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Left: Field Forum participants pose on rocks of the Western Metamorphic Belt. Right: Lincoln Hollister imparts his enthusiasm about rocks in the
Coast Mountains batholith. Photos by Chris Mattinson.

juxtaposes high-grade metamorphic rocks of the Central Gneiss Central Gneiss Complex. The structural and tectonic framework
Complex with greenschist facies rocks of Stikinia. Higher in the for this event is not well understood. Thrust faulting likely played
detachment system, rocks within Stikinia are cut by both high- a significant role, especially within the Central Gneiss Complex,
and low-angle normal faults. Evidence of this extensional fault- but its cause and relation to proposed strike-slip faulting remains
ing is largely lacking in areas to the north and south. Forum par- uncertain. Similarly, whether the prominent crustal break
ticipants examined the main elements of this complex orogen currently marked by the 65–55 Ma Coast shear zone was the locus
and participated in lively discussion of existing models, funda- of older strike-slip faulting is unknown. The final stage of
mental questions regarding batholith growth in general, and the batholith construction at this latitude was marked by crustal
central Coast Mountains batholith in particular, and directions extension in the early Tertiary; the apparent lack of this crustal
for future work. Some of these thoughts are summarized in the collapse along strike in the batholith leaves open questions
following section and may help guide future researchers to use regarding the significance of extension in batholith evolution, the
the Coast Mountains batholith to address key questions about driving forces of extension, and the tectonic framework of the
crustal evolution at convergent margins. Coast Mountains batholith in early Tertiary time.
3. What are the causal relationships between magma generation,
QUESTIONS ABOUT BATHOLITH GROWTH deformation, and metamorphism?
AND EVOLUTION Voluminous plutons in the Coast Mountains result in limited
Batholiths are the exhumed roots of magmatic arcs and contain preservation of metamorphic rocks. Thus, it is difficult to evaluate
evidence of the processes that form continental crust. These pro- whether metamorphism resulted in partial melting or played a less
cesses and those related to batholith evolution continue to pose direct role in HFE. Geochronologic data indicate that some meta-
several problems in modern geology. Some of these questions, morphism was synchronous with ca. 80 Ma HFE within the Coast
discussed during the forum, follow. Mountains batholith. Lu-Hf garnet ages of >100 Ma in the
1. What are the processes and conditions responsible for the Western Metamorphic Belt (Wolf et al., 2010) indicate that the
observed temporal and spatial variations in magmatism? earliest metamorphism along the western flank of the Coast
Gehrels et al. (2009) and Cecil et al. (2018) document the timing Mountains batholith preceded HFE. Additional studies are needed
of intrusion along more than 1000 km of the Coast Mountains to better document the timing of metamorphism within and adja-
batholith. The data demonstrate both the across-strike variation cent to the Coast Mountains batholith and to integrate these events
and the episodic nature of magmatism. In addition, Cecil et al. with the structural and tectonics evolution of the batholith.
(2018) document that brief high flux events (HFE) vary tempo- 4. What is the contribution of sediments to magmatism?
rally along the strike of the Coast Mountains batholith. Future The limited preservation of metamorphic rocks also makes
work is needed to associate these HFE with specific crustal and evaluation of sediment contributions to magma generation dif-
mantle processes. ficult. Thus, possible relamination of sediments to the base of
2. What processes are responsible for the structural framework the crust may only be evaluated through isotopic and trace
of the Coast Mountains batholith during batholith growth, and element signatures.
how did these processes affect magmatism? 5. What drives magma generation at mid to lower crustal levels
Late Cretaceous crustal thickening is best demonstrated by (e.g., Kasiks Sill)?
metamorphic P-T-t paths from the Western Metamorphic Belt Plutons within the Central Gneiss Complex contain evidence for
along the western flank of the Coast Mountains batholith and the
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