RESOLVING "OUTBOARD" EQUATORIAL PERI-GONDWANALAND DURING THE EARLY PALEOZOIC: A HIMALAYAN PERSPECTIVE

The arrangement and evolution of the “outboard” equatorial peri-Gondwanan terranes of Sibumasu (western Yunnan, eastern Burma, Thailand and Malaysia), Indochina (Vietnam), western Burma, and the two southern terranes of Tibet (Lhasa and Qiangtang blocks) during the early Paleozoic is one of the most significant unresolved problems in Phanerozoic paleogeography. The boundaries, relative positions, and timing of accretion of these peri-Gondwanan blocks are very poorly constrained, and the identity of the “hanging” margin to western Australia remains obscure. We approach this problem through a comparative analysis of the detrital zircon spectra, trilobite faunas, and paleoenvironments of Cambrian rocks throughout this region. We are examining whether the Himalayan margin was continuous between the western and eastern Himalayan syntaxes during Cambrian time. While the stratigraphy of the northwestern Himalaya suggests a tectonic event around the time of the Cambro-Ordovician boundary, our data are inconsistent with recent models for this event that include significant thrust-induced subsidence and southward sediment transport. No such C-O event is clear in the Bhutanese Himalaya, where latest Cambrian faunas share affinities with western Yunnan, Thailand, and Vietnam, and may suggest continuity between these regions, and separation from the Indian margin, at this time. Stratigraphic similarities between the northwestern Himalayan margin and the South China Block (SCB) support suggestions that the western margin of the SCB was located close to the Himalaya during the late Neoproterozic and early Cambrian.