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in equilibrium with haf zburgite. OPXT 1 and LAL cunccvrcseene . but in
disequil ibrium wit h dunite . Conseque ntly. as the 5i-satu rated flu id passed from
harzburgite. OPXT I or l Al cnnocvrexeone into dunite , it reacted with olivine
to lorm pyroxene (reaction R5.2):
IR5.2J 0 1 + 5i-saturated Fluid .... Px + 5i-undersaturated Fluid
Fluid in equilibr ium with ha rzburgile and OPXT I reacted to form OPXT II.
Cfinopv rcxenite in webstennc veins associated with OPXT II, indicate thai the
fluid was in equilibrium w ith LAL c linopyroxeni18. The scarc ity of clinopyroxene
associated with OPXT II. agrees with the fie ld evidence that LAL
cuoccvrcxeone was a relatively minor reactant with respect to harlbu rgite and
OPXT I. Such an origin for OPXT II is similar to the hyd rothermal production
of pyroxene according to Bowen and Tutt le (19491. In keeping with their
model , OPXT II does not extend into the HALPPG, wh ich are the source of
fluid .
Similar ffuld-rock interactions havebeen documented in other localit ies.
A classic example are the pvrcxemte-amptnbchta layers in the Seiad cco-ciex.
California, which have a hydrothermal origin (Loomis and Gottschalk , 1981).
1 nese authors stated that as a fluid equilibrates with peridot ite, the
hyd rothermal cvroxeoe s that precipitate wi ll be similar in composi tion to those
in the pencctite. The OPXT II have the modal compositio n 01 harzburg ite,
when considered as a bulk sample with thei r dunite host, ar,,j have mineral
chem istry andCNPGE patter ns sim ilar to harzburgite . These feat ures are proof
that OPXT II precipitated from flui d that was in equilibrium with harzburgite .