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The Role of Water in the Magmatic and Tectonic Evolution of Metamorphic Core Complexes: A stable Isotope Study of the Southern Omineca Crystalline Belt, British Columbia, Canada


Holk, Gregory James (1997) The Role of Water in the Magmatic and Tectonic Evolution of Metamorphic Core Complexes: A stable Isotope Study of the Southern Omineca Crystalline Belt, British Columbia, Canada. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/pkn3-p364.


The oxygen isotope data in this study delineate 2 major episodes of water-rock interaction related to the metamorphic, plutonic, and tectonic development of the metamorphic core complexes in the southern Omineca belt. Episode 1 is a Paleocene pre­-extensional metamorphic/magmatic-hydrothermal event. The occurrence of isotopically uniform quartz (δ¹⁸O = 12.5 ± 0.5‰) and feldspar (10.9 ± 0.7‰) throughout different rock types indicates that much of a 6-km-thick section of the mid-crustal Selkirk allochthon underwent internally buffered ¹⁸O/¹⁶O homogenization during Paleocene melting and decompression as it moved up the Monashee decollement thrust ramp. Areas of uniform δ¹⁸O are those with the most leucogranite or those subjected to severe anatexis. Only locally, in the most impermeable (or refractory) zones did 180 exchange among the rocks, leucogranite melts, and aqueous fluids fail to go to completion (i.e., in the deepest parts of the section, in a marble-rich zone, around some thick amphibolites, and in most garnets). Evidence for ¹⁸O/¹⁶O heterogeneity in the protoliths of these rocks is observed in stratigraphically correlative lower-grade units elsewhere in British Columbia, as well as in garnets that coexist with isotopically homogeneous quartz. A model is introduced utilizing water as a petrologic catalyst: fluids evolved during muscovite breakdown and partial melting of pelites produce ¹⁸O/¹⁶O homogenization with only minor influx of external H₂O; this is followed by release of magmatic H₂O from these melts as they crystallize (triggering further melting of adjacent feldspathic assemblages) during and after the ~20 km uplift that occurred in the thrusting event that took place just prior to detachment faulting.

Episode 2 is a series of Eocene synextensional meteoric-hydrothermal events affecting the shallow crust along all of the major detachment faults in the region, and along some parts of the Monashee decollement; these effects were locally enhanced by added heat from some synextensional alkaline intrusions (the Coryell plutons). Very large quartz-feldspar ¹⁸O/¹⁶O disequilibrium effects were imprinted upon the rocks during exchange with hot meteoric waters (initial δ¹⁸O ~ -15); the mineral most affected was feldspar (δ¹⁸O down to -5.0). In the Valhalla core complex, the hanging wall rocks above the Slocan Lake fault are sufficiently uniform to allow us to apply open-system kinetic oxygen isotope exchange modeling, thereby placing constraints on the duration (1-3 Ma) and integrated fluid flux (≥ 10⁷ cm³H₂O/cm₂rock) for this hydrothermal metamorphism.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Geology
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Taylor, Hugh P., Jr. (advisor)
  • Silver, Leon T. (co-advisor)
Thesis Committee:
  • Silver, Leon T. (chair)
  • Taylor, Hugh P., Jr.
  • Albee, Arden Leroy
  • Wernicke, Brian P.
  • Wyllie, Peter J.
Defense Date:26 November 1996
Record Number:CaltechTHESIS:10252022-202940570
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15047
Deposited By: Tony Diaz
Deposited On:27 Oct 2022 21:22
Last Modified:27 Oct 2022 21:23

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