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The Petrology and Geochemistry of the Independence Dike Swarm, Owen’S Valley, California Sean B

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The Petrology and Geochemistry of the Independence Dike Swarm, Owen’S Valley, California Sean B Cedarville University DigitalCommons@Cedarville The Research and Scholarship Symposium The 2016 yS mposium Apr 20th, 11:00 AM - 2:00 PM The etrP ology and Geochemistry of the Independence Dike Swarm, Owen’s Valley, California Sean B. O'Donnell Cedarville University, [email protected] Follow this and additional works at: http://digitalcommons.cedarville.edu/ research_scholarship_symposium Part of the Geochemistry Commons, and the Geology Commons O'Donnell, Sean B., "The eP trology and Geochemistry of the Independence Dike Swarm, Owen’s Valley, California" (2016). The Research and Scholarship Symposium. 18. http://digitalcommons.cedarville.edu/research_scholarship_symposium/2016/poster_presentations/18 This Poster is brought to you for free and open access by DigitalCommons@Cedarville, a service of the Centennial Library. It has been accepted for inclusion in The Research and Scholarship Symposium by an authorized administrator of DigitalCommons@Cedarville. For more information, please contact [email protected]. The Petrology and Geochemistry of the Independence Dike Swarm, Owen’s Valley, California Sean B. O’Donnell, Cedarville University Department of Science and Mathematics, 251 N. Main St. Cedarville, OH 45314, [email protected] Abstract Petrography Petrologic studies are important because they provide insights into the condi- tions under which rocks form. The Late Jurassic Independence Dike Swarm is a D D series of vertical igneous dikes that crop out in eastern and southern California, and range from mac to felsic in composition. In order to examine their petrol- ogy and geochemistry, surface samples were collected from four dierent dike P P outcrops within Owen’s Valley, CA. The samples were examined through thin-section analysis under a petrographic microscope, X-ray diraction analy- sis, and X-ray uorescence analysis. Mineral composition, mineral size, major, D D trace, and rare earth element concentrations were collected from these analy- ses. Results from all samples were compared. Petrologically, the dikes range in IDS 1 PP IDS 1 XP classication from gabbro to diorite to granite, with the more gabbroic and di- oritic dikes having larger concentrations of plagioclase. The more granitic dikes have larger concentrations of quartz and potassium feldspars. There is consid- erable mineral alteration, especially among the feldspars, with some of the K K samples having been almost completely altered into clay minerals. The pres- ence of epidosite within a dike suggests the source magma incorporated coun- try rock on the way toward the surface. Geochemical analysis shows chemical K K variability among the dikes and possible source magma dierentiation within the Owen’s Valley area. Q Q Geochemical Data IDS 2 PP IDS 2 XP Background Alkali v Silica (Middlemost 1994) QAPF diagram - Si oversaturated Tawite/Urtite/Italite Q 1 - alkali-feldspar quartzolite syenite The Independence Dike Swarm (IDS) is a series of vertical igneous dikes that 15 IDS-2 Foid 2 - monzodiorite syenite P monzogabbro outcrop in Owen’s Valley, the Sierra Nevada, Inyo Range, Argus Range, and quartz-rich Foidolite Foid 3 - diorite, gabbro granitoid monzo- Syenite O syenite F 2 10 F K Mojave Desert in southeastern California. The dike swarm has north-south Foid monzo-gabbro Quartz P O 2 monzonite F F a Monzonite 1DS-4 N monzo- Monzo grano- length of almost 250 km, and an east-west length of about 40 km. The dikes Foid 1DS-3 syeno- granite tonalite gabbro diorite Monzo- granite diorite gabbro Granite 5 1DS-1 alk-fsp.granite IDS-4 1DS-2 Granodiorite IDS-6 q-diorite diorite q-alk-fsp quartz- IDS-5 Gabbroic Diorite q-gabbro above the surface. Most of the dikes in the swarm have been repeatedly Gabbro syenite syenite quartz- IDS-3 gabbro q-anorthosite Peridot Quartzolite monzonite q-monzodiorite 0 q-monzogabbro 1 syenite monzonite 2 3 IDS-1 A P dated to 148 Ma in the Late Jurassic Period, and a few have been dated to 40 50 60 70 80 90 the Mid-Cretaceous. Owens Valley is a structural trough that formed as a SiO2 graben, and stretches from Mono Lake in the north, all the way to the Coso IDS 3 PP IDS 3 XP SiO2 v Major Elements (weight %) 1DS-2 1DS-1 Range in the south. 1DS-1 1DS-2 1DS-1 1DS-3 3 2 1DS-2 1DS-3 O 2 1DS-3 TiO MgO Al 1DS-1 1DS-2 O 1DS-4 1DS-4 1DS-4 O 0.0 0.5 1.0 1.5 2.0 12 14 16 18 20 22 24 0 2 4 6 8 10 50 55 60 65 70 75 50 55 60 65 70 75 50 55 60 65 70 75 1DS-2 SiO2 SiO2 SiO2 1DS-1 1DS-3 1DS-4 Methods 1DS-3 1DS-1 1DS-4 O O 2 2 K CaO Na 1DS-3 1DS-2 1DS-2 P 1DS-2 1DS-4 1DS-1 - P 0 2 4 6 8 10 0.5 1.5 2.5 3.5 1 2 3 4 5 6 Q 50 55 60 65 70 75 50 55 60 65 70 75 50 55 60 65 70 75 Q SiO SiO SiO crops of the Independence Dike Swarm in Owens Valley, CA (IDS 1 - 2 2 2 IDS 8). From these samples thin sections were made and X-Ray Dif- 1DS-1 5 O 1DS-3 2 P fraction analysis was run by Calgary Rock and Materials Services Inc. 1DS-2 1DS-4 IDS 4 PP IDS 4 XP 0.0 0.2 0.4 0.6 0.8 1.0 in Calgary, AB. X-Ray Fluorescence analysis was performed at Texas 50 55 60 65 70 75 SiO2 Tech University for major, trace, and rare earth element concentra- MgO v Major Elements (weight %) 1DS-2 1DS-4 tions in IDS 1, IDS 2, IDS 3, and IDS 4. Petrographic analysis was per- 1DS-1 1DS-3 3 2 2 1DS-3 1DS-2 O 2 SiO TiO P P Al formed on the thin sections using a Nikon Eclipse 50i Pol micro- 1DS-2 1DS-1 1DS-3 1DS-4 1DS-1 1DS-4 scope and Br computer software. The thin section analysis consist- 45 55 65 75 0.0 0.5 1.0 1.5 2.0 12 14 16 18 20 22 24 0 2 4 6 8 10 0 2 4 6 8 10 0 2 4 6 8 10 ed of measuring and recording crystal sizes, the orientation of pla- Q O MgO MgO MgO 1DS-3 1DS-4 1DS-1 O 1DS-3 1DS-4 1DS-1 O O gioclase phenocrysts, and point counting of mineral types. For the Q 2 2 K CaO Na 1DS-3 point counting, each slide was dividing into a 4x6 grid of squares 1DS-2 1DS-2 1DS-2 1DS-4 1DS-1 0 2 4 6 8 10 0.5 1.5 2.5 3.5 1 2 3 4 5 6 0 2 4 6 8 10 0 2 4 6 8 10 0 2 4 6 8 10 MgO MgO MgO to perform point counting on. In each square a grid was overlaid in 1DS-1 5 O 1DS-3 2 the computer software which consisted of 35 crosshairs, and the P IDS 5 PP IDS 5 XP 1DS-2 1DS-4 mineral at each of these crosshairs was recorded, making for 350 0.0 0.2 0.4 0.6 0.8 1.0 0 2 4 6 8 10 MgO points counted on each slide. P P SiO v Trace Elements (weight %) Q 2 Q 1DS-1 1DS-1 1DS-2 1DS-1 1DS-3 1DS-3 Sr Zr Ba 1DS-3 1DS-2 1DS-2 1DS-4 1DS-4 1DS-4 0 400 800 1200 400 600 800 1200 100 140 180 220 Discussion O 50 55 60 65 70 75 50 55 60 65 70 75 50 55 60 65 70 75 O SiO SiO SiO 2 2 2 1DS-1 1DS-1 1DS-2 1DS-4 O The dierent dikes of the Independence Dike Swarm within Owen’s Valley 1DS-2 2 Na Ni Cr O 2 1DS-2 K are compisitionally dierent from each other. IDS 1 is gabbro, the most 1DS-3 1DS-3 1DS-3 1DS-4 1DS-4 1DS-1 0 50 100 200 300 0 50 100 200 300 0.5 1.0 1.5 2.0 2.5 mac dike of the four sampled. IDS 2 is mineralogically a granitoid, but 50 55 60 65 70 75 50 55 60 65 70 75 50 55 60 65 70 75 SiO2 SiO2 SiO2 1DS-3 1DS-3 1DS-3 chemically it is a diorite. The dierence is due to the large amounts of min- IDS 6 PP IDS 6 XP 1DS-1 1DS-2 V Zn eral alteration that has taken place with the dike. Most of the feldspars Cu 1DS-1 1DS-1 1DS-2 1DS-4 1DS-4 1DS-4 1DS-2 have been altered to clay minerals, however, much of the original chemical 0 20 40 60 80 100 0 50 100 150 200 250 0 50 100 150 200 50 55 60 65 70 75 50 55 60 65 70 75 50 55 60 65 70 75 compositon is still present. The quartz/feldspar concentration is therefore SiO2 SiO2 SiO2 relatively high compared to the amount silica in the rock. IDS 3 and IDS 6 monzodiorites, and the dikes at IDS 4 for are granites. IDS 4 has the highest E E silica concentration of all the dikes sampled. The chemical data shows wide Acknowledgements variability between all the dikes Owen’s Valley.
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