Key points identified in Hildebrand papers, and our ideas on testing these points:

1)    North America was subducted to the west under Rubia

1. Rhiana-Are there modern analogs of subduction of a continent under something like Rubia?
2. Craig-Is the architecture of the late Mesozoic arc system in Rubia consistent with west-dipping subduction?
3. Steve-Is there evidence from seismic tomography for west-dipping subduction?
4. Rachel-Are there blueschist or other subduction-related metamorphic rocks associated with the westward subduction under Rubia?
5. Kyren-Does the composition of the arc evolve appropriately for subduction of a continental margin?

2)    Rubia has Triassic through early Cretaceous plutonism that is absent from the truly North American continental margin

1. Rhiana-Are there any magmatic products on Hildebrand’s North American margin?
2. Colin-Are there early Mesozoic detrital zircons on Hildebrand’s North America sourced from Rubia?
3. Jeff-Are these magmatic bodies an island arc?  Continental arc? Back arc?
4. Jim-Do these plutons uniformly have low ⁸⁷Sr/⁸⁶Sr (below 0.706)?

3)    The ~120-80 Ma magmatism along the Mesozoic arc is far more voluminous than would be expected for a typical arc

1. Kyren-Are these volumes higher than earlier in the Mesozoic?
2. Jeff-How do these volumes compare with modern analogs?
3. Rhiana-Is Hildebrand’s model substantially different from the underthrusting of continental sediments envisioned by Ducea (and brought up in the DeCelles et al. overview)?
4. Does the arc migrate sensibly given the physical controls on the position of an arc relative to a subduction zone?

4)    Hildebrand interprets much of the classic late pC-Paloezoic “Cordilleran miogeocline” as exotic to North America

1. Colin-Are there 1.5 Ga detrital zircons (considered a characteristic of Rubia) present in Paleozoic-early Mesozoic sediments on Hildebrand’s North America?
2. Steve-Is there a break in the detrital zircons populations going west from stable North America out to the “Antler platform”?
3. Is there a change in the paleontology in the Paleozoic going from stable North America to the “Antler platform”?
4. Jeff-Do paleocurrents, clastic source regions and facies belts in Rubia make sense with Rubia’s isolation from North America?
5. Rachel-Is there a North American signal in the form of detrital zircons, bulk sediment initial Sr or other materials in Rubia?
6. Craig-Are there variations in depositional environment so abrupt on the classic North American shelf/slope that a large distance probably separated these deposits originally?

5)    Accretion of exotic terranes in the late Paleozoic and early Mesozoic did not produce any changes in Hildebrand’s North American shelf.

1. Steve-Is there really nothing changing in the shelf at these times?
2. Anne-What kinds of signals are present in modern analogs like the Apennines/Adriatic Sea and parts of Indonesia?

6)    Palinspastic restoration of the thrust belt places classically defined North American rocks west of the edge of North America as defined by 0.706 ⁸⁷Sr/⁸⁶Sr line

1. Jim-Is the 0.706 line an appropriate marker for the continental edge?
2. Rachel-Is the 0.706 line correctly or robustly defined?
3. How well do we know the geometry of the Precambrian margin of North America, and how does that affect this reconstruction?
4. Is there evidence of shortening of the lower plate that would push the 0.706 line farther west?
5. Are there alternate reconstructions that do not place classical North American sediments off the west side of the continent?

7)    The magnitude of crustal shortening/thickening in the Sevier hinterland is inconsistent with a backarc origin.

1. Craig-Are there modern backarcs with such thick crust?
2. Kyren-What is the origin of the thickness estimate (i.e., is this a robust number)?
3. Anne-What are the observational constraints on the early Tertiary thickness of the hinterland crust?

8)    Widespread asthenosphere-sourced magmatism in western Canada reflects asthenosphere rising as the west-dipping slab breaks off from North America, while roughly coeval removal of the slab produces widespread uplift of western U.S., driving Laramide deformation.

1. Colin-Do analogs for slab breakoff (e.g., Taiwan, the Himalaya) produce this kind and volume of magmatic activity?
2. Jim-Do isotopic variations in the Canadian igneous rocks support such widespread asthenospheric origins?
3. Anne-What evidence is there on the evolution of the elevation of the western U.S. over this time period?

9)    The southern end of the Sevier belt and shelf deposits and their juxtaposition with profoundly different histories requires the presence of a late Cretaceous Phoenix Fault connecting the Sevier fold-and-thrust belt with the stylistically similar belt in northeastern Mexico.

1. What is the deformational history of southern Arizona in the latest Mesozoic?