ABSTRACT
Fission-track data obtained on apatite grains from
Early Cretaceous sequences from Ocean Drilling Program
Leg 159 drill sites and from deep dives sampling along
the Côte d’Ivoire-Ghana Marginal Ridge have been
used to assess the thermal history of the Côte
d’Ivoire-Ghana Transform Margin.
Measurements demonstrate that all the apatite grains were
heated above 120°C and cooled quickly during the
Cretaceous. Apatite fission-track dating are distributed
into three groups:
1. A group, characterized by ages ranging ~110 Ma, has
been only observed on Leg 159 samples. These apatites
were found either in the deepest drilled strata, which
were heated above 120°C as also indicated by
hydrothermalism evidences, or in Upper Cretaceous dated
strata. In the second case, the apatites are obviously
reworked. We believe that the thermal event, postdated by
the 110-Ma cooling age, would have been generated by
mechanical frictions along an intracontinental transform,
active between the African and Brazilian parting
basement. The Lower Cretaceous heated formations would
subsequently have been locally eroded, to the south
and/or the west of the Leg 159 sites. The eroded and
reworked material, including 110-Ma apatite grains, would
have been then redeposited within the Upper Cretaceous
sediments.
2. A group of samples, whose ages are centered ~90 Ma,
characterize both drilled sediments and slope outcrops.
We tentatively explain this new thermal event by a second
discontinuous hydrothermal episode, which may have
occurred up to Turonian times, along the
southward-shifted active transform.
3. Cooling ages between 80 and 70 Ma, apparently
restricted within the central and western part of the
Côte d’Ivoire-Ghana Marginal Ridge, may postdate a
new localized heating, which we tentatively interpret as
a consequence of a contact between the transform margin
and a southern passing oceanic accretionary center.
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1Mascle, J., Lohmann, G.P., and
Moullade, M. (Eds.), 1998. Proc. ODP, Sci. Results,
159: College Station, TX (Ocean Drilling Program).
2UPRES-A5025 CNRS Laboratoire de
Géodynamique des Chaînes Alpines, Université de
Grenoble-I, 15 rue Gignoux, F38031 Grenoble Cedex,
France. bouillin@ujf-grenoble.fr
3Geosciences-Azur, Laboratoire de
Geodynamique sous-marine, BP 48, F06230
Villefranche/Mer, France.
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