DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Tectonic History of the Northern Nabitah Fault Zone, Arabian Shield, Kingdom of Saudi Arabia James E. Quick and Paul S. Bosch Open-File Report 90- Report prepared by the U.S. Geological Survey in cooperation with the Deputy Ministry for Mineral Resources, Saudi Arabia This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and strati graphic nomenclature. I/ USGS, Denver, CO 1990 CONTENTS Page Page ABSTRACT. .. 1 Undivided ultramafic tectonite...... 17 Interlayered gabbro & peridotite.... 18 INTRODUCTION. Gabbro.............................. 18 Basalt and diabase.................. 18 GEOLOGY OF SELECTED AREAS................... 2 Metabasalt.......................... 18 Bi'r Tuluhah............................ 2 Breccia............................. 18 Overview............................ 5 Uadi Khadra phyllonite (mylonite)... 19 Hulayfah group...................... 5 Granodiorite........................ 19 Shammar group....................... 6 Faulting............................ 19 Fault-zone rocks ................... 6 Folding............................. 19 Metasedimentary rocks........... 6 Synthesis........................... 24 Silicic volcanic rocks.......... 6 MetabasaIt...................... 6 Jabal al Qub............................ 24 Amphibolite..................... 6 Overview............................ 26 Ultramafic rocks, undivided..... 7 Ultramafic rocks.................... 26 Marble ......................... 8 Amphibolite......................... 27 Cumulus gabbro.................. 8 Metadiorite......................... 27 Quartz diorite and microdiorite. 8 Granodiorite and Rharaba complex.... 28 Granitic rocks and late gabbro.. 8 Volcanic and sedimentary rocks...... 28 Nabitah faults...................... 8 Tonalite and undivided granite...... 29 Najd faults......................... 8 Faulting............................ 29 Folding............................. 9 Folding............................. 29 Lithologic sequence................. 11 Fault kinematics.................... 30 Geochronology....................... 11 Geochronology....................... 31 Synthesis........................... 12 Synthesis........................... 31 Bi'r Nifazi............................. 12 GEOCHEMISTRY................................ 31 Overview............................ 12 Geochemical techniques.................. 31 Interlayered ultramafic and Geochemical results..................... 32 mafic rocks....................... 13 Petrogenesis and immobile elements.. 32 Gabbro.............................. 13 Darb Zubaydah ophiolite............. 32 Hypabyssal intrusive rocks.......... 13 Bi'r Tuluhah........................ 35 Interbedded pillow basalt and lahar Spinel analyses..................... 38 deposits.......................... 14 Jabal Mardah gossans................ 14 REGIONAL SYNTHESIS.......................... 42 Interbedded basaltic flows Terranes................................ 42 and flow breccia.................. 15 Nabitah faulting........................ 42 Interbedded wacke, shale, and tuff.. 15 Afif terrane............................ 42 Undivided volcanic rocks............ 15 Nabitah volcanic arc................ 42 Dacite.............................. 15 Rharaba complex..................... 42 Basalt.............................. 15 Opiolitic rocks of the western Carbonate-replaced basalt, Afif terrane...................... 43 diabase, and gabbro............... 16 Amphibolite of the western Upper Proterozoic intrusive rocks... 16 Afif terrane...................... 43 Structure........................... 16 Hijaz terrane....................... 44 Geochronology....................... 16 Asir terrane........................ 44 Synthesis........................... 16 Bi'r Umq suture..................... 44 Offset of the Asir terrane and Wadi Khadra............................. 17 the Bi'r Umq suture............... 44 Overview............................ 17 TECTONIC MODEL.............................. 45 DATA STORAGE.... 54 Sumatra................................. 45 Kuril Arc............................... 45 ACKNOWLEDGMENTS. 55 California.............................. 46 Applications to Saudi Arabia............ 46 REFERENCES...... 64 IMPLICATIONS FOR GOLD MINERALIZATION........ 50 APPENDIX........ 69 Nabitah Zone............................ 50 Foothills Fault Zone and the Mother Lode District.................. 51 Conclusions............................. 54 ILLUSTRATIONS [Plates in pocket] PLATE 1. Geologic map of the Bi'r Tuluhah area. 2. Geologic map of the Hulayfah area. 3. Geologic map of the Bi'r Nafazi area. 4. Geologic map of the Wadi Khadra area. 5. Geologic map of the Jabal al Qub area. FIGURE 1. Map showing location of Arabian Shield and distribution of major suture zones............................................. 3 2. Geologic map of the Nuqrah-Mahd adh Dhahab vicinity.................. 4 3. Equal-area-projection diagrams showing the orientations of F^ fold axes and Iineations in the Bi'r Tuluhah area organized by lithology................................................... 9 I 4. Block diagram showing the shape and orientation of small asymmetric folds in the metatuff unit at Bi'r Tuluhah........... 10 5. Equal-area-projection diagrams showing the orientations of F? fold axes and Iineations in the Bi'r Tuluhah area organized by Ii thology............................. r ...................... 11 6. View (from north to south) of the northernmost gossan at Jabal Mardah.............................I...................... 14 7. An outcrop of polymict breccia in the Wadi Khadrah area. 20 8. Oblique air photo showing contact between phyllonite and moderately deformed cumulus gabbro and peridotite...!....................... 20 9. Effects of deformation on plagioclase-phyric diabase at Wadi Khadra..............................j....................... 21 10. Equal-area projection diagrams showing orientations of fold axes and Uneations in the Wadi Khadra area................ 22 11 FIGURE 11. Folded quartz veins on horizontal outcrop surfaces in the Wadi Khadra phyllonite...................................... 23 12. Outcrop of the Wadi Khadra phyllonite showing F3 folds.............. 25 13. Block diagram of the Wadi Khadra phyllonite......................... 26 14. Equal-area-projection diagrams showing orientations of fold axes and Iineations in the Jabal al Qub area............... 30 15. AFM diagrams for volcanic rocks and hypabyssal rocks of the Darb Zubaydah opMolite......................................... 33 16. Compositional (^O-SiOO diagrams for volcanic rocks and hypabyssal rocks of the Darb Zubaudah ophiolite................. 33 17. Compositional (Ti-Zr) diagrams for volcanic rocks and hypabyssal rocks of the Darb Zubaydah ophiolite............................ 34 18. Zr-Ti-Y ternary diagrams for volcanic rocks and hypabyssal rocks of the Darb Zubaydah ophiolite.................................. 35 19. AFM diagrams for rocks of the Bi'r Tuluhah area..................... 36 20. Compositional (^O-SiC^) diagrams for rocks of the Bi'r Tuluhah area............................................... 37 21. Compositional (Tr-Zr) diagrams for rocks of the Bi'r Tuluhah area... 39 22. Zr-Ti-Y ternary diagrams for rocks of the Bi'r Tuluhah area......... 40 23. Plot of Cr-value versus Fe-value for the average compositions of primary spinel in serpentinite samples from the Nabitah fault zone...................................................... 41 24. Maps illustrating the modern tectonic elements of Sumatra and Japan north of Hokkaido........................................ 47 25. Maps illustrating analogous geologic and tectonic features in California and the Arabian Shield.............................. 48 26. Simplified geologic maps of the northern Sierra Nevada mountains showing the Foothills Fault Zone, the MeIones Fault, goldmines, and major lithologies........................ 53 TABLES TABLE 1. Characteristics of ancient gold mines in the vicinity of the Nabitah fault zone.............................................. 56 2. Au-Ag geochemical values for selected samples from ancient mines of the Nabitah fault zone....................................... 62 ill TECTONIC HISTORY OF THE NORTHERN NABITAH FAULT ZONE, ARABIAN SHIELD, KINGDOM OF SAUDI ARABIA By JAMESE.QUICK AND PAULS.BOSCH ABSTRACT Geologic mapping combined with structural, petrographic, and geo- chemical investigations were used to evaluate the motion and paleogeographic setting of the northern Nabitah fault zone. The orientation and asymmetry of small structures in three areas along the fault zone suggest that motion was primarily left-lateral strike slip. East of the fault zone, the Afif terrane is underlain by a north-trending granodioritic batholith that is interpreted to be the plutonic core of a volcanic arc (herein named the Nabitah arc) whose activity was coincident with Nabitah faulting. Available geochronologic data indicate that the Nabitah fault zone and arc were active at 710 Ma and that activity may have continued until about 670 Ma. Relicts of a prebatholithic island-arc ophiolite crop out as roof pendants and septa east of the fault zone. Analysis of petrologic, geochemical, and geochronologic data suggests that these rocks may have formed a terrane older than 800 Ma that was continuous from the Nabitah fault zone to the Nuqrah belt. These rocks may have been moved northward by Nabitah faulting from an original