Structure and kinematics of the Livingstone Mountains border fault zone, Nyasa (Malawi) Rift, southwestern Tanzania

Walter H. Wheeler, Jeffrey A. Karson

Research output: Contribution to journalArticle

43 Scopus citations

Abstract

Reconnaissance mapping of the Livingstone Mountains border fault zone (LMBFZ) at the northern end of the Nyasa (Malawi) Rift in SW Tanzania constrains the geometry and movement history of this typical rift border fault. The fault is a narrow zone of complex brittle deformation, striking 320°, that overprints and reactivates an older ductile shear zone. Long, straight, NW-trending border fault segments are offset by minor NE-trending faults. These two orthogonal fault sets integrate along strike to produce an overall curved fault trace that is concave towards a major depositional basin in the rift. A typical section through the fault zone shows an E to W progression from gneissic country rock through ductilely deformed country rock, into a zone overprinted by closely spaced fractures and grading into an intensely fractured, massive, flinty, aphanitic mylonite band at the lakeshore. Pseudotachylite veins, probably generated during seismic movement on the border fault, are common within and near the aphanitic mylonite. Slickensides indicate dextral oblique-slip, whereas shear belts and rolled porphyroclasts with complex tails in the older ductile shear zone indicate sub-horizontal sinistral motion. The adjacent rift basin is typical of other East African Rift Basins, and contains at least 4 km of Recent to perhaps Mesozoic sediment. Whereas the minimum net slip on the LMBFZ, in the dominant slickenside direction, is on the order of 10 km, regional geologic considerations suggest that dominantly strike-slip motion preceded the oblique-slip phase that produced the LMBFZ and the adjacent rift basin.

Original languageEnglish (US)
Pages (from-to)393-413
Number of pages21
JournalJournal of African Earth Sciences
Volume8
Issue number2-4
DOIs
StatePublished - 1989
Externally publishedYes

ASJC Scopus subject areas

  • Geology
  • Earth-Surface Processes

Fingerprint Dive into the research topics of 'Structure and kinematics of the Livingstone Mountains border fault zone, Nyasa (Malawi) Rift, southwestern Tanzania'. Together they form a unique fingerprint.

  • Cite this