TY - JOUR
T1 - Rock-buffered fluid-rock interaction in deformed quartz-rich turbidite sequences, eastern Australia
AU - Gray, David R.
AU - Gregory, Robert T.
AU - Durney, David W.
PY - 1991
Y1 - 1991
N2 - Quartz vein 18O/16O ratios across
a 500 km transect through the Lachlan fold belt of southeastern Australia are
remarkably uniform (±1–1.5 permil) at both local (centimeter to meter) and
regional (over 104 km2) scales. They define isotopic
zones that correlate with the tectonic divisions of the Cambrian through
Devonian (dominantly Ordovician) quartz-rich turbidites determined by regional
mapping. From west to east these divisions are (1) Stawell, δ18O=14.7±1.1
(47 samples); (2) Bendigo-Ballarat, δ18O=17.5±1.3 (204 samples); (3)
Melbourne, δ18O=19.0±1.6 (80 samples); (4) Tabberabbera, δ18O=16.3±1.9
(12 samples); and (5) Omeo, δ18O=14.4±1.0 (26 samples). Isotope
profiles across zone boundaries, and intrazone fault zones particularly within
the Bendigo-Ballarat zone, show steps indicating abrupt changes across faults
with little or no evidence of fluid mixing within the fault zones. δ18O
values of veins are insensitive to relative age, type of vein, and immediate
host rock lithologies. The δ18O values of coexisting vein and host
rocks show nonequilibrium relationships which can be explained in terms of rock
buffering under conditions of low fluid/rock ratios (water/rock ≪
1). Limited D/H determinations on fluid inclusions fall mainly in the range −70 and −100, with one value as low as
−140. These low deuterium values when considered in the context of
paleolatitude may have been inherited from deutrium-depleted detrital minerals
and do not necessarily require the direct penetration of meteoric fluids to
midcrustal depths. The work suggests that vein formation is possible in regions
where the integrated water/rock (w/r) ratio is very low (w/r ≪
1) as long as a pervasive fluid phase is present. This fluid appears to achieve
a steady state isotopic composition on scales of hundreds of meters, and once a
quasi steady state has been reached, the isotopic compositions of the resultant
quartz veins are rather insensitive to the diachronous and nonisothermal
conditions under which vein growth occurs. Advective cycling of the fluid on
this scale is by episodic dilatancy “pumping” in fracture networks associated
with localized faulting.
AB - Quartz vein 18O/16O ratios across
a 500 km transect through the Lachlan fold belt of southeastern Australia are
remarkably uniform (±1–1.5 permil) at both local (centimeter to meter) and
regional (over 104 km2) scales. They define isotopic
zones that correlate with the tectonic divisions of the Cambrian through
Devonian (dominantly Ordovician) quartz-rich turbidites determined by regional
mapping. From west to east these divisions are (1) Stawell, δ18O=14.7±1.1
(47 samples); (2) Bendigo-Ballarat, δ18O=17.5±1.3 (204 samples); (3)
Melbourne, δ18O=19.0±1.6 (80 samples); (4) Tabberabbera, δ18O=16.3±1.9
(12 samples); and (5) Omeo, δ18O=14.4±1.0 (26 samples). Isotope
profiles across zone boundaries, and intrazone fault zones particularly within
the Bendigo-Ballarat zone, show steps indicating abrupt changes across faults
with little or no evidence of fluid mixing within the fault zones. δ18O
values of veins are insensitive to relative age, type of vein, and immediate
host rock lithologies. The δ18O values of coexisting vein and host
rocks show nonequilibrium relationships which can be explained in terms of rock
buffering under conditions of low fluid/rock ratios (water/rock ≪
1). Limited D/H determinations on fluid inclusions fall mainly in the range −70 and −100, with one value as low as
−140. These low deuterium values when considered in the context of
paleolatitude may have been inherited from deutrium-depleted detrital minerals
and do not necessarily require the direct penetration of meteoric fluids to
midcrustal depths. The work suggests that vein formation is possible in regions
where the integrated water/rock (w/r) ratio is very low (w/r ≪
1) as long as a pervasive fluid phase is present. This fluid appears to achieve
a steady state isotopic composition on scales of hundreds of meters, and once a
quasi steady state has been reached, the isotopic compositions of the resultant
quartz veins are rather insensitive to the diachronous and nonisothermal
conditions under which vein growth occurs. Advective cycling of the fluid on
this scale is by episodic dilatancy “pumping” in fracture networks associated
with localized faulting.
UR - http://www.scopus.com/inward/record.url?scp=0026277972&partnerID=8YFLogxK
U2 - 10.1029/91JB01639
DO - 10.1029/91JB01639
M3 - Article
AN - SCOPUS:0026277972
SN - 0148-0227
VL - 96
SP - 19681
EP - 19704
JO - Journal of Geophysical Research
JF - Journal of Geophysical Research
IS - B12
ER -