LATE CRETACEOUS PLUTONIC AND METAMORPHIC OVERPRINT OF PROTEROZOIC

METASEDIMENTS OF ONTARIO RIDGE, EASTERN SAN GABRIEL MOUNTAINS, CALIFORNIA

A Thesis

Presented to the

Faculty of

California State Polytechnic University, Pomona

In Partial Fulfillment

Of the Requirements for the Degree

Master of Science

In

Geological Sciences

By

Scott B. Zylstra

2017 ACKNOWLEDGEMENTS

Many thanks to Drs. Jonathan Nourse and Nicholas Van Buer for countless hours

in research, assistance and editing on this project; to Zhan Peng, Anthony LeBeau and

Karissa Vermillion for laboratory assistance; to the MENTORES program and the Cal Poly

Geology Department for funding; to Joshua Schwartz and Carl Jacobson for valuable

insight; and to Jennifer, Gwendolyn and Lydia Jean Zylstra, without whom this work would not be possible (and with whom sometimes has been scarcely possible).

iii ABSTRACT The rifting of Rodinia, particularly in western Laurentia, has been a longstanding geologic problem, as Proterozoic rocks in the western U.S. are few and far between. The eastern San Gabriel Mountains contain a large metasedimentary package that has never been dated or thoroughly mapped. We present U-Pb detrital zircon geochronology results of 439 grains dated at CSUN’s LA-ICPMS; also 24 plutonic grains and 19 metamorphic rims of detrital grains analyzed on Stanford’s SHRIMP-RG, along with a detailed map, cross section and stratigraphic column for these Ontario Ridge metasediments. Probability plots of 206Pb/207Pb ages for five quartzite samples show

three distinct peaks at ~1200, 1380-1470 and 1740-1780 Ma. Maximum depositional age is constrained by 3 grains between 906 to 934 Ma, which are 11-28% discordant.

The ~1200 Ma peak distinguishes the Ontario Ridge quartzites, and is rarely seen in the western U.S. There are a few minor possible western sources, or, due in part to similarities with the Big Bear Group (Barth and Wooden, 2009), the rocks may represent sediment shed from Rodinia’s conjugate rift pair with western Laurentia. (Barth and

Wooden, 2009). The detrital age signature also appears to match preliminary data from the Potato Mountain block (Premo et al., 2007), displaced ~8 km from the main metasediment body by the left-lateral San Antonio Canyon fault. The metasediments are intruded by pre-metamorphic granodiorite of Icehouse Canyon (85.9±0.6 Ma) and post-metamorphic quartz diorite of Ontario Peak (75.8±0.9 Ma). Two quartzites, metamorphosed to upper-amphibolite facies, contain zircons with

iv metamorphic rims (75.7±1.2 Ma: 12 grains and 76.7±2.4 Ma: 7 grains), consistent with the last documented plutonic and metamorphic event in the San Gabriel Mountains.

These new data provide important keys for future research into the Proterozoic and

Mesozoic history of southwestern North America, including the breakup of Rodinia.

v TABLE OF CONTENTS

SIGNATURE PAGE ...... ii ACKNOWLEDGEMENTS ...... iii ABSTRACT ...... iv LIST OF FIGURES ...... viii INTRODUCTION ...... 1 Location and Access: ...... 1 Previous Work ...... 3 Purpose and Objectives ...... 4 Research Questions and Hypotheses ...... 5 METHODS ...... 8 Geologic Mapping ...... 8 Sample Collection ...... 9 Zircon Separation...... 9 U/Pb Analyses at California State University: Northridge ...... 13 U/Pb Analyses at Stanford ...... 15 RESULTS ...... 17 Rock Units of the Eastern San Gabriel Mountains ...... 17 Young Quaternary ...... 17 Older Quaternary ...... 19 Tertiary Volcanics ...... 20 Tertiary/Cretaceous Mylonites ...... 20 Cretaceous Granitoids ...... 27 Triassic Plutonics ...... 34 Ontario Ridge Metasediments ...... 34 Cucamonga Granulite ...... 57 Precambrian Basement ...... 58 Stratigraphy of the Ontario Ridge Metasediments ...... 59 Member 10 ...... 60 Member 9 ...... 61 Member 8 ...... 61

vi Member 7 ...... 62 Member 6 ...... 63 Member 5 ...... 64 Member 4 ...... 65 Member 3 ...... 66 Member 2 ...... 66 Member 1 ...... 67 Geochronology of the Ontario Ridge Study Area...... 68 DISCUSSION ...... 78 Precambrian Basement...... 78 Ontario Ridge Metasediments ...... 79 General Distribution and Thickness ...... 79 Structure ...... 82 Original Stratigraphy ...... 87 Age ...... 91 Cretaceous Plutonics and Metamorphism ...... 112 CONCLUSIONS ...... 114 Recommendations ...... 116 REFERENCES ...... 118 APPENDICES ...... 122 21 Summary of U-Pb Zircon Analyses: Stanford University SHRIMP lab Summary of U-Pb-Th Detrital Zircon Analyses: CSUN ICP-MS lab Plate 1: Geologic Map of Ontario Ridge Metasediments Plate 2: Stratigraphic Section of Ontario Ridge Metasediments Plate 3: Structural Cross Section Through Ontario Ridge Metasediments

vii LIST OF FIGURES

Figure 1: Overview ...... 2 Figure 2: Snow and pines ...... 3 Figure 3: Glass mount ...... 13 Figure 4: Metamorphic zircon ...... 14 Figure 5: Igneous zircons ...... 15 Figure 6: CL images ...... 15 Figure 7: Quaternary looking down ...... 19 Figure 8: Quaternary looking up ...... 19 Figure 9: Spring Hill landslide toe ...... 21 Figure 10: Cascade Canyon landslide ...... 22 Figure 11: Mylonite with large feldspars ...... 24 Figure 12: Arkose thin section ...... 25 Figure 13: Subarkose thin section with very large feldspar ...... 26 Figure 14: Lithic arenite ...... 27 Figure 15: San Antonio fault ...... 29 Figure 16: Clean Cretaceous granite ...... 30 Figure 17: Micro-fault in tonalite ...... 31 Figure 18: Tonalite and fog ...... 32 Figure 19: Tonalite and pine ...... 33 Figure 20: Hills of tonalite ...... 34 Figure 21a: Hornblende quartz monzonite cataclasite ...... 35 Figure 21b: Porphyritic hornblende quartz monzonite with rounded feldspar inclusions...... 36 Figure 22: S-folded biotite paragneiss ...... 38 Figure 23: Hornblende-biotite schistose paragneiss ...... 39 Figure 24: Fine-grained schistose gneiss ...... 40 Figure 25: Garnet in biotite gneiss ...... 41 Figure 26: Plane-polarized opaque vein ...... 42 Figure 27: Cross-polarized opaque vein...... 43 Figure 28: Anomalous amphibolite ...... 44 Figure 29: Leucogranite and hornfels ...... 45 Figure 30: Schist rind ...... 45 Figure 31: Brecciated quartzite ...... 46 Figure 33: Cascade to Barrett Canyons ...... 46 Figure 34: Calc-silicate and fog ...... 47 Figure 35: Massive calc-silicate ...... 48

viii Figure 36: Meta-siltstone ...... 49 Figure 37: Convolutely folded marble ...... 50 Figure 38: Folded marble ...... 51 Figure 39: Z-folded metachert ...... 51 Figure 40: Coarse-grained marble ...... 52 Figure 41: Fine-grained marble ...... 53 Figure 42: Coarse- and fine-grained marble ...... 54 Figure 43a: Quartzite with mica ribbons ...... 55 Figure 43b: Quartzite with more mica ...... 56 Figure 44: Clean quartzite ...... 57 Figure 45: Rusty quartzite ...... 57 Figure 46: Quartzite in broken blocks ...... 58 Figure 47: Kerkhoff Canyon’s imposing cliffs ...... 58 Figure 48: Kerkhoff Canyon looking up the talus ...... 59 Figure 49: Crenulated corundum+graphite schist from above ...... 60 Figure 50: Crenulated corundum+graphite schist from the side ...... 60 Figure 51: Precambrian gneiss ...... 62 Figure 52: Geologic map Bighorn Peak ...... 65 Figure 53: Geologic map Kerkhoff Canyon ...... 67 Figure 54: Geologic map Member 5 ...... 69 Figure 55: Probability Plots ORM ...... 73 Figure 56: Quartzite 1610 ...... 75 Figure 57: Quartzite 1619 ...... 76 Figure 58: Quartz diorite 1603 ...... 77 Figure 59: Concordia 1603 ...... 78 Figure 60: Granodiorite 1616 ...... 79 Figure 61: Concordia 1616 ...... 80 Figure 62: Panorama with fog ...... 83 Figure 63: Geologic map Icehouse Canyon ...... 83 Figure 64: Geologic map Cucamonga Peak...... 84 Figure 65: Cucamonga Peak eastward ...... 84 Figure 66: Marble anticline ...... 85 Figure 67: Isoclinal amphibolite ...... 86 Figure 68: Subtle amphibolite fold ...... 87 Figure 69: Migmatite fold ...... 87 Figure 70: Ontario Ridge east flank ...... 89 Figure 71: Gently dipping quartzite ...... 90 Figure 72: Panorama dead tree ...... 94

ix Figure 73: Ehlig’s geologic map ...... 96 Figure 73a: Potato Mountain correlation ...... 100 Figure 73b: Pinto Mountain correlation ...... 101 Figure 73c: Big Bear Group correlation ...... 103 Figure 73d: Big Bear Group/miogeoclinal correlation ...... 104 Figure 73e: Mojave/Yavapai correlation ...... 106 Figure 73f: Grand Canyon correlation 1 ...... 107 Figure 73g: Grand Canyon correlation 2 ...... 108 Figure 74: Southern California bedrock current distribution ...... 109 Figure 75: Southern California bedrock pre-Cenozoic distribution ...... 110 Figure 76: North American provinces ...... 112 Figure 77: Rodinia ...... 114 Figure 78: Barrett Canyons ...... 117 Figure 79: Ontario Ridge ...... 118 Figure 80: Cascade Ridge ...... 119

x INTRODUCTION

Location and Access: The San Gabriel Mountains in Los Angeles County, California, are mostly composed of Proterozoic and Mesozoic intrusive and metamorphic rocks. In the eastern half of the San Gabriels, specifically on and around Ontario, Bighorn and Cucamonga

Peaks, just to the east of Mt. Baldy Road, is an extensive package of metasedimentary rocks. For simplicity, these will herein be referred to as the Ontario Ridge metasediments, because around Ontario Ridge the rock units are the best exposed and most accessible. The word accessible is used somewhat facetiously, as nowhere are these rocks very accessible at all without great effort. That is why these rocks are very poorly understood and rarely described, despite their proximity to the enormous Los

Angeles populace and inclusion in an otherwise geologically well-defined mountain range.

The San Gabriel Mountains in general consist of rumpled mountains around

5,000 feet high, but to the east rise suddenly and dramatically to over 10,000 feet at their highest point at Mt. San Antonio (10,064’). The Ontario Ridge metasediments,

which wrap around the tallest peaks (all over 8,500’) on extremely steep slopes, are

among the least accessible rocks in California. Not only is the relief problematic, but

bedrock exposure itself is very limited for the southwestern U.S., and where it is

exposed, it is often on steep impassable cliffs. Where there are no cliffs, the terrain is

generally either covered in dense forest with thorny or slippery underbrush or thick

1 chaparral, which was condemned as “too low to give shade, too high to see over, and too thick to go through” (Robinson & Christiansen, 2013). The result is a very intriguing group of rocks in an area which is almost impossible to reach (see Figures 1 and 2 and

Plate III).

Figure 1 View of Ontario Ridge and the Ontario Ridge metasediments from the northwest. Hogback landslide crosses San Antonio Creek in lower middle, with Barrett Canyon to its upper right. Just south (above) that is the Spring Hill landslide.

Figure 2 View east up Barrett Canyon south fork, showing the difficult terrain of the area, including the cliffy outcrops and snow.

2 Previous Work Mapping has already been done in the area, but several problems with previous maps exist. The most comprehensive published map and report, Ehlig’s dissertation of

1958, is very thorough and accurate in many areas, as he personally mapped by foot much of the Ontario Ridge metasediments. However, his work was done before the plate tectonics theory was fully developed, and so, though exceptional research for the time, it contains several inaccuracies, especially in the rock description and interpretation sections. Any report, no matter how well-executed, done before such a revolutionary theory must be re-evaluated. Ehlig’s map also does not reach to the full extent of the metasediments.

May and Walker (1989) categorized several “terranes” in the San Gabriel

Mountains, naming the block including the Ontario Ridge metasediments the San

Antonio terrane. May characterized this as screens and pendants of metasedimentary rocks entrained in Cretaceous tonalite to granodiorite, bounded by mylonitic belts on the south and north. The metasediments are uniformly metamorphosed to upper amphibolite facies, with no evidence of multiple episodes of deformation (though these may have been obliterated by the latest foliation). Mylonitic deformation and plutonism were estimated to be roughly concurrent, with the northern and southern margins of the terrane undergoing earlier and more pervasive deformation. The

“Ontario Ridge metasediments” (ORM) named in this study are differentiated from the

San Antonio terrane in that the terrane encompasses the metasediments, intrusions and mylonite belts, while the ORM refer exclusively to the metasediments.

3 Jonathan Nourse has spent almost three decades doing field work and mapping in the eastern San Gabriel Mountains. His field notes and maps have proven invaluable resources for this study, including his 7.5’ Mt. Baldy Quadrangle map (Nourse et al,

1998) and unpublished mapping done in Icehouse Canyon between 1991-2000. Dibblee

and Minch (2002) essentially borrowed from Nourse’s field maps and Ehlig’s map (1958)

to create the geologic map of the Mt. Baldy Quadrangle. This is the most recent

integrated map of the Ontario Ridge metasediments, but contains many inaccuracies.

The map also does not encompass all of the metasediments, which extend further east

into the Cucamonga quadrangle. Morton and Matti (2002) have mapped the

Cucamonga quadrangle, but detail is sparse: the metasediments for the most part remain undivided. A detailed, accurate, integrated map encompassing the majority of the Ontario Ridge metasediments is needed.

Purpose and Objectives

The main purpose of this project is to better understand the Ontario Ridge metasediments. As there was, before this time, little known in general about the rocks, the research questions discussed below are very generalized and basic, and future projects can further investigate more interesting conclusions garnered in this work.

The objectives of this project are to map the ORM thoroughly in at least 1:24,000

scale to assess their lithology, stratigraphy and structure, to create a detailed

stratigraphic column and cross section, to sample quartzites and plutonics in varied stratigraphic units, and to perform zircon geochronology to better understand the

4 plutonic and metamorphic history of the units. The sum of the data should inform local

and regional correlations of the ORM to other pendants or groups.

Research Questions and Hypotheses As previously stated, the Ontario Metasediments are often inaccessible and

poorly exposed. As such, there is not a great deal of literature about the rock units,

although a few publications, such as Ehlig (1958), May (1989) and Barth et al. (1991) have given fairly detailed descriptions of some units. The research questions on the subject are, of necessity, very simple, and may be broken down into five basic questions that are briefly discussed below and later addressed in much greater detail:

1. What are the lithologies present in the metasediments and what depositional

and tectonic history do they record?

2. What is the stratigraphy of the metasediments, what is the nature and extent of

foliation and folding, and are any units overturned?

3. What are the ages of provenance of the metasediments, and what is their

maximum depositional age?

4. Can the metasediments be correlated to any other rock units, locally, regionally

or globally?

5. What are the implications and constraints for Late Cenozoic strike-slip fault

displacements?

These questions will be discussed in the Results and Discussion sections of this

paper.

5 The stratigraphy of the rock units (research question 2) can be tentatively

interpreted based upon map patterns and crosscutting relations: for example, if the

metasediments unconformably overly a gneiss of Precambrian age, the metasediments

must be younger than this basement. However, the rock ages can be much better

constrained by the use of detrital zircon geochronology. Detrital zircons can be extracted with some difficulty from quartzites, and if at least 4 samples from different stratigraphic horizons are collected, there is a possibility for at least ascertaining an average age for the metasedimentary package; and, under fortuitous circumstances, the age of different units within the stratigraphic sequence can be determined (research question 3).

The metasediments contain, in part, a relatively pure tan to white quartzite, arkosic in areas, with very little to no bedding and a fine-grained light blue to grey bedded marble in the area. Diblee and Minch (2002) have the cleanest and easiest to read geologic map of the area, but it was largely mapped at a distance and borrowed from Nourse (1998). They also only mention one other metasedimentary unit (which further underscores the need for more detailed mapping): a dark grey, foliated mica schist to gneiss (to phyllite). This is a significant unit, but although Diblee uses it wherever there is not quartzite or marble, there are additional mappable units, such as a calc-silicate gneiss marked by sillimanite, diopside and grossular garnet and a very heavily altered siliceous unit that may represent some sort of impure metasediment such as a metagreywacke or meta-arkose. These metasediments are frequently intruded by Cretaceous granitic rocks, noted by the author to be approximately

6 monzogranite to syenogranite in composition, but ranging according to Diblee and

Minch (2002) from granitic to quartz monzonite to possibly granodiorite in composition.

Both the mapping and detrital zircon geochronology, coupled with literature research, can lead to correlation of the metasedimentary package to other metasedimentary units in Southern California and around the world (research question

4). Part of this research is on a small-scale, such as the correlation of the nearby Potato

Mountain block with the ORM, which can help constrain Late Cenozoic fault slip

(research question 5); however, correlations can also take on immense implications, some of a much larger scope than a master’s thesis can address, such as in the breakup of Rodinia. As noted in the background information section, even the timing of the breakup of Rodinia is poorly constrained, and detrital zircon data from the San Gabriel

Mountains, which may be related to Rodinia rifting, can help to constrain this.

Another of the main questions about the area is structural in nature: do the metasediments represent a large interbedded package of limestone, shale, sandstone and wackestone, or are they folded and overturned, perhaps repeatedly? In the cross section from Diblee and Minch (2002), the rocks are seen as an interbedded, unfolded very thick sequence of uniformly northeast-dipping units, although the reality may be much more complex. In order to tell if any of these units are overturned or even folded, detailed structural mapping must take place. On the large scale, attitudes must be taken all over the mapping area to determine the general trend of the units, to determine if they nearly always do trend northeast, or if there are conflicting patterns present.

7 METHODS

Geologic Mapping

The most comprehensive and straightforward approach that can neatly and

thoroughly answer all of these questions is by way of a detailed and accurate geologic

map. As noted, mapping has already been done in the area, but several problems with

previous maps exist - see discussion in Previous Work. A new high-resolution geologic

map of the study area was produced, largely based on first-person observations to

ensure maximum precision and accuracy, with minimal interpolation of rock units based

on laser range finder surveys and/or orientation of rock units in other map areas. It definitively identifies all lithologies present (research question 1), and when a significant rock unit is not of mappable scale, it is described and noted in the legend.

The map was done at a small enough scale so that individual metasedimentary units can be distinguished, but large enough so that the entirety of the Ontario Ridge metasediments can be visualized. A small scale aids in finding fine stratigraphic patterns, while a large scale maintains the geologic “big picture” of the entire metasedimentary package, so a careful balance should be maintained. All adjacent rock units are related in some way and affect or are affected by their neighbors, so the lithologies adjacent to the metasediments should be carefully mapped as well.

Geologic mapping was conducted over the course of many day trips and an overnight trip into the high country of the San Gabriel Mountains and the Cucamonga

Wilderness. Strikes and dips were taken by the author or assistants at the locations shown, or in rare cases taken at distance by sight. Most of the map area has been

8 directly traversed and observed firsthand, and in areas that could not be accessed due to topography, brush, and/or time constraints, gaps were filled in by sight from distance or by laser range finder, or in the most remote, rare cases, units mapped were taken from Nourse (1998 and unpublished 1991-2000), Morton and Matti (2001) or Dibblee

(2002).

Sample Collection 6 quartzite samples, shown in Plates 1 and 2, were strategically taken from varying stratigraphic horizons, and 25 hand samples of all present lithologies were collected. Hand samples were cut and processed into thin sections and were visually analyzed for mineral assemblage and deformation fabrics, which should yield information of metamorphic facies and protolith composition.

Zircon Separation The quartzite samples were then crushed using a 10-pound sledgehammer against the rock, which was set on a hardened steel plate with a two-fold wooden board behind. Each sample was crushed into 1-cm maximum diameter pieces, then run through a rock pulverizer which crushed the quartzites to very fine sand (30 microns maximum diameter). The pulverizer, sledgehammer, steel plate, workspace and all associated equipment had to be painstakingly and thoroughly cleaned before and after each sample was run so as not to cross-contaminate samples.

As quartzite is primarily composed of quartz with some feldspar and/or lithics, an extensive separation process was necessary to find and extract as much zircon as

9 possible from each sample (100-150 zircons in each sample is considered robust enough

for detrital geochronologic data). This began with sifting an industrial (10-centimeter

diameter) neodymium magnet through the sand to remove the obviously magnetic

minerals. Next was the use of a Gemeni water table used to separate the heavy

minerals, such as zircon (density 4.65 g/cm3), from the light minerals, such as quartz and

feldspars. The water table and all equipment used also had to be flawlessly cleaned

before and after each sample was run. At this point, the cleaning process, which may be

the most time-consuming of all the zircon preparation steps, becomes crucial, as the fraction of zircon is increasing at such a rate that the chances of a stray grain being recorded is higher.

This yielded a collection of heavy minerals of about 50 grams, which were then

allowed to soak first in acetic acid and then hydrogen peroxide for at least 24 hours

each. This was to remove carbonates and sulfide minerals such as pyrite. The samples

were then run through two separate heavy liquids, first lithium metatungstate and then methylene iodide, which ideally removed residual quartz and feldspar from the zircon.

Zircon has a quite low magnetic susceptibility, even relative to other traditionally

“nonmagnetic” minerals like sphene and rutile. Thus, the next step in zircon separation was to run the sand of each through a Frantz magnetic separator to further remove sphene and other heavy minerals with higher magnetic susceptibilities than zircon. Each sample, now less around 25 grams, was run through the Frantz at a high angle at least twice, and a few samples that still appeared to have a large proportion of other minerals were run through the Frantz twice more at a much lower angle and orientation.

10 The samples, which now were reduced to 400-500 grains, could then be added

to tape mounts on thin glass slides which would eventually be polished into grain

mounts. Ideally, these grains will already be almost all zircons, and in the case of igneous zircons often are, but for 3 out of 4 of these metasedimentary samples the zircons had to be picked by hand from the reduced sample and placed individually on the grain mount (see Figure 3).

11

Figure 3 Reflected light image of grain mount with quartzites dated at Cal State Northridge: sample 1610 on top and 1601 below, with standards in the center, R33 on left and 91500 on right.

12 U/Pb Analyses at California State University: Northridge Once the grain mounts were prepared they were taken to California State

University-Northridge (CSUN) and cathodiluminescence (CL) images were taken using a

scanning electron microscope (see Figures 4 and 5). The images were then stitched

together and maps created of each sample mount using PowerPoint (as seen in Figure

6). The samples were then dated using Northridge’s Laser-ablation Inductively-coupled

Plasma Mass Spectrometer (LA-ICP-MS).

Figure 4 Cathodiluminescence image of detrital zircon from sample 1616. Note the wavy metamict rim.

13

Figure 5 Cathodiluminescence images from detrital zircons of sample 1603 dated at Cal State Northridge. Note the many euhedral igneous layers around the rims.

Figure 6 Cathodiluminescence image of detrital zircons from sample 1610 showing my system of numbering grains to be spotted. All grains that were large enough and did not have suspicious dark spots were spotted.

Laser ablation works by focusing a laser beam on a sample to generate fine particles. After this, the ablated particles are transported to a secondary excitation

14 source of the ICP-MS instrument, where the sampled mass is ionized. The excited ions

in the plasma torch then undergo elemental and isotopic analysis in a mass spectometer detector. (Russo et al., 1999).

A great effort was made so that zircons were extracted, picked and ablated at

random, with no preference for grain size or shape, excluding only grains that were too

small to be ablated by the laser. In this way grain ages should represent a random

sampling and not be biased in any way.

During the dating process, standards of known age, specifically MADDER (~513

Ma) and Temora (~417 Ma) were used for the Stanford samples, and Temora-2 (~404

Ma), R-33 (~419 Ma), Plesovice (~336 Ma), and 91500 (~1047 Ma) were used for the

Northridge samples. These standards were run by themselves for quality control at the

beginning of each analysis day (3 days), and then were interspersed among the grains of

unknown grains to prevent machine drift. As each grain was analyzed, it was numbered

(Figure 6) on the CL map.

U/Pb Analyses at Stanford Both detrital and plutonic zircons were analyzed on the Stanford/USGS SHRIMP-

RG (Sensitive High-Resolution Ion Microprobe, Reverse Geometry). Plutonic sample mounts were prepared according to the steps detailed above, as were the detrital mounts, except in the latter case zircons were placed with their widest, flattest sides face down on an indium mount. When used in depth-profiling mode, the SHRIMP has high enough spatial precision (see Ireland, 2014) to analyze metamorphic rims even

15 when they are only a few microns thick around older detrital cores, revealing an age of latest metamorphism of the metasediments.

16 RESULTS

This section includes the lithology of all the rocks in the eastern San Gabriel

Mountains, the stratigraphy of the Ontario Ridge metasediments, and the result of

geochronology work done on plutonic and detrital zircons around the ORM.

Rock Units of the Eastern San Gabriel Mountains Below follows a complete list of the rocks of the San Antonio terrane, including

the Ontario Ridge metasediments, Precambrian gneisses west of the San Antonio

Canyon fault, Triassic and Cretaceous intrusives (and occasionally volcanics), and

overlying Quaternary landslide blocks, talus and alluvium. Wording used is a

combination of the author’s, mapping from Nourse (Nourse et al, 1998) including

unpublished mapping in Icehouse Canyon from 1991-2000, Dibblee & Minch’s geologic

map of the Mt. Baldy Quadrangle (2002), and Morton & Matti’s geologic map of the

Cucamonga quadrangle (2001). Also included are the author’s comments based on thin section analysis and multiple photos of representative outcrops.

Young Quaternary Qt: Late Quaternary talus breccia and other angular colluvium, poorly consolidated and generally unvegetated (see Figures 7 and 8).

17

Figure 7 View looking west-southwest from halfway up Kerkhoff Canyon, showing a good example of Quaternary talus, steep along the sides of the canyon (right) and gently sloping along the bottom of the canyon.

Figure 8 View looking east up Kerkhoff Canyon, showing large quartzite cliffs in the top right and Quaternary talus in the valley below.

Qa: Late Quaternary alluvium, generally restricted to modern drainages.

Unconsolidated, moderately sorted braided stream deposits composed of rounded boulders to medium sand.

18 Older Quaternary Qoa: Older Quaternary alluvial terraces, subhorizontally bedded, with basal

unconformities intermittently preserved as much as 50 m above modern-day San

Antonio Creek. Bottom layers composed of rounded cobbles and boulders are typically

overlain by new alluvium. May interfinger with Qls deposits. Outcrops near the southern front of the range.

Ql: Sizeable Quaternary landslide with anomalous vegetation and characteristic

geomorphology. Poorly sorted angular debris or colluvial wedges, moderately

consolidated, may be heavily vegetated (See Figures 9 and 10).

Figure 9 Toe of the Spring Hill landslide block, looking east from the north side of Cascade Canyon. The block is several dozen meters thick.

19

Figure 10 Part of the zone of depletion of the Spring Hill landslide, looking north from Cascade Canyon east of the Barrett-Stoddard road.

Tertiary Volcanics Tr: Tertiary rhyolite porphyry dikes and sills. Dacite and quartz latite varieties are less common. Distinguished by prominent subspherical quartz phenocrysts, with sparse biotite. . 40Ar/39Ar analyses indicate a latest Oligocene age (P. Weigand, unpublished data). Geochemically identical (Nourse and others, 1998) to porphyritic biotite granite of

Telegraph Peak, which yields latest Oligocene to Early Miocene ages (May and Walker,

1989 {U/Pb}; Miller and Morton, 1977 {K/Ar}; P. Weigand, unpublished data {40Ar/39Ar}).

Most occurrences not visible at map scale, except two small blocks in southeast and

northwest.

Tertiary/Cretaceous Mylonites bbm: Late Cretaceous prograde “black belt” mylonite mostly composed of quartz and mica that is largely retrograded to amphibolite and greenschist-grade mylonite and

cataclasite. Exposed east of lower San Antonio Canyon (Hsui, 1961; May, 1986; May and

20 Walker, 1989). May also contain hornblende granulitic gneiss, locally containing

sillimanite, garnet and diopside; severely metamorphosed from Ontario Ridge

metasediments, but predominantly Kt. Locally contains lenses of white marble and

(sample 1607) intact foliated xenoliths composed of large fractured and broken

feldspars with mylonitized intergrowths of mica. This north-dipping shear zone

separates footwall cg from hanging wall Kt and ms. See figures 11-14 for thin section

examples.

Figure 11 Cross-polarized thin section view of heavily sheared mylonite with very large lightly altered and "scratched" porphyroclasts of feldspar.

21

Figure 12 Cross-polarized thin section with highly mylonitized quartz and mica ribbons enveloping relatively pristine feldspar porphyroclasts.

22

Figure 13 Another example of a cross-polarized thin section with highly mylonitized quartz ribbons enveloping relatively pristine feldspar porphyroclasts, some very large.

23

Figure 14 Cross-polarized thin section view of biotite-quartz mylonite.

KTmy: Mylonitized orthogneisses, retrograded and sheared during movement on the Vincent thrust. This unit, restricted to the lowermost 10-1000m of the upper plate,

structurally overlies lower plate Pelona Schist along a concordant, low-angle fault

contact. Penetrative Late Cretaceous-Paleocene mylonitic fabric associated with

chlorite-epidote alteration (Ehlig, 1981; Jacobson et al., 1989) is superimposed on older

mylonitic and/or amphibolite facies crystalloblastic fabric. Intruded by unfoliated

Triassic dikes and sills. Protoliths include Precambrian gneisses, Triassic Mt. Lowe

24 plutonic suite, Triassic quartz diorite, Jurassic biotite granodiorite, Cretaceous quartz diorite, and pegmatite/leucogranite of Late Jurassic or Late Cretaceous age. See Figure

15.

25

Figure 15 Strain of the San Antonio Canyon fault seen in highly mylonitized quartzite (KTmy) near the north end of Barrett-Stoddard Road.

26 Cretaceous Granitoids Kg: Late Cretaceous fine- to medium-grained, subporphyritic, weakly foliated

leucocratic biotite monzogranite to granodiorite. Composed of essentially sodic

plagioclase feldspar, K-feldspar and quartz in nearly equal proportions, and minor

amounts of biotite mica akes. Hard but brittle; weathers o-white. Intrudes as small

stocks, dikes and sills into Kt, bbmy, and ms units on and around Ontario Ridge (May and

Walker, 1989) and west of Lower San Antonio Canyon. See figure 16.

Figure 16 Cretaceous granite (Kg). This rock frequently has this clean, fresh appearance, with little to no metamorphic foliation. It has a weak magmatic foliation, which can be seen by the biotite elongation roughly parallel to the hammer handle.

Kt: Fairly uniformly mylonitized tonalitic rocks. Homogeneous, gray, porphyroblastic mylonite; zone is 200 to 400 m in width. Mylonite is tonalite composition, but ranges to diorite and monzogranite locally. Very fine-grained to

aphanitic, having porphyroclasts of plagioclase, quartz, and most notably porphyroclasts

or porphyroblasts of hornblende as much as 3 cm in length. Most elongate

27 porphyroclasts or porphyroblasts show strong preferential orientation down dip.

Includes dark-gray to black, aphanitic mylonite and ultramylonite layers approximately 3

cm thick. Quartz diorite near Ontario Peak which shows no metamorphic foliation was

dated at 75.8±0.9 Ma. See Figures 17-21.

Figure 17 Micro-fault in pegmatite dike in Cretaceous tonalite (Kt). This tonalite appears to have a metamorphic foliation, especially in the region of the fault.

28

Figure 18 View looking west from Ontario Ridge. Some Kt in left foreground.

29

Figure 19 Prominent outcrop of Cretaceous tonalite with characteristic rounded weathering. This is the locality of dated sample SZ 1603.

30

Figure 20 View looking south from Stoddard Peak. Tan outcrops are tonalite (Kt). May and Walker’s dated Kt sample (1989) was taken from these outcrops.

31

Figure 21a Cross-polarized thin section view of hornblende quartz monzonite cataclasite.

32

Figure 21b Cross-polarized thin section view of porphytic hornblende quartz monzonite with small rounded quartz and feldspar inclusions.

Kc: Massive to foliated charnockite. Forms irregular to tabular masses as much as 2 km long. Near-white, medium to coarse grained. Consists mainly of plagioclase and hypersthene, biotite, garnet, and quartz. Much of charnockite has been affected by retrograde metamorphism, which affects not only charnockite, but surrounding granulitic gneiss.

33 Kq: Quartz diorite exposed north of the San Gabriel fault on the south face of

Mount San Antonio and Bear Canyon; contains abundant xenoliths of TRd. Intruded by

Kg and pegmatite.

Ki: Late Cretaceous medium grained, porphyritic hornblende-biotite granodiorite

to hornblende quartz monzonite to monzonite (sample 1612), with some sericitized

feldspars, quartz often in small rounded inclusions, and large hornblende often resorbed

by feldspars. Moderately to weakly foliated. Occurs on Mt. San Antonio, Ontario Ridge,

and Glendora Ridge. Sample with weak metamorphic foliation from Falling Rock Canyon

dated at 85.9±0.6 Ma in this study. Porphyritic granodiorite on south wall of Icehouse

Canyon contains K-feldspar phenocrysts up to 4 cm long.

Triassic Plutonics TRd: Triassic or Jurassic(?) biotite+/- hornblende quartz diorite or diorite, ne to

medium grained, poorly to moderately foliated, commonly recrystallized. Spatially

associated with the Triassic Mt. Lowe intrusive suite. Some phases are intruded by a

Triassic biotite quartz monzonite. Contains abundant pCg and pCa to Precambrian

biotite augen gneiss to biotite granodiorite xenoliths. Rarely contains irregular bodies of

poorly foliated gabbro or pyroxenite, medium to coarse grained. This gabbroic unit may

be strongly recrystallized, with mafic minerals replaced by biotite.

Ontario Ridge Metasediments ms: Undifferentiated metasedimentary rocks at upper amphibolite facies, strongly foliated and isoclinally folded at middle-upper amphibolite facies. Intruded by

34 Ki, Kt, and Kg units in that order. Maximum depositional age 906-934 Ma (see Discussion

section).

g: Biotite paragneiss (Figures 22-24), garnet-biotite-quartzofeldspathic gneiss

(Figure 25), hornblende-biotite-quartzofeldspathic schist with small circular interspersed

quartz (Figures 26 and 27), amphibolite (Figure 28) and migmatite with well-developed

mm-cm scale chevron isoclinal folds. Intruded by and deformed with leucocratic biotite

granite (Figure 29) or pegmatite dikes and veins. Ubiquitous among ms, sometimes only

as crusts on q (Figures 30 and 31). May weather into orange-brown slopes (see Figures

32 and 33).

Figure 22 Biotite schistose paragneiss with tight s-folds.

35

Figure 23 Cross-polarized thin section view of a bt-hbl schistose quartzofeldspathic gneiss. Note the biotite and amphiboles are very large, while the quartz and feldspars are much smaller. This could indicate a porphyroclastic origin for biotite and amphiboles.

36

Figure 24 Cross-polarized thin section view of hornblende-biotite fine-grained schistose gneiss.

37

Figure 25 The biotite schistose paragneiss can locally contain large (4 cm) subhedral garnets which are riddled with inclusions.

38

Figure 26 Plane-polarized thin section view of an opaque vein in a heavily altered phyllitic schist.

39

Figure 27 Cross-polarized thin section view of an opaque vein that creates(?) fine-grained alteration of surrounding biotite-quartzofeldspathic phenocrysts.

40

Figure 28 Cross-polarized thin section view of amphibolite and opaque minerals and veins which fracture anomalously large amphibole phenocrysts.

41

Figure 29 Leucogranite with subhedral andradite. This is likely a leucosome. The country rock is a metasandstone that has been contact metamorphosed to hornfels facies.

Figure 30 Hbl+bt schist forms a melanocratic rind on quartzite. This rind may prevent the quartzite from eroding, or else the rind may be preserved because of its close contact with the quartzite.

42

Figure 31 Example of brecciated quartzite in biotite schist which forms a rind on the quartzite. This schistose rind is common on quartzites, but in this case the brecciated quartz pebbles indicate that according to protoliths, the quartz arenite is older than the shale.

Figure 33 View looking north from Peak 6857' (where sample SZ 1701 was collected) up Ontario Ridge, showing metasediments and plutonics of unknown composition between Cascade Canyon and Barrett Canyons.

43 cs: Tightly folded or massive (Figures 34 and 35) calc-silicate gneiss composed of

calcite and quartz banding, diopside, wollastonite, forsterite and occasionally grossular.

Figure 34 Calc-silicate outcrop near Bighorn Peak along Ontario Ridge.

44

Figure 35 Massive calc-silicate boulder on the ridge south of Cascade Canyon.

mss: Rusty-looking fine-crystalline meta-sandstone (see Figure 36) with traces of

hematite, pyrite and lazurite and protoliths of lithic arenite, arkose with large feldspars

and some high birefringence minerals (sample 1620C), feldspathic litharenite and

sublitharenite, the last composed of very fine-grained quartz with some small and very

large lithics (mica and amphibole with larger medium-sized, moderately rounded

plagioclase grains, and some larger high birefringence lithics, with some large

porphyroblasts or veins of quartz (sample 1620A-B). Sample 1620A also contains veins

of an opaque mineral, usually surrounding a fine-grained or very fine-grained matrix of

micas.

45

Figure 36 Foliated meta-siltstone on Ontario Ridge with some original bedding preserved.

m: Complexly folded (Figures 37 and 38) calcite to dolomite marble (Figure 39),

pristine in certain locales (1622C), fine to medium-crystalline, bedded, white (calcite) to

medium to light blue-gray (dolomite), often contains small rounded forsterite (sample

1608 and 1622C – see Figures 40-42).

46

Figure 37 Example of convoluted folding in marble.

47

Figure 38 Typical fold in marble. Grey and white bands generally composed of calcite and tan bands dolomite. Found in large marble swath in Member 3.

Figure 39 Marble with interbedded chert in complex z-folds.

48

Figure 40 Cross-polarized thin section view of marble with large and small-scale calcite phenocrysts and fractured forsterite.

49

Figure 41 Cross-polarized thin section view of a typical medium-grained marble with some forsterite.

50

Figure 42 Cross-polarized thin section view of very large-grained marble with some forsterite in close contact with olivine-plagioclase schist.

q: Quartzite, variably sheared (sample 1620 – see Figure 43), occasionally white

(as in Figure 44) but more often with orange-colored weathered surfaces (Figures 45

and 46). May have very large grains, occasional forsterite and small rounded feldspar

inclusions (sample 1601B), or may present highly sheared quartzite ribbons with some

mica ribbons and oddly pristine euhedral feldspar (sample 1605B). May contain a

significant component of feldspar and biotite, or small lithics and small rounded

quartz(?) inclusions. May form large cliffs on the flanks of Ontario Ridge (Figures 47 and

51 48). Some mica fish and large heavily altered feldspar porphyroblasts present (Sample

1604).

Figure 43a Typical quartzite viewed in cross-polarized light. Both large- and small-scale quartz ribbons and some mica ribbons.

52

Figure 43b Typical quartzite viewed in cross-polarized light. Both large- and small-scale quartz ribbons and some mica ribbons.

53

Figure 44 Clean white quartzite from the ridge bridging North and South Barrett Canyons.

Figure 45 Red-weathering subarkosic quartzite with banded layers of plagioclase visible underneath pencil.

54

Figure 46 Typical messy, broken blocks of quartzite outcrops, in Barrett Canyon. Cliffs of presumed quartzite seen on south ridge of Barrett Canyon South Fork on right.

Figure 47 View looking south-southwest at immense quartzite cliffs south of Kerkhoff Canyon. The lower cliffs in the foreground have a brown appearance which is due to mostly surficial weathering.

55

Figure 48 View looking east up the upper reaches of Kerkhoff Canyon. On the right (south) are the large quartzite cliffs where sample SZ1619 was collected, and on the left (north) is a leucogranite, although they look identical from this distance.

c: Corundum granofels to schist, exposed in landslide blocks on Barrett-Stoddard

Road, and in place on Ontario Ridge (see Figures 49 and 50). Marker bed that contains euhedral pink corundum.

56

Figure 49 Crenulated very finely crystalline corundum+graphite schist.

Figure 50 Crenulated very finely crystalline corundum+graphite schist.

Cucamonga Granulite cg: Mylonitized orthogneisses, retrograded and sheared during movement on the Vincent thrust. This unit, restricted to the lowermost 10-1000m of the upper plate,

57 structurally overlies lower plate Pelona Schist along a concordant, low-angle fault contact. Penetrative late Cretaceous-Paleocene mylonitic fabric associated with chlorite- epidote alteration (Ehlig, 1981; Jacobson et al., 1989) is superimposed on older mylonitic and/or amphibolite facies crystalloblastic fabric. Intruded by unfoliated Tr dikes and sills. Protoliths include pC gneisses, Triassic Mt. Lowe plutonic suite, TRd,

Jurassic plutonics, Kq, and pegmatite/leucogranite of Late Jurassic or Late Cretaceous age.

Precambrian Basement pCa: Augen gneiss, light gray, gneissoid quartz monzonite to granodiorite, composed of feldspar, quartz and biotite and large porphyroblasts (augen) of K-feldspar

(microcline); in Mint Canyon quadrangle radiometric age ca. 1.65-1.7 Ga (Silver, 1971;

Barth et al. 1995); includes mixtures of unit pCg. One mappable outcrop in northwest corner of map.

pCg: Undifferentiated Paleoproterozoic fine-grained Mendenhall gneiss recrystallized under upper amphibolite facies (see Figure 51). Composes wall rocks to pCa. Finely banded, millimeter-scale foliation may appear mylonitic. Commonly displays recumbent isoclinal folds and preserves multiple generations of deformational fabric.

Oldest basement lithology recognized in the western San Gabriel Mountains (Silver,

1971; Barth et al., 1995). Derived from texturally diverse igneous and/or immature sedimentary protoliths with felsic to mafic compositional ranges.

58

Figure 51 Outcrop of Precambrian gneiss just west of Mt. Baldy Road, also west of San Antonio Canyon. Dip is southwest like the regional trend.

Stratigraphy of the Ontario Ridge Metasediments Much of the main field data from the project are contained in Plate 1, the

geologic map of the Ontario Ridge metasediments. The map both provides a detailed

view of the structure and stratigraphy of the metasediments as well as their local

context, including all rocks with which they are in contact on every side. More detailed

results on the stratigraphy and structure of the ORM are presented in Plate 2, a pseudo-

stratigraphic column of the entire section inspired by and including data from Ehlig

(1958), with the metasediments divided into 10 general members and described in detail. This column is to scale and gives a visual representation of all lithologies in the section, as well as their thickness and resistance to erosion. Each member is also described below:

59 Member 10 Upper portion leucocratic migmatite with minor melanocratic gneiss and locally

containing small pods of hornblende rock derived from marble; melanocratic gneiss in

lower portion; large swath of marble in lower portion with basal calc-silicate and calc-

silicate east of Bighorn Peak, sparse quartzite outcrops. Also includes quartzite layer

near Shortcut Ridge with ~1 m of biotite-hornblende-quartz gneiss near center.

Migmatite: light gray, medium to fine-grained; vague irregular compositional

layering, layers locally intrude one another; ptygmatically folded; thin irregular aplite

bodies common; average composition about 55% feldspar, 35% quartz and 10%

hornblende; biotite locally present; scattered euhedra of sphene usually visible in hand

specimen.

Melanocratic gneiss: conspicuously banded with dark gray layers 1-10 cm thick

alternating with whitish gray layers mostly less than 5 cm thick; layers irregularly to

semiregularly folded with wavelengths of a few inches; fold axes subparallel; dark layers

fine-grained, foliated, compositionally variable but typically about 60% hornblende

and/or biotite, 30% plagioclase and 10% quartz; light layers fine- to medium-grained, occassionally of an aplitic texture, lenticular with irregular shapes, composed of quartz and feldspar.

Quartzite: light gray, granoblastic, fine- to medium-grained; very thin poorly-

defined bedding; tightly folded in most outcrops with fold amplitudes of tens to

hundreds of cm, sheared folds locally simulate crossbedding; average quartz content

about 80%, biotite most common accessory.

60 210 meter thickness

Member 9 Gneisses and migmatites dominant; migmatite extensively developed along

south side of Icehouse Canyon; roughly 15 meters of dolomite marble and minor calc- silicate rocks 80 meters below top of member; minor marble and calc-silicate rocks interbedded near base; graphite-rich schists locally present.

Gneisses: dominantly melanocratic, fine-grained, highly deformed; contains irregular quartzofeldspathic layers; essential constituents biotite, hornblende, feldspar and quartz.

Migmatite: melanocratic, fine- to medium-grained; irregularly banded to non-

banded, non-banded portions aplite-like in appearance; about 20 to 40% quartz, 50 to

60% feldspar, and 10 to 20% hornblende and/or biotite.

Dolomite marble: white, medium- to coarse-grained; essential constituents

dolomite, calcite and forsterite; locally contains small pods of spinel-phlogopite rock;

squeezed into large lenticular bodies between Kerkhoff and Icehouse canyons.

274 meter thickness

Member 8 White to medium gray quartzite, commonly stained red-brown by iron oxides,

fine- to medium-grained; bedding very thin and generally indistinct; tight, small-scale

folds abundant in some places; dominantly granoblastic quartz; sillimanite, biotite and

orthoclase important constituents in some strata; mylonitized at northern and southern

61 edges; zircon as a minor accessory. Sparse outcrops of marble. On Ontario Ridge outcrops are mainly tonalite with blebs of quartzite (see Figure 52).

290 meter thickness

Figure 52 Excerpt from geologic map (see Plate I) of Ontario Peak, Bighorn Peak and Icehouse Saddle. Note the swath of Black belt mylonite near the northern margin of the San Antonio terrane. Tonalite (Kt) generally in the south and Icehouse granodiorite (Ki) in the north around Icehouse Saddle. Also note large calc-silicate outcrop in lower right corner.

Member 7 Quartzofeldspathic biotite gneisses, graphite-sillimanite-biotite schist and minor

interbeds and pockets of quartzite and marble; mostly gneiss east of Ontario Ridge;

schist dominant west of Ontario Ridge; some significant outcrops of marble on Ontario

Ridge and some quartzite and marble on the west flank (see Figure 53).

1701 meter thickness

62 Member 6 Thin-bedded sequence of quartzite layers with cyclically interbedded hornfels

and schist (see Figure 53); some hydrothermally altered metasandstone including meta-

arkose, meta-lithic arkose and meta-litharenite around Barrett-Stoddard Road with

abundant hematite and some lazurite; outcrops typically stained with hematite; pyrite

and graphite present in most rocks; sparse well-bedded marble outcrops. Thick, white,

medium-grained, granoblastic quartzite about 50 meters thick may be part of this

member, but its relationship is unclear as it cannot be traced to Ontario Ridge; thin

bedded in lower portion with interbeds of schist and gneiss near base; bedding

indistinct in upper portion; very resistant to weathering.

Figure 53 Excerpt of geologic map (see Plate I) showing the lower reaches of Ontario Ridge, Barrett Canyon in lower left corner and Kerkhoff Canyon in the upper left corner. Note large swath of quartzite

63 near Kerkhoff Canyon/Barrett Canyon North Fork which becomes covered by a landslide in its upper reaches.

Hornfels: fine- to very fine-grained gray grains on fresh surface; very hard;

irregular fracture; in laminated beds mostly 35 to 100 cm thick; composition variable, includes includes diopside-quartz rock, tremolite-plagioclase-quartz rock; tremolite- quartz-albite rock and slightly schistose muscovite-bearing rocks; mostly associated with quartzites.

Quartzite: mostly gray, fine grained; interbedded with hornfels and schist; about

16 meters of indistinctly bedded, white to light gray quartzite near middle of member.

Schists: fine-to very fine-grained; varieties include scapolite-quartz-muscovite-

plagioclase schist, sillimanite-biotite schist, cordierite-anthophyllite schist; as much as

25% graphite in some strata.

Marble: medium to dark gray, fine- to medium-grained, in laminated beds 1 to 4

feet thick; external deformation of beds slight, internally lamina commonly boudinaged

or contorted or less commonly brecciated; forsterite dominant calc-silicate mineral.

1658 meter thickness

Member 5 Dominantly corundum granofels to schist (Ehlig’s “plagioclase rock”) with minor

sillimanite-biotite schist locally present near base, scattered beds of quartzite and some

marble interbedded near top; grades upward and westward into marble in Cascade

Canyon; pyrite and graphite present in most rocks; good exposures limited to the upper

half of Cascade Canyon but present in landslide blocks along Barrett-Stoddard road

north of Cascade Canyon (see Figure 54).

64

Figure 54 Excerpt from the geologic map (see Plate I) showing peak 6857' and the enigmatic member 5 (labeled c). The marble units in members 3 and 4 may form a syncline with metasandstone/biotite gneiss in the core, east-southeast of Spring Hill.

Plagioclase rock: thin-bedded to laminated; gray on fresh surface, red-brown on weathered surface; very fine-grained in lower Cascade Canyon grading to fine-to medium-grained in upper part of canyon; as much as 80% albite or oligoclase; plagioclase granoblastic, unzoned and untwinned or only slightly twinned; several percent graphite and pyrite generally present; accessories present in some strata include corundum, sillimanite, tremolite and rutile.

114 meter thickness

Member 4 Quartzite: very resistant; forms steep crested ridge south of Cascade Canyon; outcrops typically craggy and jointed; massive to vague parallel stratification; sugary

65 white; composed of more than 90% quartz in medium-grained highly sutured granules; oligoclase and potassium feldspar in small anhedral grains principal minor accessories; bedding locally marked by concentrations of zircon and rutile; metasomatic feldspar locally present along healed fractures particularly near quartz monzonite; muscovite widely distributed as small inconspicuous plates scattered over joint surfaces.

119 meter thickness

Member 3 Dolomite marble with calc-silicate rock interbedded in lower half; contains scattered interbeds of biotite-quartz-plagioclase gneiss and quartzite in upper and middle portions, with hydrothermally altered, hematite-stained meta-arkose, meta lithic arkose and meta-lithic arenite exposed near Barrett-Stoddard Road in the upper section.

Dolomite marble: white to light gray, medium to coarse-grained; ranges from nearly pure dolomite to as much as 40% forsterite and chondrodite in a calcite matrix; small thin pods of red-brown phlogopite and dark green spinel abundant along some horizons; massive appearing on fresh surfaces, differential solution of calcite brings out laminated bedding on weathered surfaces.

357 meter thickness

Member 2 Upper portion dominantly melanocratic biotite gneiss with some laminated calc- silicate rock interbedded near top; exposures poor. Middle portion mostly dolomite marble; lower portion interbedded dolomite marble and calc-silicate rock; might

66 represent synclinally infolded part of member 3; contact with member 3 poorly exposed.

Dolomite marble: white, fine- to medium-grained; 80 to 90% calcite plus dolomite, 10 to 20% pale green diopside, pale yellow forsterite and light red-brown phlogopite in variable proportions; contains abundant rolls, pods and angular plates of calc-silicate rock three inches or less in maximum dimension which weather from the marble.

Melanocratic gneiss: fine to medium-grained; biotite, quartz and plagioclase essential minerals; garnets abundant in some strata; cordierite and sillimanite accompany garnet in a few strata.

Calc-silicate rocks: laminated and color bands reflect variations in mineralogy; green diopsidic augite rock, red-brown biotite-andesine schist and white marble most common layers, less common layers composed of red garnet or red garnet in white wollastonite; pronounced differential weathering of layers; small-scale folding common, folds generally disharmonic and not uncommonly ruptured.

98 meter thickness

Member 1 Quartzite, meta-arkose and biotite gneiss with minor calc-silicates and marble; overlies intrusive quartz diorite in vicinity of Stoddard Flat; only uppermost 100 feet and lowermost 200 feet of stratigraphic significance: the former biotite gneiss with minor calc-silicates, marble and quartzite and the latter quartzites to meta-arkoses with some

67 biotite gneiss to schist on fringes. Some of these quartzites may be vein quartz, with

<30 micron zircon and minute sulfide minerals.

Gneiss: biotite-quartz-oligoclase gneiss most common type; biotite 15 to 25%, quartz about 30% and oligoclase about 40%; orthoclase generally present in small amounts; biotite concentrated in schistose lamellae separating layers and lenses of medium-grained granoblastic quartz and feldspar; small scale folding common; grades into biotite-hornblende-quartz-plagioclase migmatite near quartz diorite contact; light and dark constituents only vaguely segregated and foliation very irregular in migmatites.

Laminated calc-silicate rocks and a variety of plagioclase, quartz, amphibole, biotite garnet and sillimanite-bearing gneisses form uppermost 100 feet of member; individual units laterally continuous for at least 1 mile east of Stoddard Canyon Truck Trail; garnet and sillimanite associated with biotite-rich strata; garnets vary greatly in size from one strata to the next; garnets as much as 5 cm. in diameter; small pods of bedded calc- silicate rock locally isolated in quartzofeldspathic gneiss.

131 meter thickness

Total thickness of the Ontario Ridge metasediments

4952+/-200 meters = 16245+/-800 feet = 3.08+/-0.15 miles

Geochronology of the Ontario Ridge Study Area Six quartzites were collected from different stratigraphic positions in the San

Antonio terrane and dated at Stanford’s SHRIMP-RG or Cal State Northridge’s LA-ICPMS.

These are all marked in their respective locations in the geologic map (Plate 1) as well as in the pseudo-stratigraphic column (Plate 2). All the probability plots of 206Pb/207Pb ages

68 are shown in Figure 55, and data is shown in Table 1. They are, from stratigraphic top to bottom:

Figure 55 Age probability plots from five quartzite samples from the Ontario Ridge metasediments. The top graph is a probability plot for all five samples combined. The ~1200 Ma peak is the most uniformly distributed peak along with the ~1440 Ma peak. See Table 1 for a complete list of all data.

69 JN1713 ± SZ1701 ± SZ1619A ± SZ1610 ± SZ1605A ± 1000 65.0 710 75.0 950.0 55.0 906.0 33.5 910.0 55.0 1670 60.0 1064 42.5 990.0 49.5 995.0 28.5 934.0 38.5 1782 31.5 1074 33.5 1007.0 41.5 1055.0 30.5 1015.0 34.5 1797 39.5 1087 42.5 1019.0 42.0 1059.0 34.0 1053.0 32.5 1820 48.5 1130 50.0 1025.0 32.5 1059.0 38.0 1060.0 34.5 1821 44.5 1137 47.0 1037.0 35.0 1061.0 36.0 1122.0 35.5 1831 30.5 1143 42.0 1053.0 29.0 1078.0 42.0 1148.0 32.5 1842 20.0 1152 46.5 1096.0 42.5 1085.0 32.5 1152.0 27.5 1848 48.0 1160 60.0 1100.0 35.0 1089.0 36.5 1154.0 28.5 1850 55.0 1166 40.0 1140.0 50.0 1089.0 34.5 1163.0 43.0 1853 25.0 1176 43.5 1142.0 33.5 1097.0 34.5 1167.0 39.5 1856 35.0 1180 60.0 1149.0 40.5 1101.0 39.5 1182.0 31.0 1863 20.5 1190 38.5 1171.0 39.0 1127.0 35.5 1190.0 23.0 1875 39.0 1198 43.5 1177.0 29.5 1129.0 39.0 1195.0 30.0 1882 21.5 1218 46.5 1188.0 40.5 1133.0 23.5 1197.0 34.0 1885 25.0 1220 45.5 1190.0 50.0 1137.0 38.0 1205.0 43.5 1888 26.5 1233 32.5 1192.0 35.5 1145.0 32.5 1207.0 30.0 1892 25.0 1252 28.5 1195.0 48.0 1163.0 32.5 1209.0 34.5 1895 14.5 1259 35.5 1197.0 39.5 1172.0 34.5 1217.0 35.0 1905 21.5 1260 50.0 1209.0 33.0 1179.0 30.5 1223.0 40.5 1909 40.0 1282 49.0 1209.0 44.0 1180.0 29.0 1234.0 34.0 1910 50.0 1285 36.0 1216.0 28.5 1183.0 36.0 1236.0 42.0 1919 49.5 1291 45.0 1220.0 40.0 1185.0 28.5 1242.0 33.0 1927 23.5 1298 45.0 1244.0 42.5 1189.0 33.0 1248.0 30.5 1939 22.0 1302 49.5 1244.0 36.0 1190.0 47.5 1263.0 41.5 1943 31.0 1310 65.0 1245.0 35.0 1207.0 39.5 1272.0 41.5 1949 26.0 1315 49.0 1247.0 41.5 1211.0 36.0 1279.0 32.5 1949 24.5 1336 35.0 1269.0 35.5 1224.0 40.0 1310.0 50.0 1955 22.0 1360 39.0 1270.0 47.0 1237.0 25.5 1312.0 44.5 1957 28.0 1364 49.0 1273.0 29.5 1238.0 39.5 1316.0 41.5 1974 21.0 1370 31.0 1274.0 47.5 1241.0 30.0 1339.0 32.5 1979 41.0 1371 41.0 1320.0 33.0 1258.0 32.5 1348.0 33.0 1980 24.0 1390 55.0 1321.0 31.5 1258.0 35.0 1353.0 30.0 1999 38.0 1409 45.5 1332.0 34.0 1263.0 35.5 1357.0 43.5 2103 19.5 1428 42.0 1333.0 48.0 1264.0 23.5 1370.0 26.0 2125 28.5 1428 32.5 1339.0 33.0 1275.0 35.0 1390.0 25.0 2156 46.5 1437 30.0 1364.0 38.0 1277.0 40.0 1416.0 30.5 2549 22.5 1446 27.5 1366.0 39.5 1288.0 46.5 1423.0 40.0 2550 39.5 1451 41.0 1370.0 36.0 1296.0 37.5 1426.0 41.0 2558 19.5 1476 31.5 1374.0 42.0 1301.0 32.5 1427.0 44.0 2682 23.0 1496 43.5 1380.0 55.0 1321.0 40.0 1428.0 33.0 2689 14.0 1502 30.5 1386.0 35.0 1333.0 34.0 1432.0 40.5 2767 32.5 1530 50.0 1405.0 39.5 1341.0 30.5 1435.0 39.5 1530 50.0 1406.0 49.0 1359.0 35.5 1435.0 30.0 1533 41.5 1416.0 35.0 1364.0 26.0 1436.0 26.0 1551 29.5 1416.0 41.5 1365.0 32.0 1437.0 42.0 1562 41.0 1437.0 30.0 1365.0 33.0 1437.0 27.0 1641 31.0 1438.0 34.0 1368.0 34.5 1439.0 34.5 1652 34.5 1439.0 37.5 1370.0 37.5 1445.0 30.5 1670 55.0 1439.0 36.0 1372.0 36.5 1448.0 27.0 1677 38.0 1452.0 47.5 1374.0 27.5 1454.0 31.0 1677 32.5 1456.0 38.5 1386.0 33.5 1456.0 29.0 1680 44.0 1457.0 46.0 1394.0 40.5 1458.0 39.0 1682 34.0 1458.0 30.0 1399.0 24.0 1460.0 31.5 1697 39.5 1462.0 31.5 1405.0 30.5 1463.0 32.0 1700 55.0 1464.0 37.0 1411.0 30.0 1480.0 32.5 1700 39.5 1470.0 60.0 1424.0 33.0 1487.0 26.0 1700 35.0 1481.0 33.0 1424.0 25.0 1506.0 37.5 1715 28.0 1489.0 26.0 1428.0 34.0 1524.0 26.5 1725 38.5 1507.0 43.5 1434.0 31.0 1538.0 25.5 1732 49.0 1510.0 33.0 1435.0 34.0 1545.0 36.0 1739 42.5 1516.0 37.5 1440.0 29.0 1571.0 22.0 1740 42.0 1564.0 32.5 1449.0 24.0 1624.0 39.5 1744 22.5 1570.0 34.5 1460.0 24.0 1650.0 27.0 1745 36.0 1572.0 31.0 1463.0 30.0 1654.0 24.0 1748 26.0 1579.0 35.5 1464.0 28.0 1669.0 27.0 1754 28.5 1581.0 33.5 1472.0 32.5 1671.0 29.0 1755 37.5 1584.0 37.0 1477.0 33.0 1705.0 44.5 1776 29.0 1584.0 44.5 1478.0 35.0 1715.0 22.5 1779 27.5 1585.0 29.5 1481.0 30.5 1726.0 30.0 1780 50.0 1592.0 34.5 1511.0 39.5 1734.0 34.5 1781 23.5 1603.0 35.0 1516.0 40.0 1742.0 35.5 1785 22.5 1620.0 25.0 1536.0 44.5 1743.0 27.5 1789 25.0 1620.0 35.5 1618.0 25.0 1750.0 37.5 1794 32.5 1622.0 29.0 1624.0 48.5 1757.0 26.5 1797 35.5 1626.0 32.0 1636.0 29.0 1758.0 39.5 1800 40.0 1635.0 39.0 1640.0 30.0 1762.0 39.0 1802 26.0 1638.0 27.5 1642.0 30.5 1762.0 27.0 1807 34.5 1642.0 42.0 1680.0 31.0 1767.0 30.0 1812 36.0 1644.0 38.0 1692.0 26.5 1774.0 46.0 1812 34.5 1656.0 32.0 1708.0 36.5 1774.0 43.5 1814 44.5 1659.0 40.5 1716.0 26.5 1775.0 32.0 1814 46.5 1685.0 41.5 1728.0 26.5 1786.0 36.0 1814 45.0 1720.0 28.0 1730.0 28.5 1796.0 23.5 1848 38.0 1731.0 46.5 1744.0 34.0 1798.0 35.0 1853 45.0 1767.0 40.0 1758.0 26.0 1799.0 28.5 1868 31.5 1775.0 39.0 1767.0 23.5 1800.0 27.5 1876 41.5 1783.0 40.5 1772.0 27.0 1807.0 35.0 1877 30.0 1840.0 32.5 1816.0 29.5 1808.0 32.0 1888 29.5 1842.0 38.5 1822.0 28.0 1812.0 46.5 1905 38.5 1853.0 29.0 1844.0 29.0 1832.0 22.5 1915 30.5 1861.0 31.5 1848.0 24.5 1834.0 23.0 1932 30.5 1867.0 35.5 1934.0 22.5 1846.0 29.0 1955 48.0 1872.0 29.5 2084.0 28.0 1984.0 26.0 2158 47.0 1894.0 40.5 2277.0 27.5 1988.0 31.0 2388 35.0 1894.0 34.5 2461.0 29.0 2000.0 60.0 2603 41.5 2480.0 31.5 2518.0 28.0 2527.0 26.0 2715 32.0 2576.0 33.5 2623.0 26.0 2799.0 36.5 3033 33.0 2632.0 36.0 2692.0 24.0 3270 70.0

Table 1 Ages and 2-sigma errors from all 5 quartzite samples from the Ontario Ridge metasediments.

70 Sample SZ 1605A, from North Ontario Ridge, was dated at Northridge. The

probability plot (see Figure 55) shows peaks at ~1200, ~1440-1450, ~1770-1780 Ma, and

some miniscule older peaks at ~1980-1990, ~2530-2540, and ~2800 Ma.

SZ 1610, a thin quartzite layer from middle Ontario Ridge, was dated at

Northridge. The probability plot of Figure 44 shows a broad peak extending from 1070-

1260 Ma and centered around ~1200 but with spires at 1170 and 1250 Ma, another

broad peak between 1380-1460 but with its highest point at 1460 Ma. It has another

broad peak with its top spire at ~1730-1740 but with minor peaks at ~1630-1640 and

~1820-1830 Ma. It also has older miniscule peaks at ~1930-1940, ~2080-2090, ~2270-

2280, ~2460-2520, ~2620-2630 and ~2690 Ma.

SZ 1619, from Kerkhoff Canyon, was dated at Northridge. The stratigraphic

position of this unit remains somewhat anomalous, as it is fairly steeply dipping (~65

degrees) compared to the sample 1610 topographically above on Ontario Ridge (~34

degrees), and their connection is unknown. The Kerkhoff Canyon unit (1619) may

correspond to the thin quartzite layer on Ontario Ridge (1610), it may dip underneath it

or above it, or it may be cut off by unconformity or faulting. It has a minor peak at

~1030-1040 Ma, peaks at ~1200, ~1440, ~1610, and ~1870 Ma, and miniscule older

peaks at ~2470-2480 and ~2590-2600 Ma.

Sample SZ 1701, from around Peak 6857 southeast of Cascade Canyon, was

dated at Northridge.

71 Samples SZ 1601 and JN 1713 are both from near Stoddard Peak. 1601 did not garner enough zircons of sufficient size on the mount to date, and JN1713 had ~40 zircons that were dated at Northridge.

Two of the quartzites, 1610 and 1619, were found to contain zircons with metamict rims, and so were also analyzed by depth profiling with an ion beam at

Stanford’s SHRIMP-RG in the method described above. 12 grains were found to have ages of 75.7±1.2 Ma (Sample 1610) and 7 grains at 76.7±2.4 Ma (Sample 1619), consistent with the last documented metamorphic event in the San Gabriels. Unlike the

LA-ICP-MS ages presented later, all SHRIMP ages are 207 Pb-corrected 206 Pb/238 U ages. See Figures 56 and 57.

72

Two plutonic rocks that intrude the Ontario Ridge metasediments were dated at

the SHRIMP-RG. These are also marked on Plate 1 and Plate 2, and are 1616: a pre- metamorphic granodiorite of Icehouse Canyon, dated at 85.9±0.6 Ma, and 1603: a post- metamorphic quartz diorite of Ontario Peak, dated at 75.8±0.9 Ma. See Figures 58-61.

73

74

75

76

Three additional samples were collected and run through the complete zircon

separation process. Sample 1601, from Stoddard Flat, was completely processed for

zircon. It contained <200 zircon grains, but almost all of these were 10 microns or

smaller in width, proving impossible to date with Northridge’s laser. Sample 1702, from

Stoddard Flat, yielded predominantly rutile but contained enough zircon to analyze at a later time. Sample JN 1712, collected from Stoddard Peak, was a biotite gneiss with quartzitic layers. A 10 kg block of this metasiltstone to metamudstone yielded no zircon but abundant rutile.

77 DISCUSSION

This section reviews interpretations for the rocks of the eastern San Gabriel

Mountains, from Precambrian basement to the Ontario Ridge metasediments to

Cretaceous plutonic rocks.

Precambrian Basement The oldest basement lithology recognized in close proximity to the Ontario Ridge

metasediments (ORM), the Mendenhall gneiss, lies on the west side of the San Antonio

Canyon fault. It is described in the Rock Units section, and has been recrystallized under

upper-amphibolite facies, and commonly displays recumbent isoclinal folds similar to those present in most units of the ORM. The Mendenhall gneiss preserves more

generations of deformational fabric than the Ontario Ridge metasediments. It also

contains a late-stage augen gneiss in the northwest corner of the map dated at 1670-

1690 Ma (Premo et al., 2007).

Two other samples worth noting (see Premo et al., 2007) are two biotite granite

augen gneiss samples, one from Cobal Canyon near Potato Mountain (just southwest of

Plate I’s map) dated at ~1770 Ma, and another from a float block in the Cow Canyon

landslide (west-central of Plate I’s map) dated at ~1746 Ma. The latter is probably

derived from bedrock sources in upper Kerkhoff Canyon. Both of these samples

probably represent the “missing” Precambrian basement not yet identified on Ontario

Ridge.

78 Ontario Ridge Metasediments

General Distribution and Thickness The San Antonio terrane (see Figure 62), east of San Antonio Canyon in the San

Gabriel Mountains of southern California (part of the Transverse Ranges), has been interpreted to be a large sheared and mylonitized block of late Cretaceous granitoids and plutonic rocks, containing a large pendant or screen block of generally northeast-

dipping metasediments of previously unknown age (May and Walker, 1989). They

extend from about Stoddard Flat in the south to the southern slopes of Icehouse Canyon

in the north, where they become highly sheared and jumbled with more northern

terranes (Icehouse Canyon is the southern limit of May and Walker’s Middle Fork

Complex [1989 – see Figure 63]). They range from the San Antonio Canyon fault (more

or less equivalent with San Antonio Canyon) in the west to Cucamonga Peak (Figure 64),

where the outcrops cease being relatively continuous units and become smaller

pendant outcrops within Cretaceous plutons (see Figure 65). These smaller blocks, like the main block of the ORM and the San Antonio terrane itself, trend east-northeast until they abut the San Jacinto fault at the northeast end of the San Gabriel Mountains.

Traveling eastward, the plutonics become more prevalent until they overwhelm the metasediments, which at their furthest extent east are limited to a few outcrops. A total structural thickness for each member of the metasediments, measuring from

Stoddard Flat to Icehouse Canyon perpendicular to strike and using average dips for each member, has been calculated at 4952+/-200 meters, and each member’s thickness is included in the stratigraphic section (Plate III). This represents the total strained

79 thickness, resulting from pervasive amphibolite facies deformation of the ORM.

Figure 62 Panoramic view clockwise from Ontario Ridge. The ridge in the middle points due south. Some biotite gneiss to migmatite in foreground. Fog covers San Bernardino/Los Angeles Counties, and Mt. San Antonio is in the background on the right.

Figure 63 Excerpt from geologic map (see Plate I) showing the Icehouse Canyon area, part of the Middle Fork Complex of May and Walker (1989). The fragmented nature of outcrops, augmented by Quaternary cover, is evident near the Icehouse Canyon Fault, which parallels the canyon. Note large marble swath by Delker Canyon (lower right).

80

Figure 64 Excerpt of geologic map (see Plate I) showing Ontario Peak (left), Bighorn Peak (center) and Cucamonga Peak (right). Note the apparent left-lateral fault that runs through the canyon separating Ontario and Cucamonga Peaks.

Figure 65 View from Cucamonga Peak looking east at the various metasediments (often eroding darkly) and intrusives along the ridge.

81 Structure Most units of the ORM contain numerous small-scale (dozens of centimeter to

meter-scale) recumbent isoclinal folds. These are especially abundant in marble and

calc-silicate units (see Figure 66), in which the folding is often chaotic, with hinge axes in

almost every orientation. This chaotic blend, combined with the observation that many of the marble and calc-silicate outcrops are merely blocks entrained in plutonics or mylonitized units calls into question the validity of measurements taken in those units, great care was taken to record on the final map the strikes, dips and fold axes that most closely approximated the average regional trend.

Figure 66 Outcrop-scale anticline in marble plunging towards the author.

82 Biotite gneisses to amphibolites to migmatites also have recumbent isoclinal

folds, which may be at very fine (cm-scale) scale to larger (outcrop) scale (see Figures

67-69). There are even folds in quartzitic units, though, like the limestones on occasion, these tend to be more massive and cliff- or ridge-forming, and not forming obvious folds

even from a distance.

Figure 67 Small-scale isoclinal fold in migmatitic amphibolite.

83

Figure 68 Broad fold in migmatitic amphibolite and leucogranite.

Figure 69 Outcrop-scale fold in ambhibolitic migmatite just west of Cucamonga Peak.

Away from the fold hinges, all members fairly consistently strike west-northwest

(see Figure 70), but dips seem to systematically and problematically vary. They range from ~30 degrees (as in Figure 71) to ~70 degrees, although they do consistently dip to

84 the north. In general, the units become steeper from south to north and from

topographically higher to lower. This could indicate that the whole sequence represents

one large fold with an axial plane that strikes parallel to foliation (west-northwest), with

the Ontario Ridge metasediments essentially representing the forelimb of the large fold,

with the backlimb above eroded away (see Plate III). This is hard to verify, though, as

the units which may or may not vary in dip steepness are difficult, if not impossible to

follow from Barrett-Stoddard Road to Ontario Ridge due to intensely steep terrain and

vegetation/talus/landslide cover. A good example of this is the thick quartzite unit

halfway up Kerkhoff Canyon, which is steeply dipping (~65 degrees) compared to the

quartzite unit directly topographically above it (~35 degrees), and the connection

between the two is unknown. The Kerkhoff unit may dip below or above the Ontario

Ridge unit, or it may be cut off by faulting or depositional variation.

Figure 70 View looking south-southwest from canyon west of Cucamonga Peak towards Ontario Ridge. Note the convoluted nature of metasediments and plutonic rocks, where it is not possible to distinguish the units from a distance.

85

Figure 71 Relatively shallow dipping (~34 degrees) quartzite outcrop along Ontario Ridge at the location of sample SZ 1610.

A quick glance at Plate II reveals that the ORM is likely not one large nappe: the

members and their constituents in the upper members do not mirror those below.

There is likely some repetition of individual units: for example, the cyclic interbeds of

hornfels and quartzite in Member 6, but there is no strong evidence that the members

themselves are repeated, suggesting each member represents a stratigraphic unit itself,

progressing from oldest in the south (Member 1) to youngest above in the north

(Member 10). This is partially supported by the geochronology results – for example,

see Figure 55, in which sample JN 1713, the southernmost sample, lacked several of the

younger peaks of the other samples.

86 Because of the ambiguous nature of the lithologies and without any significant

marker beds aside from Member 5, another structural possibility is that the variation of

northward dips between 30 and 70 degrees is more systematic than originally viewed, and that the Ontario Ridge sequence represents several folds of the type described above, with northward-dipping axial planes. Whether the ORM represents one large fold or several is still unresolved, but may be resolved by detailed systematic structural mapping of s- and z-folds throughout.

Original Stratigraphy Plate III gives a succinct view of what the stratigraphy of the Ontario Ridge metasediments may have been when they were first deposited, and was inspired by and

created with the help of Ehlig’s pseudo-stratigraphic column (1958). The sequence

begins at its lowest point with a relatively thick sequence of meta-sandstone, which in

the field appears as “dirty quartzite” (in the vicinity of sample JN 1713). This grades into

a relatively large amount of biotite gneiss (members 1 through 3-in the vicinity of

Sample JN 1712). Members 1 through 3 could represent the end stage of a

transgressive sequence, with frequent small variations in space and/or time leading to

the deposition of calc-silicates and the interbedded nature of the units, but the overall

pattern being from sandstone to shale to limestone. The meta-sandstone, not quite

quartz arenite, which mostly appears towards the bottom of the unit is also consistent

with a rift environment, with mostly continental sediments mixed with a few lithics and

feldspars. The calc-silicates may also indicate estuarine deposits, with a marly mix of

calcic and clastic sediment deposition.

87 Member 5 Member 5 is by far the most enigmatic member of the ORM. Ehlig (1958) has

labelled the protolith of the anomalous “plagioclase rock,” nearly completely composed of granoblastic plagioclase with a few percent graphite and pyrite and euhedral corundum as a frequent accessory mineral, as a metasomatized argillite (metapelite).

This seems to be reasonable, as pelites usually contain much aluminum and commonly

graphite and pyrite when the protolith is an organic-rich black shale. But metapelites

usually also have a fair amount of magnesium and iron, so at high metamorphic grade

micas react with plagioclase and typically form garnet and/or hypersthene, such as in

the Cucamonga Granulite. Metasomatism therefore would be necessary to add sodium

and calcium, while removing iron and magnesium.

However, that Member 5 is unique is problematic. The other biotite gneisses in

the area are most likely metapelites, so why were they not metasomatized as Member

5? An alternate theory is that Member 5 was a paleosol, as these are often quite rich in

aluminum and perhaps iron. Metasomatism would still be necessary to add enough

sodium and calcium to make plagioclase, but it would require less extreme

metasomatism than the pelite hypothesis. Under the paleosol hypothesis, much of the

ORM sequence could be weakly metasomatized, with a little noticed effect in most of

the units except the paleosol, or Member 5 could be more metasomatized than the

other units due to fractures or some other factor.

Paleosols accumulate in areas of relative tectonic quiescence, where the rate of

aggradation is less than the rate of pedogenesis. They can occur in a wide variety of

88 environments, including alluvial and palustrine, or even shallow marine environments if sea level has recently dropped, exposing marine sediments (Kraus, 1999). If the ORM is related to the rifting of Rodinia (and Members 1-4 are consistent with this hypothesis),

Member 5 could represent a small organic-rich backarc basin. Alternately, the paleosol could record an unconformity with Precambrian basement. If the latter is the case,

Member 5 would need to be the lowest unit in the ORM – but this contradicts the geochronologic data, which suggests that sample JN 1713, in member 1, is the oldest unit.

Member 6 is anomalous in terms of the hornfels. This “hornfels,” however, is really almost a biotite gneiss, but finer-grained and with more metasomatism. This may be the same metasomatism that affected Member 5. Otherwise, the protolith sequence of interbedded shale and quartz arenite, with some limestone and dirtier sandstone suggests cyclic transgressions and regressions until Member 7, in which sea level appears to be relatively stable shallow marine, with some minor transgressions and regressions illustrated by the marbles and quartzites, respectively, followed by a stable beach environment (Member 8), with a minor transgression shown by the limestone.

Members 9 and 10 dominantly stay in the low-energy, potentially shallow- marine domain, but also contain transgressive and regressive fluctuations shown by marble and quartzite, respectively, with the quartzite near the top of the sequence, suggesting a minor general regression. The calc-silicates in these two units indicate either a depositional environment fluctuating between subaerial and subaqueous or an estuarine environment.

89 Assuming the ORM (Figure 72) represents a relatively intact upright depositional sequence (not duplicated by folds), one can deduce the following interpretation: The overall pattern in the stratigraphy of the ORM begins with deposition of potential rift sediments (member 1), then transgression (members 1-3) followed by a quick and relatively long-lasting regressive phase (member 4) capped by a potential backarc paleosol (member 5). Then follows a period of cyclic transgression and regression, followed by a long shallow marine period with a shorter period of subaerial deposition

(beach environment) in the middle. All of the members, especially 1, 9 and 10 have pockets or layers of other lithologies present, representing minor transgressions/regressions or spatial variations in depositional environments.

Figure 72 Panoramic view clockwise from Ontario Peak, with dead tree facing south-southeast. From left to right: Mt. San Antonio, Ontario Ridge, fog covering Los Angeles County, and Sunset Peak. Tonalite in foreground on peak top.

No broad overall transgression or regression can be seen in the ORM. Thin and thick quartzite layers appear throughout, and though marble is mostly seen in member

3, it also appears throughout. Biotite gneiss (or its close relative hornfels) increases in abundance in younger strata, indicating that the latter end of deposition could have been in a low energy, potentially shallow marine environment.

90 Age The Ontario Ridge metasediments were of previously unknown age - one of the principal purposes of the project was to determine this. As these are metasedimentary rocks, there are at least two potentially useful ages - detrital ages and ages of metamorphism. The latter will be discussed in a later section, and the results for the former are shown in Figure 55. Our five samples show two major peaks which are essentially shared among all three samples, at ~1200 and ~1440 Ma, several prominent peaks that are either large in one sample or small but shared among at least two samples, and many smaller peaks, often in the middle Neoproterozoic or middle

Paleoproterozoic or older. The maximum depositional age for the sequence is constrained by 3 grains between 906 to 934 Ma, which are 11-28% discordant (see

Figure 55).

Local Correlations The main group of metasediments observed in this study are east of the San

Antonio Canyon Fault (which almost directly runs along San Antonio Canyon); specifically, they wrap around Ontario and Cucamonga peaks, and then peter off to the east-northeast until they reach the San Jacinto fault near Lytle Creek. Metasediments which appear related to those on Ontario Ridge do outcrop elsewhere in the San Gabriel

Mountains, such as the Placerita Formation and the Potato Mountain block, as well as several smaller outcrops along the southern front of the range (see Figure 73).

91

Figure 73 Simplified geologic map of the San Gabriel Mountains, showing the several locations of probably related Neoproterozoic metasediments: on the East, the ORM; southwest of that the Potato Mountain block and further west the Placerita Canyon/Limerock Canyon assemblages. The age data from the Potato Mountain block mentioned at the bottom of the Figure has been recently renumbered to Figure 73a.

The Placerita Formation is also known as the Limerock Canyon assemblage

(Powell, 1993 and Oakshott, 1998), since in Limerock Canyon the 2,000 to greater than

5,000 feet thick section of marble, quartzite and sillimanite-cordierite schist is the most continuous (Oakshott, p. 51). The formation is predominantly marble, and so no radiometric dating has been done on it, the author only stating it “is probably Triassic or older...although an earlier Paleozoic or Precambrian age...cannot be excluded”

(Oakshott, pp. 51-52). The formation outcrops south of the dextral South Branch San

Gabriel fault, so the Placerita Formation could have been removed westward from the

Ontario Ridge group by faulting. Detrital zircon geochronology is necessary in this area.

92 Potato Mountain, in northeast Claremont, is also largely composed of similar metasedimentary rocks (Heaton, 2010), and seems directly related to the Ontario Ridge group, appearing to be faulted away from the latter by the left-lateral San Antonio

Canyon fault with a displacement of 8-10 km (Nourse, 1994), with the lower part of the section buried in the footwall of the Sierra Madre thrust. The northeast corner of this block appears in the southwest corner of Plate I. Neither the Potato Mountain block nor the Placerita Canyon assemblage (both shown in Figure 73) seem to preserve as complete a stratigraphy as that present in the Ontario Ridge metasediments - thus the need to study the latter as opposed to sundry other outcrops.

Except for a detrital zircon study done as part of Precambrian rock study (Premo et al., 2007) using 25 zircons from the Potato Mountain block (analyzed on the

Stanford/USGS SHRIMP-RG), the metasediments in the San Gabriel Mountains have not yet been dated. This gives valuable information to correlate with the ORM dated in this study, but the data from Potato Mountain cannot be considered sufficient to form unrefutable conclusions. Detrital zircon ages become more statistically valid with the analysis of more grains, and a robust dataset is generally considered to be at least 100 grains. Before Premo’s work, no radiometric dating had been done for the Ontario

Ridge metasediments in any potentially correlated locations in the San Gabriel

Mountains. Their SHRIMP analyses provided important high-precision age constraints

• Premo’s data is shown in figure 73a compared with our detrital zircon

probability plots from the ORM. Both major peaks from our detrital

zircon data, at 1200-1270 Ma and ~1440 Ma, match two major peaks

93 from Potato Mountain. A prominent ~1800 Ma peak and two minor

Paleoproterozoic peaks also match our data, making a strong case for these two large pendants to be chronologically equivalent. Hence, sinistral displacement along the Late Cenozoic San Antonio Canyon fault is supported.

94

95 Regional Correlations and Comparisons There are other similar metasedimentary packages in southern California of

Cambrian to Neoproterozoic age, notably in the San Bernardino Mountains (the Big Bear

Group) and the Pinto Mountains of the Mojave Desert (Barth et al., 2009). The Pinto

Mountain Group (see Figure 73b) has been interpreted to be deposited 1.63 to 1.45 Ga,

as it has none of the common peaks from ~1.4 Ga basement. It is possible that zircons

from the ORM and the Pinto Mountain Group contain zircons derived from the same

1.7-1.85 Ga source, but the ORM in general is demonstratively younger than the Pinto

Mountain group. JN 1713, the apparent oldest member of the ORM, however, may be correlated more closely with the Pinto Mountain Group, as its maximum depositional age is significantly older than the rest of the ORM.

Barth also conducted geochronology in three locations of the Big Bear Group, which are compared to the ORM in Figure 73c. Our 1200 and 1440 Ma major peaks match surprisingly well with much of the Big Bear samples’ prominent 1060, 1640-1650

and 1870 Ma peaks, and minor 910, 1840-1860, 1980 and 2630 Ma peaks. One of the

peaks that best matches ours from Big Bear group is 1257-1148 Ma, which, as shown

later, is almost absent in the western United States. It is likely that the Big Bear Group

and Ontario Ridge group were derived from similar sources, or possibly that they are a

continuation of essentially the same units, though lithologically variant due to lateral

facies changes. Specifically, the Big Bear Group is predominantly quartzite, but the

Ontario Ridge metasediments are largely biotite gneiss. Perhaps the two sequences

represent the edge of a basin, with the ORM representing deeper water in the south,

96 and the Big Bear Group representing a more shallow water/beach environment to the

north.

Part of the Big Bear group was not deposited until 0.62-0.55 Ga, likely after the

ORM, but the youngest peaks of the Big Bear Group only come from one location

(Lightning Gulch, in the middle of the section). However, Wildhorse Meadows’s youngest peak is ~900 Ma and Moonridge is ~1050 Ma. Given this data, it appears deposition had largely ceased in the Big Bear Group by ~900 Ma, similar to the ORM, but at least in Lightning Gulch deposition continued until 0.62-0.55 Ma. It should be noted that this youngest age is after the accepted date for the rifting of Rodinia, so minor deposition from Laurentian sources may have continued in some parts of the Big Bear

Group.

97

Figure 73d adds to 73c the miogeoclinal sequence of western Laurentia (which terminated in the late Proterozoic) for comparison with the Big Bear group and the

ORM. The miogeocline shares our 1400 Ma major peak and the prominent 1650 Ma

98 peak, but not the 1200 Ma major peak like the Big Bear Group. Our samples are also largely missing the largest peak in the miogeocline, at around 1730 Ma, that may be derived from widespread plutons in the Mojave Desert, Arizona, New Mexico, and

Colorado.

99

100

Figure 73e compares specific miogeocinal units with the ORM (see Wooden et al., 2012). The Wood Canyon and Zabriskie quartzites share our major 1440 peak and

1650-1770 prominent peak. Our samples do not match well with the immense broad

101 peak centered around 1100 Ma of the Uinta Mountains Group, so are likely not related to that group. From the Yavapai units also compared in Figure 44e, the Tapeats

Sandstone matches the major 1440 Ma peak, prominent 1740-1780, and minor 1940 and 2090 Ma peaks, and the Unkar group matches our major 1270, 1440, and 1660-

1770 peaks and minor 1830 and 2090 Ma peaks. Overall, our samples provide good matches to late Paleoproterozoic to early Mesoproterozoic sources from the miogeoclinal sequence and its 1650-1770 peak and to the Yavapai province and its

1740-1770 peak, but all are missing the major 1200 Ma peak present in our samples suggests that at that time the Ontario Ridge group (and presumably Big Bear group) were being derived from a different source.

102

103

104

The overall similarities between the Big Bear Group and ORM and their contrast with the miogeocline lead us to the same conclusion as Barth et al. (2009), that for both the Big Bear Group and ORM, at least some of the sediment sources from different

105 provenances than the miogeoclinal sequence. Though meta-sandstones of the ORM

were metamorphosed at too high a grade to show paleocurrent directions, if the ORM

represents an extension of the Big Bear group, then both may represent sediments shed

from Rodinia’s conjugate rift pair with Laurentia (see Global Correlations section).

Figure 74 shows distribution of Proterozoic basement and Proterozoic and

Paleozoic sedimentary cover, including the Ontario Ridge metasediments of the eastern

San Gabriel Mountains and the Big Bear Group of the San Bernardino Mountains. Figure

75 shows the distribution of these rocks pre-translation of the San Andreas and other

faults.

Figure 74 Regional map from Premo et al., 2007, showing various types of bedrock. The light blue are includes Neoproterozoic metasedimentary rocks that may correlate with our samples, like the Big Bear group and Pinto Mountain group, though others cannot be well correlated.

106

Figure 75 Map from Premo et al. (2007) like that in Figure 74, except this shows the rocks as they were likely originally distributed geographically, before being displaced by the San Andreas and other faults. Note that some metasedimentary rocks, such as the Big Bear group, are in closer proximity to the ORM.

Part of Figure 73f shows the Appalachian orogeny (see Gehrels et al., 2011) for comparison with peaks of the ORM. Peaks of this match our minor peaks at 910, 1040,

1070, 2590-2630 and 2680 Ma, prominent peaks at 1260, 1610-1660, 1740-1770 Ma and 1870 major peak at 1440 Ma. The Grenville orogen could potentially be the source for our minor 1070 peak, and the Mazatzal province could be the source for our 1.61-

1.66 Ga peaks.

Although some of our peaks match peaks from miogeoclinal sediments, overall the ORM likely does not originate from the Mojave miogeocline, as that has late-phase plutonism from 1.69 to 1.64 Ga, which forms a gap in our detrital record, nor from the

Ivanpah Orogeny, which occurred between 1.71 to 1.69 Ga. Wooden et al. (2012), who also summarized Proterozoic zircon geochronology from the western U.S., found pre-

107 orogenic orthogneisses (1.79-1.73 Ga) that may match our samples and post-Ivanpah intrusives (1.69-1.64 Ga) which do not match our samples.

Figure 76 shows geographically the location of many potential sources for the

ORM metasediments. As previously stated, there are peaks in these samples that could correlate to many of the North American provinces, including the Yavapai 1.70-1.80 Ga,

Mazatzal 1.62-1.70 Ga, Antler, Grenville, Appalachian and Ouachita orogenies. The

Yavapai and Mazatzal provinces likely contributed to the majority of the late

Paleoproterozoic peaks, especially the Mazatzal, while the orogens largely further east contributed to minor earlier peaks.

108

Figure 76 Map from Gehrel’s et al., 2011, showing many geologic provinces of North America. Many of these are potential sources for zircons from the ORM. The miogeocline is not a good exact match to the detrital peaks of the ORM, and none of the provinces here can thoroughly explain the 1.2 Ga peak present in the ORM and Big Bear group. Both the Mazatzal and Yavapai provinces fit well with some of our major peaks, especially the Mazatzal, and there are matches to minor peaks from the Antler, Ouachita, Grenville and Appalachian orogenies.

Potential Resolutions for Ontario Ridge Metasediment Provenance The most enigmatic peak by far of our detrital zircon geochronology is the major

~1200 Ma peak present in all our samples, which is unmatched in essentially all compared rocks except for the Big Bear group. The San Gabriel anorthosite, dated at

1180-1190 Ma by Barth (1995) overlaps with our age peak. This anorthosite also produces a wide spread of detrital zircon ages centered ~1200 Ma in the Miocene

Soledad Basin (C. Jacobson, personal communication, 2017). Zircons related to the anorthosite can concord with Stewart et al.’s (2001) description of silicic volcanic fields

109 now largely buried and/or destroyed by erosion (Barth, p. 237). These volcanic fields

may have been the equivalent to the San Gabriel anorthosite, and created our detrital

age peak at ~1200 Ma.

Timmons et al. (2001a-b) found ~1.23 Ga tephra deposits in the Bass limestone,

the basal member of the Unkar Group. These may be slightly younger than the

Allamoore/Castner/Mescal units, which are typically ~1.25-1.26 Ga (Marsaglia, 2002).

Both could act as a source for our 1.2 Ga peak. A granite from El Pozito in Sonora,

Mexico was dated at 1206 Ma (Bright et al., 2014). All of these are potential sources for our ~1200 Ma peak, but require a large transport system (likely fluvial) that has not yet been accounted for.

Any of these Southwest North American sources could be matches to the ORM’s detrital zircon peak at 1200. Alternatively, as in Barth et al.’s (2009) theory (see Regional correlations section), both the Big Bear group and ORM could have been shed off from

Rodinia’s conjugate rift pair with Laurentia (perhaps one of the continents shown in

Figure 77). This last hypothesis is supported by paleocurrent direction from the southwest in the Big Bear group, but the current direction may have been very localized.

110

Figure 77 Schematic map showing two possible Rodinia configurations: SWEAT, where Australia is west of Canada and Antarctica west of the U.S., and AUSWUS where Australia is further south, west of the U.S. with Antarctica to the south. The location of the San Gabriel Mountains is in North America just east of the lower white star in Australia., and there are matches to minor peaks from the Antler, Ouachita, Grenville and Appalachian orogenies.

More evidence and research is needed to accurately verify any of these hypotheses, but at this point the San Gabriel anorthosite and related volcanics seem the most likely source, since it is the simplest and most local. These volcanic and plutonic rocks could have occurred in a restricted basin, leaving the ~1200 Ma peak to be present only in the San Gabriel and San Bernardino Mountains (Big Bear Group).

111 Cretaceous Plutonics and Metamorphism The San Antonio terrane (SAT) of May and Walker (1989) consists of the large pendants of Ontario Ridge metasediments incorporated into a framework of Cretaceous plutonics (tonalite-granodiorite-granite). All these units are together mylonitized, especially in their southern and northern margins. The SAT is bordered on its north by strings of the Middle Fork Complex (May and Walker, 1989), a highly sheared zone surrounding the Icehouse Canyon fault (north section of map), on the northwest (NW section of map) by the San Gabriel terrane including Precambrian gneisses (Premo et al.,

2007) and Cretaceous quartz diorite (Nourse and Premo, 2016), and on the south by the

Cucamonga terrane, which contains a high-grade granulite complex (southern portion of

map).

May & Walker (1989) found pervasive mylonitization in the San Antonio terrane, especially on its northern and southern margins, which juxtaposed it with the

Cucamonga terrane in the south in a sinistral fashion between 88 and 78 Ma. Based off zircon depth profiling done in indium mounts from two quartzites at Stanford’s SHRIMP-

RG, metamorphic rims were dated at 75.7±1.2 Ma (12 grains) and 76.7±2.4 Ma (7

grains). This is roughly consistent with the youngest age from May and Walker (see

Discussion section).

May and Walker found in large measure that magmatism occurred at roughly the

same time as metamorphism, and recent work from Schwartz et al., (2016) supports

that conclusion. Schwartz found the mid-crustal tonalites in the San Antonio terrane

(SAT) to be cut by syn- to post-kinematic granodiorite or granite dikes. Using single

112 zircon grains on ICPMS, they dated igneous zircon cores from a metatonalite at 85.8±0.6

Ma and two of the syn- to post-kinematic granitic dikes at 76.2±0.5 and 74.0±0.7 Ma.

Using multi-grain analyses via ID-TIMS (isotope dilution thermal ion mass spectrometry),

May and Walker (1989) found the tonalite of the Cucamonga terrane to be emplaced at

88±3 Ma, but their SAT sample had an ambiguous pattern of discordance. The authors

gave their best estimate at 85 Ma for emplacement of the SAT tonalite collected from a

locality directly southeast of Stoddard Flat. They also dated an undeformed biotite

granite at 78+/-8 Ma, which they gave as the minimum age for mylonitization during juxtaposition of the SAT with the CT.

In our data from the Stanford/USGS SHRIMP, an Icehouse Canyon granodiorite that shows a weak mylonitic foliation was dated at 85.9±0.6 Ma. A quartz diorite near

Ontario Peak that shows no metamorphic foliation was dated at 75.8±0.9 Ma.

Interestingly, though the dates from our study are almost identical to Schwartz and May and Walker’s data, the lithologies are different.

Data from this study roughly agrees and expounds upon the posits of May and

Walker (1989), that the Cretaceous plutons were emplaced at roughly the same time as metamorphism and mylonitization, and therefore such plutonic rocks can be found at various stages of kinematic history. ~76-77 Ma ages from metamorphic quartzite rims dated in this study are coincident with the time of latest plutonism (quartz diorite of

Ontario Ridge, this study, and granitic dikes from Schwartz et al., 2016). The 86 Ma

Icehouse Canyon granodiorite shows mylonitization not observed in the Ontario Ridge quartz diorite. According to data from this study, plutonism around the ORM occurred

113 between 87-76 Ma, with mylonitization occurring by ~86 Ma, and the last metamorphic

event occurring ~76 Ma.

CONCLUSIONS The Ontario Ridge metasediments (ORM) preserve a thick (nearly 5 km), near-

continuous northeast-dipping section (see Figures 78 and 79) of Proterozoic rocks with a maximum depositional age between 906-934 Ma (except JN 1713, which is older). They preserve a mostly cyclic stratigraphy between beach and shallow marine environments, with possible early rift and then regressive phases. In Late Cretaceous time the section became a pendant caught in a deforming batholith, including a pre-metamorphic

Icehouse Canyon granodiorite dated at 85.9±0.6 Ma and a post-metamorphic quartz diorite dated at 75.8±0.9 Ma. Mylonitization around the margins of the SAT and pervasive metamorphism to upper amphibolite facies was roughly time-equivalent with the later magmatism, with metamict rims from two quartzites dated at 75.7±1.2 Ma (12 grains) and 76.7±2.4 Ma (7 grains).

114

Figure 78 Barrett Canyon viewed from the east, with the North Fork on the left and south fork on the right. The geology of the lower reaches of these canyons is well-constrained, but the upper reaches contain deep bramble-covered canyons and immense cliffs.

Figure 79 View from Ontario Ridge north of Ontario Peak looking north towards fog in Apple Valley below. Note the sporadic and highly physically weathered nature of the outcrops.

Probability plots for detrital zircons from five quartzites of the ORM match very well with those from the Potato Mountain block, supporting the theory that the sinistral

San Antonio Canyon fault separated these two blocks. The best regional match to our

115 probability plots in the western United States is the Big Bear group (Barth et al., 2005).

If both the ORM and Big Bear group are essentially the same units, they could record sediments shed from Laurentia’s conjugate rift pair with Rodinia, with the ORM representing a basinward extension of the Big Bear Group, or their detritus could originate in part from the San Gabriel anorthosite and associated volcanics.

Regardless of sediment transport direction, the location of the ORM at the abruptly truncated Late Proterozoic rift margin of Southwest Laurentia makes them a candidate for studies of Rodinia. Perhaps similar sedimentary basins exist in Australia,

Antarctica or other proposed conjugate rift pairs with western Laurentia.

Recommendations Much work remains for the Ontario Ridge metasediments (Figure 80). A more detailed structural analysis can be done on the ORM, such as systematically mapping s- and z-folds. This might resolve whether the section is upright and intact or repeated by larger-scale folding, with multiple overturned zones.

Additional samples, including those already collected and processed, can be dated to obtain a more complete spectrum of detrital ages. Although this project encompassed the majority of the ORM, similar studies may be carried out on the smaller pendants further east, from Cucamonga Peak to the San Jacinto fault. The Placerita

Canyon and Limerock Canyon assemblages should also be mapped, sampled and dated.

116

Figure 80 View of ridge south of Cascade Canyon from south, showing (from top to bottom) interbedded quartzite and leucogranite, and marble on bottom left.

One of the least understood problems in tectonic history is the arrangement of

Rodinia: specifically, which continent lay to the west of North America. Previous models

have suggested Western North America’s conjugate rift pair could be Australia or

Siberia, among others. Also, similar sediments in the San Bernardino Mountains just

east of the San Gabriels have proposed western sources (Barth et al., 2005). Analysis of

the ORM and Big Bear Group and comparisons with other sources have yielded sparse

potential matches for the 1200 Ma peak in the western U.S., and so have led more

credence to the idea that these sediments could have been, in part, shed from

Laurentia’s conjugate rift pair during Rodinia. To thoroughly test this theory may

involve travel to other countries and years of analysis to investigate other international

sources, and is far beyond the scope of this project. A thorough understanding of the

117 provenance of the Ontario Ridge metasediments and Big Bear group should help

constrain the configuration of Rodinia and the timing and nature of its breakup.

REFERENCES Barth, A.P., Jacobson, C.E., and May, D.J., Mesozoic evolution of basement terranes of the San Gabriel Mountains, Southern California: Summary and field guide, GSA Field Guide, 1991.

Barth, A.P., Wooden, J.L., Tosdal, R.M., Morrison, J., Dawson, D.L., and Hernly, B.M., Origin of gneisses in the aureole of the San Gabriel anorthosite complex and implications for the Proterozoic crustal evolution of southern California, Tectonics, v. 14, i. 3, p. 736-752, 1995.

Barth, A.P., Wooden, J.L., Coleman, D.S., and Vogel, M.B., 2009, Assembling and Disassembling California: A Zircon and Monazite Geochronologic Framework for Proterozoic Crustal Evolution in Southern California: The Journal of Geology, Vol. 117, No. 3, pp. 221-239, Stable URL: http://www.jstor.org/stable/10.1086/597515.

Bright, R.M., Amato, J.M., Denyszyn, S.W., and Ernst, R.E., 2014, U-Pb geochronology of 1.1 Ga diabase in the southwestern United States: Testing models for the origin of a post-Grenville large igneous province, Lithosphere, v. 6, no. 3, p. 135-156.

DeLand, J.T., Stratigraphy and Structure of the Mendenhall Gneiss, South-Central San Gabriel Mountains, California, Undergraduate Senior Thesis presented to the faculty of the Geological Sciences Department, California State Polytechnic University, Pomona, California, May 22, 2003.

Diblee, T.W., and Minch, J.A., 2002, Geologic map of the Mount Baldy quadrangle, Los Angeles and San Bernardino Counties, California, Diblee Geological Foundation Dibblee Foundation Map DF-90, scale 1:24,000 scale.

Ehlig, P.L., The geology of the Mount Baldy Region of the San Gabriel Mountains, California, University of California, Los Angeles, 1958.

Ehlig, P.L., Ehlert, K.W. and Crowe, B.M., Offset of the upper Miocene Caliente and Mint Canyon formations along the San Gabriel and San Andreas faults, 1975.

Hazelton, G.B., and Nourse, J.A., 1994, Constraints on the direction of Miocene extension and degree of crustal tilting in the eastern San Gabriel Mountains, southern California: Geological Society of America Abstracts with Programs, v.

118 26, no. 2, p. 58.

Heaton, D.E., Comparison of Late Cretaceous Plutonic rocks across the San Antonio Canyon Fault, San Gabriel Mountains, Geological Sciences Department California State Polytechnic University Pomona, CA, Senior Thesis Submitted in partial fulfillment of requirements for the B.S. Geology Degree.

Heaton, D. and Nourse, J., 2010, Comparison of Late Cretaceous Plutonic Rocks across the Left-lateral San Antonio Canyon Fault, San Gabriel Mountains, California, in Saint, P., Herzberg, M. and Zaprianoff, B. (eds.), Geology and Hydrology in the Eastern San Gabriel Mountains Through the River of Time: Field Trip Guidebook for South Coast Geological Society, June 18-19, pp. 117-124.

Ireland, T.R., Reference Module in Earth Systems and Environmental Sciences, Treatise on Geochemistry (Second Edition), 2014, v. 15, pp. 385-409.

Jacobson, C.E. and Dawson, M.R., Geochemistry and origin of mafic rocks from the Pelona, Orocopia, and Rand Schists, southern California, Earth and Planetary Science Letters, v. 92, i. 3-4, p. 271-385, 1989, https://doi.org/10.1016/0012- 821X(89)90061-7.

Kraus, M.J., Paleosols in clastic sedimentary rocks: their geologic applications, Earth- Science Reviews v. 47, pp. 41-70, 24 March 1999.

May, J.D. and Walker, N.W., Late Cretaceous juxtaposition of metamorphic terranes in the southeastern San Gabriel Mountains, California: Geologic Society of America Bulletin v. 101 no. 10, p. 1246-1267. September 1989. Doi: 10.1130/0016- 7606(1989)101<1246:LCJOMT>2.2.CO;2.

Miller, W.J., 1934, Geology of the western San Gabriel Mountains of California: Clifornia University at Los Angeles, Math and Physical Science, v. 1, p. 331-344.

Morton, D.M., Matti, J.C., Cossette, D.M, and Koukladas, Geologic map of the Cucamonga Peak 7.5’ quadrangle, San Bernardino County, California, Open-File Report 2001-311, 2001.

Nourse, J. A. and Premo, Wayne R., New Shrimp-Rg U-Pb Zircon and Sr Analyses From Jurassic and Late Cretaceous Plutonic Sheets in the East-Central San Gabriel Mountains, California, Geological Society of America Abstracts with Programs, Cordilleran Section - 112th Annual Meeting, 4–6 April, 2016.

Nourse, Jonathan A., Acosta, Ruben G., Stahl, Erin R., and Chuang, Mathew K., 1998, Basement geology of the 7.5 minute Mt. Baldy and Glendora quadrangles, San Gabriel Mountains, California, GSA Abstracts with Programs, v. 30, no. 5, p. 56.

119

Oakshott, G.B., Geology and Mineral Deposits of San Fernando Quadrangle: Los Angeles County, California, California Division of Mines, Bulletin 172, February 1998.

Robert E. Powell, "Chapter 1: Balanced palinspastic reconstruction of pre-late Cenozoic paleogeology, southern California: Geologic and kinematic constraints on evolution of the San Andreas fault system", The San Andreas Fault System: Displacement, Palinspastic Reconstruction, and Geologic Evolution, Robert E. Powell, R. J. Weldon, II, Jonathan C. Matti, 1993.

Premo, Wayne. R., Nourse, Jonathan A., Castineiras, Pedro, and Kellogg, Karl, 2007, New SHRIMP-RG U-Pb zircon ages and Sm-Nd analyses of Proterozoic metamorphic rocks of the San Gabriel basement terrane: Keys for Laurentian crustal reconstruction?, Abstract in Ores and Orogenesis: A Symposium Honoring the Career of William R. Dickinson, Arizona Geological Society, Tucson, AZ, p. 150- 151.

Robinson, J.W. and Christiansen, D., 2013, Trails of the Angeles: 100 Hikes in the San Gabriels, Wilderness Press, 9th Edition, p. 5.

Russo, R.E., Mao, X.L., Liu, H.C., Yoo, J.H., and Mao, S.S., Applied Physics A 69 [Supplemental], S887-S894, 1999.

Silver, E.A., Transitional tectonics and late Cenozoic structure of the continental margin off Northernmost California, GSA Bulletin, v. 82, i. 1, p. 1-22, 1971, DOI: https://doi.org/10.1130/0016-7606(1971)82[1:TTALCS]2.0.CO;2

Schwartz, J.J., Wiesenfeld, J.A., and Lackey, J.S., Cretaceous batholith construction during episodic garnet granulite-facies metamorphism in the San Gabriel Mountains, Southern California, G.S.A. Cordilleran Section 112th Annual Meeting, Paper No. 18-6, 2016.

Stewart, J. H.; Gehrels, G. E.; Barth, A. P.; Link, P. K.; Christie-Blick, N.; and Wrucke, C. T. 2001. Detrital zircon provenance of Mesoproterozoic to Cambrian arenites in the western United States and northwestern Mexico. Geol. Soc. Am. Bull. 113:1343– 1356.

Timmons, J.M., Karlstrom, K.E., Heiszler, M.T., and Bowring, S.A., 2001a, A synthesis from the Unkar Group of Grand Canyon, and inferences on late Mesoproterozoic intracratonic sedimentation and deformation in the Western U.S.: Geological Society of America Abstracts with Programs, v. 33, no. 5, p. 20.

Timmons, J.M., Karlstrom, K.E., Heizler, M.T., 2001b, Proterozoic multistage (ca. 1.1 and 0.8 Ga) extension recorded in the Grand Canyon Supergroup and establishment

120 of northwest- and north-trending tectonic grains in the southwestern United States: Geological Society of America Bulletin, v. 113, p. 163-180. Wooden, J.L., Barth, A.P., and Mueller, P.A., 2012, Crustal growth and tectonic evolution of the Mojave crustal province: Insights from hafnium isotope systematics in zircons, Lithosphere, doi: 10.1130/L218.1.

121 APPENDICES

Summary of U-Pb Zircon Analyses: Stanford University SHRIMP lab 1. Sample SZ1610 detrital zircon rims dated at Stanford: 2. Sample SZ1619 detrital zircon rims dated at Stanford: 3. Sample SZ1603: quartz diorite of Ontario Ridge 4. Sample SZ1616: granodiorite of Falling Rock Canyon

Summary of U-Pb-Th Detrital Zircon Analyses: CSUN ICP-MS lab

Plate 1: Geologic Map of Ontario Ridge Metasediments--supplemental file

Plate 2: Stratigraphic Section of Ontario Ridge Metasediments--supplemental file

Plate 3: Structural Cross Section Through Ontario Ridge Metasediments— supplemental file

122 Errors are 1 unless otherwise specified S Age 204corr 207corr q 208corr 204corr 204corr % 7-corr 7-corr Total Total S-K C-Pb C-Pb C-Pb 206Pb 206Pb i 206Pb 207Pb 208Pb Dis- d S

q ppm ppm ppm ppm 232Th % 206Pb % 208Pb % com 206 207 208 /238U 1 i /238U 1 /238U 1 /206Pb 1 /232Th 1 cor- d E N

u Spot Name U Th 206* 208* /238U err /238U err /232Th err Pb /204 /206 /206 Age err m Age errr Age err Age err Age err dant SZ1610-1.1 393 9 3.8 -0.10 0.02 15 0.0119 1.1 0.0337 48.8 73 18.59 0.840 2.070 66.5 2 72.8 1 74.0 1 #NUM! #NUM! -2146 -1250.49 #NUM! SZ1610-7.1 320 8 3.2 0.02 0.02 5.76 0.0116 2.2 0.0169 18.1 73 18.59 0.840 2.070 66.9 2 73.4 2 73.4 2 -1100 633 -1762 -526.55 +107 SZ1610-8.1 384 7 3.8 0.05 0.02 1.84 0.0121 1.0 0.0654 10.8 74 18.59 0.840 2.070 72.4 1 74.4 1 74.1 0.9 #NUM! #NUM! -533 -428.67 #NUM! SZ1610-11.1 344 8 3.4 0.03 0.02 1.24 0.0118 1.3 0.0169 16.5 75 18.59 0.840 2.070 70.3 1 74.6 1.0 74.6 1.0 #NUM! #NUM! -1132 -366.33 #NUM! SZ1610-5.1 370 7 3.7 0.06 0.02 8.56 0.0120 1.3 0.0341 15.1 75 18.59 0.840 2.071 71.2 1 75.1 1.0 74.8 1 #NUM! #NUM! -1131 -424.45 #NUM! SZ1610-3.1 411 6 4.1 0.00 0.01 1.71 0.0123 1.0 0.0703 19.0 75 18.59 0.840 2.071 67.9 3 75.4 1 75.6 1.0 -348 932 -3631 -1647.54 +120 SZ1610-2.1 513 6 5.3 0.02 0.01 6.12 0.0123 0.9 0.0613 35.6 77 18.59 0.841 2.071 73.1 1 76.7 0.9 76.6 1 #NUM! #NUM! -1882 -997.64 #NUM! SZ1610-10.1 415 8 4.3 -0.04 0.02 1.26 0.0124 1.5 0.0334 23.6 77 18.59 0.841 2.071 74.9 2 77.3 1 77.9 1 #NUM! #NUM! -944 -423.98 #NUM! SZ1610-12.1 339 6 3.6 0.07 0.02 5.93 0.0125 1.1 0.0472 14.7 78 18.58 0.841 2.071 71.7 2 78.3 0.9 77.8 1.0 #NUM! #NUM! -2366 -782.55 #NUM! SZ1610-6.1 431 8 4.5 -0.01 0.02 6.42 0.0124 3.3 0.0160 21.8 79 18.58 0.841 2.071 71.1 3 78.5 3 78.8 3 -681 464 -2587 -857.27 +111 SZ1610-4.1 305 25 9.3 0.84 0.09 23 0.0375 19.2 0.0832 31.4 225 18.36 0.850 2.082 226 43 225 43 219 46 368 337 802 296 +39 SZ1610-9.1 439 20 25.8 -0.36 0.05 31 0.0698 51.4 0.0427 60.9 426 18.04 0.864 2.098 431 214 426 214 432 218 776 83 331 254 +46 0.5 13 Mean age of coherent group (N=10) 75.7 age error (95% conf., without error in Std) 1.2 MSWD 2.37 Probability 0.01 age error (95% conf., with error in Std) 1.2

Std Grouped 2 error bars 5.7 100 data-point error ellipses are 68.3% conf. 95 900 90 5.5 85 700 80 500 5.3 75 UO/U 70 300 5.1 65 100 60 55 4.9 0 102030 50 0510 Hours Errors are 1 unless otherwise specified Age 204corr 207corr q 208corr 204corr 204corr % 7-corr 7-corr Total Total S-K C-Pb C-Pb C-Pb 206Pb 206Pb i 206Pb 207Pb 208Pb Dis- d

S

q ppm ppm ppm ppm 232Th % 206Pb % 208Pb % com 206 207 208 /238U 1 i /238U 1 /238U 1 /206Pb 1 /232Th 1 cor- d E N

u Spot Name U Th 206* 208* /238U err /238U err /232Th err Pb /204 /206 /206 Age err m Age err r Age err Age err Age err dant SZ1619-3.1 251 16 1.9 0.59 0.07 0.00 0.0118 0.8 0.1252 4.3 58 18.62 0.839 2.069 73.6 1 58.1 0.7 50.3 1 2946 74 2211 119 +98 SZ1619-2.1 211 6 2.1 -0.02 0.03 0.00 0.0120 0.8 0.0134 21.8 75 18.59 0.840 2.071 70.1 2 75.4 0.7 76.1 0.6 #NUM! #NUM! -1251 -495.67 #NUM! SZ1619-1.1 228 10 2.3 0.04 0.04 3.97 0.0120 2.2 0.0085 16.2 76 18.59 0.841 2.071 72.3 2 76.3 2 76.2 2 #NUM! #NUM! -507 -161.27 #NUM! SZ1619-7.1 141 4 1.5 0.03 0.03 2.10 0.0121 1.0 0.0136 19.4 77 18.59 0.841 2.071 69.2 2 77.1 0.8 76.8 0.8 -125 193 -1791 -537.83 +156 SZ1619-6.1 239 14 2.5 0.03 0.06 3.85 0.0124 1.0 0.0074 17.6 79 18.58 0.841 2.071 78.2 1.0 78.8 1.0 79.1 0.8 -270 529 -12 -66.06 +130 SZ1619-5.1 283 77 20.2 2.24 0.28 49 0.0847 45.7 0.0458 68.7 513 17.90 0.871 2.105 521 229 513 229 508 242 935 51 833 561 +46 SZ1619-8.1 436 10 78.5 -4.51 0.02 0.00 0.2171 0.8 0.1879 6.9 1226 16.66 0.928 2.180 1246 9 1226 9 1259 9 1553 46 -3263 -1129.13 +22 0.5 8 Mean age of coherent group (N=4) 76.7 age error (95% conf., without error in Std) 2.4 MSWD 2.94 Probability 0.03 age error (95% conf., with error in Std) 2.4

Std Grouped  5.5 100 2 error bars data-point error ellipses are 68.3% conf. 95 1300 90 5.4 85 80 900 5.3 75 UO/U 70 500 5.2 65 60 100 55 5.1 0102030 50 Hours 02468  Errors are 1 unless otherwise specified S Age 204corr 207corr q 208corr 204corr 204corr % 7-corr 7-corr Total Total S-K C-Pb C-Pb C-Pb 206Pb 206Pb i 206Pb 207Pb 208Pb Dis- d

S  q     ppm ppm ppm ppm 232Th % 206Pb % 208Pb % com 206 207 208 /238U 1 i /238U 1 /238U 1 /206Pb 1 /232Th 1 cor- d E N

u Spot Name U Th 206* 208* /238U err /238U err /232Th err Pb /204 /206 /206 Age err m Age err r Age err Age err Age err dant SZ1603-1.1 513 235 5.0 0.64 0.473 0.48 0.01152 0.6 0.00334 5.7 73 18.59 0.840 2.070 73.6 0.5 73.4 0.5 74.4 0.6 203 107 64.3 4 +64 SZ1603-15.1 425 152 4.2 0.55 0.368 0.26 0.01153 0.7 0.00410 6.3 74 18.59 0.840 2.070 73.1 0.6 73.8 0.5 73.4 0.6 -336 242 69.3 7 +122 SZ1603-2.1 787 539 8.0 1.83 0.707 0.74 0.01179 0.8 0.00378 3.5 76 18.59 0.840 2.071 75.4 0.6 75.6 0.6 75.5 0.7 -41 89 74.5 3 +287 SZ1603-7.1 715 316 7.3 1.08 0.456 0.18 0.01183 0.6 0.00382 4.4 76 18.59 0.841 2.071 75.5 0.5 75.8 0.5 75.7 0.6 -88 110 72.9 4 +186 SZ1603-12.1 675 338 6.9 1.09 0.517 0.35 0.01191 1.0 0.00361 4.9 76 18.59 0.841 2.071 76.2 0.7 76.3 0.7 76.7 0.9 11.4 87 71.0 4 -570 SZ1603-3.1 784 401 8.0 1.34 0.529 0.19 0.01197 0.6 0.00396 4.5 76 18.59 0.841 2.071 76.7 0.5 76.3 0.5 76.4 0.6 262 62 79.9 4 +71 SZ1603-16.1 637 279 6.5 0.87 0.452 0.22 0.01192 0.8 0.00347 4.9 76 18.59 0.841 2.071 76.3 0.6 76.4 0.6 76.9 0.7 20.5 79 68.9 4 -274 SZ1603-9.1 460 153 4.8 0.48 0.344 0.52 0.01204 0.6 0.00361 6.9 77 18.59 0.841 2.071 76.9 0.5 77.0 0.6 77.4 0.6 28.3 170 68.1 6 -173 SZ1603-8.1 662 255 6.9 0.96 0.398 0.20 0.01202 1.1 0.00399 5.0 77 18.59 0.841 2.071 76.9 0.9 77.2 0.9 76.8 1.0 -98 84 79.2 4 +180 SZ1603-10.1 335 147 3.5 0.51 0.454 0.72 0.01210 0.7 0.00398 6.8 77 18.59 0.841 2.071 77.7 0.6 77.4 0.6 77.4 0.7 226 115 82.6 6 +66 SZ1603-5.1 452 179 4.7 0.57 0.410 0.61 0.01207 2.0 0.00345 6.5 77 18.59 0.841 2.071 77.2 2 77.5 2 77.8 2 -63 105 67.8 5 +224 SZ1603-11.1 610 293 6.4 1.07 0.495 0.19 0.01218 1.3 0.00421 4.6 78 18.59 0.841 2.071 77.8 1 77.8 1 77.5 1 49.5 103 81.4 4 -58 SZ1603-13.1 644 334 6.7 1.24 0.536 0.18 0.01216 0.6 0.00422 4.1 78 18.58 0.841 2.071 77.7 0.5 77.8 0.5 77.3 0.6 1.6 104 82.1 4 -4771 SZ1603-14.1 726 321 7.6 1.14 0.457 0.34 0.01223 0.6 0.00404 4.3 78 18.58 0.841 2.071 78.1 0.5 78.2 0.5 78.1 0.6 -16 100 77.4 4 +594 SZ1603-6.1 584 279 6.3 0.93 0.493 1.23 0.01257 3.6 0.00371 6.3 81 18.58 0.841 2.071 80.4 3 80.6 3 81.0 3 16.9 88 73.5 5 -379 0.5 16 Mean age of coherent group (N=13) 75.8 with wt stdev: age error (95% conf., without error in Std) 0.9 75.8 +- 2.8 MSWD 5.49 Probability 0.00 age error (95% conf., with error in Std) 0.9

2 error bars Std Grouped data-point error ellipses are 2sigma 88

5.5 86 84 82

82

UO/U 5.3 80 74 78

76

5.1 74 0 5 10 15 20 25 72 Hours 0 5 10 15  Errors are 1 unless otherwise specified S Age 204corr 207corr q 208corr 204corr 204corr % 7-corr 7-corr Total Total S-K C-Pb C-Pb C-Pb 206Pb 206Pb i 206Pb 207Pb 208Pb Dis- d

S  q     ppm ppm ppm ppm 232Th % 206Pb % 208Pb % com 206 207 208 /238U 1 i /238U 1 /238U 1 /206Pb 1 /232Th 1 cor- d E N

u Spot Name U Th 206* 208* /238U err /238U err /232Th err Pb /204 /206 /206 Age err m Age err r Age err Age err Age err dant SZ1616-8.1 636 271 7.2 0.98 0.441 0.50 0.01312 0.9 0.00399 4.8 84 18.58 0.841 2.071 83.9 0.7 84.1 0.7 84.3 0.8 -34 91 78.0 4 +350 SZ1616-1.1 303 152 3.5 0.59 0.520 1.11 0.01342 0.7 0.00447 6.2 86 18.57 0.841 2.071 85.8 0.6 85.7 0.6 85.6 0.8 119 123 87.8 6 +28 SZ1616-5.1 663 217 7.6 0.79 0.338 0.91 0.01337 0.6 0.00396 5.4 86 18.57 0.841 2.071 85.5 0.5 85.8 0.5 86.0 0.6 -49 87 76.9 5 +277 SZ1616-2.1 601 222 6.9 0.89 0.381 0.42 0.01345 0.9 0.00458 5.1 86 18.57 0.841 2.071 85.6 0.8 86.0 0.9 85.7 0.9 -124 185 83.1 6 +170 SZ1616-7.1 550 292 6.4 1.19 0.548 3.30 0.01343 0.7 0.00433 8.2 86 18.57 0.841 2.071 85.5 0.6 86.4 0.6 85.9 0.9 -358 157 81.6 7 +125 SZ1616-9.1 506 84 5.9 0.32 0.171 1.30 0.01346 0.6 0.00392 8.8 86 18.57 0.841 2.071 86.1 0.6 86.4 0.6 86.4 0.6 -57 93 75.0 8 +253 SZ1616-4.1 552 358 6.4 1.46 0.670 0.50 0.01357 1.4 0.00455 6.4 87 18.57 0.841 2.071 86.6 1 86.9 1 86.3 1 -45 104 89.2 6 +296 SZ1616-6.2 630 261 7.3 1.01 0.429 1.20 0.01359 1.2 0.00438 4.9 87 18.57 0.841 2.071 87.2 1 86.9 1 86.9 1 203 77 90.9 5 +57 SZ1616-3.1 1204 492 14.4 2.12 0.423 0.46 0.01395 2.8 0.00493 6.0 89 18.57 0.841 2.072 88.9 2 89.1 2 88.6 3 -4 79 93.7 6 +2178 0.5 10 Mean age of coherent group (N=9) 85.9 age error (95% conf., without error in Std) 0.5 MSWD 1.33 Probability 0.22 age error (95% conf., with error in Std) 0.6

 Std Grouped 96 2 error bars data-point error ellipses are 2sigma 94 96 5.5 92 92 90 88 UO/U 5.3 88

86 84

84 80 5.1 0 5 10 15 20 25 82 Hours 0246810 All Anayses Combined: 439 grains

SZ16105A; 98 grains

SZ1610; 99 grains

SZ1619A; 99 grains

SZ 1701; 100 grains AgeProbability

JN 1713; 43 grains

800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 Age (Ma) All Anayses Combined; 439 grains

SZ1605A; 98 grains

SZ1610; 99 grains

SZ1619A;

AgeProbability 99 grains

SZ 1701; 100 grains

JN 1713; 43 grains

800 1000 1200 1400 1600 1800 2000 Age (Ma) High U/Th Metamorphic Overgrowths on Zircon from Sample SZ1605A (2 grains) and SZ 1619A (13 Grains) Probability

Age

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

Pb206/U238 Age in Ma Detrital Zircon U‐Pb Results from Ontario Ridge‐‐Analyzed on ICP‐MS at CSUN: April and August, 2017 Sample Pb207/Pb206 Pb207/U235 Pb206/U238 SZ1610 ppm U ppm Th U/Th Th/U Age 2 sigma 1 sigma Age Age % discordance Comment Z03_1 323 121.7 2.654 0.377 2084 56.0 28.0 1910 1781 14.5% Z03_10 182.3 135 1.350 0.741 1772 54.0 27.0 1727 1708 3.6% Z03_11 170.9 130.8 1.307 0.765 1449 48.0 24.0 1456 1430 1.3% Z03_12 1303 640 2.036 0.491 1059 68.0 34.0 1084 1087 ‐2.6% Z03_13 436 273 1.597 0.626 1848 49.0 24.5 1830 1789 3.2% Z03_14 474 243 1.951 0.513 1145 65.0 32.5 1017 916 20.0% Z03_15 65.7 83.4 0.788 1.269 1211 72.0 36.0 1244 1248 ‐3.1% Z03_16 214 231 0.926 1.079 1365 64.0 32.0 1303 1271 6.9% Z03_17 254 176.7 1.437 0.696 1374 55.0 27.5 1164 1034 24.7% Z03_18 201 185.1 1.086 0.921 1680 62.0 31.0 1473 1329 20.9% Z03_19 112.8 132.6 0.851 1.176 1097 69.0 34.5 865 798 27.3% Z03_2 257 427 0.602 1.661 1440 58.0 29.0 1440 1454 ‐1.0% Z03_20 223.7 288.4 0.776 1.289 1399 48.0 24.0 1092 937 33.0% Z03_21 954 508 1.878 0.532 1434 62.0 31.0 1270 1167 18.6% Z03_22 115 164 0.701 1.426 1183 72.0 36.0 1079 1020 13.8% Z03_23 303 223 1.359 0.736 1180 58.0 29.0 1240 1247 ‐5.7% Z03_24 1160 893 1.299 0.770 2692 48.0 24.0 2690 2691 0.0% Z03_25 342 177.6 1.926 0.519 1636 58.0 29.0 1285 1073 34.4% Z03_26 297 132.6 2.240 0.446 1463 60.0 30.0 1557 1612 ‐10.2% Z03_27 575 390 1.474 0.678 1435 68.0 34.0 1347 1281 10.7% Z03_28 148.5 212 0.700 1.428 1478 70.0 35.0 1447 1448 2.0% Z03_29 316 241 1.311 0.763 1767 47.0 23.5 1783 1790 ‐1.3% Z03_3 169.9 152 1.118 0.895 1934 45.0 22.5 1877 1867 3.5% Z03_30 70.4 52.2 1.349 0.741 1364 52.0 26.0 1312 1301 4.6% Z03_31 447 170 2.629 0.380 1758 52.0 26.0 1306 1042 40.7% Z03_32 125.8 107.8 1.167 0.857 1386 67.0 33.5 1419 1447 ‐4.4% Z03_33 605 172 3.517 0.284 1263 71.0 35.5 1127 1061 16.0% Z03_34 19.4 18.7 1.037 0.964 1275 70.0 35.0 1236 1224 4.0% Z03_35 180 187 0.963 1.039 1061 72.0 36.0 1031 1023 3.6% Z03_36 337 196 1.719 0.582 1424 66.0 33.0 1380 1358 4.6% Z03_37 820 231 3.550 0.282 1237 51.0 25.5 1087 1003 18.9% Z03_38 260 167 1.557 0.642 1708 73.0 36.5 1490 1353 20.8% Z03_39 470 440 1.068 0.936 1477 66.0 33.0 1411 1389 6.0% Z03_4 135.3 221 0.612 1.633 1264 47.0 23.5 1237 1238 2.1% Z03_40 508 108 4.704 0.213 995 57.0 28.5 999 1007 ‐1.2% Z03_41 396 501 0.790 1.265 1241 60.0 30.0 1124 1077 13.2% Z03_42 121.4 119.8 1.013 0.987 1424 50.0 25.0 1188 1063 25.4% Z03_43 893 443 2.016 0.496 1179 61.0 30.5 1211 1225 ‐3.9% Z03_44 232 132.1 1.756 0.569 1618 50.0 25.0 1465 1397 13.7% Z03_45 353 259 1.363 0.734 2518 56.0 28.0 2332 2147 14.7% Z03_46 686 324 2.117 0.472 1258 65.0 32.5 1207 1199 4.7% Z03_47 601 493 1.219 0.820 1728 53.0 26.5 1739 1722 0.3% Z03_48 206 131.8 1.563 0.640 1185 57.0 28.5 1210 1218 ‐2.8% Z03_49 373 379 0.984 1.016 2623 52.0 26.0 2414 2152 18.0% Z03_5 441 424 1.040 0.961 1133 47.0 23.5 1055 1016 10.3% Z03_50 217 542 0.400 2.498 2277 55.0 27.5 2218 2176 4.4% High Th/U Z03_51 118.8 103.3 1.150 0.870 1172 69.0 34.5 1097 1068 8.9% Z03_52 104.4 99.9 1.045 0.957 1411 60.0 30.0 1378 1350 4.3% Z03_53 494 584 0.846 1.182 1238 79.0 39.5 1087 1014 18.1% Z03_54 199 170.5 1.167 0.857 1089 73.0 36.5 1098 1089 0.0% Z03_55 142.7 184.3 0.774 1.292 1370 75.0 37.5 1402 1423 ‐3.9% Z03_56 183.5 92.3 1.988 0.503 1640 60.0 30.0 1340 1174 28.4% Z03_57 306 25.7 11.907 0.084 1744 68.0 34.0 1585 1475 15.4% Z03_58 35 62.6 0.559 1.789 1365 66.0 33.0 1299 1225 10.3% Z03_59 164.7 44.5 3.701 0.270 1190 95.0 47.5 1131 1115 6.3% Z03_6 480 266 1.805 0.554 1692 53.0 26.5 1566 1484 12.3% Z03_60 329 150 2.193 0.456 1301 65.0 32.5 1231 1165 10.5% Z03_61 109.4 65.6 1.668 0.600 1129 78.0 39.0 1188 1189 ‐5.3% Z03_62 143 74.4 1.922 0.520 1822 56.0 28.0 1778 1771 2.8% Z03_63 693 289 2.398 0.417 1464 56.0 28.0 1357 1302 11.1% Z03_64 38 63.5 0.598 1.671 1372 73.0 36.5 1255 1170 14.7% Z03_65 219 112.8 1.941 0.515 1368 69.0 34.5 948 769 43.8% Z03_66 329 171 1.924 0.520 1642 61.0 30.5 1606 1571 4.3% Z03_67 155.3 95 1.635 0.612 1137 76.0 38.0 1197 1222 ‐7.5% Z03_68 373 159 2.346 0.426 1224 80.0 40.0 1179 1178 3.8% Z03_69 122 68.2 1.789 0.559 1536 89.0 44.5 1438 1369 10.9% Z03_7 73.8 49.1 1.503 0.665 1055 61.0 30.5 1084 1073 ‐1.7% Z03_70 300 142.7 2.102 0.476 1333 68.0 34.0 1237 1177 11.7% Z03_71 50.6 88.6 0.571 1.751 1277 80.0 40.0 1248 1243 2.7% Young grain used to constrain maximum Z03_72 114.7 50 2.294 0.436 906 67.0 33.5 1022 1024 ‐13.0% depositional age Z03_73 318 132.2 2.405 0.416 1359 71.0 35.5 1255 1182 13.0% Z03_74 190 77 2.468 0.405 1101 79.0 39.5 711 606 45.0% Z03_75 517 192 2.693 0.371 1716 53.0 26.5 1662 1628 5.1% Z03_76 237 71 3.338 0.300 2461 58.0 29.0 2346 2200 10.6% Z03_77 168.4 104.4 1.613 0.620 1511 79.0 39.5 1072 875 42.1% Z03_78 108 59.4 1.818 0.550 1394 81.0 40.5 1347 1273 8.7% Z03_79 414 190.7 2.171 0.461 1189 66.0 33.0 1051 991 16.7% Z03_8 194 113.8 1.705 0.587 1405 61.0 30.5 1442 1471 ‐4.7% Z03_80 321 119.1 2.695 0.371 1816 59.0 29.5 1692 1558 14.2% Z03_81 325 115.6 2.811 0.356 1296 75.0 37.5 1178 1075 17.1% Z03_82 777 362 2.146 0.466 1089 69.0 34.5 1092 1068 1.9% Z03_83 131.8 98 1.345 0.744 1341 61.0 30.5 1205 1102 17.8% Z03_84 361 134.8 2.678 0.373 1428 68.0 34.0 1077 904 36.7% Z03_85 1109 287 3.864 0.259 1163 65.0 32.5 1052 961 17.4% Z03_86 118.9 71.5 1.663 0.601 1472 65.0 32.5 1412 1399 5.0% Z03_87 150.9 73.7 2.047 0.488 1516 80.0 40.0 1454 1382 8.8% Z03_88 24.5 30.3 0.809 1.237 1078 84.0 42.0 952 885 17.9% Z03_89 66.9 66.3 1.009 0.991 1059 76.0 38.0 972 940 11.2% Z03_9 410 213.5 1.920 0.521 1460 48.0 24.0 1399 1353 7.3% Z03_90 87.1 50 1.742 0.574 1085 65.0 32.5 1033 1033 4.8% Z03_91 134.2 47.5 2.825 0.354 1207 79.0 39.5 1186 1193 1.2% Z03_92 109.1 89.7 1.216 0.822 1844 58.0 29.0 1743 1731 6.1% Z03_93 65.1 31.6 2.060 0.485 1127 71.0 35.5 1067 1070 5.1% Z03_94 550 116.4 4.725 0.212 1258 70.0 35.0 1036 957 23.9% Z03_95 190 101.7 1.868 0.535 1624 97.0 48.5 1458 1341 17.4% Z03_96 199 58 3.431 0.291 1730 57.0 28.5 1700 1700 1.7% Z03_97 167.3 114.9 1.456 0.687 1481 61.0 30.5 1339 1290 12.9% Z03_98 50.8 122.3 0.415 2.407 1288 93.0 46.5 1088 1033 19.8% Z03_99 140 110.1 1.272 0.786 1321 80.0 40.0 1264 1304 1.3% Sample Pb207/Pb206 Pb207/U235 Pb206/U238 SZ1605A ppm U ppm Th U/Th Th/U Age 2 sigma 1 sigma Age Age % discordance Comment X1605a_1 65.0 45.3 1.435 0.697 1209 69 34.5 1101 1054 12.8% X1605a_2 246.0 33.1 7.432 0.135 1437 84 42 357 208 85.5% X1605a_3 198.0 75.5 2.623 0.381 1800 55 27.5 1375 1120 37.8% X1605a_4 155.4 57.9 2.684 0.373 1846 58 29 1573 1399 24.2% X1605a_5 145.0 116.8 1.241 0.806 1650 54 27 1510 1415 14.2% X1605a_6 154.0 30.8 5.000 0.200 1786 72 36 1523 1360 23.9% X1605a_7 73.0 40 1.825 0.548 1460 63 31.5 894 693 52.5% X1605a_8 112.9 66.1 1.708 0.585 1370 52 26 1188 1089 20.5% X1605a_9 84.1 89.5 0.940 1.064 1538 51 25.5 1394 1315 14.5% X1605a_10 392.0 63 6.222 0.161 1988 62 31 1240 844 57.5% X1605a_11 112.7 54.5 2.068 0.484 1448 54 27 1387 1366 5.7% X1605a_12 84.1 41.2 2.041 0.490 1757 53 26.5 1629 1542 12.2% X1605a_13 153.1 63.6 2.407 0.415 1195 60 30 584 446 62.7% X1605a_14 100.4 92.9 1.081 0.925 1487 52 26 1451 1426 4.1% X1605a_15 603.0 66 9.136 0.109 1571 44 22 543 332 78.9% X1605a_16 129.0 74.6 1.729 0.578 1436 52 26 907 699 51.3% X1605a_17 193.0 275.1 0.702 1.425 1053 65 32.5 1055 1052 0.1% X1605a_18 61.7 18.89 3.266 0.306 1390 50 25 1353 1347 3.1% X1605a_19 468.0 514 0.911 1.098 1463 64 32 882 694 52.6% X1605a_20 462.0 89.3 5.174 0.193 1705 89 44.5 904 618 63.8% X1605a_21 101.5 51.1 1.986 0.503 1437 54 27 1452 1443 ‐0.4% X1605a_22 233.0 197 1.183 0.845 1984 52 26 1839 1724 13.1% X1605a_23 204.0 61.7 3.306 0.302 1812 93 46.5 809 522 71.2% X1605a_24 192.0 127 1.512 0.661 1834 46 23 1177 885 51.7% X1605a_25 364.0 95.2 3.824 0.262 1654 48 24 1120 862 47.9% X1605a_26 28.4 21.52 1.320 0.758 1445 61 30.5 1433 1433 0.8% X1605a_27 274.0 123.8 2.213 0.452 1190 46 23 1145 1135 4.6% X1605a_28 155.9 108.2 1.441 0.694 1152 55 27.5 1177 1178 ‐2.3% X1605a_29 31.9 89.5 0.356 2.806 1223 81 40.5 1182 1156 5.5% High Th/U X1605a_30 331.0 194.5 1.702 0.588 1715 45 22.5 1564 1469 14.3% X1605a_31 93.1 61.3 1.519 0.658 1524 53 26.5 1455 1413 7.3% X1605a_32 210.3 224.1 0.938 1.066 1154 57 28.5 1143 1122 2.8% X1605a_33 84.3 78.9 1.068 0.936 1796 47 23.5 1789 1792 0.2% X1605a_34 98.4 86.4 1.139 0.878 1279 65 32.5 1175 1128 11.8% X1605a_35 496.0 271 1.830 0.546 1060 69 34.5 425 319 69.9% X1605a_36 21.3 15.52 1.372 0.729 1207 60 30 1131 1117 7.5% X1605a_37 143.5 416 0.345 2.899 1197 68 34 1148 1108 7.4% High Th/U X1605a_38 319.0 113.8 2.803 0.357 1743 55 27.5 1326 1098 37.0% X1605a_39 81.5 70.5 1.156 0.865 1426 82 41 1426 1450 ‐1.7% X1605a_40 499.0 128.3 3.889 0.257 1762 78 39 1252 982 44.3% X1605a_41 173.8 88.2 1.971 0.507 1423 80 40 1370 1321 7.2% X1605a_42 292.0 46.9 6.226 0.161 1316 83 41.5 1113 1014 22.9% X1605a_43 555.0 77 7.208 0.139 1762 54 27 1515 1378 21.8% X1605a_44 393.0 199.1 1.974 0.507 1774 92 46 1472 1312 26.0% X1605a_45 634.0 331 1.915 0.522 1624 79 39.5 1238 1021 37.1% High U/Th; interpreted as metamorphic X1605a_46 1311.0 96.7 13.557 0.074 295 97 48.5 80.3 75.9 74.3% overgrowth; Pb206/U238 age plotted X1605a_47 162.0 46.7 3.469 0.288 1122 71 35.5 1095 1112 0.9% X1605a_48 97.6 62 1.574 0.635 1428 66 33 1366 1290 9.7% X1605a_49 427.0 75 5.693 0.176 1205 87 43.5 416 300 75.1% X1605a_50 207.0 96.5 2.145 0.466 1775 64 32 1649 1492 15.9% X1605a_51 63.5 73.9 0.859 1.164 1236 84 42 895 753 39.1% X1605a_52 227.0 78.8 2.881 0.347 1427 88 44 1213 1104 22.6% X1605a_53 191.0 84.1 2.271 0.440 1799 57 28.5 1687 1607 10.7% Young grain used to constrain maximum X1605a_54 16.0 30.7 0.522 1.914 910 110 55 850 811 10.9% depositional age X1605a_55 207.0 59.2 3.497 0.286 1807 70 35 1655 1546 14.4% X1605a_56 23.4 8.16 2.868 0.349 1272 83 41.5 1240 1258 1.1% X1605a_57 23.0 13.28 1.732 0.577 1353 60 30 1359 1341 0.9% X1605a_58 272.0 53.1 5.122 0.195 1758 79 39.5 838 534 69.6% X1605a_59 116.4 35.8 3.251 0.308 1435 79 39.5 1303 1213 15.5% X1605a_60 226.0 92.8 2.435 0.411 1798 70 35 1206 890 50.5% X1605a_61 330.0 91.5 3.607 0.277 1545 72 36 1025 773 50.0% X1605a_62 288.0 127.4 2.261 0.442 1669 54 27 1447 1286 22.9% X1605a_63 186.0 32.3 5.759 0.174 1310 100 50 950 840 35.9% X1605a_64 110.7 43.9 2.522 0.397 2799 73 36.5 2684 2500 10.7% X1605a_65 139.0 93 1.495 0.669 1312 89 44.5 1235 1205 8.2% X1605a_66 117.5 116.8 1.006 0.994 1242 66 33 1275 1281 ‐3.1% X1605a_67 166.0 94.6 1.755 0.570 1432 81 40.5 1269 1193 16.7% X1605a_68 154.5 61.8 2.500 0.400 1506 75 37.5 792 561 62.7% Young grain used to constrain maximum X1605a_69 138.0 76.5 1.804 0.554 934 77 38.5 722 672 28.1% depositional age X1605a_70 676.0 231.7 2.918 0.343 1217 70 35 646 485 60.1% X1605a_71 198.0 126.9 1.560 0.641 1163 86 43 1126 1098 5.6% X1605a_72 102.0 52.8 1.932 0.518 1348 66 33 1233 1160 13.9% X1605a_73 156.0 160 0.975 1.026 1808 64 32 1620 1472 18.6% X1605a_74 50.3 72.7 0.692 1.445 1339 65 32.5 1314 1305 2.5% X1605a_75 126.2 71.5 1.765 0.567 1439 69 34.5 1380 1333 7.4% X1605a_76 317.0 312 1.016 0.984 1416 61 30.5 1283 1186 16.2% X1605a_77 106.3 92 1.155 0.865 1767 60 30 1861 1925 ‐8.9% X1605a_78 384.0 172 2.233 0.448 1182 62 31 914 814 31.1% X1605a_79 75.2 43.8 1.717 0.582 1435 60 30 1406 1391 3.1% X1605a_80 272.0 60.7 4.481 0.223 1015 69 34.5 615 526 48.2% X1605a_81 199.0 50.7 3.925 0.255 1774 87 43.5 1505 1360 23.3% X1605a_82 297.0 54.5 5.450 0.184 1357 87 43.5 1078 945 30.4% X1605a_83 103.4 41.8 2.474 0.404 1726 60 30 1621 1532 11.2% X1605a_84 78.2 35.5 2.203 0.454 1671 58 29 1108 846 49.4% X1605a_85 83.1 99 0.839 1.191 1832 45 22.5 1828 1795 2.0% X1605a_86 186.0 200.1 0.930 1.076 1263 83 41.5 883 742 41.3% X1605a_87 333.0 87.5 3.806 0.263 1454 62 31 717 500 65.6% X1605a_88 54.8 43.4 1.263 0.792 1248 61 30.5 1293 1284 ‐2.9% X1605a_89 51.8 23.73 2.183 0.458 1234 68 34 1226 1186 3.9% X1605a_90 680.0 231 2.944 0.340 1167 79 39.5 543 409 65.0% X1605a_91 114.4 66.6 1.718 0.582 1456 58 29 1346 1271 12.7% X1605a_92 68.9 71.4 0.965 1.036 2527 52 26 2532 2534 ‐0.3% X1605a_93 485.0 333 1.456 0.687 1742 71 35.5 1092 846 51.4% X1605a_94 118.9 46.7 2.546 0.393 2000 120 60 1960 1890 5.5% X1605a_95 293.0 204 1.436 0.696 1480 65 32.5 1223 1077 27.2% X1605a_96 109.3 104.8 1.043 0.959 1750 75 37.5 1808 1810 ‐3.4% High U/Th; interpreted as metamorphic X1605a_97 17.7 ‐0.003 ‐5900.000 0.000 1540 440 220 159 75.2 95.1% overgrowth; Pb206/U238 age plotted X1605a_98 121.7 129.6 0.939 1.065 1734 69 34.5 1651 1600 7.7% X1605a_99 615.0 54.8 11.223 0.089 1458 78 39 530 333 77.2% X1605a_100 225.0 78.7 2.859 0.350 1148 65 32.5 1072 1033 10.0% Sample Pb207/Pb206 Pb207/U235 Pb206/U238 SZ1619 ppm U ppm Th U/Th Th/U Age 2 sigma 1 sigma Age Age % discordance Comment X1619_1 225.0 78.2 2.877 0.348 1142 67 33.5 1068 1033 9.5% High U/Th; interpreted as metamorphic X1619_2 87.8 ‐0.0037 ‐23729.730 0.000 520 16 8 64 57 89.0% overgrowth; Pb206/U238 age plotted X1619_3 75.3 45 1.673 0.598 1273 59 29.5 1153 1084 14.8% X1619_4 492.0 227 2.167 0.461 1320 66 33 1122 1007 23.7% X1619_5 176.0 89.4 1.969 0.508 1177 59 29.5 1132 1121 4.8% X1619_6 86.3 29.9 2.886 0.346 1037 70 35 1055 1050 ‐1.3% X1619_7 227.0 96.7 2.347 0.426 2480 63 31.5 2119 1770 28.6% X1619_8 408.0 75.7 5.390 0.186 1585 59 29.5 1460 1375 13.2% X1619_9 111.0 104.6 1.061 0.942 1853 58 29 1741 1636 11.7% High U/Th; interpreted as metamorphic X1619_10 165.0 0.075 2200.000 0.000 3630 35 17.5 850 165 95.5% overgrowth; Pb206/U238 age plotted X1619_11 69.3 64.6 1.073 0.932 1439 75 37.5 1439 1470 ‐2.2% X1619_12 139.0 109.5 1.269 0.788 1842 77 38.5 1492 1280 30.5% X1619_13 97.2 50.7 1.917 0.522 1339 66 33 1390 1405 ‐4.9% X1619_14 213.0 127.6 1.669 0.599 1416 70 35 1317 1284 9.3% X1619_15 525.0 176 2.983 0.335 1507 87 43.5 1309 1188 21.2% X1619_16 223.0 356 0.626 1.596 1209 66 33 936 845 30.1% X1619_17 324.0 327 0.991 1.009 1457 92 46 1282 1192 18.2% X1619_18 165.0 86.9 1.899 0.527 1437 60 30 1356 1264 12.0% X1619_19 262.0 150 1.747 0.573 1416 83 41.5 1345 1275 10.0% X1619_20 80.9 56.6 1.429 0.700 1894 81 40.5 1748 1601 15.5% Young grain used to constrain maximum X1619_21 83.0 31.5 2.635 0.380 950 110 55 1080 1140 ‐20.0% depositional age X1619_22 82.8 29.3 2.826 0.354 1053 58 29 1071 1073 ‐1.9% X1619_23 53.3 45.8 1.164 0.859 1872 59 29.5 1927 1990 ‐6.3% X1619_24 185.0 79 2.342 0.427 381 89 44.5 389 392 ‐2.9% Young concordant grain, probably R33 standard X1619_25 91.5 33.9 2.699 0.370 990 99 49.5 1038 1037 ‐4.7% X1619_26 86.0 29.6 2.905 0.344 1025 65 32.5 1044 1029 ‐0.4% X1619_27 153.0 58.1 2.633 0.380 1405 79 39.5 1336 1297 7.7% X1619_28 65.7 44.6 1.473 0.679 1386 70 35 1437 1465 ‐5.7% X1619_29 118.8 97.6 1.217 0.822 1840 65 32.5 1751 1644 10.7% X1619_30 116.5 50.8 2.293 0.436 1592 69 34.5 1440 1325 16.8% High U/Th; interpreted as metamorphic X1619_31 77.1 0.102 755.882 0.001 1470 6.6 3.3 151 81 94.5% overgrowth; Pb206/U238 age plotted High U/Th; interpreted as metamorphic X1619_32 118.4 0.0094 12595.745 0.000 1090 12 6 139 96 91.2% overgrowth; Pb206/U238 age plotted High U/Th; interpreted as metamorphic X1619_33 107.0 0.17 629.412 0.002 1500 14 7 209 96 93.6% overgrowth; Pb206/U238 age plotted X1619_34 139.0 145.8 0.953 1.049 1244 85 42.5 1167 1121 9.9% High U/Th; interpreted as metamorphic X1619_35 222.0 0.0665 3338.346 0.000 1370 11 5.5 182 93 93.2% overgrowth; Pb206/U238 age plotted High U/Th; interpreted as metamorphic X1619_36 104.7 0.026 4026.923 0.000 2930 7.1 3.55 399 97.7 96.7% overgrowth; Pb206/U238 age plotted X1619_37 214.0 50.5 4.238 0.236 1620 50 25 1514 1415 12.7% X1619_38 264.0 104.7 2.521 0.397 1581 67 33.5 1473 1403 11.3% X1619_39 167.0 68.2 2.449 0.408 1720 56 28 1735 1712 0.5% X1619_40 69.9 28.4 2.461 0.406 1332 68 34 1317 1266 5.0% X1619_41 116.9 50 2.338 0.428 1456 77 38.5 1383 1333 8.4% X1619_42 78.3 48.2 1.624 0.616 1364 76 38 1356 1351 1.0% X1619_43 185.0 86.9 2.129 0.470 1584 74 37 1525 1484 6.3% X1619_44 172.0 69.9 2.461 0.406 1452 95 47.5 1362 1276 12.1% X1619_45 202.7 4.76 42.584 0.023 1171 78 39 1006 953 18.6% X1619_46 144.0 118.3 1.217 0.822 1096 85 42.5 1164 1192 ‐8.8% X1619_47 107.5 51 2.108 0.474 1579 71 35.5 1630 1615 ‐2.3% X1619_48 89.5 26.1 3.429 0.292 1516 75 37.5 1216 1080 28.8% X1619_49 43.3 31.5 1.375 0.727 1470 120 60 1269 1137 22.7% High U/Th; interpreted as metamorphic X1619_50 121.0 0.045 2688.889 0.000 3010 13 6.5 432 107 96.4% overgrowth; Pb206/U238 age plotted X1619_51 204.0 151.2 1.349 0.741 1406 98 49 1286 1220 13.2% High U/Th; interpreted as metamorphic X1619_52 236.0 0.057 4140.351 0.000 1340 9.7 4.85 141 77.3 94.2% overgrowth; Pb206/U238 age plotted X1619_53 117.5 53.4 2.200 0.454 1731 93 46.5 1757 1710 1.2% X1619_54 35.6 30.1 1.183 0.846 1247 83 41.5 1260 1244 0.2% X1619_55 102.7 82.9 1.239 0.807 1439 72 36 1387 1368 4.9% X1619_56 37.4 34.3 1.090 0.917 1464 74 37 1472 1454 0.7% X1619_57 52.8 21.9 2.411 0.415 1489 52 26 1455 1405 5.6% High U/Th; interpreted as metamorphic X1619_58 56.9 0.002 28450.000 0.000 2090 12 6 294 112 94.6% overgrowth; Pb206/U238 age plotted X1619_59 185.0 146 1.267 0.789 1216 57 28.5 1007 923 24.1% X1619_60 45.5 0.1868 243.576 0.004 1220 80 40 1067 1024 16.1% High U/Th; interpreted as metamorphic X1619_61 72.7 ‐0.0062 ‐11725.806 0.000 1700 16 8 101 62 96.4% overgrowth; Pb206/U238 age plotted X1619_62 378.0 56.4 6.702 0.149 1140 100 50 1060 1016 10.9% X1619_63 35.3 21 1.681 0.595 1564 65 32.5 1347 1201 23.2% X1619_64 64.5 41 1.573 0.636 1462 63 31.5 1046 878 39.9% X1619_65 62.2 33 1.885 0.531 1638 55 27.5 1671 1665 ‐1.6% X1619_66 212.0 247 0.858 1.165 1197 79 39.5 907 814 32.0% X1619_67 18.6 28.2 0.661 1.514 1767 80 40 1508 1375 22.2% X1619_68 74.1 54.3 1.365 0.733 1867 71 35.5 1879 1856 0.6% X1619_69 230.0 38.4 5.990 0.167 1659 81 40.5 1297 1080 34.9% X1619_70 96.4 48.7 1.979 0.505 1635 78 39 1605 1563 4.4% X1619_71 186.0 69.2 2.688 0.372 1685 83 41.5 1647 1606 4.7% X1619_72 297.0 138 2.152 0.465 1192 71 35.5 1014 952 20.1% X1619_73 532.0 333 1.598 0.626 1894 69 34.5 1636 1419 25.1% X1619_74 145.0 53 2.736 0.366 1572 62 31 1609 1624 ‐3.3% X1619_75 41.1 36.4 1.129 0.886 1209 88 44 1158 1124 7.0% X1619_76 288.0 108.4 2.657 0.376 1775 78 39 1731 1711 3.6% X1619_77 137.0 66.9 2.048 0.488 1642 84 42 1568 1523 7.2% High U/Th; interpreted as metamorphic X1619_78 53.4 0.0177 3016.949 0.000 1500 24 12 241 103 93.1% overgrowth; Pb206/U238 age plotted X1619_79 430.0 250 1.720 0.581 1603 70 35 1457 1332 16.9% X1619_80 150.3 156 0.963 1.038 1481 66 33 1416 1392 6.0% X1619_81 402.0 380 1.058 0.945 1195 96 48 978 908 24.0% X1619_82 111.6 86.8 1.286 0.778 1370 72 36 1290 1239 9.6% X1619_83 34.1 40.2 0.848 1.179 1270 94 47 1300 1290 ‐1.6% X1619_84 226.0 89.3 2.531 0.395 1366 79 39.5 1305 1255 8.1% X1619_85 77.9 31.2 2.497 0.401 1019 84 42 1090 1082 ‐6.2% X1619_86 285.0 85 3.353 0.298 1438 68 34 1238 1142 20.6% X1619_87 65.4 43.2 1.514 0.661 518 23 11.5 422 399 23.0% Young discordant grain, probably R33 standard X1619_88 80.4 33.1 2.429 0.412 1007 83 41.5 1058 1068 ‐6.1% X1619_89 43.6 23 1.896 0.528 1100 70 35 1156 1162 ‐5.6% X1619_90 94.7 109.6 0.864 1.157 1622 58 29 1639 1646 ‐1.5% X1619_91 57.2 34.2 1.673 0.598 1458 60 30 1484 1487 ‐2.0% X1619_92 79.6 34.1 2.334 0.428 1321 63 31.5 1272 1200 9.2% X1619_93 103.4 38.7 2.672 0.374 1245 70 35 977 837 32.8% X1619_94 92.6 117.3 0.789 1.267 1861 63 31.5 1865 1845 0.9% X1619_95 46.8 31.7 1.476 0.677 1510 66 33 1541 1557 ‐3.1% X1619_96 39.7 13.9 2.856 0.350 1333 96 48 952 828 37.9% X1619_97 403.0 103.6 3.890 0.257 1149 81 40.5 1045 970 15.6% X1619_98 232.0 119.3 1.945 0.514 1783 81 40.5 1687 1531 14.1% X1619_99 462.0 496 0.931 1.074 1374 84 42 1191 1098 20.1% X1619_100 96.7 73.8 1.310 0.763 1570 69 34.5 1588 1626 ‐3.6% X1619_101 112.0 115.4 0.971 1.030 1380 110 55 1134 982 28.8% X1619_102 208.0 160.1 1.299 0.770 1656 64 32 1553 1470 11.2% X1619_103 109.0 113 0.965 1.037 1644 76 38 1617 1545 6.0% X1619_104 94.4 72.7 1.298 0.770 1620 71 35.5 1618 1576 2.7% X1619_105 252.0 160.2 1.573 0.636 1584 89 44.5 1470 1360 14.1% X1619_106 131.5 140.2 0.938 1.066 1190 100 50 1162 1139 4.3% X1619_107 165.2 268 0.616 1.622 2576 67 33.5 2527 2430 5.7% X1619_108 383.0 109.9 3.485 0.287 1188 81 40.5 1072 1007 15.2% X1619_109 218.0 104.1 2.094 0.478 2632 72 36 2372 2012 23.6% X1619_110 294.0 121 2.430 0.412 1626 64 32 1217 1008 38.0% X1619_111 219.0 136 1.610 0.621 1244 72 36 1132 1092 12.2% High U/Th; interpreted as metamorphic X1619_112 99.6 0.0111 8972.973 0.000 530 6.9 3.45 102.5 82.6 84.4% overgrowth; Pb206/U238 age plotted X1619_113 48.3 53.6 0.901 1.110 1274 95 47.5 1227 1174 7.8% X1619_114 94.0 55.3 1.700 0.588 1269 71 35.5 1242 1205 5.0% Sample Pb207/Pb206 Pb207/U235 Pb206/U238 JN1713 ppmU ppmTh U/Th Th/U Age 2 Sigma 1 sigma Age Age % Discordsance JN1713_1 205 299 0.686 1.459 1888 53 26.5 1857 1814 3.9% JN1713_2 126.5 126 1.004 0.996 1848 96 48 1760 1700 8.0% JN1713_3 135.9 82.1 1.655 0.604 1943 62 31 1832 1736 10.7% JN1713_4 177.5 91.8 1.934 0.517 2550 79 39.5 2586 2560 ‐0.4% JN1713_5 365 363 1.006 0.995 1782 63 31.5 1672 1573 11.7% JN1713_6 289 46.3 6.242 0.160 1670 120 60 767 461 72.4% JN1713_7 32.4 35 0.926 1.080 1910 100 50 1941 1930 ‐1.0% JN1713_8 240 183 1.311 0.763 1856 70 35 1767 1750 5.7% JN1713_9 110.6 69.6 1.589 0.629 1797 79 39.5 1836 1890 ‐5.2% JN1713_10 126 0.474 265.823 0.004 1850 110 55 1745 1690 8.6% High U/Th JN1713_11 152 167 0.910 1.099 1999 76 38 1940 1930 3.5% JN1713_12 76.1 127.9 0.595 1.681 1000 130 65 1042 1061 ‐6.1% JN1713_13 47.3 37.7 1.255 0.797 1875 78 39 1829 1740 7.2% JN1713_14 65.8 29.6 2.223 0.450 2156 93 46.5 1870 1650 23.5% JN1713_15 116 82 1.415 0.707 1919 99 49.5 1848 1860 3.1% JN1713_16 52.5 22.3 2.354 0.425 2767 65 32.5 2687 2570 7.1% JN1713_17 52.2 63.1 0.827 1.209 1821 89 44.5 1813 1750 3.9% JN1713_18 102 76.3 1.337 0.748 1979 82 41 1435 1114 43.7% JN1713_19 113 30.7 3.681 0.272 1820 97 48.5 1042 733 59.7% JN1713_20 116.8 188.4 0.620 1.613 1909 80 40 1873 1821 4.6% JN1713_21 67.1 77.7 0.864 1.158 1927 47 23.5 1887 1697 11.9% JN1713_22 48.1 48 1.002 0.998 1980 48 24 1944 1750 11.6% JN1713_23 42.3 22.2 1.905 0.525 2682 46 23 2658 2408 10.2% JN1713_24 25.66 14.69 1.747 0.572 1957 56 28 1875 1680 14.2% JN1713_25 104.1 74.7 1.394 0.718 1939 44 22 1919 1749 9.8% JN1713_26 101.6 102 0.996 1.004 1974 42 21 1943 1771 10.3% JN1713_27 186.4 200.3 0.931 1.075 1955 44 22 1914 1782 8.8% JN1713_28 30.3 45.5 0.666 1.502 1949 52 26 1935 1799 7.7% JN1713_29 104 34.4 3.023 0.331 1842 40 20 1775 1652 10.3% JN1713_30 133 72.7 1.829 0.547 2125 57 28.5 1845 1580 25.6% JN1713_31 91.8 65.8 1.395 0.717 2103 39 19.5 2001 1855 11.8% JN1713_32 268 179.3 1.495 0.669 1892 50 25 1742 1594 15.8% JN1713_33 223 146.6 1.521 0.657 2549 45 22.5 2233 1915 24.9% JN1713_34 94 65.6 1.433 0.698 1831 61 30.5 1655 1545 15.6% JN1713_35 63.4 78.5 0.808 1.238 1885 50 25 1760 1630 13.5% JN1713_36 76.5 21.9 3.493 0.286 1882 43 21.5 1716 1586 15.7% JN1713_37 160 49.6 3.226 0.310 1853 50 25 1552 1349 27.2% JN1713_38 64.2 64 1.003 0.997 1905 43 21.5 1789 1663 12.7% JN1713_39 31.2 86.6 0.360 2.776 1949 49 24.5 1776 1540 21.0% High Th/U JN1713_40 112.7 68.1 1.655 0.604 1863 41 20.5 1715 1536 17.6% JN1713_41 76.3 23.6 3.233 0.309 1895 29 14.5 1727 1552 18.1% JN1713_42 127.1 148.5 0.856 1.168 2689 28 14 2556 2323 13.6% JN1713_43 78.8 26.1 3.019 0.331 2558 39 19.5 2399 2200 14.0% Sample Pb207/Pb206 Pb207/U235 Pb206/U238 SZ1701 ppmU ppmTh U/Th Th/U Age 2 Sigma 1 sigma Age Age % Discordsance SZ1701_1 55.9 81.2 0.688 1.453 1282 98 49 1172 1145 10.7% SZ1701_2 402 174 2.310 0.433 1794 65 32.5 1346 1051 41.4% SZ1701_3 105.7 134.3 0.787 1.271 1876 83 41.5 1753 1637 12.7% SZ1701_4 389 98.2 3.961 0.252 1233 65 32.5 1126 1100 10.8% SZ1701_5 35.6 32.4 1.099 0.910 1220 91 45.5 1177 1159 5.0% SZ1701_6 293 280 1.046 0.956 1700 110 55 1413 1210 28.8% SZ1701_7 159 157.3 1.011 0.989 1533 83 41.5 1254 1121 26.9% SZ1701_8 144 99.8 1.443 0.693 1260 100 50 1191 1191 5.5% SZ1701_9 367 168 2.185 0.458 1652 69 34.5 1652 1638 0.8% High U/Th suggests metamorphic overgrowth; SZ1701_10 660 52.1 12.668 0.079 710 150 75 188 144 79.7% possibly a mixed age SZ1701_11 299 129.7 2.305 0.434 1868 63 31.5 1567 1363 27.0% SZ1701_12 93.5 46.1 2.028 0.493 1428 84 42 1406 1397 2.2% SZ1701_13 141.1 67.5 2.090 0.478 1064 85 42.5 967 940 11.7% SZ1701_14 610 161 3.789 0.264 1700 79 39.5 1053 793 53.4% SZ1701_15 536 122.3 4.383 0.228 1562 82 41 895 645 58.7% SZ1701_16 201 100.4 2.002 0.500 1776 58 29 1673 1587 10.6% SZ1701_17 413 97.7 4.227 0.237 1814 89 44.5 1205 907 50.0% SZ1701_18 208 159.8 1.302 0.768 1802 52 26 1769 1727 4.2% SZ1701_19 37.7 36.2 1.041 0.960 1310 130 65 1324 1347 ‐2.8% SZ1701_20 133 120.3 1.106 0.905 1160 120 60 1173 1215 ‐4.7% SZ1701_21 232 134.5 1.725 0.580 1814 93 46.5 1534 1340 26.1% SZ1701_22 701 136.9 5.121 0.195 1670 110 55 1056 800 52.1% SZ1701_23 534 121 4.413 0.227 3270 140 70 2140 1230 62.4% SZ1701_24 227 105.9 2.144 0.467 1409 91 45.5 1020 858 39.1% SZ1701_25 295 176 1.676 0.597 1530 100 50 1111 887 42.0% SZ1701_26 178 268 0.664 1.506 1152 93 46.5 1099 1105 4.1% SZ1701_27 227 222 1.023 0.978 1218 93 46.5 1177 1149 5.7% SZ1701_28 496 269 1.844 0.542 1853 90 45 717 399 78.5% SZ1701_29 252 167 1.509 0.663 1677 76 38 1611 1577 6.0% SZ1701_30 126.1 90.7 1.390 0.719 1390 110 55 1489 1550 ‐11.5% SZ1701_31 343 416 0.825 1.213 1848 76 38 1828 1807 2.2% SZ1701_32 761 135.1 5.633 0.178 1680 88 44 537 321 80.9% SZ1701_33 159 142.8 1.113 0.898 1755 75 37.5 1709 1683 4.1% SZ1701_34 65.9 87.5 0.753 1.328 1739 85 42.5 1726 1705 2.0% SZ1701_35 18.1 22.7 0.797 1.254 1180 120 60 1140 1154 2.2% SZ1701_36 269 51.3 5.244 0.191 1697 79 39.5 943 713 58.0% SZ1701_37 57.4 56 1.025 0.976 1877 60 30 1897 1864 0.7% SZ1701_38 207 8.1 25.556 0.039 1176 87 43.5 1123 1094 7.0% SZ1701_39 132.5 80.6 1.644 0.608 1130 100 50 1196 1226 ‐8.5% SZ1701_40 402 153.7 2.615 0.382 1336 70 35 857 697 47.8% SZ1701_41 256 162 1.580 0.633 2388 70 35 1880 1480 38.0% SZ1701_42 147 173 0.850 1.177 1451 82 41 1341 1296 10.7% SZ1701_43 305 57.4 5.314 0.188 1800 80 40 1629 1490 17.2% SZ1701_44 720 123.5 5.830 0.172 1641 62 31 1636 1620 1.3% SZ1701_45 445 98 4.541 0.220 1812 72 36 1185 880 51.4% SZ1701_46 172 115.8 1.485 0.673 1198 87 43.5 1161 1153 3.8% SZ1701_47 530 151 3.510 0.285 1259 71 35.5 918 775 38.4% SZ1701_48 545 190 2.868 0.349 1364 98 49 614 446 67.3% SZ1701_49 379 194 1.954 0.512 2603 83 41.5 2313 1980 23.9% SZ1701_50 280 18.9 14.815 0.068 1166 80 40 1198 1201 ‐3.0% High U/Th, but age is concordant SZ1701_51 199 64.7 3.076 0.325 1371 82 41 1326 1337 2.5% SZ1701_52 148.7 77.6 1.916 0.522 1740 84 42 1757 1758 ‐1.0% SZ1701_53 120.1 55.5 2.164 0.462 1496 87 43.5 1330 1254 16.2% SZ1701_54 75.4 60.4 1.248 0.801 2715 64 32 2614 2560 5.7% SZ1701_55 144.3 78.3 1.843 0.543 1780 100 50 1773 1771 0.5% SZ1701_56 879 123.6 7.112 0.141 1732 98 49 1076 753 56.5% SZ1701_57 47.2 53.5 0.882 1.133 1807 69 34.5 1713 1679 7.1% SZ1701_58 793 177 4.480 0.223 1291 90 45 628 476 63.1% SZ1701_59 326 281 1.160 0.862 1905 77 38.5 1720 1610 15.5% SZ1701_60 177 43.9 4.032 0.248 1814 90 45 1748 1694 6.6% High U/Th suggests metamorphic overgrowth; SZ1701_61 695 64.7 10.742 0.093 1725 77 38.5 1039 727 57.9% possibly a mixed age SZ1701_62 59.4 49.7 1.195 0.837 1285 72 36 1257 1235 3.9% SZ1701_63 227 55.7 4.075 0.245 1745 72 36 1706 1672 4.2% SZ1701_64 181 138.9 1.303 0.767 1748 52 26 1586 1472 15.8% SZ1701_65 661 163 4.055 0.247 1932 61 30.5 1010 645 66.6% SZ1701_66 84.7 41.1 2.061 0.485 1677 65 32.5 1667 1625 3.1% SZ1701_67 145 83 1.747 0.572 1190 77 38.5 1016 960 19.3% SZ1701_68 486 540 0.900 1.111 1682 68 34 1553 1462 13.1% SZ1701_69 68.4 118.1 0.579 1.727 1143 84 42 1066 1020 10.8% SZ1701_70 208 58.6 3.549 0.282 1797 71 35.5 1649 1515 15.7% SZ1701_71 143 58.7 2.436 0.410 1551 59 29.5 1407 1321 14.8% SZ1701_72 239 58.2 4.107 0.244 1888 59 29.5 1665 1535 18.7% SZ1701_73 111.5 82.1 1.358 0.736 1446 55 27.5 1146 995 31.2% SZ1701_74 286 111.8 2.558 0.391 1428 65 32.5 1414 1385 3.0% SZ1701_75 271 131.1 2.067 0.484 1715 56 28 1628 1540 10.2% SZ1701_76 182.8 70.1 2.608 0.383 1754 57 28.5 1557 1390 20.8% SZ1701_77 263 218 1.206 0.829 1502 61 30.5 1417 1363 9.3% SZ1701_78 226 90.5 2.497 0.400 1252 57 28.5 1196 1157 7.6% SZ1701_79 37.2 61.1 0.609 1.642 1087 85 42.5 1077 1067 1.8% SZ1701_80 100.2 36.9 2.715 0.368 1074 67 33.5 1042 1027 4.4% SZ1701_81 261 99.9 2.613 0.383 1744 45 22.5 1613 1526 12.5% SZ1701_82 154 65.1 2.366 0.423 1812 69 34.5 1747 1646 9.2% SZ1701_83 95.3 83.6 1.140 0.877 1437 60 30 1417 1386 3.5% SZ1701_84 267 95.3 2.802 0.357 1779 55 27.5 1621 1510 15.1% SZ1701_85 40.9 21.5 1.902 0.526 1370 62 31 1352 1314 4.1% SZ1701_86 62.5 27.9 2.240 0.446 1530 100 50 1303 1199 21.6% SZ1701_87 70.1 71 0.987 1.013 1915 61 30.5 1896 1851 3.3% SZ1701_88 228 116.8 1.952 0.512 1476 63 31.5 1418 1381 6.4% SZ1701_89 195 63.9 3.052 0.328 1789 50 25 1683 1605 10.3% SZ1701_90 572 110 5.200 0.192 2158 94 47 1330 920 57.4% SZ1701_91 306 76.7 3.990 0.251 1955 96 48 1790 1820 6.9% SZ1701_92 159.7 65.2 2.449 0.408 1785 45 22.5 1615 1513 15.2% SZ1701_93 232 66.2 3.505 0.285 1315 98 49 727 540 58.9% SZ1701_94 377 85.6 4.404 0.227 1700 70 35 976 700 58.8% SZ1701_95 224 47 4.766 0.210 1298 90 45 611 425 67.3% SZ1701_96 79.1 67.4 1.174 0.852 1781 47 23.5 1798 1814 ‐1.9% SZ1701_97 190 246 0.772 1.295 3033 66 33 2883 2640 13.0% SZ1701_98 164 131 1.252 0.799 1360 78 39 1138 1041 23.5% SZ1701_99 205 50.8 4.035 0.248 1302 99 49.5 493 336 74.2% High U/Th suggests metamorphic overgrowth; SZ1701_100 795 55.9 14.222 0.070 1137 94 47 377 266 76.6% possibly a mixed age Sample Pb207/Pb206 Pb207/U235 Pb206/U238 SZ1601 ppm U ppm Th U/Th Th/U Age 2 sigma 1 sigma Age Age % discordance Comment Discordant grain with high U/Th suggesting X1601_1 1280 137 9.343 0.107 120 100 50 61 60 50.4% metamorhic overprint; probably a mixed age Discordant grain with high U/Th suggesting X1601_10 410 59 6.949 0.144 1820 680 340 410 190 89.6% metamorhic overprint; probably a mixed age Discordant grain with high U/Th suggesting X1601_2 61 17.9 3.408 0.293 1190 620 310 540 820 31.1% metamorhic overprint; probably a mixed age Discordant grain with high U/Th suggesting X1601_3 13 0.76 17.105 0.058 1460 200 100 344 214 85.3% metamorhic overprint; probably a mixed age Discordant grain with high U/Th suggesting X1601_4 1011 197.4 5.122 0.195 3620 820 410 1610 540 85.1% metamorhic overprint; probably a mixed age Discordant grain with high U/Th suggesting X1601_5 360 83 4.337 0.231 1619 95 47.5 1199 988 39.0% metamorhic overprint; probably a mixed age Discordant grain with high U/Th suggesting X1601_6 510 61 8.361 0.120 1520 210 105 481 305 79.9% metamorhic overprint; probably a mixed age Discordant grain with high U/Th suggesting X1601_7 770 157 4.904 0.204 550 230 115 104 85 84.5% metamorhic overprint; probably a mixed age Discordant grain with high U/Th suggesting X1601_8 0.42 0.058 7.241 0.138 ‐800 1700 850 85 70 108.8% metamorhic overprint; probably a mixed age Discordant grain with high U/Th suggesting X1601_9 350 36 9.722 0.103 5700 2300 1150 1570 200 96.5% metamorhic overprint; probably a mixed age