Zirconium in Rutile Geothermometry: Peak Temperature Determination in the Catalina Schist

Transcription

1 Zirconium in Rutile Geothermometry: Peak Temperature Determination in the Catalina Schist By Steven Noll Advisors Dr. Penniston Dorland and Dr. Piccoli GEOL 394 4/27/2015 1

2 ABSTRACT Metamorphic rocks in subduction zones are exhumed to the surface by one of two methods: as coherent packages where rocks moved as a single unit) or as mixed blocks where rocks travel different paths to the surface. In many mélange zones, the blocks record different peak metamorphic facies, even on the outcrop scale, suggesting the blocks have moved along different paths within the subduction zone. Rocks within the Catalina Schist occur in a mélange, however the blocks within a given region in the field are of a single metamorphic facies. Due to the broad spectrum of pressures and temperatures at which a metamorphic facies can form, the question becomes whether or not the blocks within the Catalina Schist mélange might actually record different peak temperatures of formation. The zirconium content of rutile grains within four samples of varying lithologies from a single outcrop of the Catalina Schist were analyzed by using an electron probe microanalyzer in order to determine whether the Catalina Schist shows evidence of rock mixing or of rocks moving together as a package. The zirconium content of rutiles is used to calculate the peak temperature of recrystalization each sample by using the zirconium in rutile geothermometer. If the rocks record evidence for significantly different peak temperatures (outside of two sigma uncertainty of standard deviation of mean), it will suggest that they moved along different paths within the subduction zone. The calculated temperatures of the four samples have been compared to determine whether or not they likely reached different peak temperatures. I have performed petrography and analyzed rutiles from all four of the samples from the outcrop. The zirconium content used in the calculation of the temperature for each sample came from the maximum zirconium concentrations found in the centers of the crystals. The average zirconium concentrations measured within the cores of the rutiles of the samples range from 242 to 473 ppm. These concentrations lead to a calculated temperature range of 633 C to 687 C at 10 kbar (using the calibration of Tomkins et al., 2007) across all the samples. The uncertainty calculated by finding the standard deviation of mean (2σ) was approximately 20 C across all the samples. The final calculated temperatures of the samples fell within uncertainty of each other, supporting the model that these rocks moved through the subduction zone as a cohesive package. 2

3 INTRODUCTION Subduction zones occur where two tectonic plates, one oceanic and one either oceanic or continental, converge and the oceanic plate subducts into the mantle beneath the overriding plate. Volcanoes can form on the overriding plate and earthquakes occur in the area of the subduction zone. These geologic hazards make subduction zones an important area of study in order to understand the more violent workings of the earth. Geophysicists can use seismic data to image the crust and mantle within a subduction zone and geologists can study rocks formed in volcanoes, however these are indirect methods of studying subduction zones. An effective way of gathering information on the interior of a subduction zone is through the study of the metamorphic rocks exhumed from the subduction zone. These metamorphic rocks are materials that come from inside the subduction zone and provide evidence for what happens within a subduction zone. Mélange zones are thought to represent rocks from the interface between the down going subducting slab and the overlying plate, making mélange zones prime locations for geological study of the processes Figure 1 Geologic map of Santa Catalina Island. Study area is occurring within subduction zones. marked by the square. Area in square shown in Figure 3. The primary goal of this project is to Source: Dr. Sarah Penniston Dorland support a model of rock movement in a subduction zone. Do they move as a single coherent package or do rocks from one layer break off to mix with other layers (see figure 2). This model of rocks mixing together in a subduction zone was first introduced as a model of rocks moving along different paths within a subduction zone (Cloos, 1982). This mixing process leads rocks to recrystallize at different depths and therefore record differing peak temperatures. I will determine peak temperatures of metamorphic rocks found in the Catalina Schist. The method I will use is the zirconium in rutile geothermometer. The Catalina Schist is a mélange zone off the coast of California on Santa Catalina Island. The Catalina Schist contains materials that record P T conditions indicative of subduction zone environments as well as a mixture of blocks of material coming from the ultramafic mantle wedge of the subduction zone and metamorphosed basaltic and silicic material from the oceanic crust. The calculated peak temperatures of samples from a single Figure 2 Two models for subduction zones are illustrated. Rocks can move as a coherent package (left) or as a mixed package (right). Diagram is modified from Bebout (2007) amphibolite facies outcrop will then be compared. If the temperatures are significantly different, then the rocks likely did not move as a coherent package. If the peak temperatures are the same, it suggests they moved as coherent a package. 3

4 BACKGROUND There are two endmember models for behavior of rocks within a subduction zone (Bebout 2007), illustrated in figure 2. In the first model, the rocks move together as a cohesive mass during subduction, with all rocks experiencing approximately the same metamorphic conditions and therefore the same peak temperatures. In the second model, the rocks do not move together as a cohesive mass during subduction, with rocks experiencing different metamorphic conditions and therefore different peak temperatures (Bebout 2007). The samples I have studied were collected from the Catalina Schist. The Catalina Schist is located on Santa Catalina Island just off the coast of California near Los Angeles. The rocks in the schist have been interpreted to represent rocks that formed in a subduction zone based on the mineral assemblages. The metamorphic facies range from low grade lawsonite blueschist to high grade amphibolite. Rocks in the Catalina Schist occur as coherent packages in some parts of the formation and as mélange in other parts, as can be seen in figures 1 and 3. These rocks range from million years in age (Grove et al., 2008). The Catalina Schist formed when the Farallon plate subducted under the North American plate. Previous pressure and temperature estimates for the amphibolites in the Catalina Schist are approximately 8 11 kbar and C respectively, see figure 4 (Bebout, 2007; Sorensen and Barton, 1987). The rocks used for this project were taken from the sample location in figure 3. The Catalina Schist exhibits a narrower range of metamorphic facies found within a region of mélange compared to another nearby suite of subduction related metamorphic rocks, the Franciscan Complex, which exhibits a wide range of metamorphic facies in an exposure of mélange. The Franciscan Complex is located throughout the California Coast Ranges and the San Francisco Peninsula. The ages of the rocks found in the Franciscan Complex range from million years in age (McLaughlin, 1982). The Franciscan Complex is an example of the mixing model of subduction zones. Within the Franciscan Complex one can find blueschist, eclogite, and garnet amphibolite blocks within the same outcrop. Each rock records different peak temperatures and pressures Figure 4 PT diagram illustrating P T conditions specific to the amphibolite facies rocks, labeled AM, of the Catalina Schist (Bebout, 2007) Figure 3 Geologic map of a portion of the Catalina Schist. Location of samples is illustrated with a star. (Dr. Sarah Penniston Dorland) from each other. Instead of the intense mixing of rock types of different metamorphic facies within a single outcrop, as seen in the Franciscan Complex, the Catalina Schist has 1 4 km swaths of outcrops with mixed lithologies in the same metamorphic facies. The area mapped as amphibolite facies mélange dominated in figure 3 is an example of this mixing of lithologies in the same metamorphic facies. However, within 4

5 these facies there is a rather broad spectrum of temperatures and pressures of formation. This brings forward the question that I am attempting answer: do the rocks in the Catalina Schist mix together in the subduction zone or move together as a single package? I measured the zirconium content of rutile in four different Catalina Schist metamorphic rocks from a single outcrop. My hypothesis is that the zirconium content of the rutile will be significantly different in each of these rocks. This would suggest that the rocks in the Catalina Schist did not move as a coherent single package. METHODS Figure 5 Garnet Quartzite A sample Figure 6 Garnet Mica Schist sample Figure 7 Garnet Quartzite B sample Figure 8 Garnet Amphibolite sample In order to test my hypothesis I studied 4 samples from the Catalina Schist. These samples were taken from a single outcrop area approximately 100 square meters in area as marked by the star in figure 3. The samples have different lithologies and are a good representation of the rocks that can be found throughout the Catalina Schist. The four samples that I examined are a garnet amphibolite (sample A14 64F), two garnet quartzites (samples A14 64F and A14 64E), and a garnet mica schist (sample A14 64D). The rutile was identified and mapped with the petrographic microscope before rutile was analyzed. To determine the zirconium content of the rutiles, I used the Electron Probe Microanalyzer. I performed traverses across larger grains to check for zoning. To detect zoning in smaller rutile grains, analyses of grain cores and rims were performed. The concentration of zirconium oxide (ZrO 2 ) in rutile was then used to calculate a temperature. If the rutiles in different samples yield a large difference in peak temperature they most likely recrystallized at a significant distance from each other, which would support my hypothesis. 5

6 I used the zirconium in rutile geothermometer for my temperature calculations. The zirconium in rutile geothermometer uses the fact that at higher temperatures, zirconium substitutes in higher concentrations into rutile in place of titanium. Both of these elements have a +4 charge and the atomic radius for zirconium and titanium are 0.75 and 0.86 angstroms respectively, which allows zirconium to easily fit into the space that titanium would normally occupy in the bond. The use of this thermometer requires the presence of rutile, zircon, and quartz, (for an example of these phases see figure 9). All samples used in this experiment have the required phases for this geothermometer. The equilibrium reaction is ZrSiO 4 + TiO 2 > ZrO 2 (in rutile) +SiO 2. Using the zirconium concentrations measured in rutile, a peak temperature can be calculated using (for samples containing alpha quartz): ln ф where ф is ppm, P is the pressure experienced by the sample, and R is the gas constant, kj/k (Tomkins et al., 2007). Tomkins et al (2007) performed a series of experiments where pure TiO 2 was made to take up ZrO 2 until it approached equilibrium with coexisting zircon and quartz, and made ZrO 2 rich rutile give up ZrO 2 until it approached equilibrium with coexisting zircon and quartz, called forward and reversal experiments respectively. These experiments were conducted at temperatures of C and at 1, 2, and 3 GPA. The experiments were then calibrated to results from empirical studies so that they can be applied to rocks that experienced lower temperatures. For the purposes of these calculations, I used pressures estimated for these rocks, ranging from GPa consistent with the pressure estimates of Sorensen and Barton (1987). The reason I am using the alpha quartz calibration is because, at the pressures I used, the calculated temperatures of the rutile crystals that I have analyzed (see Data section) are below 800 C which is in the stability field of alpha quartz at the pressure of interest. Analyses were performed on a JEOL JXA 8900 electron probe microanalyzer. An accelerating voltage of 20 kv and cup current of 120 na were used. The following standards were used: synthetic zircon (Zr, Si), rutile (Ti), Bushveld Chromite (Al, Fe), Ilmen Mountains Ilmenite (Mn), and pure metal standards (Nb, Ta). Count times for Zr were 300 seconds on peak and 150 on each background. Zr was measured on a highintensity PETH crystal (on a small diameter Rowland circle spectrometer). An asymmetric background was used ( 2/+3 mm) to model the Zr peak. The detection limit for Zr was ppm (Appendix, pg 13) Measurements that were clearly not 100% rutile were excluded from consideration for calculations. To determine the measurements that fell outside of usable criteria I considered the total weight percent of each measurement and the amount of silicon measured. All measurements that were outside of 100% +/ 2% total weight percent were excluded. All measurements that had more than 300 parts per million of silicon were also excluded. I followed the methods of McBride (2013) for these criteria. The uncertainty for the zirconium measurements in these analyses is estimated from counting statistics from the electron probe microanalyzer and reported at the 2 sigma level. These counts assumed a Gaussian curve along which the measurements fell to give an uncertainty for each measurement. DATA Garnet Rutile Muscovite Quartz Zircon 175 microns Figure 9 Back Scattered Electron image of rutile, quartz, and zircon in the same area as each other for zirconium substitution in rutile. Other minerals are noted as well. 6

7 The first sample analyzed was the larger of the two garnet quartzites, garnet quartzite A, sample A14 64B. The rutiles in this particular sample are sparse, approximately 1% volume of rutile in the rock, estimated from the thin section. However what this sample lacks in number of rutile crystals it makes up for in crystal size. The largest rutile crystals in this sample are 3000 micrometers across. As stated earlier in the paper, I have gathered traverse analyses across the larger crystals and edge and core analyses of the smaller crystals. I have analyses from 6 rutile crystals for this sample. The results can be found in Appendix table Garnet Quartzite A Crystal A Zirconium Content (ppm) Distance Across Crystal (micrometers) Figure 10 Zirconium content of crystal A of Garnet Quartzite A. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. The zirconium content measured in the crystals in this sample ranges from 110 parts per million to 499 ppm. Many of the lower concentration measurements were analyses that had silicon concentrations greater than 300 ppm and were not included in the averages. As the graphs show, the zirconium content is higher in the cores of the crystals than at the rims (figures 9, 14 18). The average zirconium content of these crystals was calculated from the measurements that fell within analytical uncertainty of each other and with silicon concentrations less than 300 ppm. In the majority of the crystals these measurements came from the cores of the crystals. The uncertainty of zirconium concentration of the crystal was then calculated using the standard deviation of mean of the same measurements used in calculating the average zirconium content of the crystal. The rutiles in the garnet mica schist, while more abundant in number than the rutiles in the first garnet quartzite, were also far smaller, thereby having a much lower volume in the rock. There is less than.5% volume of rutile in the rock. The rutiles in this sample range from 71 microns across to 152 microns across according to measurements of the traverses across the crystals done by the EPMA. I measured the zirconium content of the grains in spots along line traverses across all the analyzed rutiles in this sample. I analyzed five rutile crystals in this sample. One sample traverse is illustrated in figure 10. 7

8 Zirconium Content (ppm) Garnet Mica Schist Crystal E Distance across Crystal (micrometers) Figure 11 Zirconium content of crystal E of garnet mica schist. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. The zirconium content in these crystals ranges from 170 parts per million to 435 parts per million. The rutiles in this sample also have lower zirconium contents in the rims than in the cores of the crystals. Crystal B has two analyses with low zirconium concentrations in the center of the crystal, but this is most likely caused by the fact that the analyses went over a crack in the crystal as can be seen in fig 20. The garnet amphibolite also had more, but smaller, rutile crystals than the garnet quartzite. There is less than.1% volume of rutile in the rock, and the crystals themselves range from 26 micrometers across to 72 micrometers across. I measured the zirconium content of the grains in spots along line traverses across all the analyzed rutile crystals in this sample. I have analyses from four of the crystals in this sample. 8

9 Garnet Amphibolite Crystal F 350 Zirconium Content (ppm) Distance across Crystal (micrometers) Figure 12 Zirconium content of crystal F of Garnet Amphibolite. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. The zirconium content measured in these crystals range from 211 parts per million to 368 parts per million. The rutiles have a relatively homogenous zirconium content within uncertainty across the majority of the sample except for one of the crystals that has lower zirconium content towards the rim. The last sample that I analyzed was garnet quartzite B (sample A14 64F). This sample had sparse rutiles that were rather small. There is only about less than.05% volume of rutile in this rock and the rutiles range from 28 micrometers to 38 micrometers in length. Garnet Quartzite B Crystal D Zirconium Content (ppm) Distance across Crystal (micrometers) Figure 13 Zirconium content of crystal D of Garnet Quartzite B. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. The zirconium content measured in these crystals range from 258 parts per million to 415 parts per million. The rutile crystals in this sample are homogenous, exhibiting little to no zoning and 9

10 consistent zirconium contents throughout the crystals within uncertainty. The rutiles in this sample were also all contained within garnets. DISCUSSION AND CONCLUSIONS The concentration of the ZrO 2 is higher in the cores, relative to the rims of the rutile grains; that is, the grains are zoned. Zoning can occur when crystals form at or above the closure temperature for zirconium diffusion in rutile, and some of the zirconium diffuses out of the rutile crystal during cooling. Using this information, the zirconium content of the cores of the crystals was used to calculate the approximate peak temperature of formation of each crystal. For each of the crystals analyzed in each sample, the average zirconium content of the crystal was calculated from the measurements acquired from the electron probe micro analyzer excluding analyses that were outliers outside of the uncertainty of measurement and also excluding any analyses that had silicon concentrations greater than 300 ppm. The uncertainty due to counting statistics was used to determine whether or not a given measurement was used in the calculation of the average. Analyses with zirconium concentrations outside the analytical uncertainty of the majority of the analyses were excluded from the calculation of the average. Outliers, such as the measurements that were on the crack in crystal B of the garnet mica schist and in the majority of the rims of the crystals, were not included in the measurement of the average. After the average was calculated for each rutile the standard deviation of the mean of the measurements used in the average was calculated to find a two sigma uncertainty of the measurements for the crystal. To calculate the zirconium content for each sample, a similar process to the approach for individual crystals was used. Crystals that recorded significantly lower zirconium concentrations than the rest of the crystals in the sample were excluded from the calculation of the average zirconium content and uncertainty. This affected only the calculations for the garnet mica schist where grain D had significantly lower zirconium concentrations than the rest of the grains. I used the average zirconium content for the sample to calculate an average temperature for the sample and used the standard deviation of mean of the zirconium content to find an uncertainty on the temperature. For garnet quartzite A, I used an average of the analytical uncertainties to calculate the uncertainty for the sample since the standard deviation of the mean calculation resulted in an uncertainty that was lower than the analytical unc ertainty. Table 1 Average zirconium content calculated for Garnet Quartzite A Table 2 Average zirconium content calculated for Garnet Mica Schist. Grain D fell outside of uncertainty of the rest of the measurements and was therefore not used in the calculation of the average. 10

11 Garnet Amphibolite Crystal Average Zr Content Uncertainty B C F Average 289 SDOM 91 Table 4 Average zirconium content calculated for Garnet Amphibolite Table 3 Average zirconium content calculated for Garnet Quartzite B The pressure used to calculate the final temperatures was 10 kbar. This falls within the range of pressures calculated for samples found within the Catalina Schist. (Sorensen and Barton, 1987) I did calculate the temperatures for different pressures for one sample, however I found that all the temperature variations are only 3 to 4 degrees Celsius for each kbar of pressure added. This is less than the uncertainty due to measurement of zirconium concentrations. Temperature ( C) Crystal 8 kbar 9 kbar 10kbar 11 kbar A 678 ( ) 682 ( ) 687 ( ) 691 ( ) B 676 ( ) 680 ( ) 685 ( ) 689 ( ) C 677 ( ) 682 ( ) 686 ( ) 691 ( ) D 676 ( ) 680 ( ) 685 ( ) 689 ( ) E 679 ( ) 683 ( ) 688 ( ) 692 ( ) F 677 ( ) 681 ( ) 686 ( ) 690 ( ) Average Table 5 Temperatures for the average zirconium concentration for six different crystals (A through F) in Garnet Quartzite A calculated at different pressures. The numbers in parenthesis are the range of temperatures within uncertainty for each crystal with the average temperature of each crystal outside the parenthesis. The final calculated temperatures are reported in Table 6: Table 6 Final Temperatures calculated for all samples at 10 kbar. Temperature is in C. 11

12 Figure 14 Final Temperatures of samples. 1 is Garnet Mica Schist, 2 is Garnet Quartzite A, 3 is Garnet Amphibolite, and 4 is Garnet Quartzite B. Error bars are uncertainty determined by standard deviation of mean of the average zirconium content of each sample. Average temperatures for these four rock samples from the same outcrop range from 646 to 686 degrees C. As shown in figure 13, the peak temperatures of all samples fall within uncertainty of each other. This reflects the fact that average zirconium content of each sample is the same within uncertainty. These results do not support my hypothesis. This suggests that all of these samples may have formed at relatively similar temperatures of formation. From this I can conclude that these samples all may have formed at similar temperatures to each other, thus supporting the single package model of subduction zone for the Catalina Schist. My calculated temperatures for these samples fell within the ranges calculated by McBride (2013). The temperatures reported by McBride were C for the amphibolite facies. The samples analyzed in that study include three amphibolite facies samples from different localities: an actinolite schist, a garnet amphibolite, and a garnet quartzite. The calculated temperatures from this study fall within the ranges calculated for the amphibolite facies by Bebout (2007) which can be seen in figure 4. 12

13 APPENDIX The electron probe microanalyzer (EPMA) is an analytical tool used to determine chemical composition of minerals. It does this by emitting a beam of electrons from a tungsten filament. An anode plate is charged with 3,000 to 30,000 volts to accelerate the electron beam toward the mineral being analyzed. The beam is focused using a series of magnetic lenses and apertures to focus the beam down to a diameter of only a few microns. The filament current determines the resolution of the image that the EPMA displays and the amount of time it takes to make an analysis. When the electron beam hits the mineral being analyzed, the mineral gives off x rays and secondary electrons. The secondary electrons and backscattered electrons (incident electrons that have interacted with the sample and lost some energy) can be used to form an image of the mineral that can be displayed on monitors connected to the EPMA. The x rays can be detected by an energy dispersive detector (EDS) and a wavelength dispersive detector (WDS). Both of these detectors require prior set up to detect specific elements in the mineral being analyzed. Once this is set up, the EDS can give an immediate display of relative concentrations of various elements in the mineral being analyzed while the WDS can give highly specific weight percentages of various elements in the mineral. However in order for the WDS to give accurate weight percentages of elements within the analyzed mineral, prior analyses must be done on various samples where the expected amount of a given element is known (standards) in order to calibrate the EPMA. Details of the operating conditions and the standards used to determine rutile compositions can be found in the body of the text. 13

14 Appendix Table 1 All Electron Probe analyses for sample A14 64B Garnet Quartzite A 14

15 No. TiO2 ZrO2 Al2O3 FeO Nb2O5 SiO2 MnO Ta2O5 Total Comment Distance (μ) Zr Content ppm No. Uncertainty % Zr Uncertainty Line 1 E Line 2 E Line 4 E Line 5 E Line 6 E Line 7 E Line 8 E Line 9 E Line 10 E Line 1 B Line 2 B Line 3 B Line 4 B Line 5 B Line 6 B Line 7 B Line 8 B Line 9 B Line 10 B Line 1 A Line 2 A Line 3 A Line 4 A Line 5 A Line 6 A Line 7 A Line 8 A Line 9 A Line 10 A Line 1 D Line 2 D Line 3 D Line 4 D Line 5 D Line 6 D Line 7 D Line 8 D Line 9 D Line 1 C Line 2 C Line 3 C Line 4 C Line 5 C Line 6 C Line 7 C Line 8 C Line 9 C Appendix Table 2 All data for Sample A14 64D Garnet Mica Schist. 15

16 No. TiO2 ZrO2 Al2O3 FeO Nb2O5 SiO2 MnO Ta2O5 Total Comment Distance (μ) Zr Content ppm No. Uncertainty % Zr Uncertainty Line 2 A Line 3 A Line 4 A Line 5 A Line 6 A Line 7 A Line 2 B Line 3 B Line 4 B Line 5 B Line 6 B Line 7 B Line 8 B Line 1 C Line 2 C Line 3 C Line 4 C Line 5 C Line 6 C Line 7 C Line 1 D Line 2 D Line 3 D Line 4 D Line 5 D Line 6 D Line 7 D Line 1 E Line 2 E Line 3 E Line 4 E Line 5 E Line 6 E Line 7 E Appendix Table 3 All data for Sample A14 64F Garnet Amphibolite. 16

17 No. TiO2 ZrO2 Al2O3 FeO Nb2O5 SiO2 MnO Ta2O5 Total Comment Distance (μ) Zr Content ppm No. Uncertainty % Zr Uncertainty Line 1 B Line 2 B Line 3 B Line 4 B Line 5 B Line 6 B Line 7 B Line 8 B Line 4 C Line 5 C Line 6 C Line 8 C Line 9 C Line 1 F Line 2 F Line 3 F Line 4 F Line 5 F Line 6 F Line 7 F Line 8 F Line 9 F Line 1 G Line 2 G Line 3 G Line 4 G Line 5 G Line 6 G Line 7 G Line 8 G Appendix Table 4 All data for Sample A14 64G Garnet Quartzite B. 17

18 Appendix Figure 1 Zirconium content of crystal B of Garnet Quartzite A. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Appendix Figure 2 Zirconium content of crystal C of Garnet Quartzite A. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Measurements 1 and 4 are rim analyses and 18 measurements 2 and 3 are core analyses. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics.

19 Appendix Figure 3 Zirconium content of crystal C of Garnet Quartzite A. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Measurements 1, 4 and 5 are rim analyses and measurements 2 and 3 are core analyses. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. Appendix Figure 4 Zirconium content of crystal C of Garnet Quartzite A. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Measurements 1, 5 and 6 are rim 19

20 analyses and measurements 2, 3, and 4 are core analyses. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. Appendix Figure 5 Zirconium content of crystal C of Garnet Quartzite A. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Measurements 1 and 5 are rim analyses and measurements 2, 3, and 4 are core analyses. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. 20

21 Appendix Figure 6 Zirconium content of crystal A Garnet Mica Schist. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. Appendix Figure 7 Zirconium content of crystal B of Garnet Mica Schist. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point 21

22 represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. Appendix Figure 8 Zirconium content of crystal C of Garnet Mica Schist. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. 22

23 Appendix Figure 9 Zirconium content of crystal D of Garnet Mica Schist. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. Appendix Figure 10 Zirconium content of crystal A of Garnet Quartzite B. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. 23

24 Appendix Figure 11 Zirconium content of crystal B of Garnet Quartzite B. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. Appendix Figure 12 Zirconium content of crystal C of Garnet Quartzite B. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. 24

25 Appendix Figure 13 Zirconium content of crystal E of Garnet Quartzite B. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. 25

26 Appendix Figure 14 Zirconium content of crystal B of Garnet Amphibolite. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. 26

27 Appendix Figure 15 Zirconium content of crystal B of Garnet Amphibolite. Red lines indicate the 2 sigma standard deviation of mean and the blue line indicates calculated average of zirconium content for this crystal. Black error bars on each data point represent 2 sigma uncertainty for each measurement based on Electron Probe Microanalyzer counting statistics. 27

28 Start End.7 mm Appendix Figure 17 Garnet Quartzite A crystal A. Line is 415 micrometers long. Dots are beginning and end of analysis run. 15 steps in between, micrometers between each step. 28

29 Start End.7 mm Appendix Figure 18 Garnet Quartzite A crystal B. Line is 154 micrometers long. Dots are beginning and end of analysis run. 6 steps in between, micrometers between each step. 29

30 .7 mm Appendix Figure 19 Garnet Quartzite A crystal E approximate core and rim analysis locations. 30

31 .7 mm Appendix Figure 20 Garnet Quartzite A crystal F. Crystlal is too small to accurately show analysis points. 31

32 End Start.35 mm Appendix Figure 21 Garnet Mica Schist crystal A. Line is micrometers long. 10 steps in between, 14.6 micrometers between each step. 32

33 End Start.35 mm Appendix Figure 22 Garnet Mica Schist crystal B. Line is 66 micrometers long. 10 steps in between, 7.4 micrometers between each step. 33

34 End Start.35 mm Appendix Figure 23 Garnet Mica Schist crystal C. Line is micrometers long. 10 steps in between, micrometers between each step. 34

35 Start End.7 mm Appendix Figure 24 Garnet Mica Schist crystal D. Line is 76 micrometers long. 10 steps in between, 8.11 micrometers between each step. 35

36 Start End.7 mm Appendix Figure 25 Garnet Mica Schist crystal D. Line is 77.3 micrometers long. 10 steps in between, 8.59 micrometers between each step. 36

37 .7 mm Appendix Figure 26 Garnet Quartzite B crystals A. Rutiles are in garnets. Crystals are too small to accurately show analysis points. 37

38 .7 mm Appendix Figure 27 Garnet Quartzite B crystal D. Rutile is in garnet. Crystals are too small to accurately show analysis points. 38

39 .7 mm Appendix figure 28 Garnet Quartzite B crystal E. Rutile is in garnet. Crystals are too small to accurately show analysis points. 39

40 Start End B End Start C.35mm Appendix Figure 29 Garnet Amphibolite crystal B and C. Lines are 53 and 65 micrometers long respectively. 10 steps in between, 5.93 and 7.2 micrometers respectively between each step. 40

41 REFERENCES Bebout, G. E., Metamorphic chemical geodynamics of subduction zones, Earth and Planetary Science Letters 260, 2007, p Cloos, M., 1982, Flow melanges: Numerical modeling and geologic constraints on the origin in the Franciscan subduction complex, California, Geological Society of America Bulletin, vol 93, issue 4, 1982, p Grove, M., Bebout, G.E., Jacobson, C.E., Barth, A.P., Kimbrough, D.L., King, R.L., Zou, Haibo, Lovera, O.M., Mahoney, B.J., Gehrels, G.E., The Catalina Schist: Evidence for middle Cretaceous subduction erosion of southwestern North America, Geological Society of America Special Papers, 2008, p Mcbride, H., 2013, Zirconium in Rutile Thermometry: Temperature Estimates for Metamorphic Rocks of the Catalina Schist McLaughlin, R.J., Kling, S.A., Poore, R.Z., McDougall, K. and Beutner, E.C. (1982). "Post-middle Miocene accretion of Franciscan rocks, northwestern California". Geological Society of America Bulletin: v. 93, p Sorensen, S. S., Barton, M. D., Metasomatism and partial melting in a subduction complex Catalina Schist, southern California, Geology, 1987, p Tomkins, H.S., Powell, R., Ellis, D.J., 2007, The pressure dependence of the zirconium in rutile thermometer, J. metamorphic Geol., 2007, 25,