Abstract ........................................................ 1
Introduction .................................................... 1
Previous Work ................................................ 3
Present Work ................................................. 5
Geology ......................................................... 5
Rock Units ................................................... 6
Proterozoic and Cretaceous Layered Gneiss ................. 6
Proterozoic Granodiorite to Granite Gneiss ................ 7
Proterozoic Porphyritic Granodiorite to Granite Gneiss .... 8
Paleozoic and Mesozoic Metasedimentary Rocks .............. 8
Jurassic Metagabbro, Metadiorite, and Amphibolite ........ 10
Late Cretaceous Granite of Tank Pass ..................... 11
Oligocene(?) and Miocene Swansea Plutonic Suite .......... 12
Rocks Probably Correlative with the Swansea Plutonic
Suite .................................................... 15
Geochronology .................................................. 15
Proterozoic Granitic Rocks .................................. 15
Jurassic Plutonic Rocks ..................................... 15
Rocks Migmatized in the Cretaceous .......................... 16
Swansea Plutonic Suite ...................................... 19
Whole-Rock and Feldspar Pb-lsotopic Compositions ............ 19
Geochemistry ................................................... 19
Analytical Methods .......................................... 19
Proterozoic Granitic Rocks .................................. 21
Jurassic Plutonic Rocks ..................................... 23
Cretaceous Plutonic Rocks ................................... 23
Swansea Plutonic Suite ...................................... 23
Comparison with Poachie Crust and Possible Origin ........ 31
Relation Between Magmatism, Extension, and Core Complex
Formation ................................................ 32
Structure ...................................................... 32
Faults ...................................................... 32
Major Folds ................................................. 34
Dikes ....................................................... 34
Lineation ................................................... 37
Foliation ................................................... 37
Minor Folds ................................................. 41
Older Foliation ............................................. 42
Summary of Structural and Metamorphic Events ................... 43
Acknowledgments ................................................ 44
References Cited ............................................... 44
Appendix. Location and Description of Analyzed Samples ......... 49
Figures
1. Map showing location of northern Harcuvar complex and
core complexes of west-central Arizona and adjacent part
of California ............................................... 2
2. Geologic map of the northern Harcuvar complex showing
locations of analyzed and(or) dated rocks ................... 4
3-12. Photographs of:
3. Migmatitic layered gneiss and granite in the eastern
Harcuvar Mountains .......................................... 7
4. Layered mylonite from layered gneiss in the eastern
Buckskin Mountains .......................................... 7
5. Mylonitic granodiorite gneiss from the eastern Buckskin
Mountains ................................................... 8
6. Mylonitic coarse-grained granite gneiss from the central
Buckskin Mountains .......................................... 9
7. Thin layers of marble in migmatitic layered gneiss in
the eastern Buckskin Mountains ............................. 10
8. Mylonitic biotite hornblende gneiss derived from gabbro
containing trondhjemite sills that have been deformed
into "fish" ................................................ 11
9. Mylonitic biotite granite in the eastern Buckskin
Mountains correlated with the Late Cretaceous granite of
Tank Pass in the Harcuvar Mountains ........................ 12
10. Mylonitic biotite granodiorite from the felsic phase of
the Swansea Plutonic Suite ................................. 13
11. Mylonitic porphyritic granite or monzogranite from
inclusion in felsicphase of the Swansea Plutonic Suite ..... 13
12. Small intrusion of granodiorite of the felsic phase of
the Swansea Plutonic Suite into layered migmatitic
gneiss ..................................................... 14
13. U-Pb zircon concordia diagram for mylonitic granitic
gneiss and mylonitic porphyritic granite and porphyritic
granodiorite inclusion in felsic rocks of the Swansea
Plutonic Suite ............................................. 18
14. U-Pb zircon concordia diagram for sample B-566 of
mylonitic horblende diorite from the eastern Buckskin
Mountains. MSWD, mean standard weighted deviation .......... 18
15. U-Pb zircon concordia diagram for sample HA-118 from a
migmatitic-looking granite layer in layered gneiss in
the eastern Harcuvar Mountains ............................. 18
16. U-Pb concordia diagrams for gabbro and granite of
the Swansea Plutonic Suite and combined with inclusions
in the suite ............................................... 20
17. Whole-rock and feldspar lead (Pb) isotopic compositions
of some rocks from the northern Harcuvar complex and
Mesozoic and Tertiary plutonic rocks in the Whipple
Mountains .................................................. 22
18. Chemical diagrams for rocks of the northern Harcuvar
complex .................................................... 24
19. More chemical diagrams for rocks of the northern Harcuvar
complex .................................................... 26
20. Chrondite-normalized rare-earth element contents of
igneous rocks in the northern Harcuvar complex ............. 27
21. Northeast-southwest crustal section through the Buckskin
Mountains based on geophysical and geologic data ........... 33
22. Areas of structural analyses in the northern Harcuvar
complex .................................................... 33
23. Structures in the Buckskin Mountains formed before,
during, and after mylonitization in the Miocene ............ 35
24. Photographs showing low-angle brittle faults in the
eastern Buckskin Mountains ................................. 36
25. Photographs showing features in mylonitized rock ........... 38
26. Structures in the Buckskin Mountains synchronous with
mylonitization ............................................. 39
27. Structures in the Little Buckskin Mountains formed during
and after mylonitization during the Miocene ................ 40
28. Structures in the eastern Harcuvar Mountains formed
before and during mylonitization ........................... 40
29. Photograph showing hinge of northeast-trending fold
formed by mylonitic granite gneiss ......................... 42
30. Photograph showing minor tight folds in mylonitic
biotite-hornblende gneiss .................................. 42
Tables
1. U-Pb ages of rocks in the northern Harcuvar complex ......... 16
2. Analytical data and ages of zircons from the northern part
of the Harcuvar complex in the lower plate of the Rawhide
detachment fault in the Buckskin and eastern Harcuvar
Mountains ................................................... 17
3. Whole-rock and feldspar (F) Pb-isotopic compositions of
rocks from the northern Harcuvar complex and from
Cretaceous and Tertiary plutonic rocks from the Whipple
Mountains ................................................... 21
4. Major-oxide and trace-element concentrations in some
Proterozoic granitic rocks and inclusions in the Swansea
Plutonic Suite .............................................. 25
5. Major- and trace-element concentrations in some Jurassic
and Cretaceous plutonic rocks from the northern part of
the Harcuvar complex ........................................ 28
6. Major-oxide and trace-element concentrations in rocks of
the Swansea Plutonic Suite .................................. 30
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