geodynamically more straightforward
than large-scale, wholesale continental
Douwe J. J. van Hinsbergen
*, Peter C. Lippert
and Wentao Huang
Department of Earth Sciences, Utrecht University,
Utrecht, e Netherlands.
Department of Geology
& Geophysics, University of Utah, Salt Lake City,
Department of Geosciences, University of
Arizona, Tucson, AZ, USA.
Published online: 1 December 2017
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NaturE GEosciENcE | VOL 10 | DECEMBER 2017 | 878–880 | www.nature.com/naturegeoscience
© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
Reply to ‘Unfeasible subduction?’
Rowley and Ingalls reply — The physics
of subduction is dictated by the relative
densities of crustal materials to the density
of the asthenosphere. Crust that has
undergone eclogite facies metamorphism
has densities exceeding those of the
asthenosphere and is continuously
subductable. This physical mechanism
could account for the loss of crust in the
India–Asia collision, and is supported by
tomographic images that are interpreted to
reveal a thick (about 19 km, approximately
half the thickness of the incoming Indian
crust) layer of eclogitized lower crust
subducted into the mantle beneath the
Himalaya during only the last 10 million years
or less of convergence
southern Tibet has been elevated (more than
4 km) since at least 55 million years ago. This
equates to more than 60-km-thick continental
crust, sufficient to support continuous
production of eclogites within the Himalayan
core — and beneath at least southern
Tibet — throughout the orogen’s collision
history. This source of negative buoyancy
could contribute to ongoing post-collisional
convergence between India and Asia.
Eclogites in Tso Morari
and Kaghan Valley
demonstrate that upper-crustal eclogites were
produced during early collision. The fraction
of exhumed relative to subducted upper
crustal eclogite is unknown. It is possible
that considerable volumes of upper-crustal
eclogites were permanently subducted into
the mantle during rapid convergence (more
than 150 km per million years) early in the
collision. This has yet to be constrained by
In our mass-balance calculations, we cite
an erosional volume of 5± 1× 10
the India–Asia collision. Virtually all of this
material derives from upper-crustal sources.
This volume is equivalent to about 1,400 ±
300 km of upper-crustal convergence, if it
is partitioned over a domain with a width
of about 2,000 km and thickness of 18 km.
About 1,400 km of upper-crustal convergence
— plus the approximately 1,000 km of
shortening reconstructed from preserved
structures within the Himalayas
to a total upper-crustal shortening of about
2,400 km. Subduction of the corresponding
eclogitized lower crust thus yields a reasonable
mass balance of this system.
Regarding differences in magnetic
anomaly patterns north and south of the
Wallaby Fracture Zone, it has long been
recognized that the opening history of
basins off the west coast of Australia is
complicated. Several ridge jumps occurred in
this region throughout the Cretaceous
Supplementary Section 1). This variability is
responsible for the differences in magnetic
anomaly data that van Hinsbergen and
colleagues cite as evidence against our
interpretation. Furthermore, the magnetic
anomalies and early mid-ocean ridge
spreading in this region are well modelled
with only two plates — Greater India and
Neo-Tethys to the west and Australia to the
east — just as we argued.
The proposal of an oceanic Greater
was based on palaeomagnetic
data that have since been dismissed
There is also no geological evidence
supporting this hypothesis. Early Cretaceous
palaeomagnetic data used to infer a limited
palaeogeographic source region, within
about 800 km of cratonic India, all came
from the southernmost edge of the Tethyan
Himalaya; the most proximal part. These
data cannot constrain the northern margin
of Greater India during the Cretaceous or at
any younger time, and have no bearing on
the hypothetical Greater Indian Basin.
In their comment, van Hinsbergen
and colleagues mischaracterize existing
provenance arguments (see Supplementary
Section 2). Indeed, provenance data have
been used to argue against the Greater
Indian Basin hypothesis. Detrital zircon
data from Eocene clastics of the Lesser
Himalaya indicate a Tethyan Himalayan
. These data are incompatible with
the Greater Indian Basin hypothesis, which
suggests the Lesser Himalaya would have
been separated from Tethyan Himalayan
sources by an approximately 2,600-km-wide
ocean basin in the mid-Eocene. Plus, the
ophiolites of central Pakistan were obducted
by the Palaeocene
and buried by the early
, so cannot be the source of early-
to-middle Eocene ophiolitic detritus.
Finally, we note that although there is
no accretionary prism along the Andean
margin of South America despite thousands
of kilometres of subduction, the record of
Andean arc magmatism is the hallmark of
this history. The absence of a subduction-
associated magmatic record places the
putative Greater Indian Basin in stark
contrast with the geologic history of South
America. In our view, there is a growing
body of data that increasingly support
our interpretation involving an expansive
Greater India and large-scale subduction
of mostly lower continental crust into the
mantle during the India–Asia collision. ❐
* and Miquela Ingalls
Department of the Geophysical Sciences,
e University of Chicago, Chicago, IL, USA.
Department of Geological Sciences, University of
Colorado, Boulder, CO, USA.
Published online: 1 December 2017
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