Golconda Summit, Nevada

Transcription

1 Penn quartzite Golconda Summit, Nevada Penn volcanics Penn ls hilltop Cambrian shales Penn LANF? Thrust? Golconda Thrust Golconda Summit, I80. Above highway where trucks are, Cambrian Preble Frm (phyllitic shale) under Antler Peak ls, Penn-Perm reef ls--juxtaposed on Iron Point fault (thrust on old maps, LANF in Cashman et al). Edna Mtn (Permian ss) at very top of hill. Small hill at right has Iron Point Thrust again within it. To left of highway, peak with antennae is Golconda Summit, which is Penn shale+chert of upper plate of Golconda allochthon. Ledge 1/3 way up is Antler Peak ls with brown Edna Mtn Frm above. Most of gray slopes behind is greenstone unit (basalts-andesites of Penn age) of upper plate of Golconda.

2 Miller et al., DNAG

3 Paleozoic Tectonic Domains of Nevada Pine Forest Range Hot Springs Range Jackson Mountains Humboldt Osgood Mountains Independence Mountains Granite Range Edna Mountain Elko Washoe Sonoma Range Battle Mountain Pershing East Range Tobin Range Lander Eureka Shoshone Range Storey Churchill White Pine Carson City Douglas Lyon Toiyabe Range Excelsior Mountains Mineral Pilot Mountains Candelaria Hills Esmeralda Nye? Lincoln Legend Nolan Belt Domain Antler Overlap Domain Golconda Domain and Home Ranch subterrane Black Rock-Jackson Domain Clark Crafford, Geosphere, 2008 Crafford notes lower plate pretty undeformed, but upper plate hammered in places relatively undeformed Tr on top. Also discuss Nolan belt, which is defined by Crafford as having continental affinity but higher grade metamorphism and west-verging thrusting in pre-mid-penn

4 Gehrels and Dickinson, Am J Sci. 1995

5 Both of these are Golconda allocthon sections. Independence Mtns in NE Nevada Riley et al., GSA SP 347, 2000

6 Figure 5. Relative age-probability curves for Paleozoic strata of Cordilleran miogeocline (Gehrels, this volume) and lower Paleozoic strata of Roberts Mountains allochthon (Gehrels et al., this volume, Chapter 1), Shoo Fly Complex (Harding et al., this volume), and Yreka terrane (Wallin et al., this volume). Ages of Trinity terrane intrusive rocks are from Wallin et al. (1995). B.C. British Columbia. Numbers in boxes refer to provenance links listed in Table 1. Gehrels et al., GSA SP 347, 2000

7 Gehrels et al., GSA SP 347, 2000 Figure 5. Relative age-probability curves for Paleozoic strata of Cordilleran miogeocline (Gehrels, this volume) and lower Paleozoic strata of Roberts Mountains allochthon (Gehrels et al., this volume, Chapter 1), Shoo Fly Complex (Harding et al., this volume), and Yreka terrane (Wallin et al., this volume). Ages of Trinity terrane intrusive rocks are from Wallin et al. (1995). B.C. British Columbia. Numbers in boxes refer to provenance links listed in Table 1.

8 Gehrels et al., GSA SP 347, 2000 Riley et al., GSA SP 347, 2000 Figure 7. Results of statistical comparisons of detrital zircon ages from

9 Miller et al., DNAG

10 Miller et al., DNAG Note lots of volcaniclastics as well as plutonic rocks

11 Miller et al., DNAG

12 Miller et al., DNAG

13 Miller et al., DNAG

14 Miller et al., DNAG

15 Miller et al., DNAG

16 Miller et al., DNAG

17 Miller et al., DNAG

18 Gehrels et al., GSA SP 347, 2000 What is the relationship of the Golconda rocks to North America? Back to detrital zircons [which are only a small part of sediment volume]

19 Original interpretation in 2000 is that all the terranes were connected Gehrels et al., GSA SP 347, 2000

20 Age (Ma) Slaven Chert (n=192) Elder Sandstone (n=189) Upper Vinini Fm McAfee Quartzite Lower Vinini Fm Snow Canyon Fm Figure 5. Relative age-probability curves for Paleozoic strata of Cordilleran mio(n=194) geocline (Gehrels, this volume) and lower Paleozoic strata of Roberts Mountains allochthon (Gehrels et al., this volume,(n=184) Chapter 1), Shoo Fly Complex (Harding et al., this volume), and Yreka terrane (Wallin et al., this volume). Ages of Trinity (n=189)terrane intrusive rocks are from Wallin et al. (1995). B.C. British Columbia. Numbers in boxes refer to provenance (n=189) links listed in Table Ksituan, and the Great Bear arcs (Hoffman, 1989; Ross, 1991; Villeneuve et al., 1993) (Fig. 7). The Ma grainsg.e. are similar in age Gehrels et to al.accreted terranes in the PRA region, including the Buffalo Head and Chincaga terranes (Hoffman, 1989; Ross, 1991; Villeneuve et al., 1993) (Fig. 7). The Ma grains are similar in age to Archean terranes in the PRA region, including the Nova and Hearne terranes (Hoffman, 1989; Ross, 1991; Villeneuve et al., 1993) (Fig. 7). The Hf isotope data are consistent with provenance in the PRA region. The Ma grains have a wide range of values, from juvenile and moderately juvenile through evolved (εhf(t) +10 to 15), similar to those of other units interpreted to originate in the PRA region (Gehrels and Pecha, 2014). The Ma grains are more narrowly grouped, with moderately juvenile to evolved values of εhf(t) +3 to 6, compatible with other units originating in the PRA region (Gehrels and Pecha, 2014). The Ma grains have juvenile, moderately juvenile, and evolved values of εhf(t) +6 to 15, also compatible with PRA origin (Gehrels and Pecha, 2014). The ages of basement terranes that comprise the PRA region (Fig. 7) are all represented in the age spectra of the RMA samples (exclusive of the lower Vinini Formation). The detrital zircon U-Pb ages and Hf isotope data from these RMA strata are similar to selected passive margin strata and RMA strata analyzed in other studies (Fig. 8). The RMA strata sampled in this study (exclusive of the lower Vinini) have U-Pb age spectra similar to those of the Ordovician Valmy Formation of the RMA (Gehrels and Pecha, 2014), as well as the Eureka Quartzite and the Mount Wilson Formation (Gehrels and Pecha, 2014), and the Kinnikinic Quartzite (Barr, 2009), Ordovician units of the western Laurentian passive margin (Figs. 8 and 9). The K-S analyses of the RMA and the Ordovician passive margin units discussed above do not contradict our interpretation that the RMA strata have a common provenance with the Ordovician passive margin sandstones (Table 2). These RMA strata also show similar Hf isotope ratios to the Valmy Formation (Gehrels and Pecha, 2014) and to the Eureka Quartzite and the Mount Wilson Formation (Gehrels and Pecha, 2014) (Fig. 8). The Peace River Arch region of western Canada is the source for the RMA units in this study, exclusive of the lower Vinini Formation, and for the Ordovician passive margin sandstones. The Peace River Arch region was an uplifted region from late Neoproterozoic through Middle Devonian time (Cant, 1988; Cant and O Connell, 1988; Cecile et al., 1997). Igneous bodies in the PRA region have ages similar to the U-Pb ages of zircons in the RMA rocks sampled (Figs. 7 and 8). The U-Pb age spectra of the RMA rocks sampled are not consistent with et al., GSA SPthe Yavapai-Mazatzal terranes are derivation from Gehrels the central Laurentian craton; 347, Ga and cannot serve as 2000 a source of the Ga grains in the samples Detrital Zircon Age (Ma) Provenance of the Lower Vinini Formation The U-P age spectra of the lower Vinini Formation are consistent with provenance in north-central Laurentia. The Ma grains are similar in age to plutonic suites in roof pendants and inliers within the Challis volcanic-plutonic complex and the Idaho batholith (Lund et al., 2010). The Ma grains are consistent with the Grenville orogen; the 1420 Ma grains are consistent with the central Laurentian anorogenic granites; the Ma grains are Linde et al., Geosphere., 2016 consistent with the Yavapai-Mazatzal terranes; and the Ma grains Mountain Quartzite [Yreka terrane]) may have been derived exposed basement rocks or their platformal cover and transported Worth recalling how the use of the LA-ICPMS measurements changed the interpretation of Gehrels s group. Note the Lower Vinini still has more of a directly from basement rocks exposed along the continental mar- across the miogeocline via channels carved into the continental gin, whereas more mature sandset were probably recycled shelf al. (Finney and Perry, 1991).to southern Laurentian look except for12 those 500 Maquartz ages, which Linde et now found as inliers in Idaho batholith and Challis GEOSPHERE Volume Number 3 Linde al. zircon U-Pb geochronology and Hfattribute isotope geochemistry of the materials Roberts Mountains allochthon Detrital 8 from miogeoclinal and/or platformal strata in the Peace River Units in the Roberts Mountains allochthon and Shoo Fly volcanics areas. arch region. Complex also contain detrital zircons of and ca. 0.7 Ga, Ordovician strata of the Roberts Mountains allochthon also contain Ga grains that originated in basement rocks of the southwestern United States (provenance link 3). As concluded by Finney and Perry (1991) on the basis of biostratigraphic and facies relations, there is a strong link between lower Middle Ordovician rocks of the Vinini Formation and coeval strata of the miogeocline directly to the east. Derivation of sediment from nearby continental sources apparently resulted from a low sea-level stand, during which sand was eroded from either which were most likely shed from basement rocks exposed along the southern continental margin (Wallin, 1990a) (provenance links 1 and 6). The dominant source may have been a westward continuation of Ga rocks of the Grenville province, perhaps now preserved in the Oaxaca terrane of Mexico (Coney and Campa, 1987; Ruiz et al., 1988). The 0.7 Ga grains in the Harmony Formation were originally reported to have an uncertain provenance (Wallin, 1990a; Smith and Gehrels, 1994), but the unique occurrence of a 0.7 Ga grain in

21 2000 interpretation Gehrels et al., GSA SP 347, , 2000

22 2016 interpretation Linde et al., Geosphere., 2016 Early Ordovician Peace River Arch 2000 interpretation Gehrels et al., GSA SP 347, , Km B No Late Cambrian interpretation Valmy Lower Vinini 1000 Km 1000 Km C N Osgood/Geersten Transcontinental Ar N Peace River Arch Middle Ordovician Peace River Arch Late Silurian Peace River Arch Upper Vinini Valmy per Vinini Valmy Elder Longshore Transport Eureka Kinnikinic Transcontinental Arch Longshore Transport Eureka Kinnikinic Transcontinental Ar Transcontinental Arch subduction transform ridge 1000 Km E 1000 Km F 1000 Km N N Peace River Arch Peace River Arch RMA Transcontinental Arch Transcontinental Arch RMA Transcontinental Arch Late Devonian Middle Ordovician through Mississippian time (Blakey, 2013). Stars represent the depositional basin of Roberts Mountains allochthon (RMA) strata. White lines show the approximate approximate depositional pathways of units discussed. Transcontinental Arch (Sloss, 1988) and Peace River Arch (Ross, 1991) are superimposed. (A) Early Ordovician time. The lower Vinini tal Arch; the Valmy Formation is derived from the Peace River Arch. (B) Middle Ordovician time. The upper Vinini and Valmy formations are shed from the Peace River Arch into an oceanic Peace River Arch and transported via longshore current along the western Laurentian margin. (C) Late Silurian time. The Elder Sandstone is shed from the Peace River Arch region. (D) Middle e Peace River Arch. A Scotia-style arc has moved to the western margin of northern Laurentia, and a sinistral transpressional fault system has developed along the western margin. RMA argin by this fault system. (E) Late Devonian time. Subduction has initiated along much of the western margin of Laurentia, moving the RMA strata onto the craton. (F) Early Mississippian a into a highland on the western Laurentian margin.

23 2016 interpretation Linde et al., Geosphere., 2016 Late Devonian 2000 interpretation Gehrels et al., GSA SP 347, , 2000 Mid to Late Paleozoic Peace River Arch RMA Transcontinental Arch Figure 9. Schematic map of western North America showing our pre-

24 Figure 9. Schematic map of western North America showing our preferred paleogeography for Cordilleran margin during late Paleozoic time. Cratonal provinces and miogeoclinal strata are as shown in Figure 1. Horizontal ruled region represents arc-type terranes such as eastern Klamath terrane. Vertical ruled region represents basinal assemblages, such as Golconda allochthon, that formed in backarc basin setting. Small inverted V pattern represents extensional, east-facing arc active during emplacement of Roberts Mountains allochthon (following Burchfiel and Royden, 1991). Large inverted V pattern represents west-facing magmatic arc that is interpreted to have been active after Antler orogeny. Small black arrows show the inferred directions of crustal extension within this arc system. KT Kootenay terrane, BRT Black Rock terrane, GA Golconda allochthon, EKT eastern Klamath terrane, RMA Roberts Mountains allochthon, NST northern Sierra terrane. Large gray arrows reflect the general transport of sand that accumulated within miogeoclinal strata (Gehrels, Introduction). Figure 12. Schematic map of western North America showing our p ferred paleogeography for Cordilleran margin during Triassic time. C tonal provinces and miogeoclinal strata are as shown in Figure Horizontal ruled region represents arc-type terranes such as eastern K math terrane. Vertical ruled region represents basinal assemblages central Nevada that formed in backarc basin setting. Inverted V patte represents trace of west-facing magmatic arc outboard of Cordiller margin. Small black arrows show inferred direction of crustal extensi behind this arc system. Large gray arrows reflect the general transport sand that accumulated within miogeoclinal strata (Gehrels, this volum Introduction). KT Kootenay terrane, BRT Black Rock terrane, TT Trinity terrane, YT Yreka terrane, GA Golconda allochthon, EKT eastern Klamath terrane, RMA Roberts Mountains allochthon, NST northern Sierra terrane, TA Triassic assemblages. Gehrels et al., GSA SP 347, 2000

25 Figure 5. Relative age-probability curves for Paleozoic strata of Cordilleran miogeocline (Gehrels, this volume) and lower Paleozoic strata of Roberts Mountains allochthon (Gehrels et al., this volume, Chapter 1), Shoo Fly Complex (Harding et al., this volume), and Yreka terrane (Wallin et al., this volume). Ages of Trinity terrane intrusive rocks are from Wallin et al. (1995). B.C. British Columbia. Numbers in boxes refer to provenance links listed in Table 1. Gehrels et al., GSA SP 347, 2000

26 Colpron and Nelson, Geol Soc Lond Spec Pub 318, 2009

27 Colpron and Nelson, Geol Soc Lond Spec Pub 318, 2009 We need to start looking farther afield to see how to connect things up.

28 Colpron and Nelson, Geol Soc Lond Spec Pub 318, 2009

29 Cambrian Miogeocline in western NAM. Gehrels and Pecha, Geosphere, 2014 Alaska Northern BC Southern BC Nevada-Utah California Sonora Gehrels et al., GSA SP 347, 2000 Colprin and Nelson connect allocthons in lower Shoo Fly with northern BC based on the older TIMS detrital zircon work. Here we compare with newer stuff, and maybe OK. Lang-Duncan Peak-Culbertson

30 Allochthons in western NAM. Colpron and Nelson, Geol Soc Lond Spec Pub 318, 2009 Gehrels et al., GSA SP 347, 2000 Colprin and Nelson connect allocthons in lower Shoo Fly with northern BC based on the older TIMS detrital zircon work. Here we compare with newer stuff, and maybe OK. Lang-Duncan Peak-Culbertson

31 Figure 4. Summary of existing tectonic models for Cordilleran margin. A, Consistently west facing convergent margin with arc separated by series of marginal basins (Burchfiel and Davis, 1972, 1975; Churkin, 1974; Miller et al., 1984, 1992; Harwood and Murchey, 1990; Burchfiel etal., 1992). B, Collision of exotic arc during Antler orogeny followed by mainly west facing convergent margin (Schweickert and Snyder, 1981). C, Collision of two east-facing arc systems during Antler and Sonoma orogenies (Dickinson, 1977; Speed, 1979; Speed and Sleep, 1982; Dickinson et al., 1983). D, Generally west facing convergent margin with brief phases of east-facing subduction and extensional arc magmatism during Antler and Sonoma orogenies (Burchfiel and Royden, 1991; Burchfiel et al., 1992). Gehrels et al., SP 347, 2000 Significance of Sonoman orogen: Seems to reflect the collapse of some marginal oceanic belt between Sierran-Klamath arc to west and Roberts Mtn stuff to east. But there seem to be issues at the early end of the spectrum