1 Eastern Belt, Franciscan

2 Adapted from Ernst and McLaughlin, 2012Willows Adapted from Ernst and McLaughlin, 2012

3 Red Bluff CRO Willows Grindstone Creek

4 All units in Blueschist faciesYolla Bolly graywacke/argillite Valentine Spring Semi-schistose graywacke & argilite 1+ 2 All units in Blueschist facies 3 SFMS, thin-bedded to laminated schistose sand and shale 3

5 CRO A’ A

6 Fault interpretation drivers:Log Spring Fault Sulfur Creek Fault 1+ 2 3 Fault interpretation drivers: Belief in Age difference between SFMS & Franciscan Post-metamorphic differential uplift

7 Arguments for faulting Arguments againstJump in metamorphic grade Change in lithology and structural fabric Jump in textural grade Arguments against “metamorphic temperature was not very different” across the Eastern belt Brocker and Day, 1995 Sulfur Creek Fault and other YB faults “vertical component of post-metamorphic fault offset was small (< few km), if any.” Cloos and Copeland, 2005 Can be explained by accretionary processes Data not convincing Faults not seen in outcrop*

8 Grindstone Creek from Longpoint trail

9

10 Grindstone Creek

11 Thomes Creek

12 Thomes Creek

13 1000 m Grindstone Creek Subparallel faults spaced ~100 to 600 m apartChange in lithology and structural fabric across faults Grindstone Creek 1000 m

14 Across faults there is commonly:a change in structural fabric (e.g. strike of bedding) a change in lithology.

15 Grindstone Creek Sulfur Creek Fault B B’ 10 km

16 Sulfur Creek Fault semischist not schistose

17 1+ Textural Grades 3 2

18 Sulfur Creek Fault

19 Log Springs Fault A A’ 10 km Grindstone Creek B B’ Salt Creek

20 South Fork Mtn Schist Grindstone Creek

21 Valentine Spring Grindstone Creek

22 Grindstone Creek Salt Creek : Mudstone and….

23 Elsewhere in Eastern BeltGrindstone Creek area Contacts between units are gradational There is a lithologic difference that roughly corresponds to the the transition from textural grade 3- to 2 Elsewhere in Eastern Belt Gradational contacts…yes Lithology similar…..no Terminology??? The terms schist and semischist are useful and mappable Origin of inverse metamorphic gradient? No post-metamorphic differential uplift