, 1978, which envisions the heavily deformed lower and middle Zebra Nappe as being deposited syntectonically against the advancing toe of the upper Zebra Nappe. This new picture of internal deformation of the Zebra Nappe, along with clarified tectonic elements within the adjacent nappes and para-autochthonous Nama group, will enhance understanding of the emplacement history and possible source of the lower Naukluft Nappe Complex.