STECKLER, MICHAEL S., Lamont-Doherty Geological Observatory, Palisades, NY; GOMAA I. OMAR, University of Pennsylvania, Philadelphia, PA; GARRY D. KARNER, Lamont-Doherty Geological Observatory, Columbia University, Palisades, NY; and BARRY P. KOHN, La Trobe University, Bundoora, Australia

ABSTRACT: Pattern of Hydrothermal Circulation within the Newark Basin from Fission-Track Analysis

The Newark basin is an asymmetric extensional half-graben of late Triassic-early Jurassic age. Zircon and apatite fission-track data from the Newark rift basin and the surrounding basement reveals overprinting and resetting to approx. 180 Ma and approx. 140-150 Ma, respectively (i.e. younger than the age of the sediments). However, along the border fault of the basin, fission-track ages exhibit a broader range of ages that includes partially reset samples. The contrast between grains that were heated to >225 +/- 50 degrees C and grains that were never heated above 120 +/- 20 degrees C over a 5-10 km wide zone of gently dipping sediments indicates the presence of down-welling water as part of a hydrothermal convection system near the border faults. These fission-track results, toget er with patterns of organic maturation, precipitation of iron cements and hydrothermal minerals, paleomagnetic overprints, fluid inclusions, and base metal mineralization all attest to the existence of relatively high temperature (100-250 degrees C) hydrothermal fluids throughout the basin during and after rifting. Thus, we interpret the thermal overprinting and mineralization as due primarily to the effects of a pervasive hydrothermal flow during the Jurassic. This fluid convection within the basin may be the consequence of the high topography bordering the Newark basin. Hydrothermal flow should have ended by the time Lower Cretaceous marine coastal plain sediments covered the basin.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.