13.8 Special Methods and Processes in Diagenesis
SEA FLOOR
a PRESS URE . STRENGTH
f
I
I
I
I
I
SOFT
SEDI.MENTS
I
I
lITHOSTATIC
\
PRESSURE OF
\
SEDIMENT
\ ----------------+-~
MAGMA
I
~\ PRESSURE I
\\
RANGE
,\
OF SILL
\ \
INJECTON
\ '--_
I
\ --- ______ t. __
\
--\
-----,
\
--~ --TEN SI LE-- "" __
MAGMA
STRENGTH
DEPTH
OF SEDIMENT
lITHIFIED
LAYER
c
SAND -MUD
HYDROTHERMAL
TURBIDITES
DEPOSITS
PRECOMPACTED
BY OLDER SILL
Fig. 13.31. Basaltic sill-induced expulsion of pore
water and hydrothennal deposits in young, Gulf of
Califomia-type spreading center. a Emplacement of
sill in soft sediment. The magma pressure has to
overcome the lithostatic pressure and tensile strength
of the sediment. b Porosity-depth curves of sill-affected sediments in the Guaymas Basin (DSDP, Leg
64)_ The hatched areas signify sill-induced reduction
of porosity_ Older, more deeply buried sills are associated with lower values of heat flow (HFU), because
E
I
ln.
w
o
b
POROSITY (%)
100
200
300
I
I
j lL :1
':::::::::::' IGRADE : •
!;:::::::::::l iMETA- ..
I : lMORPHISM
:...
DISSOLVED
MICRO-FOSSIL
MEASURED
POROSITY
POROSITY CURVE
NOT AFFECTED
BY SILLS
HOLE 477 A 477
481 A
478 HFU
?
20 4
2. 9 ~
DECREASING HEAT FLOW
INCREASING AGE OF UPPERMOST SILL
d
SPREADING TROUGH
SILL-SEDIMENT COMPLEX
1 0
-ft..r.c~.~llilii1I!I~~20 :J
""
30m
30 i
10
+-H-+
NORMAL
DIKES
~
1111111
40 ka
LOW
GRADE
METAMORPH
703
SPREADING CENTER
40 ka
FEEDER DIKE OF
GREAT MAGMATIC
PULSE
sill-induced thennal anomaly dissipates with time.
c Model of successive sill intrusions and expulsion
of pore water from neighboring sediments. Hot water
migrates along sand layers and growth faults and may
deposit minerals on the sea floor. d Buildup of sillsediment complex on top of sheeted dike zone as a
result of magmatic pulses (1 through 4) in time intervals of about 10 ka; fixed spreading center, halfspreading rate 3 cmla. (Einse1e 1982b, 1986)