Geoscience Reference
In-Depth Information
Fig. 26.3
Continental heat
flow data
.
Average
Continent
Number
4405
Archean
Craton
510
Stable
Platform
290
Tecton
Continent
326
0
20
40
60
80
100
120
140
m
2
)
Heat flow (mW
/
to be noise (erosion, tectonomagmatic heating)
while it is the main signal in oceanic areas
(the plate creation process itself). Histograms
of heat flow data are far from Gaussian (Fig-
ure 26.3) so median values are often tabulated.
The uncorrected continental and oceanic heat
flow histograms have similar means and medi-
ans. Nevertheless, the mean heat flux through
the seafloor may be substantially higher than
that through continents. It may be just coin-
cidental that the most frequent values and
means of the two datasets are so close to each
other.
The non-uniform spatial distributions of both
continental and oceanic data are partly the
result of an emphasis on geothermally active and
other anomalous areas, and sedimentary basins.
The continental histogram is more peaked than
the oceanic one. This is expected if vigorous
hydrothermal circulation occurs on the seafloor.
Histogram comparisons can be misleading. Data
are often edited to eliminate unusual environ-
ments, or to force agreement with some the-
oretical expectation. This is quite common in
geochemistry; the impressive chemical unifor-
mity of MORB is partially the result of avoiding
anomalous
areas, and removing data thought to
be influenced by plumes. Oceanic heat flow and
bathymetry is likewise biased by ignoring or elim-
inating data thought to be influenced by
hotspots
.
Unbiased sampling of a heterogenous population
requires that sampling be as uniform as possi-
ble in order that statistics can be done. One can-
not test a hypothesis if a hypothesis was used
to select and prune the data. Means and stan-
dard deviations have no meaning if a hypothesis-
dependent filtering of the data has taken place
prior to the application of the statistics. In spite
of data processing and data selection, regions
that have been designated as hotspots appear not
