topic	year	publisher
Wulfenite in Arizona power point	2008	talk to Tucson Gem & Mineral Soc. 9/8/08
Wulfenite in Arizona paper	2008	in preparation
Structure of Hydrothermal Hosted Hydrocarbon Accumulations	2008	in preparation
Geologic History of Arizona power point	2008	given at musem to Paradise Valley Community College -
Tailings Geochemistry San Manuel Plant Site	2007	given at SME Arizona section December
Hydrothermal Dolomite-hosted Hydrocarbon	2003	AAPG (see abstract below)
Cracks of the World	2003	Houston Geological Society
Hydrothermal Dolomite-Hosted Methane in New York	2003	NYSERDA
Hydrothermal Oil	2002	Northwest Mining Association
Hydrothermal Dolomite-hosted Methane in New York	2002	IOGANY (see abstract below)
Yucca Mountain, Nevada power point	2002	given to SME Tucson dinner meeting
Porphyry Copper Deposits	1995	Arizona Geological Society Digest
Laramide Stratotectonics	1986	Arizona Geological Society Digest
Cenozoic Stratotectonics	1985	Soc. Econ. Paleon. & Mineral. Cenozoic Paleogeography
Cenozoic Paleogeography	1985	SEPM Cenozoic Paleogeography
Arizona Industrial Minerals	1989	Arizona Geological Society Digest
Molybdenum in Arizona	1985	USGS Open File Report 84-830
Molybdenum in Arizona	1980	Arizona Geological Survey Field Notes

 

Integrated Hydrothermal Dolomite (HTD) Gas Conceptual Exploration Model and the Identification of an Unrecognized Major Mg-Hydrocarbon Source

Stanley Keith, MagmaChem, LLC, Sonoita, Arizona
Monte Swan, MagmaChem, LLC, Evergreen, Colorado
Jan Rasmussen, Jan Rasmussen Consulting, Sonoita, Arizona

Studies of HTD Trenton-Black River gas fields of the Appalachian Basin produced an integrative HTD gas model that may explain the generation, transport, and deposition of anomalous amounts of Mg and hydrocarbon that characterize HTD and Mississippi Valley Type zinc deposits (MVT) deposits. These deposit types may identify previously unrecognized major hydrocarbon basement sources. The new model agrees with experimental data and mass-balance calculations that add new constraints to the previously enigmatic HTD gas problem, as well as basin-centered gas. The reaction sequence below utilizes constraints derived from fluid fractionation modeling, transcurrent shear-zone kinematics, geochemistry, and basement structural data. The reaction sequence (in reduced crust) is: Stage 1--generation of methane-hydrocarbon stable metagenic fluids from serpentinization of peridotite in intracratonic failed rifts or collisional sutures in the basement when triggered by compressive, convergent orogenesis and subsequent ascension through probable transpressive conduit systems; Stage 2--initial, low temperature 'passive' dolomitization of the first replaceable shelf carbonate in the overlying cratonic cover sequence; Stage 3A--early saddle dolomitization at or near depositional site; Stage 3B--late saddle dolomitization, anhydrite formation, carbon dioxide effervescence, hydrogen loss and methane unmixing; Stage 4--sulfide and hydrocarbon deposition; and Stage 5--deposition of late calcite at depositional site and illite/smectite/kaolinite clays in and marginal to depositional site. Gas-charged fluids may continue to ascend to higher levels, where they deposit gas charge in higher level sandstone reservoirs. The new hydrothermal hydrocarbon model views basin petroleum resources from the 'bottom- up', especially where that bottom is basement peridotite.

AAPG, Program with Abstracts, 2003

 

Hydrothermal Oil

Stanley Keith, MagmaChem, LLC, Sonoita, AZ, 520-455-4698, www.magmachem.com
Jan Wilt Rasmussen, Jan Rasmussen Consulting, Sonoita, Arizona
Monte Swan, MagmaChem, LLC, Evergreen, Colorado

Studies of hydrothermal dolomite (HTD)-hosted, Trenton-Black River type, gas fields of the Appalachian Basin (Keith and others, 2002) have led to an integrative hydrothermal oil model that may explain the generation, transport, and deposition of anomalous amounts of Mg and hydrocarbon that characterize HTD and closely analogous Mississippi Valley Type zinc deposits (MVT) deposits. These deposit types may be produced from previously unrecognized, major hydrocarbon sources in the peridotitic basement.

The new model agrees with experimental data (Berndt and others, 1996; Horita and Berndt, 1999; Horita and others, 2001). It also agrees with empirically constrained, mass-balance calculations that add new constraints to the previously enigmatic, HTD gas problem, as well as basin-centered gas. The reaction sequence below utilizes constraints derived from fluid fractionation modeling, transcurrent shear-zone kinematics, geochemistry, and basement structural data.

The reaction sequence (in reduced crust) is: Stage 1--generation of methane-hydrocarbon- stable metagenic fluids from serpentinization of peridotite in intracratonic failed rifts or collisional sutures in the basement when triggered by compressive, convergent orogenesis and subsequent ascension through probable transpressive conduit systems; Stage 2--initial, low temperature 'passive' dolomitization of the first replaceable shelf carbonate in the overlying cratonic cover sequence; Stage 3A--early saddle dolomitization at or near depositional site; Stage 3B--late saddle dolomitization, anhydrite formation, carbon dioxide effervescence, hydrogen loss and methane unmixing; Stage 4--sulfide and hydrocarbon deposition; and Stage 5--deposition of late calcite at depositional site and illite/smectite/kaolinite clays in and marginal to depositional site. Gas-charged fluids may continue to ascend to higher levels, where they deposit gas charge in higher level sandstone reservoirs. The new hydrothermal hydrocarbon model views basin petroleum resources from the 'bottom-up', especially where that bottom is peridotitic basement.

The above conceptual model was empirically tested at a specific site at the Glodes Corner HTD gas field in Steuben County, New York (Keith and others, 2002). Surface soil geochemical samples taken at Glodes Corner, NY, 8000 feet above a HTD-hosted gas field have produced a precise definitional tool that defines the overall gas field and also delineates the internal conduit features related to the hydrocarbon charge.

The field is within a seismically defined sag feature or collapse caused by the formation of HTD at the Trenton-Black River level. Soil geochemical patterns are strongly consistent with and specific to the above outlined fluid fractionation model within the context of a transcurrent shear-system kinematic model.

Significant lateral chemical zonation includes well-developed east to west asymmetrical patterns in CO2:O2 and ferric:ferrous ratios, hydrocarbon gases, and Na-As-Zn-K-V-Mg The east end of the field is characterized by lower oxidation state assemblages, such as higher CO2:O2 ratios, lower ferric:ferrous ratios, and greater abundances of C1 and C2 hydrocarbons with respect to C5 and C6 hydrocarbons. The east end of the field appears to be closer to a primary, northwest-striking, conduit system that was operating in left slip during fluid introduction. Fluids ascended through this conduit system, entered the field from the east, and became more oxidized as they migrated westward into east-west-striking Riedel-tensile fractures. The within-reservoir, Riedel-tensile, conduit architecture of permeability and dolomite plugging can be identified by interpretation of hydrocarbon gas distribution (C1-C2 high in conduits and trace metals, C5 and C6 gases away from the conduits). A possible southerly conduit that may have additional production potential was also defined.

The above patterns, which display strong laterality, appear to be specifically predicted by the HTD hydrothermal oil model. The predominance of reduced species gases along with elevated CO2 in the east end of the field is consistent with early Stage 3A and Stage 3B saddle dolomitization, carbon dioxide effervescence, hydrogen loss and methane mixing. The elevated base metal and hydrocarbon anomalies in the profile within the middle of the field are consistent with Stage 3B and Stage 4 base metal sulfide and hydrocarbon deposition in a later, more fractionated part of the paragenesis in the middle of the field. In the inferred more distal part of the field, high C-number gases and more oxidized geochemical signatures in the westerly geochemical profile are consistent with Stage 5 deposition of late calcite and illitic smectitic clays in the middle to western part of the Glodes Corner field.

The above pattern is consistent with cooling of an initially hot, reduced fluid that entered the field from the east, utilizing a Riedel-tensile conduit system that splayed off a more northwesterly striking conduit system. This conduit system was operating in left slip during what is inferred to be Acadian orogeny (approximately 350-400 Ma) within an inferred east-northeast to east-west-oriented, far-field maximum principal stress regime operant during the 'hard crunch' Acadian continental (Avalon-North America) assembly event. The northwest- trending primary conduit system may have been linked to a peridotitic source in the basement expressed by a coincident magnetic high and gravity low feature that occupies most of Steuben County. The foregoing geophysical signature is further interpreted to be linked with mafic sources within the Rome trough, a failed rift system of mid- to late Cambrian age.

The inferred peridotitic source in central Steuben County may be one example of a consistent linkage between HTD hosted hydrothermal oil and gas occurrences and peridotitic sources in failed rifts or orogenic sutures. Other similar examples may be the Arbuckle formation in the Ardmore-Anadarko basins of Oklahoma, the Williston basin of North Dakota, the Albion-Scipio field in southern Michigan, many fields in the Appalachian basin, the well-known Wabamun Group HTD-hosted oil and gas fields of Alberta, the Great Valley of California, Railroad Valley in Nevada, and the largest known oil field in the world - the Ghawar field of the Persian Gulf.

The provocative possibility also exists that oil and gas resources hosted in more conventional stratigraphic and structural traps (such as sandstone-hosted anticlinal traps) at higher levels in the above basins may also represent more oxidized, fractionated, leakage anomalies above the hydrothermal deposits, which typically reside near the bottoms of the above basins within close proximity to the basement.

If the hydrothermal point of view summarized above is viable, it has revolutionary implications for petroleum geology in general:
1) A significant amount of the world's oil may be derived from abiogenic sources in the basement.
2) Migration and trapping may be accompanied by abiogenic depositional reactions and transport mechanisms.
3) The oil window can be entered from high temperature/high pressure conditions via cooling and decompression of hot, hydrothermal fluids.
4) In common with many hydrothermal metal deposits (such as gold, tin and MVT deposits where smaller amounts of hydrothermal hydrocarbon material have been documented) that are derived from reduced sources, the oil and gas are formed as part of the reaction sequence associated with depositional events (mainly dolomite) that accompany cooling and depressurization of the hydrothermal fluid. This concept contrasts with current models where the reservoir environment is made by hydrothermal processes, and the oil generation and migration event occur much later.
5) A significant amount of the world's oil and gas may owe its origin to fractionation of and deposition from hydrothermal fluids (especially as a function of saddle dolomitization under reduced conditions), in common with metals deposited in hydrothermal metal deposits, which constitute most of the world's metallic mineral resources.
6) A significant amount of biogenic, basin-sourced hydrocarbons may be reworked and incorporated into hydrothermal hydrocarbon plumes originally sourced in reduced, deep basement rocks (especially peridotites).
7) Compared to metallic hydrothermal deposits, HTD deposits were formed from much larger hydrothermal plumes (about ten times the average MVT deposit and about one hundred times the average porphyry metal system).
8) Given that peridotite may be an important source of basement-sourced hydrothermal hydrocarbon systems, the ultimate source of the hydrocarbon is the mantle, as has been suggested by other workers (Gold, 1993; Kravtsov, 1985; Kropotkin, 1985; Kroptkin and Valyaev, 1976; Kropotkin and Valyaev, 1984; Kudryavtsev, 1959; and Chekaliuk, 1976). We have developed a geologically reasonable mechanism of reworking a peridotitic source via serpentinization under reduced abiogenic conditions to generate hydrocarbons out of metagenically derived basement fluids to transport them into overlying basement cover sequences.

References

Berndt, M. E., Allen, D. E., and Seyfried, W.E., Jr., 1996, Reduction of CO2 during serpentinization of olivine at 300oC and 500 bar: Geology, v. 24, no. 4, p. 351-354.

Chekaliuk, E.B., 1976, The thermal stability of hydrocarbon systems in geothermodynamic conditions: Degazatsiia Zemli I Geotektonika (P.N. Kropotkin, ed.), p. 267-272.

Gold, T., 1993, The origin of methane in the crust of the Earth: The Future of Energy Gases, U.S. Geological Survey Professional Paper 1570, p. 57-80.

Horita, J. and Berndt, M.E.,1999 , Abiogenic methane formation and isotopic fractionation under hydrothermal conditions: Science, v. 285, 13 August 1999, p. 1055-1057.

Horita, J., Allen, D.E., Berndt, M.E., and Seyfried, W.E., Jr., 2001, Biogenic vs. abiogenic isotope signatures of reduced carbon compounds: a lesson from hydrothermal synthesis experiments: Eleventh Annual V.M. Goldschmidt Conference, 3290.pdf.

Keith, S. B., Viellenave, J., Swan, M., Rasmussen, J., Fontana, J., Caprara, J., and Laux, D., (abstract), 2002, Use of soil geochemistry to define details of within-reservoir conduits and permeability related to hydrocarbon charge at Glodes Corner, a Trenton-Black River HTD gas field in Steuben County, NY: IOGANY meeting, Niagara Falls, NY, November 5, 2002.

Kravtsov, A. I., 1975, Inorganic generation of oil and criteria for exploration for oil and gas: Zakonomera. Obraz. Razmeshchniya Prom. Mestorozhd. Nefti Gaza (G.N. Dolenko, ed.), p. 38-48. Naukova Dumka: Kiev.

Kropotkin, P.N., 1985, Degassing of the Earth and the origin of hydrocarbons: International Geology Review, v. 23, p. 1261-1275.

Kroptkin, P.N., and Valyaev, B.M., 1976,Development of a theory of deep-seated (inorganic and mixed) origin of hydrocarbons: Goryuchie Iskopaemye: Problemy Geologii i Geokhimii Naftidov i Bituminoznykh Porod (N.B. Vassoevich, ed.), p. 133-144. Akademiya Nauk SSSR.

Kropotkin, P.N., and Valyaev, B.M., 1984, Tectonic control of Earth outgassing and the origin of hydrocarbons: Proceedings of the 27th International Geological Congress, v. 13, p. 395-412. VNU Science Press.

Kudryavtsev, N.A., 1959, Geological prrof of the deep origin of petroleum: Trudy Vsesoyuz. Neftyan. Nauch.-Issledovatel. Geologoraz Vedoch. Inst., no. 132, p. 242-262.

Northwest Mining Association, Spokane, WA, Dec. 2002 annual meeting, Left Lateral Leaps session.

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Use of Soil Geochemistry to Define Details of Within-Reservoir Conduits and
Permeability Related to Hydrocarbon Charge at Glodes Corner, a Trenton-Black
River HTD Gas Field in Steuben County, NY

*Stanley Keith, MagmaChem, LLC, Sonoita, Arizona

Jim Viellenave, Direct Geochemical, Golden, Colorado

Monte Swan, MagmaChem, LLC, Evergreen, Colorado

Jan Rasmussen, Jan Rasmussen Consulting, Sonoita, Arizona

John Fontana, Direct Geochemical, Golden, Colorado

John Caprara, EarthTechnics, Houston, Texas

Daniel Laux, South Branch Resources, Apache Junction, Arizona

Surface soil geochemical samples taken at Glodes Corner, NY, 8000 feet above a HTD-hosted gas field have produced a precise definitional tool that defines the overall gas field and also delineates the internal conduit features related to the hydrocarbon charge. The field is within a seismically defined sag feature or collapse caused by the formation of HTD at the Trenton-Black River level. Soil geochemistry was interpreted in terms of a fluid fractionation and a transcurrent shear-system kinematic model. Significant lateral chemical zonation includes well-developed east to west asymmetrical patterns in CO2:O2 and ferric:ferrous ratios, hydrocarbon gases, and Na-As-Zn-K-V-Mg . The east end of the field is characterized by lower oxidation state assemblages, such as higher CO2:O2 ratios, lower ferric:ferrous ratios, and greater abundances of C1 and C2 hydrocarbons, with respect to C5 and C6 hydrocarbons. The east end of the field appears to be closer to a primary northwest-striking conduit system that was operating in left slip during fluid introduction. Fluids ascended through this conduit system, entered the field from the east, and became more oxidized as they migrated westward into east-west-striking Riedel-tensile fractures. The within-reservoir, Riedel-tensile, conduit architecture of permeability and dolomite plugging can be identified by interpretation of hydrocarbon gas distribution (C1-C2 high in conduits and trace metals, C-5 and C-6 gases away from the conduits). A possible southerly conduit that may have additional production potential was also defined. The demonstrated resolution of this geochemical tool adds increased precision to current methodologies of reservoir identification and evaluation.

IOGANY talk, December 2002, Niagara Falls, NY

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Cracks of the World

or

Global Strike-Slip Fault System, Crustal Oxidation State, a New Plate Tectonic Paradigm, and Giant Resource Accumulations

a talk to Arizona Geological Society, July 3, 2001

by Stanley B. Keith, Monte M. Swan, Jan C. Rasmussen, Daniel P. Laux MagmaChem, L.L.C.

Mexico Mega-Shear System and Crustal Oxidation State

A recent tectonic synthesis of Mexico metallogeny and tectonics using the magma-metal series approach uncovered some large-scale geologic phenomena that have implications for worldwide giant petroleum and metallogenic accumulations and also lead to a more fixistic global plate tectonic paradigm. The discovery occurred through the observation of regional crustal oxidation state patterns following completion of a oxidation state map for Mexico that was based on over 4,000 oxidation state control points. The oxidation state control points variously consist of ferric/ferrous ratios for plutons (about 400) and mineral assemblages and geochemistry from plutons and mineral districts that are empirically correlated with pluton oxidation states in a global controlled data base for about 5,000 correlated case histories.

Additionally, petroleum accumulations of all sizes globally correlate with source and reservoir rocks of low oxidation state where ferric-ferrous ratios are equal to or less than 0.6. In the Mexico region, over 500 oil and gas field occurrences were used to additionally constrain crustal oxidation state. Also, petroleum occurrences can regionally coexist with other commodities (such as diamond, gold, and tin, antimony, mercury, lithium, and tantalum) which require low oxidation states for their stability throughout the source-transport-deposition process. Consequently, maps of regional crustal oxidation state in any particular area are a necessary exploration tool for a given commodity.

The Mexico oxidation state map produced a striking zig-zag pattern that, when compared with an oxidation state map for the western U.S., indicates a southeastward offset of the inferred Cambrian craton edge for some 3500 km from Cajon Pass west of Los Angeles, CA to Guatemala City, Guatemala. This offset is accomplished on west-northwest striking fault elements that form a giant country-wide shear system, referred to as the Mexico mega-shear. The Texas zone forms the nothernmost structural element of the shear system and the Motagua/Polochic fault system forms the southernmost element. Fault elements within the shear system are defined by sharply telescoped oxidation state gradients, where at least two levels of oxidation state are crossed in very short distances. A similar pattern was found for the inferred Cambrian craton edge, which is comprised of offset segments of north-northeast-striking zones of telescoped oxidation states.

The overall pattern confirms the Sonoran Mega-shear concept originally proposed by Silver and Anderson, 1974. The overall sense of the displacement of the inferred Cambrian margin is along a line of approximately N50W trend. However, the individual offsets occur along east-west to west-northwest-striking, what appear to be deep-seated fault zones that traverse the entire country of Mexico and adjacent areas. If the 3500 km offset is restored and the Gulf of Mexico is closed, Mexico and Northern Central America form a nice southward-pointed mega-peninsula that fits neatly to the coast of northwestern South America, west of Columbia and Ecuador. This reconstruction neatly removes the notorious ‘Bullard-fit problem'.

The mega-shear system is not confined solely to the country of Mexico and adjacent regions. The individual fault elements in the Mexico mega-shear appear to extend outward into the Pacific Basin, where they link nicely with the Pacific oceanic fracture system between 18oN and 42oN. A similar, even more dramatic, connection is achieved when the Mexico mega-shear system is extended to the east-southeast, where it links, almost element for element, with the central Atlantic fracture system between the equator and a latitude of 18oN. In both the Pacific and Atlantic ocean basins, the oceanic ridge system displays an apparent left offset of some 3500 km, in accord with the offset on the Mexico mega-shear system.

The offsets in the Atlantic Basin and their presumed Mexican analogs are particularly provocative. At the southern end of the Atlantic shear system, large left-handed offsets of the Atlantic mid-ocean ridge along the Romanche fracture system match well with large offsets of the inferred Cambrian craton edge along the Motagua/Polochic/Cayman trough fault system from its initial position in the Chortis block of Nicaragua-Honduras. This large offset is matched by several minor 50 to 100 km offsets in both the central Atlantic and Mexico mega-shear. About two-thirds of the way traveling northward into both systems, another large offset occurs (Guinea fracture zones in the Atlantic and the Monterrey-Parras fracture system in north-central Mexico. A series of smaller offsets occurs until the northernmost offset of about 150 km (Barracuda fracture in the Atlantic and the central portion of the Texas zone in southwestern Arizona and southeastern California).

In terms of its present known global position, the Mexico mega-shear, when correlated with its Atlantic and Pacific analogs, goes halfway around the world extending for about 180 degrees of longitude and ranging from 18o to 25o of latitude in width. The total accumulated offset of 3500 km has incrementally occurred within the last 200 million years. Much of the offset occurred between 175 and 145 Ma, 125 and 85 Ma, and 56 to 38 Ma, based on interpretation of the ages of oceanic floor. These offsets in the ocean floor correlate with major tectonic events in Mexico, such as the Oxfordian opening of the Gulf of Mexico and the mid-Cretaceous formation of the Bisbee Trough in the north part of the Mexico mega-shear system, and the Eocene opening of the Cayman Trough and left-slip movements on the correlative Motagua-Polochic fault system throughout Guatemala.

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Towards a New Plate Tectonic Paradigm

If the above global scale observations are true, then mobilistic, terrane-based, paradigms of plate tectonics may have to be revised. The mobilistic paradigm of plate tectonics has traditionally assumed that the continental plates are rigid and "float" as passive rafts on a global "conveyor belt" system linked to oceanic spreading processes. The above mega-shear observations suggest that the continents are active participants in the oceanic spreading process. Thus, a global network of transform faults apparently exists that links ocean basin to ocean basin through the continents. Hence, the continents do not appear to be tectonically inert, rigid blocks; rather, they are active, kinematic players in the oceanic spreading process. Indeed, it may be the fracture architecture of the continents that controls the specific locations of the oceanic fracture systems during incipient breakups of continental assemblies such as Pangea. Another important derivative concept is that the motion between continental and oceanic plates is not free-faced or disconnected at the trench plate boundaries. Tears in subducting oceanic crust and fracture zones in oceanic crust are anchored to and connected with analog fractures in the adjacent and overriding continental plate at the subduction zone interface.

Viewed from a dynamic point of view, the transform faults can be looked at as manifestations of large-scale motions between the lithosphere and the asthenosphere. The mega-shears largely coincide with latitude-parallel motions that define approximate great-circle planes that are perpendicular to poles of rotation approximately coincident with the Earth's rotation axis. Northward bends in this global crack system (for example, those in the Indian Ocean basin) may reflect a long-term wobbling effect around the spin axis that is ultimately a manifestation of the non-perfect, oblate-spheroid shape of and non-perfect gravity distribution within the planet. In this more fixistic view of plate tectonics, the fundamental motions of the various surface plates are along east-west lines. North-south translations are relatively minimal. For example, post-200 Ma North America/Pacific north-south plate translations in this model appear to be no greater than the distance between two large oceanic fracture zones (about 300 km).

The kinematic reference frame in the new fixistic paradigm expands from a relativistic continental scale one (such as holding Africa fixed and moving the other lithosphere plates relative to Africa) to an absolute spherical one where the lithosphere and asthenosphere are moving clockwise, or eastward relative to the spin axis (viewed from the South Pole). The clockwise eastward motion induces contrasting mega-tectonic patterns, such as flatter, with-flow, easterly-dipping subduction zones and steep, against-flow, westerly-dipping subduction zones. The subduction zones dips suggest a net eastward flow of the asthenosphere relative to the lithosphere. This net eastward motion is recorded by hot spot tracks, such as the Hawaiian hot spot track, which suggests a net eastward motion of the asthenosphere relative to the lithosphere. For example, in the case of the Hawaiian hot spot track, the asthenosphere is moving east-southeastward relative to the lithosphere at about 8 cm/yr since 43 Ma. Similarly, the Yellowstone hot spot is moving east-northeastward at 5.7 cm/yr since 16 Ma, suggesting an east-northeast moving asthenosphere. At this more global scale, the ultimate reference frame becomes the orientation of the spheres around the Earth-s spin axis. In the old plate tectonic paradigm, plate restorations were exercises in large scale kinematics whereas in the newer, more fixistic Earth-scale perspective, kinematics can be more easily integrated with dynamic considerations such as core dynamics, hot spot generation, geo-magnetism, etc. The above model is in accord with and expands upon a similar model of terrestrial plate dynamics developed by Doglioni, (1990, 1993, and 1994).

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Implications for Mineral and Energy Resources

With respect to formation of resources such as petroleum or metal deposits, strike-slip motions along the global crack system are important for:
1) the localization of metamorphic fluids (some of which may be hydrocarbon-rich) generated by dehydration during regional prograde metamorphism associated with crustal thickening;
2) focusing of metal-bearing, wet, hornblende-stable plutons associated with subduction-generated magmatism; and
3) possibly controlling ingress of possible non-biogenic mantle or lower crust-sourced hydrocarbon materials (such as methane).

Petroleum Fields

Petroleum seeps in the Lau Basin, methane discharge along ridges (e.g. 21oN), and petroleum-rich fluid inclusions associated with ‘Black Smoker' massive sulfide deposits (e.g. Guaymas basin) document that a reduced mantle is indeed a source of reduced hydrocarbon material. The above resources are typically localized in high-permeability, low-pressure sites along the transform system (for example, the deep-gas and petroleum fluids in the Anadarko basin of Oklahoma or the Grasberg porphyry-copper-gold deposit in eastern Indonesia).

An important feature of the above concept is that metamorphic fluids are required to achieve hornblende stability, which can then fractionate porphyry metal sequences or provide a non-biogenic petroleum fluid component where metamorphic fluids are generated under reduced, low oxidation state. Also, under conditions of low oxidation state, reduced hydrocarbons (i.e. methane) may be imploded into incoming gabbroic magmatism. Catalysis of the methane component (possibly across illitic clay interfaces) may occur during migration from the source to the trap site. Subsequent hydrothermal fractionation from reduced magmatism and deposition under appropriate conditions may lead to hydrothermal and, more frequently, higher rank hydrocarbon residues (resins and asphaltenes) or methane gas pockets found at many gold and tin deposits. Examples are ‘hydrothermal' oil seeps at the Yankee gold deposit and trapped hydrocarbon in fluid inclusions at the Gold Point gold deposit in Nevada. Whether any of these mechanism can lead to a commercial possibilities remain to be proven (although one oil field [Grant Canyon and Pine Valley, NV] may have had elements of the above unconventional non-biogenic oil generation mechanism at work during their formation).

Large-scale petroleum accumulations in the North America and South America plates also appear to be associated with cryptic deformation zones above tears in the subducting, mainly oceanic plates. The tears also integrate with the oceanic fracture system. Where the oceanic fractures intersect a given continental plate at subduction zones, tears in the oceanic plates are the rule rather than the exception. Flat-plate subduction is typically associated with Laramide-style basement-uplifts in the continental interior, whereas moderate- to steep-dip subduction is associated with foreland, fold-thrust deformation in the continental interior. Small oil accumulations are typically developed from biogenic sources within foreland basins formed continent-ward of moderate to steep-dipping subduction zones. The tears generally mark the north and south boundaries of the basins. In a number of cases, giant or enhanced petroleum accumulations occur where the foreland basins intersect the projection of a given slab-tear into the continental plate (for example, the Denver Basin). This pattern suggest that non-biogenic hydrocarbons sourced in the mantle or lower crust may have risen into the intersection of the slab-tear and combined with the foreland basin-, biogenically-produced hydrocarbons. The result is an anomalous augmentation of hydrocarbon materials that results in a giant petroleum accumulation. Future petroleum exploration would do well to emphasize domains of reduced crust where deformation associated with slab-tears and regional trans-current faulting related to the global crack system can be documented in both continental and oceanic regions.

Porphyry Metal Deposits

One of the striking features about the Mexico mega-shear system is that all of the metal production for base and precious metals in Mexico comes from mineral districts associated with wet, generally hornblende-bearing, plutonic sequences emplaced into deep-seated elements of the mega-shear system. Perhaps the most significant aspect of deep-seated, strike-slip faults for porphyry metal genesis is their relationship to abundant, water-rich fluid reservoirs inferred to reside in the deep-seated cracks at mid-crustal levels. As alluded to above, these fluids are instantaneously imploded into incoming, metaluminous magmatism derived from mantle sources, whereupon hornblende stability is achieved. In effect, the magmas become supercharged with a water component while they are in the gabbro system in the mid-crustal portions of the deep crack system. Because the high water content is developed early in the differentiation history of the magmas, a series of fluid exsolutions/explosions must occur during the final emplacement of the differentiation sequence into the upper crustal sites. In order to keep the sequence differentiating through to evolved granitic residues, a series of magmatic liquid-liquid fractionations must occur with hydrothermal liquid fractionations occurring upon solidification of individual hydrous magma batches.

Because the faults are commonly moving in strike-slip, the lateral kinematics results in a hook-shaped differentiation pattern of magma and metal differentiates. These hook patterns can be viewed as an additional kinematic indicator for district-scale fault movements. Because the plutons can be dated, the timing of these typically lateral motions can be quantitatively constrained. The laterality of the process results in new exploration targeting opportunities whereby the target is lateral to existing metal prospects and mine showings and not vertically beneath existing metal occurrences, as conventional exploration models emphasize. Successful applications of this more lateral approach include Candelaria and Chuquicamata in Chile and the North Carlin gold trend in Nevada.

In porphyry metal districts where strong strike-slip dynamics have been operative, torque forces may result in a more tight, spiral effect of the differentiation path. In such systems, the ore stages are emplaced extremely rapidly (within 0.5 million years) and within the precision of the geochronologic technology. Examples include the spectacular spiral, crystal cave system within the Braden pipe at El Teniente, Chile; the possibility of rotated intrusions within the Grasberg diatreme in Irian Jaya, Indonesia; the Anna Lee auriferous corkscrew in the kinematic center of the Cripple Creek diatreme in central Colorado; and apparent spiral dynamics associated with the giant Ashanti and the emerging Ntotoroso gold fields in Ghana.

In all cases, the tornadic, spiral patterns in porphyry metal systems inventoried to date are associated with world-class, giant, rapidly evolved, porphyry metal systems associated with ‘super-wet' intrusive sequences emplaced into deep-seated, kinematically active, strike-slip faults that comprise elements of the global crack system. One final observation is that within the last 150 million years, giant porphyry metal and petroleum accumulations seem to occur in or near deep-seated cracks within 45 degrees of the equator.

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Summary

The metallogenic analysis of Mexico, using the magma-metal series approach, revealed surprises that surpassed all expectations. Specifically, patterns of crustal oxidation state (as inferred from magma chemistry and mineral assemblages and geochemistry of mineral resource occurrences) revealed a country-wide, west-northwest fracture system that offsets and inferred Cambrian craton edge some 3500 km westward from its position within the Chortis block of Central America. Furthermore, this fracture system integrates with oceanic fracture systems in both the Pacific and central Atlantic ocean basins that also apparently offset both ridge systems in each ocean basin a similar amount of 3500 km.

It is now becoming apparent that the Earth is circumvented by a necklace of generally latitude-parallel faults. Much of the Earth's plate tectonics is tied to transcurrent motions on these strike-slip faults. Much of the Earth's resource endowment has been emplaced into the strike-slip fault system. The new plate tectonic dynamic driving force revolves around the Earth's rotation axis. Familiar plate tectonic driving mechanisms, such as mantle convective overturn or gravitational trench-pull, become second order driving forces relative to the Earth's spin axis. The scale of the kinematic reference frame now shifts from continents to motions between spheres (e.g., lithosphere-asthenosphere differential rotations).

Much of the major mineral and energy resource occurrences seem to be necessarily resonant within the deeply penetrating fractures of the ‘cracks of the world'. Future resource exploration for large-size petroleum and porphyry metal occurrences would do well to emphasize the definition, regional distribution, and specific characteristics of the global crack system. Specific drill targets at occurrence sites will be lateral as well as vertical to the known resource occurrences. We strongly believe that significant new energy and mineral resources remain to be discovered by integrating resource occurrences with crustal oxidation state, magma chemistry, crustal fluids, deep cracks, and a globally interconnected fracture system.

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