Open AccessMultigenetic gravity couple across a modern convergent margin: inheritance from Cretaceous asymmetric extension
Author(s) -
Kamp Peter J. J.,
Hegarty Kerry A.
Publication year - 1989
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.1989.tb05248.x
Subject(s) - geology , bouguer anomaly , forearc , cretaceous , gravity anomaly , subduction , paleontology , denudation , passive margin , cenozoic , continental margin , thinning , crust , convergent boundary , crustal recycling , continental crust , plate tectonics , tectonics , oceanic crust , rift , biology , ecology , structural basin , oil field
SUMMARY Profiles of the pronounced gravity couple associated with the Puysegur margin in New Zealand suggest that the crust of the Fiordland block, which occupies the leading edge of the overriding Pacific plate, thins rapidly trenchwards and is domed upwards. The crust beneath parts of central western Fiordland appears to be anomalously thin (10 km) and causes a major (180 mgal) positive anomaly in the forearc region. The density contrast caused by subduction of the Australia plate to upper‐mantle depths contributes little to this positive Bouguer anomaly. The radical crustal thinning cannot have originated chiefly by differential uplift coupled with erosion in response to late Cenozoic convergence, as proposed earlier by others; the amount of crustal thinning required is not consistent with the limited volume of sediment in surrounding basins. Moreover, the timing of thinning is chiefly Cretaceous, not late Cenozoic. An alternative hypothesis of tectonic denudation is invoked that attributes the crustal structure of Fiordland to Cretaceous (‐early Tertiary) asymmetric continental extension and consequent crustal thinning. Because the present crustal structure retains inherited geometry from Cretaceous tectonism, the observed positive gravity anomaly over Fiordland is not due solely to the modern plate convergence, but reflects the earlier extension, and hence the gravity couple is multigenetic.