Environmental Engineering Reference
In-Depth Information
4
High-precision U
Pb geochronology of Phanerozoic
large igneous provinces
-
seth d. burgess, terrence j. blackburn and samuel a. bowring
4.1 Introduction
Large igneous provinces (LIPs) are characterized by the intrusion and eruption of
large volumes (
>
1km
3
) of primarily basaltic magmas into and onto Earth
'
s crust and
they re
ect large-scale melting of the mantle in both continental and oceanic settings
(Bryan and Ernst,
2008
). The distribution of LIPs in space and time is used to
speculate on the role that observed deep mantle structures may play in magmatism
(e.g. Burke,
2011
) and LIPs featuring large-scale dike swarms are used in continental
reconstructions (e.g. Ernst
et al
.,
2013
). While their origin is still debated, there has
been a focus on the potential link between LIP magmatism, global environmental
perturbations such as ocean anoxia, and mass extinctions (e.g. Wignall,
2005
). Even
when a temporal correlation exists, the details of how magmatism drives environ-
mental stress and extinction remain difficult to evaluate for two major reasons. First,
the domains where LIPs are emplaced, erupted and exposed are often geographically
disparate from the stratigraphic sections where variations in marine chemistry and
biology are documented, requiring high-fidelity stratigraphic proxies in order to
correlate between sections. Second, geochronological data from LIPs generally lack
the precision needed to evaluate cause and effect at the sub-millennial time-scales
over which oceanographic and climate changes occur.
Studies of the major mass extinctions have revealed that in many cases the
extinction interval is extremely short-lived (durations on the order of thousands of
years) (e.g. Renne
et al
.,
2013
; Burgess
et al
.,
2014
) but that the recovery interval is
protracted (e.g. 0.5
-
5 Ma; e.g. D
Hondt,
2005
; Fraiser and Bottjer,
2007
;Ramezani
et al
.,
2007
; Chen and Benton,
2012
;Renne
et al
.,
2013
), and more dif
'
cult to
constrain. Radioisotopic geochronology and astrochronology are the best tools for
establishing the age and duration of biotic crises and recovery, allowing comparison
