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T. P. Thayer

Publications and source records attributed to T. P. Thayer.

13 recordsLinked to original sources
USGS2014

Thrust faults and related structures in eastern Cuba

Detailed areal mapping in central Camagüey Province and reconnaissance mapping in northern and eastern Oriente Province, Cuba, have revealed two major structural zones: (1) A zone of intense deformation, including thrust faulting, which lies north of the geographic axis of the island; and (2) a belt of domical mountains bounded on the north by Nipe Bay and the coast, and on the south by the Cauto trough and Guantilnamo basin. In Camagüey, extensive masses of serpentine and overlying tuffs have been complexly folded and overridden from the north by a block, at least 25 miles long, of limestones that form the Sierra de Cubitas and Sierra de Camaján. The overthrust carried a northern fades of Cretaceous and Eocene limestones over a southern fades of tuffaceous rocks of similar age, and had a displacement of at least six miles. In places serpentine was thrust over younger formations, and most of the shearing in the serpentine is attributed to diastrophism. A thrust zone exposed in Loma La Vigía, 15 miles north of Holguín, suggests a similar tectonic history for northern Oriente Province. Chaotic giant breccias that include waterlaid debris indicate that the overthrusts moved across the ancient land surface in both Camagüey and Oriente districts. The folding apparently began in the Cretaceous and culminated in overthrusting during early middle Eocene time. Post‐Eocene deformation appears to be limited to warping or doming to maximum angles of about 20 degrees. The zone of domical mountains is somewhat more than 100 miles long from east to west by 25 to 30 miles wide, and comprises three main units: (1) the Sierra de Nipe and (2) Sierra del Cristal domes, principally of serpentine; and (3) the Cuchillas uplift, which includes the Cuchillas de Toar and Sierra de Purlal, composed of serpentine and pre‐serpentine rocks. These uplifts are overlapped progressively on all sides by sediments ranging in age from Upper Cretaceous to Oligocene and Miocene, the older beds in places being highly folded. The mountains owe their present relief of 2000 to 4000 feet to the doming of an extensive erosion surface in the late Pliocene or early Pleistocene. The north and east flanks of the Cuchillas uplift extend below sea level, and drowned streams and elevated coral reefs show regional instability since the last major doming. ©1947. American Geophysical Union. All Rights Reserved.

Eos, Transactions, American Geophysical Union↗
USGS1973

Ironside Mountain, Oregon: A late Tertiary volcanic and structural enigma

Note: This paper is dedicated to Aaron and Elizabeth Waters on the occasion of Dr. Waters' retirement. Ironside Mountain is a 6- by 10-km block of folded rhyolite, andesite, and basalt flows of the Strawberry Volcanics bounded by a horse-shoe-shaped reverse fault and surrounded by Mesozoic rocks. The toe of the horseshoe points northeast; the fault dips outward at angles of 45° to 90°, has a minimum displacement of 600 m at the toe, and dies out or is buried at the open southwest end. Flows are folded to vertical in a crosswise anticline at the northeast end, and in a synclinal structure along the southwest edge. Local unconformities and thickening of flows in a small basin show that some deformation accompanied volcanism, which has been dated as late Miocene and early Pliocene. No centers of eruption have been identified within the Horseshoe fault. The Ironside Mountain block seems to be a unique expression of cross folding in the region. The northwest-striking Mine Ridge–Ironside anticline follows the main regional trend, and is faulted where two large down-warps strike into it from the northeast. The Ironside Mountain structure is interpreted as being a transverse compressional feature in which opposing reverse faults took the place of anticlinal folding, directly on strike with a syncline to the northeast. A horst of pre-Tertiary rocks, which has been raised at least 600 m, crosses the axes of the abutting structures; the nose of the Horseshoe fault bounds one side of it, and a range-border fault bounds the other. Cross faults, of which we found only one, are believed to have facilitated arching and longitudinal shortening within the horst.

Oregon↗
USGS1969

Alpine-type sensu strictu(ophiolitic) peridotites: Refractory residues from partial melting or igneous sediments? A contribution to the discussion of the paper: "The origin of ultramafic and ultrabasic rocks" by P.J. Wyllie

Although Alpine peridotites and basaltic lavas are widely associated in eugeosynclines and oceanic areas, their genetic ties are obscure. Three major characteristics of olivine-rich Alpine peridotite and dunite—relict cumulus textures, aggregated masses of chromitite, and intimate association with magnesium-rich gabbro — cannot be explained by partial melting of garnet peridotite to form tholeiite. Association of magnesium-rich gabbro with the chromite-bearing and so-called high-temperature Alpine peridotites is believed to present problems that have not been considered by advocates of the partial-melting hypothesis. The chromite-bearing Alpine peridotites and related feldspathic rocks are believed to have formed near the top of the mantle by gravitational differentiation processes which are largely independent of the melting processes that produce basaltic magma at depths of 50 km or more.

Tectonophysics↗
USGS1969

Peridotite-gabbro complexes as keys to petrology of mid-oceanic ridges

Two suites of olivine-rich ultramafic and feldspathic rocks appear to be present in the Mid-Atlantic Ridge: one which seems to have alkalic affinities, and one similar to the chromitite- bearing alpine peridotite-gabbro complexes. The similarities of rocks in the two environments—continental and oceanic—imply that much about the petrology of mid-oceanic ridges may be learned from studies of continental complexes, and that silicic rocks have been formed in the mantle. Although gabbros in St. Paul Rocks and similar rocks at Tinaquillo, Venezuela, and Lizard, England, have been interpreted as not comagmatic with intimately associated peridotite by some petrologists, evidence to the contrary at Lizard is discussed. Association of fresh gneissic gabbro, some containing quartz, with talcose serpentinite, amphibole schist, quartz diorite and epidotic but unsheared basalts along the Mid-Atlantic Ridge is believed to indicate presence of alpine-type rocks that occur normally in eugeosynclinal belts. Gabbro, described as partly interlayered with peridotite by gravitational differentiation, forms major parts of three widely separated ultramafic complexes which have been interpreted as slices of oceanic crust and upper mantle: the Troodos massif in Cyprus, the Bowutu Mountains in Papua, and the Camagiiey complex in central Cuba. If, as Dietz has suggested, peridotite and related rocks in eugeosynclines represent fragments of ocean rind formed along mid-oceanic ridges and moved laterally by ocean-floor spreading, gabbro must be an essential constituent of the upper mantle. This could account for many geophysical anomalies, but would complicate some postulated mechanisms involved in ocean-floor spreading.

England↗
USGS1964

Principal features and origin of podiform chro-mite deposits, and some observations on the Guleman-Soridag District, Turkey

Podiform chromite deposits occur in alpine peridotite and mafic complexes and fundamentally are tabular, pencil-shaped, or irregular in form. The chromite characteristically is anhedral and commonly shows effects of granulation and magmatic corrosion. Flow-layering, foliation, and lineation are parallel in most chromite deposits and peridotite host rocks, and normally pass through major rock units, including chromite ; locally, foliation and lineation may cross layering. Most podiform deposits are oriented with their longer dimensions essentially parallel to layering or foliation in the host peridotite, but some are crosswise. In all podiform deposits , whether parallel or crosswise, internal flow structures are, to use Hans Cloos' terminology, harmonious with those in the country rock, except where disturbed by postmagmatic faulting. The relations between podiform and stratiform deposits are analogous to those between metamorphic and sedimentary rocks. Though relict structures formed by crystal settling are preserved in some massive ore, most features in podiform deposits are due to extensive flowage during re-emplacement, under magmatic conditions. As the rules governing sedimentary rocks apply in exploration of stratiform deposits , so metamorphic principles apply to podiform deposits . Evidence is presented to show that the chromite deposits in the Gule-man-Soridag district , Turkey , are podiform ; and that the Golalan ore body is closely related to nearby gabbroic rocks of normal alpine type. The Soridag deposits are regarded as originally podiform rather than as fault segments of stratiform deposits .

Economic Geology↗
USGS1964

Pre-tertiary orogenic and plutonic intrusive activity in central and northeastern Oregon

Pre - Tertiary rocks of the Blue Mountain region of central and northeastern Oregon comprise three major sedimentary and volcanic sequences and two distinct intrusive magma series. The ages of the sedimentary-volcanic sequences are Paleozoic, Late Triassic-Late Jurassic, and middle Cretaceous (Albian to Cenomanian), respectively. The earlier intrusive magma series ranges in composition from peridotite to albite granite and was emplaced during the major orogeny in the Blue Mountain region between earlier Permian and Late Triassic time. The later intrusive magma series is related to the Idaho batholith proper, ranges from gabbro to granodiorite, and probably was emplaced during the earlier half of Cretaceous time. The emplacement of a major intrusive magma series during Permian and Triassic time suggests a much closer relationship to the northern part of the Cordillera, in Canada and Alaska, than to the southern part in southwestern Oregon and California.

Oregon↗
USGS1961

Is the Tinaquillo, Venezuela, "Pseudogabbro" metamorphic or magmatic?

The " pseudogabbro " associated with peridotite at Tinaquillo , Venezuela , is believed to be of magmatic rather than metamorphic origin principally because: (1) there are major mineralogic and compositional differences between the " pseudogabbro " and the most highly metamorphosed country rock; (2) rocks intermediate in compositional between peridotite and " pseudogabbro " are present; (3) augen of lamellar pyroxene which occur in the " pseudogabbro " but not in the country rock are of a kind found elsewhere rarely except in igneous rocks; (4) gabbroic rocks are associated with peridotite elsewhere in Venezuela and in the Carribbean region; (5) textural and structural features of the kind found in the Tinaquillo rocks are characteristic of alpine-type peridotite-gabbro complexes.

Tinaquillo↗